Embryology - User contributions [en-gb]

User:Z3258567

2009-10-22T02:19:10Z

Z3258567:

--[[User:Z3258567|Sando Rashed]] 13:26, 13 August 2009 (EST)

1. what is congenital diaphragmatic hernia how it is affect the human lung?
this is the improper growth of the diaphragm, this is a issue because it allows the organs within the abdominal region grow into the
chest cavity area and intrude with the lungs not allowing it to form properly.
--[[User:Z3258567|Sando Rashed]] 14:17, 8 October 2009 (EST)
1) adipose tissue, muscle tissue skeletal, adult skin
2)the use neural stem cells, without using viruses to reprogam the cell, and they use viruses which can affect the transcription identity of the cells, this may at times kill the cells
3)true

--[[User:Z3258567|Sando Rashed]] 13:19, 22 October 2009 (EST)

Talk:2009 Group Project 5

2009-10-15T00:18:08Z

Z3258567: /* Evaluation/ Alterations After Peer Review */

== Evaluation/ Alterations After Peer Review ==

--[[User:Z3295026|Joe Nassif]] 12:47, 14 October 2009 (EST)

• Edited structure of table of stages

• Corrected introduction " added a brief overview about frog and usage"

• In changed size of images to 200px and moved to the left to suit page

• Removed spaces and gaps between specific sections

• Formatted intro section to look neater and to flow more better

• Deleted the links and added proper reference

• Added to glossary of terms

• Added in text citations to the developments section

• Enhanced and added more definitions

• Changed reference list and changed the format it into APA format

• re-uploaded information and reference for images as stated by Mark Hill

• Added information below images for a description.

• Added links to source below images about the germa layer of frogs.

• Deleted image -unable to find copyright license in gastrualtion

• Changed to APA, had to look up dates and authors for incomplete references added by other students.

• Finished the glossary of terms

• Worked on current research about Frogs. Added relevant info about usage through history

• Proof read. Added in sentences to make the transition from history of use .

• Read through and edited spelling of development and stages

• Edit all information bout images.
--[[User:Z3295026|Joe Nassif]] 12:47, 14 October 2009 (EST)

--[[User:Z3258567|Sando Rashed]] 09:51, 15 October 2009 (EST) edited all the image names to appropriate titles, added extra current research topic, fixed up some sentence structures, removed some signatures

== Group Project Updates ==
--[[User:Z3258567|Sando Rashed]] 00:08, 13 October 2009 (EST) i got rid of a few more individual signatures
--[[User:Z3126345|Gang Liu]] 14:42, 8 October 2009 (EST)Hi group, one of the peer comments is to delete individual signature, so i got rid of all the signatures on the page.

--[[User:S8600021|Mark Hill]] 10:08, 10 October 2009 (EST) The [[2009_Group_Project_5#Stages_of_frog_embryology|stage images]] you have begun to add to your project are from [http://www.xenbase.org/anatomy/alldev.do? Xenbase - stages] it is incorrect to give UNSW Embryology as the source as my page just provides links to this external site. "Digitized images and developmental data from Nieuwkoop and Faber (1994) Normal Table of Xenopus laevis (Daudin). Garland Publishing Inc, New York ISBN 0-8153-1896-0." you will need to get permission to use these images in your project.

--[[User:Z3126345|Gang Liu]] 22:22, 11 October 2009 (EST)Thank you Dr Hill. I've just realised. Yes, i will try to get permission from authors.

--[[User:Z3126345|Gang Liu]] 09:22, 14 October 2009 (EST)Hello, Dr Hill. I have tried to contact the publisher regarding permission to reproduce their images on my group project page. So far, i have not received any replies. Could i use your images on unsw embryology?

--[[User:Z3126345|Gang Liu]] 10:12, 14 October 2009 (EST) Hello, Dr Hill I just got the permission to reproduce those images on my page.

== Project Updates ==
--[[User:Z3283499|Antonio Lee]] 10:57, 2 October 2009 (EST) Hi everyone, I will be working with you during the Lab10 Tutorial and here is the news link and PDF of the manuscript for your group exercise. I encourage you to read the paper before the tutorial. Also, please indicate next to the questions below (using either your initials or student number) which one of the four questions you wish to address.
:'''Group 5 :''' [http://www.sciencedaily.com/releases/2009/09/090918111056.htm '''Human Induced Pluripotent Stem Cells Retain Some Gene Expression Of Donor Cells'''] in Science Daily Published online 19 September 2009 [[Media:ANAT2341_Lab10_2009_Group 5 Reading.pdf|Manuscript (PDF): Transcriptional Signature and Memory Retention of Human-Induced Pluripotent Stem Cells]]

----

:'''Question 1. What is the background to the existing problem / disease condition? (z3295026)- JOE NASSIF'''
''

The discovery of neural stem cells, has lead to the exposure that a single cellular factor can be carried out to re-program and stimulate a human cellular component into a pluripotent form, allow the cell to have the ability to distinguish any category of cellular material in the human body. The ability of this process will allow the identification of common cellular material and what is not common for instance abnormal tumour cell or cancer cells, this process of iPSCs is an advantage in recognising normal and abnormal cellular matter extrinistically as the stem cell will recognise what it going to develop into, through signalling and programming. These stem cells are extremely useful in therapeutic uses, muscular dystrophies and replacement of cell into the specific regions of the human body needed to be replaced or repaired.

An arrangement of four particular factors was experimented to generate iPSCs, using knowledge involving viral vectors including viruses with the possibility to influence the transcriptional configuration of the cellular material, at times inducing the cell death process and trying to destroy cancerous material in specific regions of the body.

The mouse and human genetics in relations to iPSCs have revealed to be comparable to embryonic stem cells in relation to the cellular behaviour, gene expression and their potential to make a distinction between different types of cells.

Sequentially in regard to the advantage of reprogramming specific genetic materials, it is necessary to model processes to encourage pluripotency in the alterations of the genome, and it structures. By reprogramming neural cellular materials with the human body and creating iPSCs from human neural stem cells lacking the presence of specific viruses, the scientists developed new understanding of the function of iPSCs.'' --[[User:Z3295026|Joe Nassif]] 13:33, 8 October 2009 (EST)

----

:Question 2. What approach / method did the research team take to tackle / improve the problem? (z3255007)- Sadaf Masood

''Introduction of Viral-free, integration free reprogramming approach, where pluripotent factors Oct4 and Nanog were cloned and transferred into human fetal neural progenitor cells under high frequency, which when expressed itself, became human iPSCs. This is also considered a safe approach in clinical terms as virus will not be affecting the genome.''

:Question 3. What was the breakthrough / major advancement OR failure / drawback? and why might this be of significance?(z3126345) Gary Liu

while both mouse and human iPSCs have been shown to be similar to embryonic stem cells in terms of cell behavior, gene expression and their potential to differentiate into different types of cells, researchers had not achieved a comprehensive analysis to compare iPSCs and embryonic stem cells.

"One reason is that previous methodologies used to derive iPSCs weren't 'footprint free,'" Muotri explained. "Viruses could integrate into the genome of the cell, possibly affecting or disrupting genes."

"In order to take full advantage of reprogramming, it is essential to develop methods to induce pluripotency in the absence of permanent changes in the genome," added Fred H. Gage, PhD, a professor in the Laboratory for Genetics at the Salk Institute and the Vi and John Adler Chair for Research on Age-Related Neurodegenerative Diseases.

:Question 4. What are the next steps in moving forward? What are the next or new hurdles to overcome? --[[User:Z3258567|Sando Rashed]] 14:15, 8 October 2009 (EST)
they have been able to find out that there is a safe way to create induced pluripotent stem cells, but what they are able to research now is that do these cells they have created have a issue with there memories is it affected by using a viral free method.

==Constructive Criticism of Coordinator==
--[[User:S8600021|Mark Hill]] 08:07, 8 October 2009 (EST) The following comments are general in nature in no specific order, as it would be inappropriate to suggest specific changes and then assess the final project. Comments will be added during this week and you still have one week before final submission.

* [[:File:Fertilized_and_Unfertilised_Eggs.jpg]] [[:File:Egg_Development.jpg]] what is the original source that these images are based upon? There is no description on the image page when it opens of what the images are showing.
* Some figure legend titles could be tidier.
* There is no list of changes that have been made in response to peer review process.
* The [[2009_Group_Project_5#Stages_of_frog_embryology|stage images]] you have begun to add to your project are from [http://www.xenbase.org/anatomy/alldev.do? Xenbase - stages] it is incorrect to give UNSW Embryology as the source as my page just provides links to this external site. "Digitized images and developmental data from Nieuwkoop and Faber (1994) Normal Table of Xenopus laevis (Daudin). Garland Publishing Inc, New York ISBN 0-8153-1896-0." you will need to get permission to use these images in your project.

==Constructive Criticism of Peers==

--[[User:Z3218657|Sally Clarke]] 10:12, 1 October 2009 (EST)
Great Assignments guys

- Great use of images

- It jumps straight into the information which can be either a good and bad thing depending on what you are trying to achieve, maybe add in an introductory section which leads the reader on to the next bits of information

- is the anatomy section of the Frog Necessary - remember what we are studying here!!!

- The staging section is good except that you only link to the images - would you be able to have thumbnails of each of them in the table - it would help the information

- Wiki Pages??? Maybe not

- Try to make your information a little more succinct as you repeat information in the timeline and staging sections and remember formatting - history section etc.

- Include the information on why this model is used - advantages and disadvantages of this model maybe

- Current research is good but you should probably include some info on the genome - or a link to find out information about it

Overall its a great project!

--[[User:Z3223194|Bronwyn Lewis-Jones]] 09:06, 1 October 2009 (EST) This is a great assignment. Congratulations. Well set out and good use of applicable images. I think the most important change to make is to include an introduction which gives the reader a brief understanding about the frog (the anatomy section does a good job of this but maybe include a few sentences in an intro) and why it is used in embryology research. Also you could be more specific with your image labels (e.g. "Typical Frog" - why not give us it's biological name if possible). I think you could also cut back on some unnecessary information in the timing/staging section(s). Also it might be a good idea to remove the signatures to allow the reader to focus on the information. Hope you find this helpful. :)

--[[User:Z3218146|Julianna Lam]] 01:39, 1 October 2009 (EST) great work guys.

- history section is lacking information

- the maturation phases are too detailed and i dont think that much detail is required.

- staging and timeline is excellent. it could look better if there were more pictures added into the staging part.

- the glossary is very helpful

--[[User:Z3254857|Begum Sonmez]] 22:49, 30 September 2009 (EST)
Hello Group 5. I'd like to start off by saying that the effort you all have put into you page is impressive. The first thing I noticed was the background information on the frog such as the embryology, growth and development, anatomy, and the egg of the frog. I found this extra information informative, interesting, and due to the lack of text,easy-to-read and engaging. The video under 'The Egg' depicting Early cleavage was an interesting video. I like how it wasn't placed under timeline or stages. The reason is because timeline and stages already has enough images, and this short and simple video provides an introduction to development.

*You all might have noticed there is a problem with the formatting of the History section (the text needs to be 'pulled down' below the image 'Early Development of Frogs'. The same problem is found under the sections 'Abnormalities of the Frog', and 'Current Research'.
*I think the sentence strucutre, and punctuation of the History section should be looked at. For example, '1851 - Henby Nelson(MD): He identified a remarkable fact through frog embryo. Henby observed the first cleavage of the yolk, in the egg of the frog. And corresponds in its line of direction to the longitudinal axis of the body of the embryo of those animals;' should read:
'1851 - Henby Nelson(MD): He identified a remarkable fact through '''the''' frog embryo. Henby observed the first cleavage of the yolk in the egg of the frog. And ('''what? The Yolk?''') corresponds in its line of direction to the longitudinal axis of the body of the embryo of those animals ('''of what animals?'''). This is just something small that should be worked on just to make more sense, but the amount of text you included is good.
*Under Gametogenesis, the sentence 'Gametogenesis is a progression which frog gametes are established from cells, called germ cells.' should read 'Gametogenesis is a progression '''in''' which frog gametes are established from '''germ cells'''.' Again, this is just a small amendment, but it will still be effective.
*Good pictures under 'Egg and Fertilisation' and under 'Gastrulation'.
*Under Gastrulation, the sentence 'In frogs, metamorphosis is related with to the modifications and adaptations as a frog changes environmental habitats from an aquatic to a terrestrial mode.' should read 'In frogs, metamorphosis is related '''with or to''' the modifications and adaptations '''occuring or taking place''' as a frog changes environmental habitats from an aquatic to a terrestrial mode.'
*Too much unnecessary text under 'Maturation phases'. Try condensing the text under '4. Fertilisation of the egg' and '5.Segmentation of the Egg'.
*There is a good amount of information under the 'Structures derived from Germ-layers of frog species' section. It can be improved by listing (in dot form or numbering) the structures instead of including them all in a paragraph. I really liked this section. To the artist of the drawings: great work. I found them really helpful and relevant.
*Under 'Current Research', try to include dates for 'Transgenesis techniques for functional genomics in Xenopus' and 'Verification of messenger RNA'. Also, is there a specific example of a current research under the sub-heading 'Cell Cycle'. This would be more resourceful for the reader.
*The glossary was helpful.
Overall, well done on your efforts Group 5. The pictures are a great asset to this page.

--[[User:Z3252231|Angama Yaquobi]] 22:01, 30 September 2009 (EST)
Congratulation all the team members of group 5, the page looks amazing. Very well researched. So far one of the best looking
page with alot of informative content.Great images used throughout the entire page especially in the section of the growth and modification of frog species.However i suggest few changes can make the page look even better

* Lack of information in the section of history.

* There is too much information in the maturation phase which can be concised to make it much more easy for the readers to acquire the important information.

* For the section of current research more information is needed to give readers a more in-depth knowledge of the current research done on the model.

Overall well researched page. Well done guys. cheers.

--[[User:Z3186093|Jenny Guy]] 19:01, 30 September 2009 (EST)

Improvements:
* The frog...is a specific breed of frog used? Or are many types used for embryological research? This should be stated in the introduction. The image youve used from wiki is fine except its a "typical frog"...what is this? are you forming your page based on this frog?
* I dont believe the anatomy of the frog needs to be stated. We're researching the embryology, and yes this is going to be different to the human, so state the differences that cause embryology problems. Obviously we're going to be different but if you want to state that the frog only has 3 chambers, state that heart research wouldnt use a frog model since its not similar.
* Need to do some formatting - history heading is misplaced, i almost missed it.
* There is a hell of a lot of information to digest for the fertilisation. Would it be possible to cut some of this down? Select the best parts?
* Stages is very plain. Enough said.
* The image of the frog abnormalities...is it in the wrong spot? Shouldn't it be put close to the skeletal abnormalities paragraph - and refer to the image, and not the infectious diseases section.
* In genetics, can you explain why frogs have different numbers of chromosomes. Does this mean that some breeds of frogs can mate because they would have ill adapting chromosomes? How does the chromosomes it does have relate to human chromosomes??
* i got very confused with the subtypes of families of frogs...is the embryological research affected with modern or primative frogs?
* Has the genome been sequenced? Apparently so? Some of the english here needs to be editted. Grammar isnt good, some sentences dont make too much sense.
* Have you listed "links to related resources/research laboratories?" like Mark asked for in the marking criteria?? nope.

--[[User:Z3218792|Gabriela Pinget]] 14:36, 30 September 2009 (EST) Hello! Nice page! Mind if I criticise?

- I like the use of the anatomy of the frog to better orientate the reader. Although it is slightly superflous, it does not contain too much information to look out of place,so it looks good

-Maybe in the intro you should add a little info on why it is a model for embryological studies i.e. its advantages over the others

- I like the clear structure of the history section. It makes it very easy to read and understand.Although, the poor grammar makes it a little hard to understand (e.g. you may want to re-word what you wrote for 1976, it reads as though a woman was impregnated with a frog)

-perhaps there is a little too much detail on the growth and development of the frog. It's a little overwhelming- also quite a bit of repetition in this section

--[[User:Z3217015|Mitchell Mathieson]] 09:32, 25 September 2009 (EST) I think the looks good. However, the information is very spread out all over the place, and there is a bit of irrelevant information, such as the anatomy of the frog. There also seems to be repeated information in the stages and timelines; such as having tables and text to say the same thing. There was a heavy emphasis on the stages of development (it pretty much takes up 3/4 of the page) which probably could have been done more succinctly. The formatting needs a bit of fine tuning (heading separated from their text, and gaps everywhere), but in general it is good; the information is quite useful and well written.

--[[User:Z3224449|Elide Newton]] 14:57, 26 September 2009 (EST)HELLO GROUP 5: Well done on your assignment. my one piece of advice on your assignment is all about improving the flow and purpose of your assignment. Firstly There needs to be a introduction to the frog. why the frog is used as a model for embryology? By understanding the stages of development and timeline of the frog we can study the frog as a model. Why it is a good model and our understanding can be linked to why is has been used in the past and why it is being used currently in the future. hopefully this introduction clarifies the purpose of your information, and gives an outline to what you will cover in the assignment. also there is lots of unimportant information in regards to this assignment which is clouding your purpose of timeline, stages, genetics, past, present and future research. with this introduction paragraph, stating what topics you will cover and how these fit into using the frog as a model for embryology, hopefully it will flow better. all the best!

--[[User:Z3126328|Jin Lee]] 16:32, 26 September 2009 (EST) congulatulation Group5. The assignment looks good however, if you can make some additions it will be even better. Here is my suggestions: firstly the reference needs to be looked after. secondly some of sections are irrelevant(I found the 'anatomy of the frog' is irrelevant) and too much general information about the frog. May be better to focus on the assignment cirteria. For the history section, information is lacking(it's too brief) may be trying to add some more details about the each scietists...eg. in 1976, please mention which doctor you are reffering to. For the current research section, some more information needs. Overall, the assignment is visually well represented but may be concentrate on the main sections like timeline, stages, genetics, history and current research.

--[[User:Z3187802|Vishnnu Shanmugam]] 21:37, 26 September 2009 (EST)Great work frog group. The assignment you have put together is informative and well organized. One of the best features of the project is how clicking on the image takes you to another page with detailed and thorough explanations of the image. It is also good to see that you have added extra sections such as “abnormalities of the frog” and “the egg”. I note that too many groups are only interested in the headings specified in the marking criteria and have not done any extra work. The glossary is also a nice touch. Ways of improving the assignment:

- The background section introducing the frog needs to have information on why the frog model is useful. Include information on spawning, maintenance of specimens, genetic attributes and genetic similarities with humans.

- Although the addition of extra sections is good, it needs to be relevant to embryology. The anatomy of the frog section concentrates on the anatomy of the adult frog which is irrelevant for this project.

- The assignment should contain links to research laboratories and researchers as specified by the marking criteria. The external links do not do this.

- Remove the signature and time stamping at different sections of the assignment. The group project is collective effort, and the final presentation should not look like it has been split up. Do not worry about your contributions as these are logged and available for viewing under the “my contributions link”

- Some links in the text transfer you to Wikipedia pages on the frog....these should not be used as a source of information in academic projects.

- The assignment needs to be properly referenced as there are no references made in the actual text. see www.lc.unsw.edu.au/onlib/ref_apa.html for help with APA referencing

Overall a good project, some changes and additions are necessary to make it outstanding.

--[[User:Z3252340|Emily Wong]] 11:06, 27 September 2009 (EST) Firstly, Great work group 5. This project is very informative, well structured but a little unorganized. There is an extremely large amount of text presented. Perhaps a few more pictures or diagrams to negate some of the written work would be a way to improve the project. The work is well referenced with an extensive reference list. There is a lot of information on content that is not required. A way to improve your project would be to summarise a lot of this unnecessary information and maybe try and place it under one of the content headings. It appeared that a lot of this information was about stages or time points so maybe you could include this information in one of those sections.

--[[User:Z3217686|Thomas Dangerfield]] 14:25, 28 September 2009 (EST)Hey guys! Nice job! Plenty of information present, it just seems to jumble around a lot. Definitely needs an introduction, and possibly the first available section could be moved to after the anatomy of the frog. I don't mind the basic anatomy of the frog by the way, as it provides a little background to what the reader is going to end up with at the end of the development stage. Also the images could have a caption about what is actually happening in the image or what the images are trying to describe. There also seems to be a whole of a lot of information and plenty of images on the development and growth of the frog, but comparatively little on the genetics section. Chromosome maps can be very handy and comparisons with the human genome can help establish a picture of what you are trying to say. Just some organization and possible sifting of information would do the assignment nicely! Still, a very nice job on the frog guys!

--[[User:Z3185685|Sumaiya Rahman]] 17:16, 28 September 2009 (EST) Hey guys! Wow congrats on the assignment. I actually like the extra topics on the page. It makes it interesting and gives a lot of background knowledge to the reader. As mentioned, i am not sure why you have put in your signature stamps, this is not necessary. A lot of good images have been used but maybe instead of using figure 1, figure 2 etc. under the images; you could write what the image actually shows. I think this is what we were told to do? The links to the images in each stage are really good and help convey the information. The other thing that would help improve your page would be the addition of a glossary. Well done overall!

--[[User:Z3215682|Carly Mooney]] 11:56, 29 September 2009 (EST)
I think this was the assignment that looked the most professional. I liked the additional anatomy of the frog section, Few suggestions:
*a proper paragraphed introduction
*perhaps either in introduction of the history of the model needs a small explanation of why you use the frog as a model.
*remove the signatures, it is distracting and looks like it wasn't a group effort
*some sections were well referenced and others not, this needs to be unified.
*I think some of the sections with single images can afford to have those images enlarged slightly.
Overall this assignment looks the most unified of them all so congrats.

--[[User:Z3220040|Joanne Raffel]] 16:41, 29 September 2009 (EST) Well researched page. I would recommend including an introduction, which would make a better transition into the next section, also the growth and development, the egg and the anatomy section could have been condensed into one section. I thought there was too many main headings, I would recommend including subheadings, otherwise the information seems disjointed. I also got very confused reading through the page as I wasnt sure which heading was apart of another or whether it was something completely new. The history section was well formatted, however more information would have been appreciated as there didnt seem to be much of the actual history, more of a timeline of the frog. I thought the gametogenesis section was irrelevent. I also didnt need to know who wrote what section, this is a group assessment. Some of your headings could have been phrased more appropriately and clearer. The egg and fertilisation section would have been more impressive with subheadings rather than continuous main headings, whereby allowing the information to flow, also some of the information wasnt introduced in each section, it was just assumed. The maturation section would be better formatted in a table rather than a chunk of text. Cleavage, gastrulation, growth and modification, germ layer origin and structures derived from germ layer would be better as one section rather than multiple. The life cycle was extremly short and lacked information. The timeline was well formatted however I would have liked pictures. The staging section was organised clearly, however I would have liked to have seem part of the image rather than having to see it via the link. The abnormalities and genetics section would have been clearly as paragraphs with more information describing what is occuring rather than listing it, pictures would also be appreciated if possible. The current research section covered a number of topics however each section was very short. The glossary was appreciated however some of the words werent necessary (i.e. aquatic). Overall a very good page with some interesting images.

----

--[[User:S8600021|Mark Hill]] 01:50, 8 September 2009 (EST) Still coming along, you have a lot of interesting pieces of information and some fair images. But how do the images relate to the text and where is the linkage? It is always easier to paste a whole lot of text information without interpreting what it actually means. Some of the information is good, tough some text also looks to be sourced without referencing. Overall the page lacks an integrated feel and structure.

--[[User:S8600021|Mark Hill]] 08:45, 21 August 2009 (EST) This is a good start. It is important that the project page content/structure reflects what all members of the group have in mind. There should be a list of relevant references now on this discussion pages.

== Background Reading ==

--[[User:Z3255007|Sadaf Masood]] 21:44, 8 September 2009 (EST) This link is for you Gary
http://www.xenbase.org/xenbase/original/atlas/NF/NF1-10.html

--[[User:Z3126345|Gang Liu]] 15:18, 23 September 2009 (EST) hi could anyone tell me how to upload pictures on the main page. i'm trying to upload pictures from this link http://www.xenbase.org/xenbase/original/atlas/NF/NF1-10.html, into the last column of stages of frog embryo table. cheers!

Hey guys!!

I have only met one person in the group..and that was today in the lecture (3/08/09)

Still missing out on the third person here!

Lets decide on the animal guys before the lab!!!!

Cheers!

--[[User:Z3126345|Gang Liu]] 15:22, 16 August 2009 (EST)Hi all, I'm Gary and i've just enrolled into this subject mid-week last week. Will try to catch up with the group assignment and individual homework.

--[[User:Z3126345|Gang Liu]] 14:54, 19 August 2009 (EST)Hi group, since we are dividing the assessment. I would like to work on sections such as "The egg", "Fertilization", "Cleavage", "Gastrulation", and "Hand-drawing diagram". Thank you.

--[[User:Z3126345|Gang Liu]] 12:56, 20 August 2009 (EST)Hi all, Joe is working on the first six subheadings. And i'm happy to take whatever subheadings the rest of the group is not working on. Thank you.

--[[User:Z3126345|Gang Liu]] 14:07, 20 August 2009 (EST)Hi all, after this week's group dicussion in the lab, we split the tasks as the following:
*Joe is responsible for subheadings such as egg, fertilization, cleavage, gastrulation, differentiation and growth;
*Gary is responsible for subheadings such as anatomy of frog, timeline and stage(introduction), and abnormalities;
*Sando is responsible for subheadings such as reproduction(male and female)+random subheading;
*Sadaf is responsible for subheadings such as current research, genetics and glossary.

--[[User:Z3126345|Gang Liu]] 17:26, 23 August 2009 (EST)Hi all, should we mention ''Xenopus'', part of frog family? --[[User:Z3126345|Gang Liu]] 09:29, 27 August 2009 (EST)Please ignore this line

--[[User:Z3126345|Gang Liu]] 18:00, 26 August 2009 (EST)Joe, thank you for updating our group page. Will upload my contents as soon as possible.

Hey guys, i need the list of words for the glossary or do u want me to pick them out myself?
thanks!--[[User:Z3255007|Sadaf Masood]] 10:47, 27 August 2009 (EST)

--[[User:Z3126345|Gang Liu]] 11:24, 27 August 2009 (EST)Hi, sadaf, will upload my glossary by tomorrow. Thanks.

--[[User:Z3126345|Gang Liu]] 11:30, 27 August 2009 (EST)Hi group, i just realised there is no one doing history part. Is there anyone would like to take this part? Or else, i'll work on it. Let us know.

http://books.google.com.au/books?id=OeAf7ChZD8QC&printsec=frontcover&dq=frog+embryology&lr=#v=onepage&q=&f=false

sick website

http://www.youddl.com/

EGG:

http://www.youtube.com/watch?v=GO5YN_t1fqw
--[[User:Z3258567|Sando Rashed]] 18:17, 23 September 2009 (EST) as late as im posting this i havent had time this past week to upload my notes but im putting them up now

--[[User:Z3258567|Sando Rashed]] 18:18, 23 September 2009 (EST)Gastrulation of a frog embryology
An invagination of cells that is found in the area of the embryo where it occupies the middle of the gray crescent, this is the beginning of gastrulation.
This beginning is what creates the blastopore which in the future will become the anus, and a group of cells that would later on produce the notochord which will eventually become the backbone (also known as the speeman organizer). Stimulates the ectoderm to form neural tissue (rather than it forming skin), so it begins the staging of the neural folds, which eventually the tips of the folds will form the neural tube which will become the spinal chord and the brain.
During gastrulation three layers start forming, these layers are known as the ectoderm, endoderm and the mesoderm.
Layer Forms out of it

----
Ectoderm which may form the Brain, skin, spinal chord

----
Mesoderm which may form the Notochord, muscles, brain

----
Endoderm which may form the Inner lining of lings, bladder, thymus forms here.

--[[User:Z3258567|Sando Rashed]] 22:24, 23 September 2009 (EST)Cleavage = the repeated division of a fertilised ovum
When the zygote nucleus forms the first cleavage forms, this nucleus undergoes a number of mitosis processes, a wrinkle forms down longitudinally passing the poles of the eggs where the sperm enters. This is how the egg is split up into two halves and this process is what forms the 2-cell stage.
The process of the second cleavage is the process that allows the 4-cell stage to occur, the wrinkle runs through the poles at right angles instead of running through it longitudinally.
The 8 stage cell is formed during the third cleavage it cuts across horizontally but it cuts through closer to the animal poles rather than the vegetal poles.
As cleavages continually occur a 16 and 32 cell embryo are formed, and as these cleavages continuously occur the cells closer to the animal poles divide more rapidly and in more numbers compared to the vegetal pole. Eventually with all these cells continuously forming the blastula forms and a blastoseal which is a fluid filled cavity forms within it (no growth of the embryo has formed).
--[[User:Z3258567|Sando Rashed]] 23:06, 23 September 2009 (EST)Anatomy of a Frog
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The anatomy of a frog has many specialized features that are unique to the frog to help them live in their environment, they have long sticky tongues that help with them to grab food, they have specialized bones in the legs to help them jump.
When under water frogs are able to breathe through their skin, the oxygen is able to diffuse straight into the blood through the pores on the skin; they also have lungs that allow them to breathe on land.
In frogs they have 3 valves instead of the 4 valves in humans, they have one ventricle and two atria’s, the spiral valve does not allow blood with oxygen to mix with blood that has no oxygen.
Frogs are able to listen to sounds that have a low pitch through their skin as well as hearing sounds with a high pitch through their ears.

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The Egg

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The egg of a frog is approximately 1.6 million times larger than a normal frog cell. While all the embryological development is occurring through time it will eventually become a tadpole.
The egg can be divided into three different regions, the top part of the egg is known as the animal pole, the bottom half of the egg is known as the vegetal pole and a segment between the animal and vegetal pole is known as the gray crescent.--[[User:Z3258567|Sando Rashed]] 10:09, 24 September 2009 (EST)

Fertilization
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This occurs once the sperm cell has inserted, following the insertion of the sperm cells meiosis II is completed, there is a 30 degree position change of the cytoplasm, gray crescent allows this change to be visible in some amphibians, the gray crescent is able what determines the expect ted outline of how the frog will form. The sperm cell joins with the nuclei of the egg which forms the diploid zygote nucleus. --[[User:Z3258567|Sando Rashed]] 10:09, 24 September 2009 (EST)

2009 Group Project 5

2009-10-15T00:17:08Z

Z3258567: /* References - Frog Embryology: */

== The Embryology of Frogs ==

== The Frog ==

[[Image: Frog species .jpg|thumb|left|Image details: Wikipedia (2009) Frog species[http://en.wikipedia.org/wiki/Frog#Uses_in_agriculture_and_research].jpg]]

Frogs are scientifically identified by the structure of their long posterior limbs, a petite framework, webbed fingers and feet, budged eyes and the lack of a tail. The majority of frog species are extensively recognized as outstanding jumpers, due to their long, dominant legs, which are adaptations to progress jumping performance during activities. The Frog is one of the most frequently studied species in experimental embryology and most anatomical sciences. ''The Frog is a practically effective model for human embryological development given that the Frog:''

- Comprises of genes which can be effectively manipulated.

- Comprises of similar homogeny with humans species.

- Reproduces a large quantity of offspring in a short period of time.

- Are small species which can be simply sustained.

- Are not extremely luxurious and expensive.

== The History of the uses in agriculture and research ==

[[Image: Frog experiments .jpg|thumb|right|Image details: Scans of chemically cleared and dyed preserved deformed frogs and toads [http://www.sat.qc.ca/upload/residence/frog-04.jpg].jpg]]

There are numerous types of frog species that have been manipulated in many developmental experiments. The frog was traditionally used by countless of the early embryology investigators and presently there are several diverse molecular mechanisms regarding progression of the frog. Theses include:

'''1.''' Food source; frog legs are a delicacy and are eaten in European countries and in many parts of South American regions.

'''2.''' Frogs have the finest biochemical dissection of phenomena that take place in the egg and oocyte. Frogs are the evolutionarily closest to mammals, commonly used as a vertebrate model.

'''3.''' Frogs lay thousands of outsized eggs, from which cell extracts can be readily prepared that is capable of recapitulating most molecular phenomena in a test tube.

'''4.''' Frogs have been commonly used as a laboratory system for a very long period, and have an extensive history of producing crucial observations in countless fields of biology.

'''5.''' Frogs have a important historical connection to the study of epigenetics (John Gurdon-vertebrate cloning and reprogramming) which has been mostly performed on frog species.

'''6.''' Frogs also have very strong evidence of pattern formation and early development, as the embryos are large in size and experimentally manipulative.

'''7.''' Recent research into the biochemistry of chromatin and epigenetics has been performed with frog species and mammalian cultured cells.

'''8.''' The biggest weakness of the Frog model system is the difficulty of performing genetic experiments and analysis, as frogs are allotetraploid, meaning they take approximately a year to fully develop to sexual maturity, and the genome has not been completely sequenced. Nevertheless, biochemical manipulations of cell extracts, such as immunodepletions and application of heterologous DNAs and nuclei can avoid the need for genetic exploitation.

----

== Growth and development of the Frog ==

[[Image: Mature develop frog.jpg|thumb|Image details: Wikipedia (2009) Red Eyed Tree Frog Figure 1 Primary source:[http://en.wikipedia.org/wiki/File:Red-eyed_Tree_Frog_-_Litoria_chloris_edit1].jpg]]

* The frog is a well recognised species, abundant predominantly in ponds, swamps, though various species may also exist in damp or shady environments distant from moist habitats.

* Eggs of specific frogs are easily obtained and may be examined in from the beginning of fertilization onwards. The phases of embryonic development differs in various chordates, yet the typical phases are basically apparent in all frog species. The differences are associated principally to the amount of yolk particles present in an egg.

* The yolk particles offer nourishment of the developing embryo. The process of frog development will be discussed from the phases of gametogenesis to the adult stage.

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== The Egg ==
[[Image:Development of Poles in frog Fertilization.jpg|thumb|left|Development of Poles in Frog Fertilisation:J,Nassif 2009.jpg]]

- The embryology of a frog egg is a vast cell; its dimensions are approximately 1.4-1.6 million times larger than a typical aquatic species egg cell. Throughout the frog’s embryonic maturation period, the egg will be transformed into a tadpole encompassing millions of cells but still remains with its constant volume of genetic material, the vast prodction of cell have been illusttrated in the figure on the right revealing the production of eggs from female frogs. [http://en.wikipedia.org/wiki/Microhylidae]

- The early embryonic frog structure consists of three main segments the superior hemisphere known as the animal pole which is usually visible as a grey coloured area. The innermost layer appears to be between the outer two sections known as the gray crescent represented in black. Inferiorly, represents the vegetal pole typically lighter than the superior compartment illustrated in gold.

VIDEO RESOURCE: [http://www.youtube.com/watch?v=GO5YN_t1fqw&feature=related]

[[Image:Early Development of Frogs.jpg|thumb|left|Early Development of Frog:J,Nassif 2009.jpg]]

==History of frog embryology use ==

*'''1851''' - ''Henby Nelson''(MD): He identified a remarkable fact through the frog embryo. Henby observed the first cleavage of the yolk, in the egg of the frog. And cleaved structure corresponds in line of direction to the longitudinal axis of the body of the embryo of the frog species.

[[Image:Wilhelm Roux.jpg|thumb|right|Wilhelm Roux[http://images.google.com.au/imgres?imgurl=http://www.todayinsci.com/R/Roux_Wilhelm/RouxWilhelmThm.jpg&imgrefurl=http://www.todayinsci.com/6/6_09.htm&usg=__qRLTEMTHdZpAHxiNX12hWjcm9tA=&h=125&w=100&sz=4&hl=en&start=2&um=1&tbnid=LIKIwZTqCpk7MM:&tbnh=90&tbnw=72&prev=/images%3Fq%3DWilhelm%2BRoux%26gbv%3D2%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

*'''1888''' - ''Wilhelm Roux'': Wilhelm Roux attempted to solve the above observation by damaging one cell of a two-cell frog embryo with a hot needle. The cell stayed in place. However, it did not develop further. Its partner developed into a left or right half-embryo;

*'''1907''' - ''John Hopkins'' hospital: In order to identify the cellular source of neuronal fibres. Scientist placed small portions of frog embryo spinal cords in lymph on a microscope slide and was able to observe clear cut neuronal sprouting.

*'''1951''' - ''Robert Briggs'': Robert Briggs was able to clone a frog embryo by substituting the nucleus of an unfertilized frog egg cell with the nucleus of a frog embryo cell. This process is known as nuclear transplant, has formed the basis for all cloning.

*'''1952''' - ''Robert Briggs and T.J. King'': Robert Briggs and T.J. King used frog for test experiment. Because the size of the eggs in the frogs are enormous compared with those of mammals, which make them easier to manipulate.

*'''1976'''- Using the technique that had been successful in cloning frog embryos, the doctor transferred the nucleus of one cells into a donated egg cell. As an embryo began to develop, it was implanted into the uterus of a young woman.

*'''1997''' - ''Wilmut and Campbell'': Utilizing the cloning technique from frog embryo, Drs. Wilmut and Campbell tried the starvation technique on embryo cells to produce Megan and Morag, the world's first cloned sheep and, until now, the most famous sheep in history.

*'''2000''' - ''Tokyo University'': Scientists at Tokyo University have grown artificial eyeballs. Scientists formed them in tadpoles by using frog embryo cells.

*'''2001''' - ''Advanced Cell Technology'': Scientists from Advanced Cell Technology announced production of a human embryo clone. This is significant as its parthenogenesis has been artificially induced in frogs.

[[Image:John Gurdon .jpg|thumb|right|John Gurdon [http://images.google.com.au/imgres?imgurl=http://www.pnas.org/site/misc/images/gurdon.jpg&imgrefurl=http://www.pnas.org/site/misc/classics4.shtml&usg=__1p-GA1PdOYsxKL-cznMb3RHCm98=&h=526&w=400&sz=223&hl=en&start=1&um=1&tbnid=9k4lhuLssiWCAM:&tbnh=132&tbnw=100&prev=/images%3Fq%3DJohn%2BGurdon%26gbv%3D2%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

*'''2002''' - ''John Gurdon'': John Gurdon from Wellcome Cancer Research Institute in Cambridge experimented on cloned frog embryo.

== Gametogenesis ==

* The sexual reproduction occurs through the fusion of either mature reproductive cells or germ cells known as gametes, which include the sperm from the male frog and ova from female frog species so as to form a single cell, the fertilized zygote. The gametes are typically developed in parents of different sexes . [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

* Males gametes is a spermatozoon , the female frog gamete is an ovum. Each gamete is formed by a process, recognised as maturation or gametogenesis in gonads. The typical male frog gonads are testies in male, while the female gonads are ovaries. The synthesis of both gonads is associated with the process of fertilization. [http://en.wikipedia.org/wiki/Microhylidae]

* The zygote changes into a mature frog through the process of embryology and metamorphosis. Gametogenesis is a progression in which frog gametes are established from germ cells. Initial germ cells are called primordial germ cells, which can be recognised extremely early in the life of frog species.

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== The Egg & Fertilization ==

[[Image:Fertilized and Unfertilised Eggs.jpg|thumb|left|Fertilized and Unfertilized Eggs:J,Nassif 2009.jpg]]

[[Image:Egg Development.jpg|thumb|left|Egg Development:J,Nassif 2009.jpg]]

- This occurs once the sperm cell has inserted, following the insertion of the sperm cells meiosis II is completed, there is a 30 degree position change of the cytoplasm, gray crescent allows this change to be visible in some amphibians, the gray crescent is able what determines the expect ted outline of how the frog will form. The sperm cell joins with the nuclei of the egg which forms the diploid zygote nucleus. --Sando Rashed 10:09, 24 September 2009 (EST)

- The early phases in the development of the egg is visible, but must be studied in tadpoles throughout maturation. In embryonic tadpoles of about 10 millimetres in length, soon after the opening of the oral cavity, a pair of longitudinal ridge-like thickenings of peritoneum becomes apparent along the posterior surface of the body cavity situated near to the mesentery and along the inner boundaries of the kidneys. Genital ridges are established in all tadpoles of this age, sex is not distinct until a later period. The development of the egg is illustrated in the figure on the left revealing the structure of a developed egg and a mature of egg.

[[Image:Fertilisation life cyle.jpg|thumb|Fertilization of Life cycle:Derived from primary source:[http://en.wikipedia.org/wiki/Frog]]]

== Maturation of the Egg ==

- The eggs have currently accomplished their full size, and develop from the exterior of the ovaries like a small shot, but they still have to pass through the course of maturation before they are prepared to be fertilised. This progression of maturation relates to the nucleus almost completely.

- The nucleus component, containing the nuclear fluid that excludes through the nuclear membrane into the substance of the egg, a great segment of the nuclear reticulum vanishes and becomes degraded into separate globules known as nucleoli, but a extremely small division remains in the midpoint as a slender intricately thread recognised as the nuclear skets.
Relative to the egg getting discharged from the ovary, the follicles shatter allowing the eggs to fall into the abdominal cavity of the frog species, the egg then passes forwards, directly by the contraction of the muscular wall, somewhat by the movement of the cilia of the peritoneum, to the apex of the oviduct, which positioned at the anterior compartment of the body cavity opposite to the roots of the respiratory organs.

- The terminal part of the oviduct establishes a thin-walled pouch capable of great swelling, inside which the eggs gathers in large numbers. In conclusion, the eggs are migrated out through the cloaca into water which the albuminous investments of the eggs rapidly augment to form the gelatinous mass of the frogs spawn.

== Maturation phases ==

'''1. Nuclear skein''', moves from the midpoint of the egg to its outer surface, which it reaches opposite the midpoint of the black pole. The skein, subsequently an unevenly twisted thread, now presumes the specific arrangement of a nuclear spindle, for instance may be visible in the nucleus of an epithelial or additional cell instantly prior to division of the cell occurs.[http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

'''2. The first Polar Body,''' regarding the instance the egg is laid, but prior to its fertilistion, the egg develops a considerably flattened appearance at its upper or black pole, a definite sum of fluid being exuded among the egg and the vitelline membrane. The nuclear spindle currently separate into two identical segments, one of which remains with the egg, and the supplementary is extruded as the first polar body, a small ovoidal white globule, which is situated on the surface of the egg surrounding the exuded peri-vitellline fluid.

'''3. The Second Polar Body''', half of the nuclear spindle that stay behind then splits into two equivalent divisions, one of which remains inside the egg as the female pronucleus, whereas the other segment is extruded as the second polar body, a small white globule extremely related to the first polar body, and like this positioned in the perivitelline fluid on the superior portion of the egg.

'''4. Fertilisation of the egg''', includes the synthesis of the spermatozoon with to egg, specifically, synthesis of the nuclei of these two bodies. The spermatozoa, subsequent to being shed over the seed by the male, distribute vigorously by means of their extended tails, break through the gelatinous investment of the female eggs, bore their way through the vitelline membrane and so go through into the eggs themselves, which they penetrate relative to the superior or black hemispheres.
* Subsequently, an hour following the spermatozoon has entered; a progression may be visible projecting within from the exterior segement of the egg, with a liquid spot in the mid point. This liquid centre is the nucleus of the spermatozoon, and is said to be the male pronucleus, it break through beyond into the female egg, transporting the specialised pigment into it, so that it appears bounded by a pigmented capsule linked with the exterior of the egg by a pigmented stalk.

* By this instance, the second polar body has been established and extruded, and the female pronucleus is merely the only component of the primary egg nucleus still present. Both the male and female pronuceli, which are at initially distance separate to each other, merge and after having enlarged significantly in size then fuse mutually about two and half hours after fertilisation has originated to produce the segmentation nucleus.
* The segmentation nucleus is a huge sphere-shaped vesicle embedded in delicately granular protoplasm, and bounded by a distinct capsule of pigment, its arrangement by the synthesis of the male and female pronuclei completes the action of fertilisation. Specifically female pronucleus may be observe as an imperfect nucleus, and consequently result in the course of fertilisation. The nucleus of the spermatozoon or male pronucleus, replaces the component of the egg- nucleus which has been misplaced as the polar bodies.

'''5. Segmentation of the Egg''', the initial phase of growth consist in constant separation of the egg, whereby it becomes transformed from the unicellular state, which is everlasting only in the lowest species, to muliticelluar state charactertics of all higher species. To these early processes of growth the names segmentation is specified. Shorty subsequent to the competition of fertilisation and arrangement of the segmentation nucleus this later misplaces its sphere-shaped appearance and develops to be spindle-shaped, the yolk granules at the equivalent instance showing a tendency to develop into lines distributing outwards from the distal segment of the spindle.
* The nucleus now split into two halves, which shift away from one another, the yolk granules are likely to combined themselves around the two nuclei, and a slender vertical plate of delicately granular substance is left, dividing the egg.[http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

* Superiorly the eggs depression now becomes visible, initially as a small cavity and then develops as a groove, which almost immediately extends all round, and speedily deepening, splits the egg into two entirely separate halves along a plane equivalent with the vertical plane.

* Shorty after, the two nuclei soon separate again into two, and therefore a second cleft is created in the same state as before, its additionally in the vertical plane, however in a plane at 90 degrees to the initial one, and on its finishing point the egg comprises of four accurately similar segments, each containing a nucleus. The third cleft is horizontal in shape, but not equal, lying closer to the superior than the lower pole, it segregates each of the four cells into, an superior smaller and a inferior larger pole

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== Cleavage ==

[[Image: Frog Cleavage development.jpg|thumb|left|Cleavage Process details:[http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/F/FrogEmbryology.html].jpg]]

* The egg of the frog is scientifically identified as’ telolecithal’ meaning there is a outsized amount of yolk concentrated at a single pole, in contrast to the concentration of cytoplasm and the site of the nucleus. The cleavage phases are holoblastic, therefore the total and after the second cleavage they are asymmetrical .The initial cleavage stage appears about two and half to three hours after fertilization. It commences as a minor depression in close proximity to the centre of the animal hemisphere. It appears as if some interior force is pushing the surface the egg towards the centre. This small upturned fold steadily continues in the form of a channel until it surrounds the egg. This groove is shallow in the commencement, but develop into deeper eventually separating the fertilized egg into two halves recognised as the blastomeres. [The figure on the left symbolise the development and growth of the frog embryo during cleavage].

* Internally the separation is mitotic, consequently each daughter cell contains a nucleus resulting from the copulation nucleus of the fertilised egg. This cleavage is vertical, the two cells are indistinguishable in respect of cytoplasm, pigment and yolk. The subsequent cleavage appears about an hour after the first. The channel of this cleavage begins at the centre of the animal hemisphere, is at right angles to the first and is vertical. This divides the egg into four blastomeres. The fourth blastomere so produced are not qualitatively equal, since of these only two contain the material from the gray crescent. The cleavage begins about thirty minutes after the second is completed or four hours after fertilisation. the cleavage plane of the third furrow is horizontal and slightly above the equator. Thus the four upper cells are a little smaller than the four lower cells. The smaller blastomeres are called micromeres and the larger blastomeres are called macromeres. The fourth cleavages follow 20 minutes after the third and tend to be vertical. This is usually a double furrow.

* The cleavage rate is accelerated with each of the early divisions and since the blastomeres are of unequal size and have varying amounts of cytoplasm and yolk, synchronous cleavage is lost and there is an obvious overlapping of the division. The upper most cells divide more rapidly than the lowermost cells. From this point onwards perfect symmetry in cleavage and in blastomere is very rare, although the embryo developed perfectly. The fifth cleavage is also doubled, appearing first in the upper hemisphere and then in the lower.

* The cleavage thus far follows the rule that each cleavage plane comes in at right angles to the previous one. The subsequent divisions become so irregular that it is previous one. The subsequent division become so irregular that it is impossible to trace out any plan or procedure. The segmentation continues more rapidly in the pigmented regions, since at that place the protoplasm is most dense, whereas, yolk which is very abundant in the vegetal side delays cell division. The multicelluar embryo at this stage is called morula by some biologists.

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== Gastrulation ==

[[Image:FROG GASTRULATION .jpg|thumb|left|Frog Gastrulation Image details:[http://www.google.com.au/imgres?imgurl=http://bio1903.nicerweb.com/Locked/media/ch47/47_12FrogGastrulation.jpg&imgrefurl=http://bio1903.nicerweb.com/Locked/media/ch47/gastrulation-frog.html&h=540&w=480&sz=46&tbnid=N78sHjELreGGSM:&tbnh=132&tbnw=117&prev=/images%3Fq%3Dfrog%2B-%2Bgastrulation&hl=en&usg=__4VK9FYLft0W-4lBe6p5EtQAMiaI=&ei=qPy5SurtMJvE6wON8JmdAg&sa=X&oi=image_result&resnum=4&ct=image].jpg]]

''The phase of Blastulation is followed by the unique developmental progression of gastrulation. The process of frog gastrulation involves the following processes.''

'''1. Epiboly Phase'''

The pigmented cellular materials of blastula have the propensity to overgrow the yolk cells within the developing content. This course which is known as epiboly commences gradually in the final blastula and rapidly accelerates with advancing gastrulation development. The cellular matter within the animal pole reproduces and matures on all sides except in area surrounding the dorsal lip of the blastopore has been established.

'''2. Convergence'''

Scientists suggested that the unfolding was thought to result in spreading of the superficial cells over a substrate with suitable absorption properties. Consequently epiboly and convergence are an outcome to this spreading tendency, which is actually increased by a reduction in surface tension of the distributing cells.

'''3. Rotation'''

The epiboly phase is maintained until the region of the dorsal lip has migrated and is a to some extent greater than 90 degrees and the region of the white blastopore is reduced to small circular rings. This section will be positioned away from the developing vegetal pole. Laterally the complete developing gastrula has been rotated to a horizontal axis, allowing it to lie at right angles to the original median plane of the egg. Therefore, the course of rotation is such that the dorsal lip is practically pushed backwards in one direction as rapid or quicker than epiboly moves it forward in the other. The outcome will be that the blastopore produced at roughly the vegetal pole is posterior, and the dorsal and ventral lips are essentially dorsal and ventral. This in addition allows the eggs to form the antero-ventral side of the potential embryo whilst the area marked by the grey crescent is to develop the dorsal segment.

'''4. Invagination'''

Visible is a small fissure- like invagination which is apparent in the middle between the equator and the vegetal segment. The most superior or dorsal border of the cleft produce the dorsal lip of the blastopore. This imput move back and forth on the dorsal plane near the dorsal lip and migrates around the boundaries of the blastocoel in company with the extension of the lateral lips. This adapted invagination is maintained until the blastocoel cavity has been almost abolished; excluding the slender opening separating epiblasts from the hypoblast, the new segment formed is known as the archenteron cavity.

'''5. Involution'''

- Additional to previous course of action a distinct involution also occurs at the blastoporal borders. This is mainly dynamic at the median dorsal lip and gradually more less as it shifts across either side until it reaches the ventral lip where it constant.Throughout this progression, cells positioned beside the superior boundaries of the blastoporal lip migrate over the lip to the interior portion of the lip. These cells are remained within the embryo along the internal edge of the blastopore. This indicates the root of archenteron is composed of involuted cells and beyond this the external layer known as the ectoderm. The base and lateral sides are enclosed mainly of endodermal cellular material, which have been established from larger yolk cells, situated in the vegetal pole of the blastula.

- In the final phases of the gastrula development, the cells contributing to the floor of the archenteron, thin out significantly where they surround the blastocoel.
The hemispherical shaped dorsal lip of blastopore which become visible at the commencement of the gastruation stage carry on to augment, initially becoming semicircular, then transform into a horse shoe shaped and then finally forming into circular band. The band is the accomplished by the blastopore. Various yolk cells of vegetal pole present in the section are crowed into the blastoporal cavity where they form a gathering identified as a yolk plug. Blastopore rapidly reduces in size while the archenteron is still developing and becomes completely formed in the final stage; the yolk plug appears as only a small oval on the gastrula.

==Growth and Modification of Frog Species==

'''1. Changes in habits and habitats:'''

'''a)''' In frogs, metamorphosis is related with or to the modifications and adaptations occuring or taking place as a frog changes environmental habitats from an aquatic to a terrestrial mode. Metamorphosis has modified the adaption of frogs as this alteration it began during the aquatic adaptations in the surface of water to breathe air. Subsequently, it continues the terrestrial surroundings, therefore the frog species become abundant in vegetation area allowing the frog to transform in to amphibious species.

'''b)''' The transition during metamorphosis is linked with a change in food chain. The tadpoles being the embryonic origin of frogs are herbivorous, feeding on algae and green matter, which they collect by the adapted feature such as their teeth surrounding their mouths. Adult frogs, alternatively, are classified as carnivorous feeding on insects and worms. Occasionally, they also consume larger prey, for instance smaller frogs species and even little birds and rodents which they dominant and ingest.

[[Image:Development of frog from sperm to mature structure.jpg|thumb|left|Development of Frog from sperm to mature structure Image details:J,Nassif 2009.jpg]]

'''2. Changes in Morphology'''

These include the decrease or complete absence of specific organs or structures which are essential during development of early frog embryology, but not critical in the mature frog species. The significant alterations of this nature include the following developmental structures.

'''a)''' The long tail of the tadpole alongside the fin folds is absorbed again during metamorphosis and becomes absent at the final stage of the metamorphosis.

'''b) '''The developing gills are resorted, the gill clefts are congested and the branchial cavities start to become absent. The reabsorbtion of gills also takes place by autolysis.

'''c)''' The teeth of the perioral disc additionally the homey lining of the jaws are shed.

'''d)''' The lateral line sense organs within the skin of tadpoles vanish throughout metamorphosis.

'''e)''' The cloacal tube begins to condensed and reduced.

'''f)''' Various blood vessels, together with parts of the aortic arches, are reduced during mature development.

(The figure on the left represents the transformation from a tadpole to a developing structure.)[http://science.jrank.org/pages/2862/Frogs-Adult-morphology.html]

'''3. Progressive or constructive changes'''

This process comprises of the development of specific organs which mature into functional systems only during metamorphosis.

'''a)''' During development the limbs continue to augment in size and differentiation. The forelimbs, which in the tadpole mature under the opercular membrane, which then break through to the exterior. Simultaneously there is a increase in the length and strength of the hind limbs, joints develop in them and the toes become visible.

'''b)''' The middle ear becomes apparent in relation with the first pharyngeal pouch. The tympanic membrane matures. It is bounded by circular tympanic cartilage which allows the frog to retain air.

'''c)''' The visual organs bulge up on the dorsal surface of the head developing the nictitating membrane.

'''d)''' There is augmentation of the tongue and the formation of thevomerina teeth.

[[Image: Growth model.jpg|thumb|Growth Model Image details:J,Nassif2009:]]

'''4. Remodelling of some structures'''

Systematic organs which operate both in the early embryonic larva and the mature adult change their differentiation during metamorphosis so as to meet the requirements of the adult mode of life and due to the habitat adaptations. The figure on the right illustrates structures developing from specic germ cell layers.

'''a)''' The skin of the embryonic tadpole is lined with a double-layered epidermis. The number of layers of cells in the epidermis augments throughout metamorphosis. Superficial surface layers become cornified. Multicellular mucous and serous glands originate in the skin. The pigmentation of the skin continuously changes, new patterns and colour start to form.

'''b)''' There is a lengthening of the mouth gap as a result of rotation of the quadrate cartilage and the true jaws become functional.

'''c)''' The tongue rapidly progresses and becomes larger and more muscular.

'''d)''' The eyes become more specialised.

'''e)''' In early tadpoles, the GIT is extremely long and wound up into a spiral folds. The intestine become greatly lengthened in herbivorous species due to the vegetables food chain.[http://en.wikipedia.org/wiki/Frog]

'''5. Development of the reproductive system'''

(The figure below represents the reproductive and development cycle of a frog as it transform from egg to frog specie.)

In tadpoles, right after the mouth is being formed, two indentation like thickenings of peritoneum begin to appear near the body cavity (dorsal surface), which is nearest to the mesentery which is near the developing kidneys. These appear in all tadpoles.

These indentations appear here because of a change in the endothelial cells, everywhere else they are usually flat looking cells but they undergo a change and in this particular area become somewhat cuboidal/columnar.

Later on the indentations become more obvious due to the epithelial cells replicating numerously to form a thick layer. The posterior two thirds of the indentation for the female is the ovary and for the male it is the testis. The third that is left differentiates and becomes fat for the body.

[[Image: Mature frog life cyle.jpg|thumb|200px|left|Mature from life cycle Image details:Derived from primary source:http://www.scienceclarified.com/images/uesc_01_img0038.jpg]]

[[Image: Developing frog.jpg|thumb|Developing Frog Image details:
[[Image: Mature develop frog.jpg|thumb|Image details: Red eyed tree frog litoria chloris source:[http://en.wikipedia.org/wiki/File:Red-eyed_Tree_Frog_-_Litoria_chloris_edit1.jpg]].jpg]]

===Delamination===

Delamination indicates a mass separating a group of cellular matter from other cellular groups. It has been illustrated that the division of notochord, mesoderm and endoderm tissues from each other to form distinct cellular masses is completed by the progression of delamination, subsequent to these materials moving to the inside throughout gastrulation. During the developing gastrula, the germ layers are all recognized. These distinct segments of the embryo develop from these germ tissue layers.

===Polarity and Rotation===

Throughout fertilisation to the beginning of gastrulation, the frog’s egg continues in the original location in relation to its polarity. Subsequent to gastrulation its polarity begins to differentiate. This progression is linked with migration of materials within the gastrula and can be responsible for the alterations of the centre of gravity.

===Closing of Blastopore===

Subsequent to the formation of the gastrula, the blastopore is visible as a tiny round circular filled cavity containing the yolk plug. As it continues to reduce in dimension, it represented as a pear-shaped outline through the mutual approach of its lateral lips. Through it final progression these fuse entirely to produce a longitudinal groove, the streak which continue dorsally and ventrally in a small aperture. The inferior aperture closes, resulting in a depression called the anal pit. The superior region remains open for some period and begins to as the neural groove is laid down.

===Post Gastrulation or Organogenesis===

Throughout the duration of pre-gastrulation, all tissues for different organs vanish from the surface of blastula and migrate inside to take their final arrangement in the embryo structure where organs are developed from their potential regions. Consequently organogenesis transfers an embryo into free larva structure.

----

==Germ-layer origin of various body tissues==
[[Image: Development Models of Frog.jpg|thumb|right|Figure 13 Image details:Vertebrate Structure and Development.jpg]]

Ectoderm will give raise to structures such as skin, brain, spinal cord, neurons and sense receptors.
Mesoderm will give raise to structrues such as notochord, muscles, blood, bone and sex organs.
Endoderm will give raise to sturctures such as inner lining of gut, liver, pancreas, lungs and bladder, thyroid and parathyroid glands and thymus.

== Structures derived from Germ-layers of frog species ==

[[Image:Development of Frog Layers.jpg|thumb|left|Development of Frog Layers Primary source[http://www.bio.miami.edu/~cmallery/150/physiol/sf19x11b.jpg]Image details:J,Nassif 2009.jpg]]

[[Image:Development of frog layers.jpg|thumb|left|Development of Frog Layers Primary source [http://www.bio.miami.edu/~cmallery/150/physiol/sf19x11b.jpg]Image details:J,Nassif 2009.jpg]]

'''Ectoderm '''

''Establishes the epidermal segments and its derivatives, to the frog’s nervous system. The ectoderm also contributes to :''

1. The olfactory and auditory epithelium.

2. The retina and lens of the eye.

3. Sensory organs.

4. The epithelial lining of the oral cavity and the anus.

5. The pineal and pituitary body.

'''Mesoderm'''

''Mesoderm originates:''

1. Connective tissue.

2. Muscles, except the notochord.

3. Blood vessels.

4. Lymphatics.

5. The peritoneum and the urinary and reproductive system.

6. The dermis, parts of the eye excluding lens, cornea, and conjunctiva.

'''Endoderm'''

''From the endoderm arises:''

1. The epithelial lining to the gut and oesophagus, stomach, intestine, bile duct.

2. The hepatic cells of the liver, respiratory tract, larynx, trachea and lungs.

3. The lining of the urinary bladder, pancreas thyroid and thymus.

[The two figures reveal the development of structures deriving from the celluar components of the embryology of the frog].[Structures derived from Germ-layers of frog species ]

==Life cycle of a frog==

'''Fertilization-egg''':

The female lays eggs in the spring. A group of fertilized eggs is called spawn;

'''7-10 days''':

Fertilized egg feed on remaining yolk which is in its gut. Their gills, mouth and tail have poorly developed. Begin to swim and feed on algae;

'''10-30 days(4 weeks):'''

A layer of skin grows over gills. Teeth begin to appear. A coiled gut start to develop. This is aid in digestion;

'''30-60 days(6-9 weeks):'''

Legs being to grow and head is more distinct. Start to eat insects. Arms begin to grow;

'''60-80 days(12 weeks):'''

Resemble a frog. Still have remaining tail;

'''80-140 days(20 weeks):'''

Fully developed, spend most of time out of water. Majority of frog live between 4-15 years.

==Timeline of frog development==

Development of egg and embryo at temperature 18 degree celsius.

'''0 hours''' - fertilization of the egg

'''1 hours''' - formation of the gray crescent due to pigment migration

'''3.5 hours''' - early cleavage

'''4.5 hours''' - blastula stage(coeloblastula with eccentric blastocoel

'''26 hours''' - gastrulation

'''26 hours''' -'' early'' - crescent shaped dorsal lip

'''34 hours''' - ''middle''- semicircular blastoporal lip

'''42 hours''' - ''late'' - circular blastoporal lip

'''50 hours''' - neurulation

'''50 hours''' - ''early'' - medullary plate

'''62 hours''' -'' middle''- neural folds converging

'''67 hours''' - ''late'' - neural tube formed and ciliation of embryo

'''84 hours''' - tail bud stage(early organogeny)

'''96 hours''' - muscular response to tactile stimulation

'''118 hours''' - early heart beat, development of gill buds

'''140 hours''' - hatching and gill circulation

'''162 hours''' - mouth opens and cornea becomes transparent

'''192 hours''' - tail fin circulation established

'''216 hours''' - degeneration of external gills, formation of operculum, development of embryonic teeth

'''240 hours''' - opercular fold over brachial chamber except for spiracle and internal gills

'''255 hours''' - prolonged larval stage with refinement of organs

'''270 hours''' - development of hindlimbs, internal development of forelimbs in opercular cavity

'''275 hours''' - projection of forelimbs through operculum, left side first

'''280 hours''' - absorption of the tail and reduction in size of the gut

'''284 hours''' - metamorphosis complete, emergence from water as miniature, air breathing frog

==Stages of frog embryology==
--[[User:S8600021|Mark Hill]] 08:40, 9 October 2009 (EST) [[Talk:2009_Group_Project_5#Constructive_Criticism_of_Coordinator|see my comment on images]]

The rate of development of the egg and embryo will depend upon the temperature at which they are kept. The approximate schedule of development at 23 degree celsius is provided below.

{| border='1px'
|+ Table 1: Stages of frog development
!Stage !!Time since fertilisation (hours)!!Stage Characteristic !!Embryo characteristic !!Image of frog stage
|-
|1
|0.00-1.30
|fertilization of the egg, post fertilization
|animal hemisphere, gray crescent and vegetal hemisphere are present
|[[File:Stage01ventral.jpg|100px]]
|-
|2
|1.30-2.00
|splits into two cells
|appearance of first cleavage furrow
|[[File:Stage02ventral.jpg|100px]]
|-
|3
|2.00-2.15
|becomes four cells
|appearance of second cleavage furrow
|[[File:Stage03dorsolat.jpg|100px]]
|-
|4
|2.15-2.45
|becomes eight cells
|appearance of third cleavage furrow
|[[File:Stage04dorsolat.jpg|100px]]
|-
|5
|2.45-3.00
|becomes sixteen cells
|appearance of fourth cleavage furrow
|[[File:Stage05dorsal.jpg|100px]]
|-
|6
|3.00-3.30
|becomes thirty-two cells
|appearance of fifth cleavage furrow
|[[File:Stage06animal.jpg|100px]]
|-
|6.5
|3.30-4.00
|blastula stage
|Three dorsal folds become visible as a result of endoderm invagination. Pole cells no longer visible on surface
|[[File:Stage065dorsal.jpg|100px]]
|-
|7
|4.00-5.00
|Gastrulation stage
|two primary germ layers. epiblast and endoderm
|[[File:Stage07ventral.jpg|100px]]
|-
|8
|5.00-7.00
|neurulation
|medullary plate, neural folds and neural tube
|[[File:Stage08animal.jpg|100px]]
|-
|9
|7.00-9.00
|germ layer
|complete lip involution encircling yolk
|[[File:Stage09veg.jpg|100px]]
|-
|10
|9.00-11.00
|early gastrula
|two primary germ layers
|[[File:Stage10veg.jpg|100px]]
|-
|10.5
|11.00-11.45
|gastrula
|two germ layers
|[[File:Stage105vegb.jpg|100px]]
|-
|11
|11.45-12.30
|medulla plate
|Yolk sac protrudes dorsally, labium moves to midline on ventral side
|[[File:Stage11veg.jpg|100px]]
|-
|11.5
|12.30-13.15
|continuation of medulla plate
|start closing the plate
|[[File:Stage115veg.jpg|100px]]
|-
|12
|13.15-14.15
|early neurula
|thickened ectoderm give rise to CNS
|[[File:Stage12veg.jpg|100px]]
|-
|12.5
|14.15-14.45
|neural folds
|expansion of cavity
|[[File:Stage125postdors.jpg|100px]]
|-
|13
|14.45-16.15
|neural folds
|continue expanding cavity
|[[File:Stage13postdors.jpg|100px]]
|-
|14
|16.15-17.30
|neural folds
|continuation of cavity
|[[File:Stage14postdors.jpg|100px]]
|-
|15
|17.30-18.15
|tail bud stage
|early organogeny
|[[File:Stage15postdors.jpg|100px]]
|-
|16
|18.15-18.45
|tail bud stage
|posterior ventral view
|[[File:Stage16ant.jpg|100px]]
|-
|17
|18.45-19.45
|tail bud stage
|anterior view
|[[File:Stage17ant.jpg|100px]]
|-
|19
|20.45-21.45
|neural fold close complete
|dorsal view
|[[File:Stage19dorsal.jpg|100px]]
|-
|20
|21.45-22.30
|early tail bud
|anterior view
|[[File:Stage20dorsal.jpg|100px]]
|-
|21
|22.30-24.00
|termination of neural crest
|progress to next stage
|[[File:Stage21ant.jpg|100px]]
|-
|22
|24.00-24.45
|prolonged development
|elongation
|[[File:Stage22lat.jpg|100px]]
|-
|23
|24.45-26.15
|elongation of embryo
|later view
|[[File:Stage23lat.jpg|100px]]
|-
|24
|26.15-27.30
|continuation of elongation of embryo
|dorsal view
|[[File:Stage24latsmall.jpg|50px]]
|-
|25
|27.30-29.30
|organs development
|embryo elongates and develops dorsal thickening
|[[File:Stage25dorsal.jpg|50px]]
|-
|26
|29.30-31.15
|elongation
|dorsally forms neural and brain cavity
|[[File:Stage26lat.jpg|50px]]
|-
|27
|31.15-32.30
|elongation of embryo
|dorsal view
|[[File:Stage27lat.jpg|50px]]
|-
|28
|32.30-35.00
|further development
|lateral view
|[[File:Stage28lat.jpg|50px]]
|-
|29-30
|35.00-37.30
|tail bud
|growth
|[[File:Stage29-30lat.jpg|50px]]
|-
|31
|37.30-40.00
|prolonged development
|bud development
|[[File:Stage31lat.jpg|50px]]
|-
|32
|40.00-44.30
|early muscular development
|elongation
|[[File:Stage32lat.jpg|50px]]
|-
|33-34
|44.30-50.00
|muscular movement
|apparatus for locomotion
|[[File:Stage33-34lat.jpg|50px]]
|-
|35-36
|50.00-53.30
|muscular movement
|apparatus for locomotion
|[[File:Stage35-36lat.jpg|50px]]
|-
|37-38
|53.30-56.30
|heart beat
|develops apparatus
|[[File:Stage37-38lat.jpg|50px]]
|-
|39
|56.30-66.00
|mouth opens
|cornea transparent
|[[File:Stage39latsmall.jpg|50px]]
|-
|40
|66.00-76.00
|gill circulation
|hatching
|[[File:Stage40lat.jpg|50px]]
|-
|41
|76.00-80.00
|tail, fin circulation
|circulation
|[[File:Stage41lat.jpg|50px]]
|-
|42
|80.00-86.00
|internal gills, operculum
|opercular fold, teeth
|[[File:Stage42lat.jpg|50px]]
|-
|43
|86.00-98.00
|operculum complete
|operculum closed on right
|[[File:Stage43lat.jpg|50px]]
|-
|46
|98.00-106.00
|metamorphosis
|emergence from water as miniature, operculum complete|
|[[File:Stage46lat.jpg|50px]]
|-
|}

==Abnormalities of frog==

Abnormalities of frog could be caused by multiple factors. These include change in climate, predators, parasites, bacteria, fungi, viruses or pollution and contaminants such as pesticides, metals and fertilizer.[http://www.fws.gov/contaminants/documents/frogsrefup_septoct_2006.pdf]

The Abnormalities are further classified into different categories. These categories are:

===1. Infectious Diseases:===

'''Perkinsus Symptoms-''' caused by perkinsus-like protozoan organism. Symptoms include swollen viscera that leads to a bloated body and and infected swollen heart

'''Ichthyophonus symptoms-''' cause by parasitic genus, where symptoms include a swollen tail resorption site that matches the surrounding skin in color and translucency.

[[Image:Abnormalities of Frog species.jpg|thumb|left|Figure A Image details[waterwatchadelaide.net.au].jpg]]

===2. Surficial Abnormalities:===

Surficial abnormalities as the one that are visible on the surface of the skin. This includes abnormal pigmentation, , subcutaneous hemorrhaging, wounds due to trauma or from a predator
Edema is a fluid-filled swelling under skin whihc is also a surficial abnormality.

===3. Skeletal Abnormalities:===

This is further classified into three more categories:

'''a. Skeletal Malformations-'''

* Microcephaly (small head or blunt snout)
*Scoliosis (Curved spine in lateral direction)
*Shrunken Limb (Micromelia)
*Amelia (Completely missing limb with no stump)

'''b. Skeletal Abnormalities of Unclear Etiology-'''

This condition arises when a frog has ectromelia (missing limb), brachydactyly (missing digits) or other such condition with no visible trauma or external damage, then this will be classified as the Skeletal abnormality of unclear etiology.

'''c. Skeletal Injuries-'''

Any limb missing or broken due to trauma or other related reason which shows clear evidence of it is classified as skeletal injury

===4. Eye Abnormalities:===

Most common includes-

'''i. Anophthalmia:''' Skin covers the eye socket as there is no eye

'''ii. Abnormal Iris Coloration:''' Reduced pigment in either one eye or both resulting in two different colours of the iris at times

'''iii. Abnormal size or shape:''' Both eyes either deviating from each other or size of pupil or iris is different than the other eye

[http://www.fws.gov/contaminants/Amphibian/pdfs/AbnormalitySOP_woutpics_Jan08.pdf ]

==Genetics==

There are a wide variety of species that differ from each other when it comes to genetics and their functioning.

'''TAXONOMY:''' '''Phylum''' ''Chordata'' / '''Sub Phylum''' ''Vertebrata'' / '''Class''' ''Amphibia'' / '''Order''' ''Anura''

Their are more than two dozen different families of frogs, where suborders are:

'''1. ARCHAEBATRACHIA-''' most primitive frogs

'''2. MESOBATRACHIA-''' linked between the Archaebatrachia and Neobatrachia

'''3. NEOBATRACHIA-''' most modern frogs

{| border='4px'
|+ '''General Info:'''
! !!
|-
| '''Number of frogs' species'''
| 5280
|-
| '''Smallest frog genome size:'''
| 0.95pg, Ornate burrowing frog
|-
| '''Largest frog genome size:'''
| 13.40pg, Ornate horned frog
|-
| '''Mean of frogs' genome'''
| 4.68pg ± 0.13
|-
|}

[http://www.genomesize.com]

*Majority of frogs have only 22 to 26 chromosomes and polyploid is very common where they are almost bisexual.

*Polyploid Amphibians reduce their total cell number such that they acheive the same body size as diploids. One of the most unsual forms of polypoidy in amphibians is the water frog ''Rana esculenta'' from Europe and Western Asia.

* The species with larger genomes have more genes for e.g. the frog genus ''Xenopus'' includes 16 species, with genome sizes ranging from 3.5 x 10^9 bp to 1.6 x 10^10 bp. These differences have arisen by numerous events of polyploidization within the past 40 million years or so. The ancestral chromosome number for the genus seems to have been 18, but there are species with 36, 72 and 105 chromosomes [http://www.xenbase.org/common/]

* Further information on the complete genome sequencing of Xenopus Laevis is provided by '''NCBI Xenopus Genome Resources''' [http://www.ncbi.nlm.nih.gov/nuccore/BC077223?ordinalpos=1&itool=EntrezSystem2.PEntrez.Sequence.Sequence_ResultsPanel.Sequence_RVDocSum]

{| border='4px'
|+ '''Difference within two families'''
! '''SPECIES''' !! ''X.LAEVIS'' !! ''X.TROPICALIS''
|-
| '''PLOIDY'''
| Allotetraploid
| Diploid
|-
| '''NO. OF CHROMOSOMES'''
| 36 chromosomes
| 20 chromosomes
|-
| '''GENOME SIZE'''
| 3.1 x 10^9 bp
| 1.7 x 10^9 bp
|-
| '''EGG SIZE'''
| 1-1.3 mm
| 0.7-0.8 mm
|-
| '''GENERATION TIME'''
| 1-2 years
| 4 months
|-
|}
[http://www.xenbase.org/common/]

===Genome Sequencing===

Since Frog has a huge family with many different species, only few main species that are used widely for the purposes of experiments have their genome sequenced.

''Xenopus tropicalis'' has one of the smallest genomes among amphibians and has the shortest generation time- four to six months and the only diploid genome among the 14 Xenopus species. This means it has no more than two copies of most genes, whereas the other species of Xenopus have four copies of most genes (pseudotetraploid). US Department of Energy's Joint Genome Institute (JGI) in Walnut Creek, California, initiated the X. tropicalis Genome Project, finding 1,700 million base pairs.
[http://www.genome.gov/Pages/Research/Sequencing/BACLibrary/xenopusTropicalis.pdf]

Complete and detailed genome of Xenopus Tropicalis is available from '''NCBI Xenopus Database''' [http://www.ncbi.nlm.nih.gov/nuccore/BC075559?ordinalpos=1&itool=EntrezSystem2.PEntrez.Sequence.Sequence_ResultsPanel.Sequence_RVDocSum]

===Xenopus oocytes===

* The oocytes provide an important expression system for molecular biology.

* By injecting DNA or mRNA into the oocyte or developing embryo, scientists can study the protein products in a controlled system. This allows rapid functional expression of manipulated DNAs (or mRNA). This is particularly useful in electrophysiology, where the ease of recording from the oocyte makes expression of membrane channels attractive.

* One challenge of oocyte work is eliminating native proteins that might confound results, such as membrane channels native to the oocyte.

* Translation of proteins can be blocked or splicing of pre-mRNA can be modified by injection of Morpholino antisense oligos into the oocyte (for distribution throughout the embryo) or early embryo (for distribution only into daughter cells of the injected cell).
[http://www.staff.unibe.ch/sigel/xenopus.html]

===Xenopus Laevis===

* ''Xenopus Laevis'' is an important model organism in developmental biology. X. laevis is tetraploid and reaches sexual maturity in 1 to 2 years. What makes it important in developmental biology is its large and easily manipulable embryo.

* Extracts from the eggs of X. laevis frogs are also commonly used for biochemical studies of DNA replication and repair, as these extracts fully support DNA replication and other related processes in a cell-free environment which allows easier manipulation.

* The Human chorionic gonadotropin hormone (hCG) is present in the urine of the pregnant women in large quantities only. This hormone in the urine induces X.laevis oocyte production which formed the basis of first well-documented method of pregnancy testing X. laevis is also notable for its use as the first well-documented method of pregnancy testing when it was discovered. Today, commercially available HCG is injected into Xenopus males and females to induce mating behavior and breed these frogs in captivity at any time of the year. [http://www.statemaster.com/encyclopedia/Xenopus-laevis]
===Gene cluster===

* The alpha and beta globin genes are closely linked in small cluster of frogs compared to human and chicken

* The similarity of architecture of two clusters found in X.laevis supports the tetraploid origin

* The two loci encoding the muscle specific creatine kinase isoenzymes and have large differences in developmental profile, therefore suggesting that duplicate loci that have not undergone silencing are not simply redundant copies but have acquired specialization.

* Contains twice number of genes for proteins i.e. haemoglobin and sarcomeric actin serum albumin compared with other species

----

==Current Embrology Research==

Currently, a number of fields have benefited from the development of frog embrology. These include cloning, verification of messenger RNA, and Cell cycle.

===Cloning===
[[Image:Robert Briggs.jpg|thumb|left|Figure 16 Image details:Robert Briggs.jpg]]

In 1952, Robert Briggs and Thomas J King cloned northern leopard frogs using a method of nuclear transfer. Briggs and King's experiment was similar to that envisioned - and piloted using salamanders - by Hans Spemann in his 1938 proposal for a 'fantastical experiment'. Later, John Gurdon extended this work and showed that nuclei from differentiated cells could support development, although less well than those from early embryos. [http://genome.wellcome.ac.uk/doc_WTD020799.html]

Lemaitre et a. (2005) from MRC Cancer Cell Unit, Cambridge, U.K. worked on experiments that demonstrated that importance of serial nuclear transplantation for the sucessful cloning of frogs. He demonstrated that exposure of somatic-cell nuclei (erythrocyte nuclei) and sperm nuclei to an extract of mitotic cell extract reorganizes the chromatin into shorter loops and allows replication at much shorter intervals along the DNA. This increases the efficiency of DNA replication in mammalian cell-free systems.

===Transgenesis techniques for functional genomics in Xenopus===

Transgenesis in Xenopus is made possible due to large embryos, a reliable fate map, ease of microinjection, ease of dissection/micromanipulation and existence of the neuroendocrine reflex of background adaptation as a model for activation/inact.

Recently, Hajime Ogino and Haruki Ochi from Nura Institute of Science and Technology in Japan focused on the genomic resources and principles of the transgenesis techniques in Xenopus, and discusses their applications to genome wide network analysis, with emphasis on the use of bioinformatics tools, these studies were undertake in 2009. This is necessary to understand the gene regulatory networks that control vertebrate development. [http://www.ingentaconnect.com/content/bsc/dgd/2009/00000051/00000004/art00001%3Bjsessionid=4ah96rms73gcu.alexandra]

Xenopus used to be a problem in earlier days when it came to transgenesis. Current methods involves isolated sperm nuclei from Xenopus testis that are microinjected into unfertilized eggs. The generated transgenic tadpoles contain 5-35 copies of the integrated plasmid that are expressed in all cells. If desired, expression of the transgene can be directed to the appropriate tissue and at the appropriate time by using specific promoters, mostly the Xenopus POMC gene promoter (isolated from a Xenopus genomic DNA library) to specifically direct expression of green fluorescent protein (GFP) at high levels to the intermediate pituitary cells, which can either be over expressed or inhibited.[http://molanphys.ruhosting.nl/transgenesis.htm]

[[File:Transgenesis.JPG]]

===Verification of messenger RNA===

While the existence and role of messenger RNA (mRNA) was known in bacteria, in the 1960s it was still debated whether it also existed in vertebrates. Taking haemoglobin mRNA from immature red blood cells and injecting it into a Xenopus oocyte, John Gurdon showed that the haemoglobin protein was indeed produced. Producing proteins in Xenopus oocytes has proved to be extremely useful in cell biology, in particular for the study of receptor proteins.[http://genome.wellcome.ac.uk/doc_WTD020799.html]

===Cell Cycle===

As they develop outside the mother, frog eggs are well stocked with the proteins needed to drive the development of the embryo. Studies of these processes has shed considerable light on the processes involved in cell division - termed the cell cycle. [http://genome.wellcome.ac.uk/doc_WTD020799.html]

===Limb development in Xenopus Laevis===

[[Image: Frog Limb development.jpg|thumb|right|From Limb Development Image details:Primary source:[http://images.google.com.au/imgres?imgurl=http://www.sciencedaily.com/images/2006/06/060616130718.jpg&imgrefurl=http://www.sciencedaily.com/releases/2006/06/060616130718.htm&usg=__xliPsPAvheUBME_kjv_q7auiFbo=&h=333&w=300&sz=11&hl=en&start=2&um=1&tbnid=y_ntJtmkRSK7WM:&tbnh=119&tbnw=107&prev=/images%3Fq%3DLimb%2Bdevelopment%2Bin%2BXenopus%2BLaevis%26ndsp%3D18%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

Donald D. Brown (2005),Department of Embryology, Carnegie Institution of Washington demonstrated factors related to limb development of Xenopus Laevis. Thyroid hormone (TH) is found to be required for limb development in this frog. Specific cell types in the growing limb were targeted for expression of a dominant negative form of the TH receptor by sperm-mediated transgenesis. Limb muscle development, the innervation of muscle from the spinal cord, and cartilage growth can be inhibited without affecting patterning of the limb or differentiation of other cell types. Remodeling of the skin occurs late in metamorphosis after the limb has formed. The coordination of these independent programs is affected in part by the control that TH exerts over DNA replication in all cell types of the limb. [http://www.pnas.org/content/102/35/12455.full]

Further Detailed for the above issue is discussed in the following journal article: '''Early Limb Development of Xenopus Laevis, University of Leeds''' [http://dev.biologists.org/cgi/reprint/26/2/169]

===Growth factor signalling in the pattern of the mesoderm and neuroectoderm of the xenopus===

with current research being undertaken by scientist it has been found that a important factor in the formation of the mesoderm in the xenopus are peptide growth factors. scientist are interested in these peptide growth factors and are trying to understand if they will be able to use them to produce a fully organized embryo. we know that the mesoderm is not fully organized until the gastrula stage, so scientist are focusing on this stage only and trying to understand the different patterns that occur here.

The frog is used in this research because the embryo is well suited for it as the tissues of the frog can be dissected with ease as well as other factors that will help the scientist with their research like isolating the tissues of the frog. there are several methods and tools they use to help them achieve their goal, they can use time lapse video microscopy to see the morphogenetic movements that occur in the gastrula and neurula stages (helps with understand the patterns and signals that occur in the embryo).

An example the scientist have used to study the growth factor signals within the frog at a early stage in development is they inject RNA wild type and mutant growth factors they can produce a cell that secretes growth factors or a cell that is unable to secrete growth factors. this is important because it helps them understand the signals and where they are being produced from as well as transmitted from the mesoderm during the gastrula stage.

The Scientist have also found out that FGF (fibroblast growth factors) signalling is important in these events to produce a fully organized embryo. They made a embryo that has FGF signalling throughout the blastula stage but where the FGF signalling is not acquired through the gastrula stage. This showed that FGF signalling is important if the mesoderm is to stay intact. They came down to a conclusion where embryos that had a mesoderm that had FGF signalling during its induction and that had a compromised FGF signalling during the gastrula stage, the embryo did not form a notochord or any muscles. [http://www.gurdon.cam.ac.uk/~amayalab/Current.Research.Interests.html]

----

== Glossary ==

[[Image: Frog species.jpg|thumb|left| Frog Species Image details:Primary source:www.olympus.co.jp/.../080925/large/p02L.jpg].jpg]]

*'''Amphibian:'''

''Relating to or characteristic of animals of the class amphibia.Amphibians are found in the taxonomic class of amphibia, amphibians are capable of both occupying and successfully living in both land and aquatic communities.amphibian''

*'''Augmentation:'''

''Enlargement/Increase in cellular size.''

*'''Autolysis:'''

''breakdown of a part or whole cell or tissue by self-produced enzymes''

*'''Blastomeres:'''

''The undifferentiated cells formed by cleavage of the fertilised ovum. This includes cells in the cleavage, morula, and blastula stages of the embryo''

*'''Carnivorous:'''
''
Flesh-eating; subsisting on animals as food.''

*'''Cleavage:'''

''he repeated division of a fertilised ovum ''

* '''Cleft:'''

''an opening, fissure, or V-shaped indentation made by or as if by splitting''

*'''Chordate:'''

''Members of a diverse phylum of animals that, as embryos, possess a (1) notochord; (2) a dorsal, hollow nerve cord, (3) pharyngeal gill slits; and (4) a post-anal tail''

''The act or state of splitting or dividing of a cell, particularly during the telophase of (animal) cell division.''

*'''Cytoplasm:'''

''The cytoplasm (of both eukaryotes and prokaryotes) is where the functions for cell expansion, growth, metabolism, and replication are carried out''

* '''Epiboly:'''
''The expansion of one cell sheet over other cells, as takes place during gastrulation''

*'''Fertilization:'''

''A process in sexual reproduction that involves the union of male (sperm) and female (ovum) gametes (each with a single, haploid set of chromosomes) to produce a diploid zygote.''

*'''Gamete:'''
''A reproductive cell (male (sperm) or female (egg)) that has only half the usual number of chromosomes''

*'''Gametogenesis:'''

''process leading to the production of gametes. The development and maturation of sex cells through meiosis.Another name for meiosis where a diploid cell is divided into two haploid cells with half the chromosome content of the diploid parent cell.''

*'''Herbivorous:'''

''eating plants; of or pertaining to the herbivora.''

*'''Holoblastic:'''

''The complete division of an isolecithal or microlecithal egg into blastomeres''

*'''Invagination:'''

''One of the methods by which the various germinal layers of the ovum are differentiated.''

*'''Isoenzymes:'''

''Isozymes (also known as isoenzymes) are enzymes that differ in amino acid sequence but catalyze the same chemical reaction.''

*'''Mesentery:'''

'' membranous fold attaching various organs to the body wall.''

*'''Metamorphosis:'''

''A change in the form and often habits of an animal after the embryonic stage during normal development.''

*'''Neuroendocrine:'''

''Neuroendocrine [IPA nʊəroʊˈɛndəkrɪn] cells are cells that release a hormone into the circulating blood in response to a neural stimulus.''

*'''Organogenesis:'''

''The part of embryonic development where the body's main organs develop.''

*'''Peritoneum:'''

''The smooth serous membrane which lines the cavity of the abdomen, or the whole body cavity when there is no diaphragm, and, turning back, surrounds the viscera, forming a closed, or nearly closed, sac.''

*'''Perivitelline space:'''

''The perivitelline space is the space between the zona pellucida and the plasma membrane (sometimes called the vitelline membrane) in a fertilized ovum.''

*'''Polyploidy:'''

''Cells with three or more sets of chromosomes.''

*'''Pronucleus:'''

''the nucleus of the ovum or sperm after fertilization but before they fuse to form the nucleus of the zygote ''

*'''Protoplasm:'''

''The fluid living content of the cell that consists of two major divisions, the cytoplasm and the nucleoplasm (cell nucleus). It is composed mainly of nucleic acids, proteins, lipids, carbohydrates, and inorganic salts''

*'''Segmentation:'''

''division of some metazoan bodies (such as annelida and Arthropoda) into repeated parts, segments. Segmentation can be homomeric (more or less the same) or heteromeric(different from each other).''

*'''Terrestrial:'''

''Of or on the ground, of the habitat of a plant, on land as opposed to in water, or on the ground as opposed to on another plant.''

*'''Transgenesis:'''

''Transgenesis is the process of introducing an exogenous gene - called a transgene - into a living organism so that the organism will exhibit a new property and transmit that property to its offspring.''

*'''Yolk:'''

''nutritive material of an ovum stored for the nutrition of an embryo''

*'''Zygote:'''

''The cell from which an organism develops, that results from the fertilization of the egg by the sperm.''

''Primary Resource "Biology- Online Dictionary''[http://www.biology-online.org/dictionary/Main_Page]

== References - Frog Embryology: ==

[[Image:Frog Research.jpg|thumb|left|Research being done on a Frog Image details:[http://images.google.com.au/imgres?imgurl=http://www.odt.co.nz/files/story/2008/09/university_of_otago_zoology_senior_lecturer_phil_b_3343259744.jpg&imgrefurl=http://www.odt.co.nz/on-campus/university-otago/21670/dunedin-frog-man-wins-zoo-award&usg=__JvJJU5QfOnIwY2bk4xo64UXuJRs=&h=600&w=404&sz=22&hl=en&start=14&um=1&tbnid=AbsP89yWcUiilM:&tbnh=135&tbnw=91&prev=/images%3Fq%3Dfrog%2Bresearch%26hl%3Den%26um%3D1].jpg]]

1. Savage, J. M. (2002). The Amphibians and Reptiles of Costa Rica. University of Chicago Press, Chicago [http://www.springerlink.com/content/vv015277w1746llw/]

2. Ford, L.S.; D.C. Cannatella (1993). "The major clades of frogs". Herpetological Monographs 7: 94–117 [http://digimorph.org/specimens/Xenopus_laevis/]

3. Tyler, M. J. (1994). Australian Frogs A Natural History. Reed Books [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.gracilenta.html]

4. Cogger, H.G.; R.G. Zweifel, and D. Kirschner (2004). Encyclopedia of Reptiles & Amphibians Second Edition. Fog City Press [http://en.wikipedia.org/wiki/Microhylidae]

5. Beltz, Ellin (2005). Frogs: Inside their Remarkable World. Firefly Books [http://unjobs.org/authors/ellin-beltz]

6. Tyler, M. J. (1994). Australian Frogs A Natural History. Reed Books [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

7. Moury JD, Hanken J (1995) Early cranial neural crest migration in the direct-developing frog, Eleutherodactylus coqui. Acta
Anatomica (Basel) 153, 243-253.

8.Raynaud A (1985) Development of limbs and embryonic limb reduction. In Biology of the Reptilia (ed. Gans C, Billett F), pp.
59-148. New York: John Wiley.[http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=9309]

9. Hanken J (1986) Developmental evidence for amphibian origins. In Evolutionary Biology (ed. Hecht MK, Wallace B, Prance GT), 20, pp. 389-417. New York: Plenum Press. [Hanken J (1986) Developmental evidence for amphibian origins. In Evolutionary Biology (ed. Hecht MK, Wallace B, Prance GT), 20, pp. 389-417. New York: Plenum Press.]

10. Elinson RP (1990) Direct development in frogs : wiping the recapitulationist slate clean. Seminars in Developmental Biology
1, 263-270.

11. Beebee, T. J. C. 1996. Ecology and Conservation of Amphibians. Chapman and Hall. London. [http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V5X-3SVHMKH-1X&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=1021245355&_rerunOrigin=google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=825868e10cd178d16a8a0e5ad14dc5ef]

12. Lehtinen, R. M. 2002. The use of screw pines (Pandanus spp.) by amphibians and reptiles in Madagascar. Herpetological Bulletin 2002:20–25.

13. Parris, K. M. and M. A. McCarthy. 1999. What influences the structure of frog assemblages at forest streams. Australian Journal of Ecology 24:495–502. CrossRef

14. Zug, G. R. 1993. Herpetology: An Introductory Biology of Amphibians and Reptiles. Academic Press. San Diego, CA.

15. Slack,J.M.W., Darlington,B.G., Heath,J.K. and Godsave,S.F. (1987)Mesoderm induction in early Xenopus embryos by heparin-binding growth factors. Nature, 326, 197-200.

16. Melton,D.A. (1990) Activins are expressed early in Xenopus embryogenesis and can induce axial mesoderm and anterior structures. Cell, 63, 485-493.

17. Harland,R.M. and Misher,L. (1988) Stability of RNA in developing Xenopus embryos and identification of a destabilizing sequence in TFIIIA RNA. Development, 102, 837-852.

18. Cunliffe,V. and Smith,J.C. (1992) Ectopic mesoderm formation in Xenopus embryos caused by widespread expression of a Brachyury homologue. Nature, 358, 427-430.

19. Kinoshita,K., Bessho,T. and Asashima,M. (1993) Competence prepattern in the animal hemisphere of the 8-cell-stage Xenopus embryo. Devel. Biol., 160, 276-284.

20. LaBonne,C., Burke,B. and Whitman,M. (1995) Role of MAP kinase in mesoderm induction and axial patterning in Xenopus development. Development, 121, 1475-1486.

21. Green,J.B.A., New,H.V. and Smith,J.C. (1992) Responses of embryonic Xenopus cells to activin and FGF are separated by multiple dose thresholds and correspond to distinct axes of the mesoderm. Cell, 71, 731-739.

22. Grainger R., Blumberg B., Harland R., Amemiya C., Importance of Xenopus Tropicalis to biomedical and biological research, Benaroya Research Institute, Virginia Mason Research Center [http://www.genome.gov/Pages/Research/Sequencing/BACLibrary/xenopusTropicalis.pdf ]

23. Gregory, T.R. (2005). Animal Genome Size Database. [http://www.genomesize.com]

24. U.S Fish and Wildlife Services, ABNORMALITY CLASSIFICATION SOP, [http://www.fws.gov/contaminants/Amphibian/pdfs/AbnormalitySOP_woutpics_Jan08.pdf ]

25. Donald D. Brown*, Liquan Cai*, Biswajit Das*, Nicholas Marsh-Armstrong‡, Alexander M. Schreiber*, and Rejeanne Juste*(2005), Thyroid hormone controls multiple independent programs required for limb development in Xenopus laevis metamorphosis [http://www.pnas.org/content/102/35/12455.full]

26. Ogino, Hajime; Ochi, Haruki, Resources and transgenesis techniques for functional genomics in Xenopus, Development Growth & Differentiation, Volume 51, Number 4, May 2009 , pp. 387-401(15) [http://www.ingentaconnect.com/content/bsc/dgd/2009/00000051/00000004/art00001%3Bjsessionid=4ah96rms73gcu.alexandra]

27. Giles Newton (2004) Why the frog? The Human Genome, [http://genome.wellcome.ac.uk/doc_WTD020799.html]

28. NCBI Xenopus Genome Database, ''Xenopus laevis cDNA clone MGC:79055 IMAGE:4679899, complete cds'' [http://www.ncbi.nlm.nih.gov/nuccore/BC077223?ordinalpos=1&itool=EntrezSystem2.PEntrez.Sequence.Sequence_ResultsPanel.Sequence_RVDocSum]

29. NCBI Xenopus Genome Database, ''Xenopus tropicalis cDNA clone MGC:89509 IMAGE:6992565, complete cds'' [http://www.ncbi.nlm.nih.gov/nuccore/BC075559?ordinalpos=1&itool=EntrezSystem2.PEntrez.Sequence.Sequence_ResultsPanel.Sequence_RVDocSum]

28. Xenbase, [http://www.xenbase.org/common/]

29. Donders Center for Neuroscience & Nijmegen Center for Molecular Life Sciences (NCMLS), Beyond the genome (Xenopus transgenesis for functional genomics),Faculty of Science, Radboud University [http://molanphys.ruhosting.nl/transgenesis.htm]

30. Nation Master, [http://www.statemaster.com/encyclopedia/Xenopus-laevis]* (no available year or author)

31. Amaya Lab, [http://www.gurdon.cam.ac.uk/~amayalab/Current.Research.Interests.html]

== External Links ==
[[Image:Frog links.jpg|thumb|left|Smart Frog Image details:[http://images.google.com.au/imgres?imgurl=http://2.bp.blogspot.com/_o93AaY0GzH4/SjY_ZYv0PII/AAAAAAAAAgk/skruNc2yN78/s400/computer%2Bfrog.jpg&imgrefurl=http://hellaheaven-ana.blogspot.com/2009/06/talking-frog-contemporary-fairy-tale.html&usg=__oxji1TGLV2Fi7xe0dnlmuYk8gDo=&h=288&w=288&sz=16&hl=en&start=2&um=1&tbnid=ywZd4zpdxC5plM:&tbnh=115&tbnw=115&prev=/images%3Fq%3Dfrog%2Bon%2Bcomputer%26hl%3Den%26um%3D1].jpg]]

1. Frog embryology [http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/F/FrogEmbryology.html Frog Embryology]

2. Frog cellular materials [http://www.xenbase.org/xenbase/original/cell/cell.html xenbase]

3. The zoology of frog species [http://worms.zoology.wisc.edu/frogs/mainmenu.html zoology frogs]

4. Frog cycle [http://www.bioethics.gov/images/sc_images/frog_dev.gif bioethics frog] Just a little cycle of FROG'S life cycle

5. Frog Embryology [http://embryology.med.unsw.edu.au/OtherEmb/Frog.htm UNSW Embryology]

6. Frog Research [http://apps.carleton.edu/campus/library/now/exhibits/wallcharts/frog/ carleton library exhibit]

{{Template:Projects09}}
[[Category:Frog]]

2009 Group Project 5

2009-10-15T00:12:48Z

Z3258567: /* Current Embrology Research */

== The Embryology of Frogs ==

== The Frog ==

[[Image: Frog species .jpg|thumb|left|Image details: Wikipedia (2009) Frog species[http://en.wikipedia.org/wiki/Frog#Uses_in_agriculture_and_research].jpg]]

Frogs are scientifically identified by the structure of their long posterior limbs, a petite framework, webbed fingers and feet, budged eyes and the lack of a tail. The majority of frog species are extensively recognized as outstanding jumpers, due to their long, dominant legs, which are adaptations to progress jumping performance during activities. The Frog is one of the most frequently studied species in experimental embryology and most anatomical sciences. ''The Frog is a practically effective model for human embryological development given that the Frog:''

- Comprises of genes which can be effectively manipulated.

- Comprises of similar homogeny with humans species.

- Reproduces a large quantity of offspring in a short period of time.

- Are small species which can be simply sustained.

- Are not extremely luxurious and expensive.

== The History of the uses in agriculture and research ==

[[Image: Frog experiments .jpg|thumb|right|Image details: Scans of chemically cleared and dyed preserved deformed frogs and toads [http://www.sat.qc.ca/upload/residence/frog-04.jpg].jpg]]

There are numerous types of frog species that have been manipulated in many developmental experiments. The frog was traditionally used by countless of the early embryology investigators and presently there are several diverse molecular mechanisms regarding progression of the frog. Theses include:

'''1.''' Food source; frog legs are a delicacy and are eaten in European countries and in many parts of South American regions.

'''2.''' Frogs have the finest biochemical dissection of phenomena that take place in the egg and oocyte. Frogs are the evolutionarily closest to mammals, commonly used as a vertebrate model.

'''3.''' Frogs lay thousands of outsized eggs, from which cell extracts can be readily prepared that is capable of recapitulating most molecular phenomena in a test tube.

'''4.''' Frogs have been commonly used as a laboratory system for a very long period, and have an extensive history of producing crucial observations in countless fields of biology.

'''5.''' Frogs have a important historical connection to the study of epigenetics (John Gurdon-vertebrate cloning and reprogramming) which has been mostly performed on frog species.

'''6.''' Frogs also have very strong evidence of pattern formation and early development, as the embryos are large in size and experimentally manipulative.

'''7.''' Recent research into the biochemistry of chromatin and epigenetics has been performed with frog species and mammalian cultured cells.

'''8.''' The biggest weakness of the Frog model system is the difficulty of performing genetic experiments and analysis, as frogs are allotetraploid, meaning they take approximately a year to fully develop to sexual maturity, and the genome has not been completely sequenced. Nevertheless, biochemical manipulations of cell extracts, such as immunodepletions and application of heterologous DNAs and nuclei can avoid the need for genetic exploitation.

----

== Growth and development of the Frog ==

[[Image: Mature develop frog.jpg|thumb|Image details: Wikipedia (2009) Red Eyed Tree Frog Figure 1 Primary source:[http://en.wikipedia.org/wiki/File:Red-eyed_Tree_Frog_-_Litoria_chloris_edit1].jpg]]

* The frog is a well recognised species, abundant predominantly in ponds, swamps, though various species may also exist in damp or shady environments distant from moist habitats.

* Eggs of specific frogs are easily obtained and may be examined in from the beginning of fertilization onwards. The phases of embryonic development differs in various chordates, yet the typical phases are basically apparent in all frog species. The differences are associated principally to the amount of yolk particles present in an egg.

* The yolk particles offer nourishment of the developing embryo. The process of frog development will be discussed from the phases of gametogenesis to the adult stage.

----

== The Egg ==
[[Image:Development of Poles in frog Fertilization.jpg|thumb|left|Development of Poles in Frog Fertilisation:J,Nassif 2009.jpg]]

- The embryology of a frog egg is a vast cell; its dimensions are approximately 1.4-1.6 million times larger than a typical aquatic species egg cell. Throughout the frog’s embryonic maturation period, the egg will be transformed into a tadpole encompassing millions of cells but still remains with its constant volume of genetic material, the vast prodction of cell have been illusttrated in the figure on the right revealing the production of eggs from female frogs. [http://en.wikipedia.org/wiki/Microhylidae]

- The early embryonic frog structure consists of three main segments the superior hemisphere known as the animal pole which is usually visible as a grey coloured area. The innermost layer appears to be between the outer two sections known as the gray crescent represented in black. Inferiorly, represents the vegetal pole typically lighter than the superior compartment illustrated in gold.

VIDEO RESOURCE: [http://www.youtube.com/watch?v=GO5YN_t1fqw&feature=related]

[[Image:Early Development of Frogs.jpg|thumb|left|Early Development of Frog:J,Nassif 2009.jpg]]

==History of frog embryology use ==

*'''1851''' - ''Henby Nelson''(MD): He identified a remarkable fact through the frog embryo. Henby observed the first cleavage of the yolk, in the egg of the frog. And cleaved structure corresponds in line of direction to the longitudinal axis of the body of the embryo of the frog species.

[[Image:Wilhelm Roux.jpg|thumb|right|Wilhelm Roux[http://images.google.com.au/imgres?imgurl=http://www.todayinsci.com/R/Roux_Wilhelm/RouxWilhelmThm.jpg&imgrefurl=http://www.todayinsci.com/6/6_09.htm&usg=__qRLTEMTHdZpAHxiNX12hWjcm9tA=&h=125&w=100&sz=4&hl=en&start=2&um=1&tbnid=LIKIwZTqCpk7MM:&tbnh=90&tbnw=72&prev=/images%3Fq%3DWilhelm%2BRoux%26gbv%3D2%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

*'''1888''' - ''Wilhelm Roux'': Wilhelm Roux attempted to solve the above observation by damaging one cell of a two-cell frog embryo with a hot needle. The cell stayed in place. However, it did not develop further. Its partner developed into a left or right half-embryo;

*'''1907''' - ''John Hopkins'' hospital: In order to identify the cellular source of neuronal fibres. Scientist placed small portions of frog embryo spinal cords in lymph on a microscope slide and was able to observe clear cut neuronal sprouting.

*'''1951''' - ''Robert Briggs'': Robert Briggs was able to clone a frog embryo by substituting the nucleus of an unfertilized frog egg cell with the nucleus of a frog embryo cell. This process is known as nuclear transplant, has formed the basis for all cloning.

*'''1952''' - ''Robert Briggs and T.J. King'': Robert Briggs and T.J. King used frog for test experiment. Because the size of the eggs in the frogs are enormous compared with those of mammals, which make them easier to manipulate.

*'''1976'''- Using the technique that had been successful in cloning frog embryos, the doctor transferred the nucleus of one cells into a donated egg cell. As an embryo began to develop, it was implanted into the uterus of a young woman.

*'''1997''' - ''Wilmut and Campbell'': Utilizing the cloning technique from frog embryo, Drs. Wilmut and Campbell tried the starvation technique on embryo cells to produce Megan and Morag, the world's first cloned sheep and, until now, the most famous sheep in history.

*'''2000''' - ''Tokyo University'': Scientists at Tokyo University have grown artificial eyeballs. Scientists formed them in tadpoles by using frog embryo cells.

*'''2001''' - ''Advanced Cell Technology'': Scientists from Advanced Cell Technology announced production of a human embryo clone. This is significant as its parthenogenesis has been artificially induced in frogs.

[[Image:John Gurdon .jpg|thumb|right|John Gurdon [http://images.google.com.au/imgres?imgurl=http://www.pnas.org/site/misc/images/gurdon.jpg&imgrefurl=http://www.pnas.org/site/misc/classics4.shtml&usg=__1p-GA1PdOYsxKL-cznMb3RHCm98=&h=526&w=400&sz=223&hl=en&start=1&um=1&tbnid=9k4lhuLssiWCAM:&tbnh=132&tbnw=100&prev=/images%3Fq%3DJohn%2BGurdon%26gbv%3D2%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

*'''2002''' - ''John Gurdon'': John Gurdon from Wellcome Cancer Research Institute in Cambridge experimented on cloned frog embryo.

== Gametogenesis ==

* The sexual reproduction occurs through the fusion of either mature reproductive cells or germ cells known as gametes, which include the sperm from the male frog and ova from female frog species so as to form a single cell, the fertilized zygote. The gametes are typically developed in parents of different sexes . [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

* Males gametes is a spermatozoon , the female frog gamete is an ovum. Each gamete is formed by a process, recognised as maturation or gametogenesis in gonads. The typical male frog gonads are testies in male, while the female gonads are ovaries. The synthesis of both gonads is associated with the process of fertilization. [http://en.wikipedia.org/wiki/Microhylidae]

* The zygote changes into a mature frog through the process of embryology and metamorphosis. Gametogenesis is a progression in which frog gametes are established from germ cells. Initial germ cells are called primordial germ cells, which can be recognised extremely early in the life of frog species.

----

== The Egg & Fertilization ==

[[Image:Fertilized and Unfertilised Eggs.jpg|thumb|left|Fertilized and Unfertilized Eggs:J,Nassif 2009.jpg]]

[[Image:Egg Development.jpg|thumb|left|Egg Development:J,Nassif 2009.jpg]]

- This occurs once the sperm cell has inserted, following the insertion of the sperm cells meiosis II is completed, there is a 30 degree position change of the cytoplasm, gray crescent allows this change to be visible in some amphibians, the gray crescent is able what determines the expect ted outline of how the frog will form. The sperm cell joins with the nuclei of the egg which forms the diploid zygote nucleus. --Sando Rashed 10:09, 24 September 2009 (EST)

- The early phases in the development of the egg is visible, but must be studied in tadpoles throughout maturation. In embryonic tadpoles of about 10 millimetres in length, soon after the opening of the oral cavity, a pair of longitudinal ridge-like thickenings of peritoneum becomes apparent along the posterior surface of the body cavity situated near to the mesentery and along the inner boundaries of the kidneys. Genital ridges are established in all tadpoles of this age, sex is not distinct until a later period. The development of the egg is illustrated in the figure on the left revealing the structure of a developed egg and a mature of egg.

[[Image:Fertilisation life cyle.jpg|thumb|Fertilization of Life cycle:Derived from primary source:[http://en.wikipedia.org/wiki/Frog]]]

== Maturation of the Egg ==

- The eggs have currently accomplished their full size, and develop from the exterior of the ovaries like a small shot, but they still have to pass through the course of maturation before they are prepared to be fertilised. This progression of maturation relates to the nucleus almost completely.

- The nucleus component, containing the nuclear fluid that excludes through the nuclear membrane into the substance of the egg, a great segment of the nuclear reticulum vanishes and becomes degraded into separate globules known as nucleoli, but a extremely small division remains in the midpoint as a slender intricately thread recognised as the nuclear skets.
Relative to the egg getting discharged from the ovary, the follicles shatter allowing the eggs to fall into the abdominal cavity of the frog species, the egg then passes forwards, directly by the contraction of the muscular wall, somewhat by the movement of the cilia of the peritoneum, to the apex of the oviduct, which positioned at the anterior compartment of the body cavity opposite to the roots of the respiratory organs.

- The terminal part of the oviduct establishes a thin-walled pouch capable of great swelling, inside which the eggs gathers in large numbers. In conclusion, the eggs are migrated out through the cloaca into water which the albuminous investments of the eggs rapidly augment to form the gelatinous mass of the frogs spawn.

== Maturation phases ==

'''1. Nuclear skein''', moves from the midpoint of the egg to its outer surface, which it reaches opposite the midpoint of the black pole. The skein, subsequently an unevenly twisted thread, now presumes the specific arrangement of a nuclear spindle, for instance may be visible in the nucleus of an epithelial or additional cell instantly prior to division of the cell occurs.[http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

'''2. The first Polar Body,''' regarding the instance the egg is laid, but prior to its fertilistion, the egg develops a considerably flattened appearance at its upper or black pole, a definite sum of fluid being exuded among the egg and the vitelline membrane. The nuclear spindle currently separate into two identical segments, one of which remains with the egg, and the supplementary is extruded as the first polar body, a small ovoidal white globule, which is situated on the surface of the egg surrounding the exuded peri-vitellline fluid.

'''3. The Second Polar Body''', half of the nuclear spindle that stay behind then splits into two equivalent divisions, one of which remains inside the egg as the female pronucleus, whereas the other segment is extruded as the second polar body, a small white globule extremely related to the first polar body, and like this positioned in the perivitelline fluid on the superior portion of the egg.

'''4. Fertilisation of the egg''', includes the synthesis of the spermatozoon with to egg, specifically, synthesis of the nuclei of these two bodies. The spermatozoa, subsequent to being shed over the seed by the male, distribute vigorously by means of their extended tails, break through the gelatinous investment of the female eggs, bore their way through the vitelline membrane and so go through into the eggs themselves, which they penetrate relative to the superior or black hemispheres.
* Subsequently, an hour following the spermatozoon has entered; a progression may be visible projecting within from the exterior segement of the egg, with a liquid spot in the mid point. This liquid centre is the nucleus of the spermatozoon, and is said to be the male pronucleus, it break through beyond into the female egg, transporting the specialised pigment into it, so that it appears bounded by a pigmented capsule linked with the exterior of the egg by a pigmented stalk.

* By this instance, the second polar body has been established and extruded, and the female pronucleus is merely the only component of the primary egg nucleus still present. Both the male and female pronuceli, which are at initially distance separate to each other, merge and after having enlarged significantly in size then fuse mutually about two and half hours after fertilisation has originated to produce the segmentation nucleus.
* The segmentation nucleus is a huge sphere-shaped vesicle embedded in delicately granular protoplasm, and bounded by a distinct capsule of pigment, its arrangement by the synthesis of the male and female pronuclei completes the action of fertilisation. Specifically female pronucleus may be observe as an imperfect nucleus, and consequently result in the course of fertilisation. The nucleus of the spermatozoon or male pronucleus, replaces the component of the egg- nucleus which has been misplaced as the polar bodies.

'''5. Segmentation of the Egg''', the initial phase of growth consist in constant separation of the egg, whereby it becomes transformed from the unicellular state, which is everlasting only in the lowest species, to muliticelluar state charactertics of all higher species. To these early processes of growth the names segmentation is specified. Shorty subsequent to the competition of fertilisation and arrangement of the segmentation nucleus this later misplaces its sphere-shaped appearance and develops to be spindle-shaped, the yolk granules at the equivalent instance showing a tendency to develop into lines distributing outwards from the distal segment of the spindle.
* The nucleus now split into two halves, which shift away from one another, the yolk granules are likely to combined themselves around the two nuclei, and a slender vertical plate of delicately granular substance is left, dividing the egg.[http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

* Superiorly the eggs depression now becomes visible, initially as a small cavity and then develops as a groove, which almost immediately extends all round, and speedily deepening, splits the egg into two entirely separate halves along a plane equivalent with the vertical plane.

* Shorty after, the two nuclei soon separate again into two, and therefore a second cleft is created in the same state as before, its additionally in the vertical plane, however in a plane at 90 degrees to the initial one, and on its finishing point the egg comprises of four accurately similar segments, each containing a nucleus. The third cleft is horizontal in shape, but not equal, lying closer to the superior than the lower pole, it segregates each of the four cells into, an superior smaller and a inferior larger pole

----

== Cleavage ==

[[Image: Frog Cleavage development.jpg|thumb|left|Cleavage Process details:[http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/F/FrogEmbryology.html].jpg]]

* The egg of the frog is scientifically identified as’ telolecithal’ meaning there is a outsized amount of yolk concentrated at a single pole, in contrast to the concentration of cytoplasm and the site of the nucleus. The cleavage phases are holoblastic, therefore the total and after the second cleavage they are asymmetrical .The initial cleavage stage appears about two and half to three hours after fertilization. It commences as a minor depression in close proximity to the centre of the animal hemisphere. It appears as if some interior force is pushing the surface the egg towards the centre. This small upturned fold steadily continues in the form of a channel until it surrounds the egg. This groove is shallow in the commencement, but develop into deeper eventually separating the fertilized egg into two halves recognised as the blastomeres. [The figure on the left symbolise the development and growth of the frog embryo during cleavage].

* Internally the separation is mitotic, consequently each daughter cell contains a nucleus resulting from the copulation nucleus of the fertilised egg. This cleavage is vertical, the two cells are indistinguishable in respect of cytoplasm, pigment and yolk. The subsequent cleavage appears about an hour after the first. The channel of this cleavage begins at the centre of the animal hemisphere, is at right angles to the first and is vertical. This divides the egg into four blastomeres. The fourth blastomere so produced are not qualitatively equal, since of these only two contain the material from the gray crescent. The cleavage begins about thirty minutes after the second is completed or four hours after fertilisation. the cleavage plane of the third furrow is horizontal and slightly above the equator. Thus the four upper cells are a little smaller than the four lower cells. The smaller blastomeres are called micromeres and the larger blastomeres are called macromeres. The fourth cleavages follow 20 minutes after the third and tend to be vertical. This is usually a double furrow.

* The cleavage rate is accelerated with each of the early divisions and since the blastomeres are of unequal size and have varying amounts of cytoplasm and yolk, synchronous cleavage is lost and there is an obvious overlapping of the division. The upper most cells divide more rapidly than the lowermost cells. From this point onwards perfect symmetry in cleavage and in blastomere is very rare, although the embryo developed perfectly. The fifth cleavage is also doubled, appearing first in the upper hemisphere and then in the lower.

* The cleavage thus far follows the rule that each cleavage plane comes in at right angles to the previous one. The subsequent divisions become so irregular that it is previous one. The subsequent division become so irregular that it is impossible to trace out any plan or procedure. The segmentation continues more rapidly in the pigmented regions, since at that place the protoplasm is most dense, whereas, yolk which is very abundant in the vegetal side delays cell division. The multicelluar embryo at this stage is called morula by some biologists.

----

== Gastrulation ==

[[Image:FROG GASTRULATION .jpg|thumb|left|Frog Gastrulation Image details:[http://www.google.com.au/imgres?imgurl=http://bio1903.nicerweb.com/Locked/media/ch47/47_12FrogGastrulation.jpg&imgrefurl=http://bio1903.nicerweb.com/Locked/media/ch47/gastrulation-frog.html&h=540&w=480&sz=46&tbnid=N78sHjELreGGSM:&tbnh=132&tbnw=117&prev=/images%3Fq%3Dfrog%2B-%2Bgastrulation&hl=en&usg=__4VK9FYLft0W-4lBe6p5EtQAMiaI=&ei=qPy5SurtMJvE6wON8JmdAg&sa=X&oi=image_result&resnum=4&ct=image].jpg]]

''The phase of Blastulation is followed by the unique developmental progression of gastrulation. The process of frog gastrulation involves the following processes.''

'''1. Epiboly Phase'''

The pigmented cellular materials of blastula have the propensity to overgrow the yolk cells within the developing content. This course which is known as epiboly commences gradually in the final blastula and rapidly accelerates with advancing gastrulation development. The cellular matter within the animal pole reproduces and matures on all sides except in area surrounding the dorsal lip of the blastopore has been established.

'''2. Convergence'''

Scientists suggested that the unfolding was thought to result in spreading of the superficial cells over a substrate with suitable absorption properties. Consequently epiboly and convergence are an outcome to this spreading tendency, which is actually increased by a reduction in surface tension of the distributing cells.

'''3. Rotation'''

The epiboly phase is maintained until the region of the dorsal lip has migrated and is a to some extent greater than 90 degrees and the region of the white blastopore is reduced to small circular rings. This section will be positioned away from the developing vegetal pole. Laterally the complete developing gastrula has been rotated to a horizontal axis, allowing it to lie at right angles to the original median plane of the egg. Therefore, the course of rotation is such that the dorsal lip is practically pushed backwards in one direction as rapid or quicker than epiboly moves it forward in the other. The outcome will be that the blastopore produced at roughly the vegetal pole is posterior, and the dorsal and ventral lips are essentially dorsal and ventral. This in addition allows the eggs to form the antero-ventral side of the potential embryo whilst the area marked by the grey crescent is to develop the dorsal segment.

'''4. Invagination'''

Visible is a small fissure- like invagination which is apparent in the middle between the equator and the vegetal segment. The most superior or dorsal border of the cleft produce the dorsal lip of the blastopore. This imput move back and forth on the dorsal plane near the dorsal lip and migrates around the boundaries of the blastocoel in company with the extension of the lateral lips. This adapted invagination is maintained until the blastocoel cavity has been almost abolished; excluding the slender opening separating epiblasts from the hypoblast, the new segment formed is known as the archenteron cavity.

'''5. Involution'''

- Additional to previous course of action a distinct involution also occurs at the blastoporal borders. This is mainly dynamic at the median dorsal lip and gradually more less as it shifts across either side until it reaches the ventral lip where it constant.Throughout this progression, cells positioned beside the superior boundaries of the blastoporal lip migrate over the lip to the interior portion of the lip. These cells are remained within the embryo along the internal edge of the blastopore. This indicates the root of archenteron is composed of involuted cells and beyond this the external layer known as the ectoderm. The base and lateral sides are enclosed mainly of endodermal cellular material, which have been established from larger yolk cells, situated in the vegetal pole of the blastula.

- In the final phases of the gastrula development, the cells contributing to the floor of the archenteron, thin out significantly where they surround the blastocoel.
The hemispherical shaped dorsal lip of blastopore which become visible at the commencement of the gastruation stage carry on to augment, initially becoming semicircular, then transform into a horse shoe shaped and then finally forming into circular band. The band is the accomplished by the blastopore. Various yolk cells of vegetal pole present in the section are crowed into the blastoporal cavity where they form a gathering identified as a yolk plug. Blastopore rapidly reduces in size while the archenteron is still developing and becomes completely formed in the final stage; the yolk plug appears as only a small oval on the gastrula.

==Growth and Modification of Frog Species==

'''1. Changes in habits and habitats:'''

'''a)''' In frogs, metamorphosis is related with or to the modifications and adaptations occuring or taking place as a frog changes environmental habitats from an aquatic to a terrestrial mode. Metamorphosis has modified the adaption of frogs as this alteration it began during the aquatic adaptations in the surface of water to breathe air. Subsequently, it continues the terrestrial surroundings, therefore the frog species become abundant in vegetation area allowing the frog to transform in to amphibious species.

'''b)''' The transition during metamorphosis is linked with a change in food chain. The tadpoles being the embryonic origin of frogs are herbivorous, feeding on algae and green matter, which they collect by the adapted feature such as their teeth surrounding their mouths. Adult frogs, alternatively, are classified as carnivorous feeding on insects and worms. Occasionally, they also consume larger prey, for instance smaller frogs species and even little birds and rodents which they dominant and ingest.

[[Image:Development of frog from sperm to mature structure.jpg|thumb|left|Development of Frog from sperm to mature structure Image details:J,Nassif 2009.jpg]]

'''2. Changes in Morphology'''

These include the decrease or complete absence of specific organs or structures which are essential during development of early frog embryology, but not critical in the mature frog species. The significant alterations of this nature include the following developmental structures.

'''a)''' The long tail of the tadpole alongside the fin folds is absorbed again during metamorphosis and becomes absent at the final stage of the metamorphosis.

'''b) '''The developing gills are resorted, the gill clefts are congested and the branchial cavities start to become absent. The reabsorbtion of gills also takes place by autolysis.

'''c)''' The teeth of the perioral disc additionally the homey lining of the jaws are shed.

'''d)''' The lateral line sense organs within the skin of tadpoles vanish throughout metamorphosis.

'''e)''' The cloacal tube begins to condensed and reduced.

'''f)''' Various blood vessels, together with parts of the aortic arches, are reduced during mature development.

(The figure on the left represents the transformation from a tadpole to a developing structure.)[http://science.jrank.org/pages/2862/Frogs-Adult-morphology.html]

'''3. Progressive or constructive changes'''

This process comprises of the development of specific organs which mature into functional systems only during metamorphosis.

'''a)''' During development the limbs continue to augment in size and differentiation. The forelimbs, which in the tadpole mature under the opercular membrane, which then break through to the exterior. Simultaneously there is a increase in the length and strength of the hind limbs, joints develop in them and the toes become visible.

'''b)''' The middle ear becomes apparent in relation with the first pharyngeal pouch. The tympanic membrane matures. It is bounded by circular tympanic cartilage which allows the frog to retain air.

'''c)''' The visual organs bulge up on the dorsal surface of the head developing the nictitating membrane.

'''d)''' There is augmentation of the tongue and the formation of thevomerina teeth.

[[Image: Growth model.jpg|thumb|Growth Model Image details:J,Nassif2009:]]

'''4. Remodelling of some structures'''

Systematic organs which operate both in the early embryonic larva and the mature adult change their differentiation during metamorphosis so as to meet the requirements of the adult mode of life and due to the habitat adaptations. The figure on the right illustrates structures developing from specic germ cell layers.

'''a)''' The skin of the embryonic tadpole is lined with a double-layered epidermis. The number of layers of cells in the epidermis augments throughout metamorphosis. Superficial surface layers become cornified. Multicellular mucous and serous glands originate in the skin. The pigmentation of the skin continuously changes, new patterns and colour start to form.

'''b)''' There is a lengthening of the mouth gap as a result of rotation of the quadrate cartilage and the true jaws become functional.

'''c)''' The tongue rapidly progresses and becomes larger and more muscular.

'''d)''' The eyes become more specialised.

'''e)''' In early tadpoles, the GIT is extremely long and wound up into a spiral folds. The intestine become greatly lengthened in herbivorous species due to the vegetables food chain.[http://en.wikipedia.org/wiki/Frog]

'''5. Development of the reproductive system'''

(The figure below represents the reproductive and development cycle of a frog as it transform from egg to frog specie.)

In tadpoles, right after the mouth is being formed, two indentation like thickenings of peritoneum begin to appear near the body cavity (dorsal surface), which is nearest to the mesentery which is near the developing kidneys. These appear in all tadpoles.

These indentations appear here because of a change in the endothelial cells, everywhere else they are usually flat looking cells but they undergo a change and in this particular area become somewhat cuboidal/columnar.

Later on the indentations become more obvious due to the epithelial cells replicating numerously to form a thick layer. The posterior two thirds of the indentation for the female is the ovary and for the male it is the testis. The third that is left differentiates and becomes fat for the body.

[[Image: Mature frog life cyle.jpg|thumb|200px|left|Mature from life cycle Image details:Derived from primary source:http://www.scienceclarified.com/images/uesc_01_img0038.jpg]]

[[Image: Developing frog.jpg|thumb|Developing Frog Image details:
[[Image: Mature develop frog.jpg|thumb|Image details: Red eyed tree frog litoria chloris source:[http://en.wikipedia.org/wiki/File:Red-eyed_Tree_Frog_-_Litoria_chloris_edit1.jpg]].jpg]]

===Delamination===

Delamination indicates a mass separating a group of cellular matter from other cellular groups. It has been illustrated that the division of notochord, mesoderm and endoderm tissues from each other to form distinct cellular masses is completed by the progression of delamination, subsequent to these materials moving to the inside throughout gastrulation. During the developing gastrula, the germ layers are all recognized. These distinct segments of the embryo develop from these germ tissue layers.

===Polarity and Rotation===

Throughout fertilisation to the beginning of gastrulation, the frog’s egg continues in the original location in relation to its polarity. Subsequent to gastrulation its polarity begins to differentiate. This progression is linked with migration of materials within the gastrula and can be responsible for the alterations of the centre of gravity.

===Closing of Blastopore===

Subsequent to the formation of the gastrula, the blastopore is visible as a tiny round circular filled cavity containing the yolk plug. As it continues to reduce in dimension, it represented as a pear-shaped outline through the mutual approach of its lateral lips. Through it final progression these fuse entirely to produce a longitudinal groove, the streak which continue dorsally and ventrally in a small aperture. The inferior aperture closes, resulting in a depression called the anal pit. The superior region remains open for some period and begins to as the neural groove is laid down.

===Post Gastrulation or Organogenesis===

Throughout the duration of pre-gastrulation, all tissues for different organs vanish from the surface of blastula and migrate inside to take their final arrangement in the embryo structure where organs are developed from their potential regions. Consequently organogenesis transfers an embryo into free larva structure.

----

==Germ-layer origin of various body tissues==
[[Image: Development Models of Frog.jpg|thumb|right|Figure 13 Image details:Vertebrate Structure and Development.jpg]]

Ectoderm will give raise to structures such as skin, brain, spinal cord, neurons and sense receptors.
Mesoderm will give raise to structrues such as notochord, muscles, blood, bone and sex organs.
Endoderm will give raise to sturctures such as inner lining of gut, liver, pancreas, lungs and bladder, thyroid and parathyroid glands and thymus.

== Structures derived from Germ-layers of frog species ==

[[Image:Development of Frog Layers.jpg|thumb|left|Development of Frog Layers Primary source[http://www.bio.miami.edu/~cmallery/150/physiol/sf19x11b.jpg]Image details:J,Nassif 2009.jpg]]

[[Image:Development of frog layers.jpg|thumb|left|Development of Frog Layers Primary source [http://www.bio.miami.edu/~cmallery/150/physiol/sf19x11b.jpg]Image details:J,Nassif 2009.jpg]]

'''Ectoderm '''

''Establishes the epidermal segments and its derivatives, to the frog’s nervous system. The ectoderm also contributes to :''

1. The olfactory and auditory epithelium.

2. The retina and lens of the eye.

3. Sensory organs.

4. The epithelial lining of the oral cavity and the anus.

5. The pineal and pituitary body.

'''Mesoderm'''

''Mesoderm originates:''

1. Connective tissue.

2. Muscles, except the notochord.

3. Blood vessels.

4. Lymphatics.

5. The peritoneum and the urinary and reproductive system.

6. The dermis, parts of the eye excluding lens, cornea, and conjunctiva.

'''Endoderm'''

''From the endoderm arises:''

1. The epithelial lining to the gut and oesophagus, stomach, intestine, bile duct.

2. The hepatic cells of the liver, respiratory tract, larynx, trachea and lungs.

3. The lining of the urinary bladder, pancreas thyroid and thymus.

[The two figures reveal the development of structures deriving from the celluar components of the embryology of the frog].[Structures derived from Germ-layers of frog species ]

==Life cycle of a frog==

'''Fertilization-egg''':

The female lays eggs in the spring. A group of fertilized eggs is called spawn;

'''7-10 days''':

Fertilized egg feed on remaining yolk which is in its gut. Their gills, mouth and tail have poorly developed. Begin to swim and feed on algae;

'''10-30 days(4 weeks):'''

A layer of skin grows over gills. Teeth begin to appear. A coiled gut start to develop. This is aid in digestion;

'''30-60 days(6-9 weeks):'''

Legs being to grow and head is more distinct. Start to eat insects. Arms begin to grow;

'''60-80 days(12 weeks):'''

Resemble a frog. Still have remaining tail;

'''80-140 days(20 weeks):'''

Fully developed, spend most of time out of water. Majority of frog live between 4-15 years.

==Timeline of frog development==

Development of egg and embryo at temperature 18 degree celsius.

'''0 hours''' - fertilization of the egg

'''1 hours''' - formation of the gray crescent due to pigment migration

'''3.5 hours''' - early cleavage

'''4.5 hours''' - blastula stage(coeloblastula with eccentric blastocoel

'''26 hours''' - gastrulation

'''26 hours''' -'' early'' - crescent shaped dorsal lip

'''34 hours''' - ''middle''- semicircular blastoporal lip

'''42 hours''' - ''late'' - circular blastoporal lip

'''50 hours''' - neurulation

'''50 hours''' - ''early'' - medullary plate

'''62 hours''' -'' middle''- neural folds converging

'''67 hours''' - ''late'' - neural tube formed and ciliation of embryo

'''84 hours''' - tail bud stage(early organogeny)

'''96 hours''' - muscular response to tactile stimulation

'''118 hours''' - early heart beat, development of gill buds

'''140 hours''' - hatching and gill circulation

'''162 hours''' - mouth opens and cornea becomes transparent

'''192 hours''' - tail fin circulation established

'''216 hours''' - degeneration of external gills, formation of operculum, development of embryonic teeth

'''240 hours''' - opercular fold over brachial chamber except for spiracle and internal gills

'''255 hours''' - prolonged larval stage with refinement of organs

'''270 hours''' - development of hindlimbs, internal development of forelimbs in opercular cavity

'''275 hours''' - projection of forelimbs through operculum, left side first

'''280 hours''' - absorption of the tail and reduction in size of the gut

'''284 hours''' - metamorphosis complete, emergence from water as miniature, air breathing frog

==Stages of frog embryology==
--[[User:S8600021|Mark Hill]] 08:40, 9 October 2009 (EST) [[Talk:2009_Group_Project_5#Constructive_Criticism_of_Coordinator|see my comment on images]]

The rate of development of the egg and embryo will depend upon the temperature at which they are kept. The approximate schedule of development at 23 degree celsius is provided below.

{| border='1px'
|+ Table 1: Stages of frog development
!Stage !!Time since fertilisation (hours)!!Stage Characteristic !!Embryo characteristic !!Image of frog stage
|-
|1
|0.00-1.30
|fertilization of the egg, post fertilization
|animal hemisphere, gray crescent and vegetal hemisphere are present
|[[File:Stage01ventral.jpg|100px]]
|-
|2
|1.30-2.00
|splits into two cells
|appearance of first cleavage furrow
|[[File:Stage02ventral.jpg|100px]]
|-
|3
|2.00-2.15
|becomes four cells
|appearance of second cleavage furrow
|[[File:Stage03dorsolat.jpg|100px]]
|-
|4
|2.15-2.45
|becomes eight cells
|appearance of third cleavage furrow
|[[File:Stage04dorsolat.jpg|100px]]
|-
|5
|2.45-3.00
|becomes sixteen cells
|appearance of fourth cleavage furrow
|[[File:Stage05dorsal.jpg|100px]]
|-
|6
|3.00-3.30
|becomes thirty-two cells
|appearance of fifth cleavage furrow
|[[File:Stage06animal.jpg|100px]]
|-
|6.5
|3.30-4.00
|blastula stage
|Three dorsal folds become visible as a result of endoderm invagination. Pole cells no longer visible on surface
|[[File:Stage065dorsal.jpg|100px]]
|-
|7
|4.00-5.00
|Gastrulation stage
|two primary germ layers. epiblast and endoderm
|[[File:Stage07ventral.jpg|100px]]
|-
|8
|5.00-7.00
|neurulation
|medullary plate, neural folds and neural tube
|[[File:Stage08animal.jpg|100px]]
|-
|9
|7.00-9.00
|germ layer
|complete lip involution encircling yolk
|[[File:Stage09veg.jpg|100px]]
|-
|10
|9.00-11.00
|early gastrula
|two primary germ layers
|[[File:Stage10veg.jpg|100px]]
|-
|10.5
|11.00-11.45
|gastrula
|two germ layers
|[[File:Stage105vegb.jpg|100px]]
|-
|11
|11.45-12.30
|medulla plate
|Yolk sac protrudes dorsally, labium moves to midline on ventral side
|[[File:Stage11veg.jpg|100px]]
|-
|11.5
|12.30-13.15
|continuation of medulla plate
|start closing the plate
|[[File:Stage115veg.jpg|100px]]
|-
|12
|13.15-14.15
|early neurula
|thickened ectoderm give rise to CNS
|[[File:Stage12veg.jpg|100px]]
|-
|12.5
|14.15-14.45
|neural folds
|expansion of cavity
|[[File:Stage125postdors.jpg|100px]]
|-
|13
|14.45-16.15
|neural folds
|continue expanding cavity
|[[File:Stage13postdors.jpg|100px]]
|-
|14
|16.15-17.30
|neural folds
|continuation of cavity
|[[File:Stage14postdors.jpg|100px]]
|-
|15
|17.30-18.15
|tail bud stage
|early organogeny
|[[File:Stage15postdors.jpg|100px]]
|-
|16
|18.15-18.45
|tail bud stage
|posterior ventral view
|[[File:Stage16ant.jpg|100px]]
|-
|17
|18.45-19.45
|tail bud stage
|anterior view
|[[File:Stage17ant.jpg|100px]]
|-
|19
|20.45-21.45
|neural fold close complete
|dorsal view
|[[File:Stage19dorsal.jpg|100px]]
|-
|20
|21.45-22.30
|early tail bud
|anterior view
|[[File:Stage20dorsal.jpg|100px]]
|-
|21
|22.30-24.00
|termination of neural crest
|progress to next stage
|[[File:Stage21ant.jpg|100px]]
|-
|22
|24.00-24.45
|prolonged development
|elongation
|[[File:Stage22lat.jpg|100px]]
|-
|23
|24.45-26.15
|elongation of embryo
|later view
|[[File:Stage23lat.jpg|100px]]
|-
|24
|26.15-27.30
|continuation of elongation of embryo
|dorsal view
|[[File:Stage24latsmall.jpg|50px]]
|-
|25
|27.30-29.30
|organs development
|embryo elongates and develops dorsal thickening
|[[File:Stage25dorsal.jpg|50px]]
|-
|26
|29.30-31.15
|elongation
|dorsally forms neural and brain cavity
|[[File:Stage26lat.jpg|50px]]
|-
|27
|31.15-32.30
|elongation of embryo
|dorsal view
|[[File:Stage27lat.jpg|50px]]
|-
|28
|32.30-35.00
|further development
|lateral view
|[[File:Stage28lat.jpg|50px]]
|-
|29-30
|35.00-37.30
|tail bud
|growth
|[[File:Stage29-30lat.jpg|50px]]
|-
|31
|37.30-40.00
|prolonged development
|bud development
|[[File:Stage31lat.jpg|50px]]
|-
|32
|40.00-44.30
|early muscular development
|elongation
|[[File:Stage32lat.jpg|50px]]
|-
|33-34
|44.30-50.00
|muscular movement
|apparatus for locomotion
|[[File:Stage33-34lat.jpg|50px]]
|-
|35-36
|50.00-53.30
|muscular movement
|apparatus for locomotion
|[[File:Stage35-36lat.jpg|50px]]
|-
|37-38
|53.30-56.30
|heart beat
|develops apparatus
|[[File:Stage37-38lat.jpg|50px]]
|-
|39
|56.30-66.00
|mouth opens
|cornea transparent
|[[File:Stage39latsmall.jpg|50px]]
|-
|40
|66.00-76.00
|gill circulation
|hatching
|[[File:Stage40lat.jpg|50px]]
|-
|41
|76.00-80.00
|tail, fin circulation
|circulation
|[[File:Stage41lat.jpg|50px]]
|-
|42
|80.00-86.00
|internal gills, operculum
|opercular fold, teeth
|[[File:Stage42lat.jpg|50px]]
|-
|43
|86.00-98.00
|operculum complete
|operculum closed on right
|[[File:Stage43lat.jpg|50px]]
|-
|46
|98.00-106.00
|metamorphosis
|emergence from water as miniature, operculum complete|
|[[File:Stage46lat.jpg|50px]]
|-
|}

==Abnormalities of frog==

Abnormalities of frog could be caused by multiple factors. These include change in climate, predators, parasites, bacteria, fungi, viruses or pollution and contaminants such as pesticides, metals and fertilizer.[http://www.fws.gov/contaminants/documents/frogsrefup_septoct_2006.pdf]

The Abnormalities are further classified into different categories. These categories are:

===1. Infectious Diseases:===

'''Perkinsus Symptoms-''' caused by perkinsus-like protozoan organism. Symptoms include swollen viscera that leads to a bloated body and and infected swollen heart

'''Ichthyophonus symptoms-''' cause by parasitic genus, where symptoms include a swollen tail resorption site that matches the surrounding skin in color and translucency.

[[Image:Abnormalities of Frog species.jpg|thumb|left|Figure A Image details[waterwatchadelaide.net.au].jpg]]

===2. Surficial Abnormalities:===

Surficial abnormalities as the one that are visible on the surface of the skin. This includes abnormal pigmentation, , subcutaneous hemorrhaging, wounds due to trauma or from a predator
Edema is a fluid-filled swelling under skin whihc is also a surficial abnormality.

===3. Skeletal Abnormalities:===

This is further classified into three more categories:

'''a. Skeletal Malformations-'''

* Microcephaly (small head or blunt snout)
*Scoliosis (Curved spine in lateral direction)
*Shrunken Limb (Micromelia)
*Amelia (Completely missing limb with no stump)

'''b. Skeletal Abnormalities of Unclear Etiology-'''

This condition arises when a frog has ectromelia (missing limb), brachydactyly (missing digits) or other such condition with no visible trauma or external damage, then this will be classified as the Skeletal abnormality of unclear etiology.

'''c. Skeletal Injuries-'''

Any limb missing or broken due to trauma or other related reason which shows clear evidence of it is classified as skeletal injury

===4. Eye Abnormalities:===

Most common includes-

'''i. Anophthalmia:''' Skin covers the eye socket as there is no eye

'''ii. Abnormal Iris Coloration:''' Reduced pigment in either one eye or both resulting in two different colours of the iris at times

'''iii. Abnormal size or shape:''' Both eyes either deviating from each other or size of pupil or iris is different than the other eye

[http://www.fws.gov/contaminants/Amphibian/pdfs/AbnormalitySOP_woutpics_Jan08.pdf ]

==Genetics==

There are a wide variety of species that differ from each other when it comes to genetics and their functioning.

'''TAXONOMY:''' '''Phylum''' ''Chordata'' / '''Sub Phylum''' ''Vertebrata'' / '''Class''' ''Amphibia'' / '''Order''' ''Anura''

Their are more than two dozen different families of frogs, where suborders are:

'''1. ARCHAEBATRACHIA-''' most primitive frogs

'''2. MESOBATRACHIA-''' linked between the Archaebatrachia and Neobatrachia

'''3. NEOBATRACHIA-''' most modern frogs

{| border='4px'
|+ '''General Info:'''
! !!
|-
| '''Number of frogs' species'''
| 5280
|-
| '''Smallest frog genome size:'''
| 0.95pg, Ornate burrowing frog
|-
| '''Largest frog genome size:'''
| 13.40pg, Ornate horned frog
|-
| '''Mean of frogs' genome'''
| 4.68pg ± 0.13
|-
|}

[http://www.genomesize.com]

*Majority of frogs have only 22 to 26 chromosomes and polyploid is very common where they are almost bisexual.

*Polyploid Amphibians reduce their total cell number such that they acheive the same body size as diploids. One of the most unsual forms of polypoidy in amphibians is the water frog ''Rana esculenta'' from Europe and Western Asia.

* The species with larger genomes have more genes for e.g. the frog genus ''Xenopus'' includes 16 species, with genome sizes ranging from 3.5 x 10^9 bp to 1.6 x 10^10 bp. These differences have arisen by numerous events of polyploidization within the past 40 million years or so. The ancestral chromosome number for the genus seems to have been 18, but there are species with 36, 72 and 105 chromosomes [http://www.xenbase.org/common/]

* Further information on the complete genome sequencing of Xenopus Laevis is provided by '''NCBI Xenopus Genome Resources''' [http://www.ncbi.nlm.nih.gov/nuccore/BC077223?ordinalpos=1&itool=EntrezSystem2.PEntrez.Sequence.Sequence_ResultsPanel.Sequence_RVDocSum]

{| border='4px'
|+ '''Difference within two families'''
! '''SPECIES''' !! ''X.LAEVIS'' !! ''X.TROPICALIS''
|-
| '''PLOIDY'''
| Allotetraploid
| Diploid
|-
| '''NO. OF CHROMOSOMES'''
| 36 chromosomes
| 20 chromosomes
|-
| '''GENOME SIZE'''
| 3.1 x 10^9 bp
| 1.7 x 10^9 bp
|-
| '''EGG SIZE'''
| 1-1.3 mm
| 0.7-0.8 mm
|-
| '''GENERATION TIME'''
| 1-2 years
| 4 months
|-
|}
[http://www.xenbase.org/common/]

===Genome Sequencing===

Since Frog has a huge family with many different species, only few main species that are used widely for the purposes of experiments have their genome sequenced.

''Xenopus tropicalis'' has one of the smallest genomes among amphibians and has the shortest generation time- four to six months and the only diploid genome among the 14 Xenopus species. This means it has no more than two copies of most genes, whereas the other species of Xenopus have four copies of most genes (pseudotetraploid). US Department of Energy's Joint Genome Institute (JGI) in Walnut Creek, California, initiated the X. tropicalis Genome Project, finding 1,700 million base pairs.
[http://www.genome.gov/Pages/Research/Sequencing/BACLibrary/xenopusTropicalis.pdf]

Complete and detailed genome of Xenopus Tropicalis is available from '''NCBI Xenopus Database''' [http://www.ncbi.nlm.nih.gov/nuccore/BC075559?ordinalpos=1&itool=EntrezSystem2.PEntrez.Sequence.Sequence_ResultsPanel.Sequence_RVDocSum]

===Xenopus oocytes===

* The oocytes provide an important expression system for molecular biology.

* By injecting DNA or mRNA into the oocyte or developing embryo, scientists can study the protein products in a controlled system. This allows rapid functional expression of manipulated DNAs (or mRNA). This is particularly useful in electrophysiology, where the ease of recording from the oocyte makes expression of membrane channels attractive.

* One challenge of oocyte work is eliminating native proteins that might confound results, such as membrane channels native to the oocyte.

* Translation of proteins can be blocked or splicing of pre-mRNA can be modified by injection of Morpholino antisense oligos into the oocyte (for distribution throughout the embryo) or early embryo (for distribution only into daughter cells of the injected cell).
[http://www.staff.unibe.ch/sigel/xenopus.html]

===Xenopus Laevis===

* ''Xenopus Laevis'' is an important model organism in developmental biology. X. laevis is tetraploid and reaches sexual maturity in 1 to 2 years. What makes it important in developmental biology is its large and easily manipulable embryo.

* Extracts from the eggs of X. laevis frogs are also commonly used for biochemical studies of DNA replication and repair, as these extracts fully support DNA replication and other related processes in a cell-free environment which allows easier manipulation.

* The Human chorionic gonadotropin hormone (hCG) is present in the urine of the pregnant women in large quantities only. This hormone in the urine induces X.laevis oocyte production which formed the basis of first well-documented method of pregnancy testing X. laevis is also notable for its use as the first well-documented method of pregnancy testing when it was discovered. Today, commercially available HCG is injected into Xenopus males and females to induce mating behavior and breed these frogs in captivity at any time of the year. [http://www.statemaster.com/encyclopedia/Xenopus-laevis]
===Gene cluster===

* The alpha and beta globin genes are closely linked in small cluster of frogs compared to human and chicken

* The similarity of architecture of two clusters found in X.laevis supports the tetraploid origin

* The two loci encoding the muscle specific creatine kinase isoenzymes and have large differences in developmental profile, therefore suggesting that duplicate loci that have not undergone silencing are not simply redundant copies but have acquired specialization.

* Contains twice number of genes for proteins i.e. haemoglobin and sarcomeric actin serum albumin compared with other species

----

==Current Embrology Research==

Currently, a number of fields have benefited from the development of frog embrology. These include cloning, verification of messenger RNA, and Cell cycle.

===Cloning===
[[Image:Robert Briggs.jpg|thumb|left|Figure 16 Image details:Robert Briggs.jpg]]

In 1952, Robert Briggs and Thomas J King cloned northern leopard frogs using a method of nuclear transfer. Briggs and King's experiment was similar to that envisioned - and piloted using salamanders - by Hans Spemann in his 1938 proposal for a 'fantastical experiment'. Later, John Gurdon extended this work and showed that nuclei from differentiated cells could support development, although less well than those from early embryos. [http://genome.wellcome.ac.uk/doc_WTD020799.html]

Lemaitre et a. (2005) from MRC Cancer Cell Unit, Cambridge, U.K. worked on experiments that demonstrated that importance of serial nuclear transplantation for the sucessful cloning of frogs. He demonstrated that exposure of somatic-cell nuclei (erythrocyte nuclei) and sperm nuclei to an extract of mitotic cell extract reorganizes the chromatin into shorter loops and allows replication at much shorter intervals along the DNA. This increases the efficiency of DNA replication in mammalian cell-free systems.

===Transgenesis techniques for functional genomics in Xenopus===

Transgenesis in Xenopus is made possible due to large embryos, a reliable fate map, ease of microinjection, ease of dissection/micromanipulation and existence of the neuroendocrine reflex of background adaptation as a model for activation/inact.

Recently, Hajime Ogino and Haruki Ochi from Nura Institute of Science and Technology in Japan focused on the genomic resources and principles of the transgenesis techniques in Xenopus, and discusses their applications to genome wide network analysis, with emphasis on the use of bioinformatics tools, these studies were undertake in 2009. This is necessary to understand the gene regulatory networks that control vertebrate development. [http://www.ingentaconnect.com/content/bsc/dgd/2009/00000051/00000004/art00001%3Bjsessionid=4ah96rms73gcu.alexandra]

Xenopus used to be a problem in earlier days when it came to transgenesis. Current methods involves isolated sperm nuclei from Xenopus testis that are microinjected into unfertilized eggs. The generated transgenic tadpoles contain 5-35 copies of the integrated plasmid that are expressed in all cells. If desired, expression of the transgene can be directed to the appropriate tissue and at the appropriate time by using specific promoters, mostly the Xenopus POMC gene promoter (isolated from a Xenopus genomic DNA library) to specifically direct expression of green fluorescent protein (GFP) at high levels to the intermediate pituitary cells, which can either be over expressed or inhibited.[http://molanphys.ruhosting.nl/transgenesis.htm]

[[File:Transgenesis.JPG]]

===Verification of messenger RNA===

While the existence and role of messenger RNA (mRNA) was known in bacteria, in the 1960s it was still debated whether it also existed in vertebrates. Taking haemoglobin mRNA from immature red blood cells and injecting it into a Xenopus oocyte, John Gurdon showed that the haemoglobin protein was indeed produced. Producing proteins in Xenopus oocytes has proved to be extremely useful in cell biology, in particular for the study of receptor proteins.[http://genome.wellcome.ac.uk/doc_WTD020799.html]

===Cell Cycle===

As they develop outside the mother, frog eggs are well stocked with the proteins needed to drive the development of the embryo. Studies of these processes has shed considerable light on the processes involved in cell division - termed the cell cycle. [http://genome.wellcome.ac.uk/doc_WTD020799.html]

===Limb development in Xenopus Laevis===

[[Image: Frog Limb development.jpg|thumb|right|From Limb Development Image details:Primary source:[http://images.google.com.au/imgres?imgurl=http://www.sciencedaily.com/images/2006/06/060616130718.jpg&imgrefurl=http://www.sciencedaily.com/releases/2006/06/060616130718.htm&usg=__xliPsPAvheUBME_kjv_q7auiFbo=&h=333&w=300&sz=11&hl=en&start=2&um=1&tbnid=y_ntJtmkRSK7WM:&tbnh=119&tbnw=107&prev=/images%3Fq%3DLimb%2Bdevelopment%2Bin%2BXenopus%2BLaevis%26ndsp%3D18%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

Donald D. Brown (2005),Department of Embryology, Carnegie Institution of Washington demonstrated factors related to limb development of Xenopus Laevis. Thyroid hormone (TH) is found to be required for limb development in this frog. Specific cell types in the growing limb were targeted for expression of a dominant negative form of the TH receptor by sperm-mediated transgenesis. Limb muscle development, the innervation of muscle from the spinal cord, and cartilage growth can be inhibited without affecting patterning of the limb or differentiation of other cell types. Remodeling of the skin occurs late in metamorphosis after the limb has formed. The coordination of these independent programs is affected in part by the control that TH exerts over DNA replication in all cell types of the limb. [http://www.pnas.org/content/102/35/12455.full]

===Growth factor signalling in the pattern of the mesoderm and neuroectoderm of the xenopus===

with current research being undertaken by scientist it has been found that a important factor in the formation of the mesoderm in the xenopus are peptide growth factors. scientist are interested in these peptide growth factors and are trying to understand if they will be able to use them to produce a fully organized embryo. we know that the mesoderm is not fully organized until the gastrula stage, so scientist are focusing on this stage only and trying to understand the different patterns that occur here.

The frog is used in this research because the embryo is well suited for it as the tissues of the frog can be dissected with ease as well as other factors that will help the scientist with their research like isolating the tissues of the frog. there are several methods and tools they use to help them achieve their goal, they can use time lapse video microscopy to see the morphogenetic movements that occur in the gastrula and neurula stages (helps with understand the patterns and signals that occur in the embryo).

An example the scientist have used to study the growth factor signals within the frog at a early stage in development is they inject RNA wild type and mutant growth factors they can produce a cell that secretes growth factors or a cell that is unable to secrete growth factors. this is important because it helps them understand the signals and where they are being produced from as well as transmitted from the mesoderm during the gastrula stage.

The Scientist have also found out that FGF (fibroblast growth factors) signalling is important in these events to produce a fully organized embryo. They made a embryo that has FGF signalling throughout the blastula stage but where the FGF signalling is not acquired through the gastrula stage. This showed that FGF signalling is important if the mesoderm is to stay intact. They came down to a conclusion where embryos that had a mesoderm that had FGF signalling during its induction and that had a compromised FGF signalling during the gastrula stage, the embryo did not form a notochord or any muscles. [http://www.gurdon.cam.ac.uk/~amayalab/Current.Research.Interests.html]

----

== Glossary ==

[[Image: Frog species.jpg|thumb|left| Frog Species Image details:Primary source:www.olympus.co.jp/.../080925/large/p02L.jpg].jpg]]

*'''Amphibian:'''

''Relating to or characteristic of animals of the class amphibia.Amphibians are found in the taxonomic class of amphibia, amphibians are capable of both occupying and successfully living in both land and aquatic communities.amphibian''

*'''Augmentation:'''

''Enlargement/Increase in cellular size.''

*'''Autolysis:'''

''breakdown of a part or whole cell or tissue by self-produced enzymes''

*'''Blastomeres:'''

''The undifferentiated cells formed by cleavage of the fertilised ovum. This includes cells in the cleavage, morula, and blastula stages of the embryo''

*'''Carnivorous:'''
''
Flesh-eating; subsisting on animals as food.''

*'''Cleavage:'''

''he repeated division of a fertilised ovum ''

* '''Cleft:'''

''an opening, fissure, or V-shaped indentation made by or as if by splitting''

*'''Chordate:'''

''Members of a diverse phylum of animals that, as embryos, possess a (1) notochord; (2) a dorsal, hollow nerve cord, (3) pharyngeal gill slits; and (4) a post-anal tail''

''The act or state of splitting or dividing of a cell, particularly during the telophase of (animal) cell division.''

*'''Cytoplasm:'''

''The cytoplasm (of both eukaryotes and prokaryotes) is where the functions for cell expansion, growth, metabolism, and replication are carried out''

* '''Epiboly:'''
''The expansion of one cell sheet over other cells, as takes place during gastrulation''

*'''Fertilization:'''

''A process in sexual reproduction that involves the union of male (sperm) and female (ovum) gametes (each with a single, haploid set of chromosomes) to produce a diploid zygote.''

*'''Gamete:'''
''A reproductive cell (male (sperm) or female (egg)) that has only half the usual number of chromosomes''

*'''Gametogenesis:'''

''process leading to the production of gametes. The development and maturation of sex cells through meiosis.Another name for meiosis where a diploid cell is divided into two haploid cells with half the chromosome content of the diploid parent cell.''

*'''Herbivorous:'''

''eating plants; of or pertaining to the herbivora.''

*'''Holoblastic:'''

''The complete division of an isolecithal or microlecithal egg into blastomeres''

*'''Invagination:'''

''One of the methods by which the various germinal layers of the ovum are differentiated.''

*'''Isoenzymes:'''

''Isozymes (also known as isoenzymes) are enzymes that differ in amino acid sequence but catalyze the same chemical reaction.''

*'''Mesentery:'''

'' membranous fold attaching various organs to the body wall.''

*'''Metamorphosis:'''

''A change in the form and often habits of an animal after the embryonic stage during normal development.''

*'''Neuroendocrine:'''

''Neuroendocrine [IPA nʊəroʊˈɛndəkrɪn] cells are cells that release a hormone into the circulating blood in response to a neural stimulus.''

*'''Organogenesis:'''

''The part of embryonic development where the body's main organs develop.''

*'''Peritoneum:'''

''The smooth serous membrane which lines the cavity of the abdomen, or the whole body cavity when there is no diaphragm, and, turning back, surrounds the viscera, forming a closed, or nearly closed, sac.''

*'''Perivitelline space:'''

''The perivitelline space is the space between the zona pellucida and the plasma membrane (sometimes called the vitelline membrane) in a fertilized ovum.''

*'''Polyploidy:'''

''Cells with three or more sets of chromosomes.''

*'''Pronucleus:'''

''the nucleus of the ovum or sperm after fertilization but before they fuse to form the nucleus of the zygote ''

*'''Protoplasm:'''

''The fluid living content of the cell that consists of two major divisions, the cytoplasm and the nucleoplasm (cell nucleus). It is composed mainly of nucleic acids, proteins, lipids, carbohydrates, and inorganic salts''

*'''Segmentation:'''

''division of some metazoan bodies (such as annelida and Arthropoda) into repeated parts, segments. Segmentation can be homomeric (more or less the same) or heteromeric(different from each other).''

*'''Terrestrial:'''

''Of or on the ground, of the habitat of a plant, on land as opposed to in water, or on the ground as opposed to on another plant.''

*'''Transgenesis:'''

''Transgenesis is the process of introducing an exogenous gene - called a transgene - into a living organism so that the organism will exhibit a new property and transmit that property to its offspring.''

*'''Yolk:'''

''nutritive material of an ovum stored for the nutrition of an embryo''

*'''Zygote:'''

''The cell from which an organism develops, that results from the fertilization of the egg by the sperm.''

''Primary Resource "Biology- Online Dictionary''[http://www.biology-online.org/dictionary/Main_Page]

== References - Frog Embryology: ==

[[Image:Frog Research.jpg|thumb|left|Research being done on a Frog Image details:[http://images.google.com.au/imgres?imgurl=http://www.odt.co.nz/files/story/2008/09/university_of_otago_zoology_senior_lecturer_phil_b_3343259744.jpg&imgrefurl=http://www.odt.co.nz/on-campus/university-otago/21670/dunedin-frog-man-wins-zoo-award&usg=__JvJJU5QfOnIwY2bk4xo64UXuJRs=&h=600&w=404&sz=22&hl=en&start=14&um=1&tbnid=AbsP89yWcUiilM:&tbnh=135&tbnw=91&prev=/images%3Fq%3Dfrog%2Bresearch%26hl%3Den%26um%3D1].jpg]]

1. Savage, J. M. (2002). The Amphibians and Reptiles of Costa Rica. University of Chicago Press, Chicago [http://www.springerlink.com/content/vv015277w1746llw/]

2. Ford, L.S.; D.C. Cannatella (1993). "The major clades of frogs". Herpetological Monographs 7: 94–117 [http://digimorph.org/specimens/Xenopus_laevis/]

3. Tyler, M. J. (1994). Australian Frogs A Natural History. Reed Books [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.gracilenta.html]

4. Cogger, H.G.; R.G. Zweifel, and D. Kirschner (2004). Encyclopedia of Reptiles & Amphibians Second Edition. Fog City Press [http://en.wikipedia.org/wiki/Microhylidae]

5. Beltz, Ellin (2005). Frogs: Inside their Remarkable World. Firefly Books [http://unjobs.org/authors/ellin-beltz]

6. Tyler, M. J. (1994). Australian Frogs A Natural History. Reed Books [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

7. Moury JD, Hanken J (1995) Early cranial neural crest migration in the direct-developing frog, Eleutherodactylus coqui. Acta
Anatomica (Basel) 153, 243-253.

8.Raynaud A (1985) Development of limbs and embryonic limb reduction. In Biology of the Reptilia (ed. Gans C, Billett F), pp.
59-148. New York: John Wiley.[http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=9309]

9. Hanken J (1986) Developmental evidence for amphibian origins. In Evolutionary Biology (ed. Hecht MK, Wallace B, Prance GT), 20, pp. 389-417. New York: Plenum Press. [Hanken J (1986) Developmental evidence for amphibian origins. In Evolutionary Biology (ed. Hecht MK, Wallace B, Prance GT), 20, pp. 389-417. New York: Plenum Press.]

10. Elinson RP (1990) Direct development in frogs : wiping the recapitulationist slate clean. Seminars in Developmental Biology
1, 263-270.

11. Beebee, T. J. C. 1996. Ecology and Conservation of Amphibians. Chapman and Hall. London. [http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V5X-3SVHMKH-1X&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=1021245355&_rerunOrigin=google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=825868e10cd178d16a8a0e5ad14dc5ef]

12. Lehtinen, R. M. 2002. The use of screw pines (Pandanus spp.) by amphibians and reptiles in Madagascar. Herpetological Bulletin 2002:20–25.

13. Parris, K. M. and M. A. McCarthy. 1999. What influences the structure of frog assemblages at forest streams. Australian Journal of Ecology 24:495–502. CrossRef

14. Zug, G. R. 1993. Herpetology: An Introductory Biology of Amphibians and Reptiles. Academic Press. San Diego, CA.

15. Slack,J.M.W., Darlington,B.G., Heath,J.K. and Godsave,S.F. (1987)Mesoderm induction in early Xenopus embryos by heparin-binding growth factors. Nature, 326, 197-200.

16. Melton,D.A. (1990) Activins are expressed early in Xenopus embryogenesis and can induce axial mesoderm and anterior structures. Cell, 63, 485-493.

17. Harland,R.M. and Misher,L. (1988) Stability of RNA in developing Xenopus embryos and identification of a destabilizing sequence in TFIIIA RNA. Development, 102, 837-852.

18. Cunliffe,V. and Smith,J.C. (1992) Ectopic mesoderm formation in Xenopus embryos caused by widespread expression of a Brachyury homologue. Nature, 358, 427-430.

19. Kinoshita,K., Bessho,T. and Asashima,M. (1993) Competence prepattern in the animal hemisphere of the 8-cell-stage Xenopus embryo. Devel. Biol., 160, 276-284.

20. LaBonne,C., Burke,B. and Whitman,M. (1995) Role of MAP kinase in mesoderm induction and axial patterning in Xenopus development. Development, 121, 1475-1486.

21. Green,J.B.A., New,H.V. and Smith,J.C. (1992) Responses of embryonic Xenopus cells to activin and FGF are separated by multiple dose thresholds and correspond to distinct axes of the mesoderm. Cell, 71, 731-739.

22. Grainger R., Blumberg B., Harland R., Amemiya C., Importance of Xenopus Tropicalis to biomedical and biological research, Benaroya Research Institute, Virginia Mason Research Center [http://www.genome.gov/Pages/Research/Sequencing/BACLibrary/xenopusTropicalis.pdf ]

23. Gregory, T.R. (2005). Animal Genome Size Database. [http://www.genomesize.com]

24. U.S Fish and Wildlife Services, ABNORMALITY CLASSIFICATION SOP, [http://www.fws.gov/contaminants/Amphibian/pdfs/AbnormalitySOP_woutpics_Jan08.pdf ]

25. Donald D. Brown*, Liquan Cai*, Biswajit Das*, Nicholas Marsh-Armstrong‡, Alexander M. Schreiber*, and Rejeanne Juste*(2005), Thyroid hormone controls multiple independent programs required for limb development in Xenopus laevis metamorphosis [http://www.pnas.org/content/102/35/12455.full]

26. Ogino, Hajime; Ochi, Haruki, Resources and transgenesis techniques for functional genomics in Xenopus, Development Growth & Differentiation, Volume 51, Number 4, May 2009 , pp. 387-401(15) [http://www.ingentaconnect.com/content/bsc/dgd/2009/00000051/00000004/art00001%3Bjsessionid=4ah96rms73gcu.alexandra]

27. Giles Newton (2004) Why the frog? The Human Genome, [http://genome.wellcome.ac.uk/doc_WTD020799.html]

28. NCBI Xenopus Genome Database, ''Xenopus laevis cDNA clone MGC:79055 IMAGE:4679899, complete cds'' [http://www.ncbi.nlm.nih.gov/nuccore/BC077223?ordinalpos=1&itool=EntrezSystem2.PEntrez.Sequence.Sequence_ResultsPanel.Sequence_RVDocSum]

29. NCBI Xenopus Genome Database, ''Xenopus tropicalis cDNA clone MGC:89509 IMAGE:6992565, complete cds'' [http://www.ncbi.nlm.nih.gov/nuccore/BC075559?ordinalpos=1&itool=EntrezSystem2.PEntrez.Sequence.Sequence_ResultsPanel.Sequence_RVDocSum]

28. Xenbase, [http://www.xenbase.org/common/]

29. Donders Center for Neuroscience & Nijmegen Center for Molecular Life Sciences (NCMLS), Beyond the genome (Xenopus transgenesis for functional genomics),Faculty of Science, Radboud University [http://molanphys.ruhosting.nl/transgenesis.htm]

30. Nation Master, [http://www.statemaster.com/encyclopedia/Xenopus-laevis]* (no available year or author)

== External Links ==
[[Image:Frog links.jpg|thumb|left|Smart Frog Image details:[http://images.google.com.au/imgres?imgurl=http://2.bp.blogspot.com/_o93AaY0GzH4/SjY_ZYv0PII/AAAAAAAAAgk/skruNc2yN78/s400/computer%2Bfrog.jpg&imgrefurl=http://hellaheaven-ana.blogspot.com/2009/06/talking-frog-contemporary-fairy-tale.html&usg=__oxji1TGLV2Fi7xe0dnlmuYk8gDo=&h=288&w=288&sz=16&hl=en&start=2&um=1&tbnid=ywZd4zpdxC5plM:&tbnh=115&tbnw=115&prev=/images%3Fq%3Dfrog%2Bon%2Bcomputer%26hl%3Den%26um%3D1].jpg]]

1. Frog embryology [http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/F/FrogEmbryology.html Frog Embryology]

2. Frog cellular materials [http://www.xenbase.org/xenbase/original/cell/cell.html xenbase]

3. The zoology of frog species [http://worms.zoology.wisc.edu/frogs/mainmenu.html zoology frogs]

4. Frog cycle [http://www.bioethics.gov/images/sc_images/frog_dev.gif bioethics frog] Just a little cycle of FROG'S life cycle

5. Frog Embryology [http://embryology.med.unsw.edu.au/OtherEmb/Frog.htm UNSW Embryology]

6. Frog Research [http://apps.carleton.edu/campus/library/now/exhibits/wallcharts/frog/ carleton library exhibit]

{{Template:Projects09}}
[[Category:Frog]]

2009 Group Project 5

2009-10-15T00:11:52Z

Z3258567: /* Current Embrology Research */

== The Embryology of Frogs ==

== The Frog ==

[[Image: Frog species .jpg|thumb|left|Image details: Wikipedia (2009) Frog species[http://en.wikipedia.org/wiki/Frog#Uses_in_agriculture_and_research].jpg]]

Frogs are scientifically identified by the structure of their long posterior limbs, a petite framework, webbed fingers and feet, budged eyes and the lack of a tail. The majority of frog species are extensively recognized as outstanding jumpers, due to their long, dominant legs, which are adaptations to progress jumping performance during activities. The Frog is one of the most frequently studied species in experimental embryology and most anatomical sciences. ''The Frog is a practically effective model for human embryological development given that the Frog:''

- Comprises of genes which can be effectively manipulated.

- Comprises of similar homogeny with humans species.

- Reproduces a large quantity of offspring in a short period of time.

- Are small species which can be simply sustained.

- Are not extremely luxurious and expensive.

== The History of the uses in agriculture and research ==

[[Image: Frog experiments .jpg|thumb|right|Image details: Scans of chemically cleared and dyed preserved deformed frogs and toads [http://www.sat.qc.ca/upload/residence/frog-04.jpg].jpg]]

There are numerous types of frog species that have been manipulated in many developmental experiments. The frog was traditionally used by countless of the early embryology investigators and presently there are several diverse molecular mechanisms regarding progression of the frog. Theses include:

'''1.''' Food source; frog legs are a delicacy and are eaten in European countries and in many parts of South American regions.

'''2.''' Frogs have the finest biochemical dissection of phenomena that take place in the egg and oocyte. Frogs are the evolutionarily closest to mammals, commonly used as a vertebrate model.

'''3.''' Frogs lay thousands of outsized eggs, from which cell extracts can be readily prepared that is capable of recapitulating most molecular phenomena in a test tube.

'''4.''' Frogs have been commonly used as a laboratory system for a very long period, and have an extensive history of producing crucial observations in countless fields of biology.

'''5.''' Frogs have a important historical connection to the study of epigenetics (John Gurdon-vertebrate cloning and reprogramming) which has been mostly performed on frog species.

'''6.''' Frogs also have very strong evidence of pattern formation and early development, as the embryos are large in size and experimentally manipulative.

'''7.''' Recent research into the biochemistry of chromatin and epigenetics has been performed with frog species and mammalian cultured cells.

'''8.''' The biggest weakness of the Frog model system is the difficulty of performing genetic experiments and analysis, as frogs are allotetraploid, meaning they take approximately a year to fully develop to sexual maturity, and the genome has not been completely sequenced. Nevertheless, biochemical manipulations of cell extracts, such as immunodepletions and application of heterologous DNAs and nuclei can avoid the need for genetic exploitation.

----

== Growth and development of the Frog ==

[[Image: Mature develop frog.jpg|thumb|Image details: Wikipedia (2009) Red Eyed Tree Frog Figure 1 Primary source:[http://en.wikipedia.org/wiki/File:Red-eyed_Tree_Frog_-_Litoria_chloris_edit1].jpg]]

* The frog is a well recognised species, abundant predominantly in ponds, swamps, though various species may also exist in damp or shady environments distant from moist habitats.

* Eggs of specific frogs are easily obtained and may be examined in from the beginning of fertilization onwards. The phases of embryonic development differs in various chordates, yet the typical phases are basically apparent in all frog species. The differences are associated principally to the amount of yolk particles present in an egg.

* The yolk particles offer nourishment of the developing embryo. The process of frog development will be discussed from the phases of gametogenesis to the adult stage.

----

== The Egg ==
[[Image:Development of Poles in frog Fertilization.jpg|thumb|left|Development of Poles in Frog Fertilisation:J,Nassif 2009.jpg]]

- The embryology of a frog egg is a vast cell; its dimensions are approximately 1.4-1.6 million times larger than a typical aquatic species egg cell. Throughout the frog’s embryonic maturation period, the egg will be transformed into a tadpole encompassing millions of cells but still remains with its constant volume of genetic material, the vast prodction of cell have been illusttrated in the figure on the right revealing the production of eggs from female frogs. [http://en.wikipedia.org/wiki/Microhylidae]

- The early embryonic frog structure consists of three main segments the superior hemisphere known as the animal pole which is usually visible as a grey coloured area. The innermost layer appears to be between the outer two sections known as the gray crescent represented in black. Inferiorly, represents the vegetal pole typically lighter than the superior compartment illustrated in gold.

VIDEO RESOURCE: [http://www.youtube.com/watch?v=GO5YN_t1fqw&feature=related]

[[Image:Early Development of Frogs.jpg|thumb|left|Early Development of Frog:J,Nassif 2009.jpg]]

==History of frog embryology use ==

*'''1851''' - ''Henby Nelson''(MD): He identified a remarkable fact through the frog embryo. Henby observed the first cleavage of the yolk, in the egg of the frog. And cleaved structure corresponds in line of direction to the longitudinal axis of the body of the embryo of the frog species.

[[Image:Wilhelm Roux.jpg|thumb|right|Wilhelm Roux[http://images.google.com.au/imgres?imgurl=http://www.todayinsci.com/R/Roux_Wilhelm/RouxWilhelmThm.jpg&imgrefurl=http://www.todayinsci.com/6/6_09.htm&usg=__qRLTEMTHdZpAHxiNX12hWjcm9tA=&h=125&w=100&sz=4&hl=en&start=2&um=1&tbnid=LIKIwZTqCpk7MM:&tbnh=90&tbnw=72&prev=/images%3Fq%3DWilhelm%2BRoux%26gbv%3D2%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

*'''1888''' - ''Wilhelm Roux'': Wilhelm Roux attempted to solve the above observation by damaging one cell of a two-cell frog embryo with a hot needle. The cell stayed in place. However, it did not develop further. Its partner developed into a left or right half-embryo;

*'''1907''' - ''John Hopkins'' hospital: In order to identify the cellular source of neuronal fibres. Scientist placed small portions of frog embryo spinal cords in lymph on a microscope slide and was able to observe clear cut neuronal sprouting.

*'''1951''' - ''Robert Briggs'': Robert Briggs was able to clone a frog embryo by substituting the nucleus of an unfertilized frog egg cell with the nucleus of a frog embryo cell. This process is known as nuclear transplant, has formed the basis for all cloning.

*'''1952''' - ''Robert Briggs and T.J. King'': Robert Briggs and T.J. King used frog for test experiment. Because the size of the eggs in the frogs are enormous compared with those of mammals, which make them easier to manipulate.

*'''1976'''- Using the technique that had been successful in cloning frog embryos, the doctor transferred the nucleus of one cells into a donated egg cell. As an embryo began to develop, it was implanted into the uterus of a young woman.

*'''1997''' - ''Wilmut and Campbell'': Utilizing the cloning technique from frog embryo, Drs. Wilmut and Campbell tried the starvation technique on embryo cells to produce Megan and Morag, the world's first cloned sheep and, until now, the most famous sheep in history.

*'''2000''' - ''Tokyo University'': Scientists at Tokyo University have grown artificial eyeballs. Scientists formed them in tadpoles by using frog embryo cells.

*'''2001''' - ''Advanced Cell Technology'': Scientists from Advanced Cell Technology announced production of a human embryo clone. This is significant as its parthenogenesis has been artificially induced in frogs.

[[Image:John Gurdon .jpg|thumb|right|John Gurdon [http://images.google.com.au/imgres?imgurl=http://www.pnas.org/site/misc/images/gurdon.jpg&imgrefurl=http://www.pnas.org/site/misc/classics4.shtml&usg=__1p-GA1PdOYsxKL-cznMb3RHCm98=&h=526&w=400&sz=223&hl=en&start=1&um=1&tbnid=9k4lhuLssiWCAM:&tbnh=132&tbnw=100&prev=/images%3Fq%3DJohn%2BGurdon%26gbv%3D2%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

*'''2002''' - ''John Gurdon'': John Gurdon from Wellcome Cancer Research Institute in Cambridge experimented on cloned frog embryo.

== Gametogenesis ==

* The sexual reproduction occurs through the fusion of either mature reproductive cells or germ cells known as gametes, which include the sperm from the male frog and ova from female frog species so as to form a single cell, the fertilized zygote. The gametes are typically developed in parents of different sexes . [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

* Males gametes is a spermatozoon , the female frog gamete is an ovum. Each gamete is formed by a process, recognised as maturation or gametogenesis in gonads. The typical male frog gonads are testies in male, while the female gonads are ovaries. The synthesis of both gonads is associated with the process of fertilization. [http://en.wikipedia.org/wiki/Microhylidae]

* The zygote changes into a mature frog through the process of embryology and metamorphosis. Gametogenesis is a progression in which frog gametes are established from germ cells. Initial germ cells are called primordial germ cells, which can be recognised extremely early in the life of frog species.

----

== The Egg & Fertilization ==

[[Image:Fertilized and Unfertilised Eggs.jpg|thumb|left|Fertilized and Unfertilized Eggs:J,Nassif 2009.jpg]]

[[Image:Egg Development.jpg|thumb|left|Egg Development:J,Nassif 2009.jpg]]

- This occurs once the sperm cell has inserted, following the insertion of the sperm cells meiosis II is completed, there is a 30 degree position change of the cytoplasm, gray crescent allows this change to be visible in some amphibians, the gray crescent is able what determines the expect ted outline of how the frog will form. The sperm cell joins with the nuclei of the egg which forms the diploid zygote nucleus. --Sando Rashed 10:09, 24 September 2009 (EST)

- The early phases in the development of the egg is visible, but must be studied in tadpoles throughout maturation. In embryonic tadpoles of about 10 millimetres in length, soon after the opening of the oral cavity, a pair of longitudinal ridge-like thickenings of peritoneum becomes apparent along the posterior surface of the body cavity situated near to the mesentery and along the inner boundaries of the kidneys. Genital ridges are established in all tadpoles of this age, sex is not distinct until a later period. The development of the egg is illustrated in the figure on the left revealing the structure of a developed egg and a mature of egg.

[[Image:Fertilisation life cyle.jpg|thumb|Fertilization of Life cycle:Derived from primary source:[http://en.wikipedia.org/wiki/Frog]]]

== Maturation of the Egg ==

- The eggs have currently accomplished their full size, and develop from the exterior of the ovaries like a small shot, but they still have to pass through the course of maturation before they are prepared to be fertilised. This progression of maturation relates to the nucleus almost completely.

- The nucleus component, containing the nuclear fluid that excludes through the nuclear membrane into the substance of the egg, a great segment of the nuclear reticulum vanishes and becomes degraded into separate globules known as nucleoli, but a extremely small division remains in the midpoint as a slender intricately thread recognised as the nuclear skets.
Relative to the egg getting discharged from the ovary, the follicles shatter allowing the eggs to fall into the abdominal cavity of the frog species, the egg then passes forwards, directly by the contraction of the muscular wall, somewhat by the movement of the cilia of the peritoneum, to the apex of the oviduct, which positioned at the anterior compartment of the body cavity opposite to the roots of the respiratory organs.

- The terminal part of the oviduct establishes a thin-walled pouch capable of great swelling, inside which the eggs gathers in large numbers. In conclusion, the eggs are migrated out through the cloaca into water which the albuminous investments of the eggs rapidly augment to form the gelatinous mass of the frogs spawn.

== Maturation phases ==

'''1. Nuclear skein''', moves from the midpoint of the egg to its outer surface, which it reaches opposite the midpoint of the black pole. The skein, subsequently an unevenly twisted thread, now presumes the specific arrangement of a nuclear spindle, for instance may be visible in the nucleus of an epithelial or additional cell instantly prior to division of the cell occurs.[http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

'''2. The first Polar Body,''' regarding the instance the egg is laid, but prior to its fertilistion, the egg develops a considerably flattened appearance at its upper or black pole, a definite sum of fluid being exuded among the egg and the vitelline membrane. The nuclear spindle currently separate into two identical segments, one of which remains with the egg, and the supplementary is extruded as the first polar body, a small ovoidal white globule, which is situated on the surface of the egg surrounding the exuded peri-vitellline fluid.

'''3. The Second Polar Body''', half of the nuclear spindle that stay behind then splits into two equivalent divisions, one of which remains inside the egg as the female pronucleus, whereas the other segment is extruded as the second polar body, a small white globule extremely related to the first polar body, and like this positioned in the perivitelline fluid on the superior portion of the egg.

'''4. Fertilisation of the egg''', includes the synthesis of the spermatozoon with to egg, specifically, synthesis of the nuclei of these two bodies. The spermatozoa, subsequent to being shed over the seed by the male, distribute vigorously by means of their extended tails, break through the gelatinous investment of the female eggs, bore their way through the vitelline membrane and so go through into the eggs themselves, which they penetrate relative to the superior or black hemispheres.
* Subsequently, an hour following the spermatozoon has entered; a progression may be visible projecting within from the exterior segement of the egg, with a liquid spot in the mid point. This liquid centre is the nucleus of the spermatozoon, and is said to be the male pronucleus, it break through beyond into the female egg, transporting the specialised pigment into it, so that it appears bounded by a pigmented capsule linked with the exterior of the egg by a pigmented stalk.

* By this instance, the second polar body has been established and extruded, and the female pronucleus is merely the only component of the primary egg nucleus still present. Both the male and female pronuceli, which are at initially distance separate to each other, merge and after having enlarged significantly in size then fuse mutually about two and half hours after fertilisation has originated to produce the segmentation nucleus.
* The segmentation nucleus is a huge sphere-shaped vesicle embedded in delicately granular protoplasm, and bounded by a distinct capsule of pigment, its arrangement by the synthesis of the male and female pronuclei completes the action of fertilisation. Specifically female pronucleus may be observe as an imperfect nucleus, and consequently result in the course of fertilisation. The nucleus of the spermatozoon or male pronucleus, replaces the component of the egg- nucleus which has been misplaced as the polar bodies.

'''5. Segmentation of the Egg''', the initial phase of growth consist in constant separation of the egg, whereby it becomes transformed from the unicellular state, which is everlasting only in the lowest species, to muliticelluar state charactertics of all higher species. To these early processes of growth the names segmentation is specified. Shorty subsequent to the competition of fertilisation and arrangement of the segmentation nucleus this later misplaces its sphere-shaped appearance and develops to be spindle-shaped, the yolk granules at the equivalent instance showing a tendency to develop into lines distributing outwards from the distal segment of the spindle.
* The nucleus now split into two halves, which shift away from one another, the yolk granules are likely to combined themselves around the two nuclei, and a slender vertical plate of delicately granular substance is left, dividing the egg.[http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

* Superiorly the eggs depression now becomes visible, initially as a small cavity and then develops as a groove, which almost immediately extends all round, and speedily deepening, splits the egg into two entirely separate halves along a plane equivalent with the vertical plane.

* Shorty after, the two nuclei soon separate again into two, and therefore a second cleft is created in the same state as before, its additionally in the vertical plane, however in a plane at 90 degrees to the initial one, and on its finishing point the egg comprises of four accurately similar segments, each containing a nucleus. The third cleft is horizontal in shape, but not equal, lying closer to the superior than the lower pole, it segregates each of the four cells into, an superior smaller and a inferior larger pole

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== Cleavage ==

[[Image: Frog Cleavage development.jpg|thumb|left|Cleavage Process details:[http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/F/FrogEmbryology.html].jpg]]

* The egg of the frog is scientifically identified as’ telolecithal’ meaning there is a outsized amount of yolk concentrated at a single pole, in contrast to the concentration of cytoplasm and the site of the nucleus. The cleavage phases are holoblastic, therefore the total and after the second cleavage they are asymmetrical .The initial cleavage stage appears about two and half to three hours after fertilization. It commences as a minor depression in close proximity to the centre of the animal hemisphere. It appears as if some interior force is pushing the surface the egg towards the centre. This small upturned fold steadily continues in the form of a channel until it surrounds the egg. This groove is shallow in the commencement, but develop into deeper eventually separating the fertilized egg into two halves recognised as the blastomeres. [The figure on the left symbolise the development and growth of the frog embryo during cleavage].

* Internally the separation is mitotic, consequently each daughter cell contains a nucleus resulting from the copulation nucleus of the fertilised egg. This cleavage is vertical, the two cells are indistinguishable in respect of cytoplasm, pigment and yolk. The subsequent cleavage appears about an hour after the first. The channel of this cleavage begins at the centre of the animal hemisphere, is at right angles to the first and is vertical. This divides the egg into four blastomeres. The fourth blastomere so produced are not qualitatively equal, since of these only two contain the material from the gray crescent. The cleavage begins about thirty minutes after the second is completed or four hours after fertilisation. the cleavage plane of the third furrow is horizontal and slightly above the equator. Thus the four upper cells are a little smaller than the four lower cells. The smaller blastomeres are called micromeres and the larger blastomeres are called macromeres. The fourth cleavages follow 20 minutes after the third and tend to be vertical. This is usually a double furrow.

* The cleavage rate is accelerated with each of the early divisions and since the blastomeres are of unequal size and have varying amounts of cytoplasm and yolk, synchronous cleavage is lost and there is an obvious overlapping of the division. The upper most cells divide more rapidly than the lowermost cells. From this point onwards perfect symmetry in cleavage and in blastomere is very rare, although the embryo developed perfectly. The fifth cleavage is also doubled, appearing first in the upper hemisphere and then in the lower.

* The cleavage thus far follows the rule that each cleavage plane comes in at right angles to the previous one. The subsequent divisions become so irregular that it is previous one. The subsequent division become so irregular that it is impossible to trace out any plan or procedure. The segmentation continues more rapidly in the pigmented regions, since at that place the protoplasm is most dense, whereas, yolk which is very abundant in the vegetal side delays cell division. The multicelluar embryo at this stage is called morula by some biologists.

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== Gastrulation ==

[[Image:FROG GASTRULATION .jpg|thumb|left|Frog Gastrulation Image details:[http://www.google.com.au/imgres?imgurl=http://bio1903.nicerweb.com/Locked/media/ch47/47_12FrogGastrulation.jpg&imgrefurl=http://bio1903.nicerweb.com/Locked/media/ch47/gastrulation-frog.html&h=540&w=480&sz=46&tbnid=N78sHjELreGGSM:&tbnh=132&tbnw=117&prev=/images%3Fq%3Dfrog%2B-%2Bgastrulation&hl=en&usg=__4VK9FYLft0W-4lBe6p5EtQAMiaI=&ei=qPy5SurtMJvE6wON8JmdAg&sa=X&oi=image_result&resnum=4&ct=image].jpg]]

''The phase of Blastulation is followed by the unique developmental progression of gastrulation. The process of frog gastrulation involves the following processes.''

'''1. Epiboly Phase'''

The pigmented cellular materials of blastula have the propensity to overgrow the yolk cells within the developing content. This course which is known as epiboly commences gradually in the final blastula and rapidly accelerates with advancing gastrulation development. The cellular matter within the animal pole reproduces and matures on all sides except in area surrounding the dorsal lip of the blastopore has been established.

'''2. Convergence'''

Scientists suggested that the unfolding was thought to result in spreading of the superficial cells over a substrate with suitable absorption properties. Consequently epiboly and convergence are an outcome to this spreading tendency, which is actually increased by a reduction in surface tension of the distributing cells.

'''3. Rotation'''

The epiboly phase is maintained until the region of the dorsal lip has migrated and is a to some extent greater than 90 degrees and the region of the white blastopore is reduced to small circular rings. This section will be positioned away from the developing vegetal pole. Laterally the complete developing gastrula has been rotated to a horizontal axis, allowing it to lie at right angles to the original median plane of the egg. Therefore, the course of rotation is such that the dorsal lip is practically pushed backwards in one direction as rapid or quicker than epiboly moves it forward in the other. The outcome will be that the blastopore produced at roughly the vegetal pole is posterior, and the dorsal and ventral lips are essentially dorsal and ventral. This in addition allows the eggs to form the antero-ventral side of the potential embryo whilst the area marked by the grey crescent is to develop the dorsal segment.

'''4. Invagination'''

Visible is a small fissure- like invagination which is apparent in the middle between the equator and the vegetal segment. The most superior or dorsal border of the cleft produce the dorsal lip of the blastopore. This imput move back and forth on the dorsal plane near the dorsal lip and migrates around the boundaries of the blastocoel in company with the extension of the lateral lips. This adapted invagination is maintained until the blastocoel cavity has been almost abolished; excluding the slender opening separating epiblasts from the hypoblast, the new segment formed is known as the archenteron cavity.

'''5. Involution'''

- Additional to previous course of action a distinct involution also occurs at the blastoporal borders. This is mainly dynamic at the median dorsal lip and gradually more less as it shifts across either side until it reaches the ventral lip where it constant.Throughout this progression, cells positioned beside the superior boundaries of the blastoporal lip migrate over the lip to the interior portion of the lip. These cells are remained within the embryo along the internal edge of the blastopore. This indicates the root of archenteron is composed of involuted cells and beyond this the external layer known as the ectoderm. The base and lateral sides are enclosed mainly of endodermal cellular material, which have been established from larger yolk cells, situated in the vegetal pole of the blastula.

- In the final phases of the gastrula development, the cells contributing to the floor of the archenteron, thin out significantly where they surround the blastocoel.
The hemispherical shaped dorsal lip of blastopore which become visible at the commencement of the gastruation stage carry on to augment, initially becoming semicircular, then transform into a horse shoe shaped and then finally forming into circular band. The band is the accomplished by the blastopore. Various yolk cells of vegetal pole present in the section are crowed into the blastoporal cavity where they form a gathering identified as a yolk plug. Blastopore rapidly reduces in size while the archenteron is still developing and becomes completely formed in the final stage; the yolk plug appears as only a small oval on the gastrula.

==Growth and Modification of Frog Species==

'''1. Changes in habits and habitats:'''

'''a)''' In frogs, metamorphosis is related with or to the modifications and adaptations occuring or taking place as a frog changes environmental habitats from an aquatic to a terrestrial mode. Metamorphosis has modified the adaption of frogs as this alteration it began during the aquatic adaptations in the surface of water to breathe air. Subsequently, it continues the terrestrial surroundings, therefore the frog species become abundant in vegetation area allowing the frog to transform in to amphibious species.

'''b)''' The transition during metamorphosis is linked with a change in food chain. The tadpoles being the embryonic origin of frogs are herbivorous, feeding on algae and green matter, which they collect by the adapted feature such as their teeth surrounding their mouths. Adult frogs, alternatively, are classified as carnivorous feeding on insects and worms. Occasionally, they also consume larger prey, for instance smaller frogs species and even little birds and rodents which they dominant and ingest.

[[Image:Development of frog from sperm to mature structure.jpg|thumb|left|Development of Frog from sperm to mature structure Image details:J,Nassif 2009.jpg]]

'''2. Changes in Morphology'''

These include the decrease or complete absence of specific organs or structures which are essential during development of early frog embryology, but not critical in the mature frog species. The significant alterations of this nature include the following developmental structures.

'''a)''' The long tail of the tadpole alongside the fin folds is absorbed again during metamorphosis and becomes absent at the final stage of the metamorphosis.

'''b) '''The developing gills are resorted, the gill clefts are congested and the branchial cavities start to become absent. The reabsorbtion of gills also takes place by autolysis.

'''c)''' The teeth of the perioral disc additionally the homey lining of the jaws are shed.

'''d)''' The lateral line sense organs within the skin of tadpoles vanish throughout metamorphosis.

'''e)''' The cloacal tube begins to condensed and reduced.

'''f)''' Various blood vessels, together with parts of the aortic arches, are reduced during mature development.

(The figure on the left represents the transformation from a tadpole to a developing structure.)[http://science.jrank.org/pages/2862/Frogs-Adult-morphology.html]

'''3. Progressive or constructive changes'''

This process comprises of the development of specific organs which mature into functional systems only during metamorphosis.

'''a)''' During development the limbs continue to augment in size and differentiation. The forelimbs, which in the tadpole mature under the opercular membrane, which then break through to the exterior. Simultaneously there is a increase in the length and strength of the hind limbs, joints develop in them and the toes become visible.

'''b)''' The middle ear becomes apparent in relation with the first pharyngeal pouch. The tympanic membrane matures. It is bounded by circular tympanic cartilage which allows the frog to retain air.

'''c)''' The visual organs bulge up on the dorsal surface of the head developing the nictitating membrane.

'''d)''' There is augmentation of the tongue and the formation of thevomerina teeth.

[[Image: Growth model.jpg|thumb|Growth Model Image details:J,Nassif2009:]]

'''4. Remodelling of some structures'''

Systematic organs which operate both in the early embryonic larva and the mature adult change their differentiation during metamorphosis so as to meet the requirements of the adult mode of life and due to the habitat adaptations. The figure on the right illustrates structures developing from specic germ cell layers.

'''a)''' The skin of the embryonic tadpole is lined with a double-layered epidermis. The number of layers of cells in the epidermis augments throughout metamorphosis. Superficial surface layers become cornified. Multicellular mucous and serous glands originate in the skin. The pigmentation of the skin continuously changes, new patterns and colour start to form.

'''b)''' There is a lengthening of the mouth gap as a result of rotation of the quadrate cartilage and the true jaws become functional.

'''c)''' The tongue rapidly progresses and becomes larger and more muscular.

'''d)''' The eyes become more specialised.

'''e)''' In early tadpoles, the GIT is extremely long and wound up into a spiral folds. The intestine become greatly lengthened in herbivorous species due to the vegetables food chain.[http://en.wikipedia.org/wiki/Frog]

'''5. Development of the reproductive system'''

(The figure below represents the reproductive and development cycle of a frog as it transform from egg to frog specie.)

In tadpoles, right after the mouth is being formed, two indentation like thickenings of peritoneum begin to appear near the body cavity (dorsal surface), which is nearest to the mesentery which is near the developing kidneys. These appear in all tadpoles.

These indentations appear here because of a change in the endothelial cells, everywhere else they are usually flat looking cells but they undergo a change and in this particular area become somewhat cuboidal/columnar.

Later on the indentations become more obvious due to the epithelial cells replicating numerously to form a thick layer. The posterior two thirds of the indentation for the female is the ovary and for the male it is the testis. The third that is left differentiates and becomes fat for the body.

[[Image: Mature frog life cyle.jpg|thumb|200px|left|Mature from life cycle Image details:Derived from primary source:http://www.scienceclarified.com/images/uesc_01_img0038.jpg]]

[[Image: Developing frog.jpg|thumb|Developing Frog Image details:
[[Image: Mature develop frog.jpg|thumb|Image details: Red eyed tree frog litoria chloris source:[http://en.wikipedia.org/wiki/File:Red-eyed_Tree_Frog_-_Litoria_chloris_edit1.jpg]].jpg]]

===Delamination===

Delamination indicates a mass separating a group of cellular matter from other cellular groups. It has been illustrated that the division of notochord, mesoderm and endoderm tissues from each other to form distinct cellular masses is completed by the progression of delamination, subsequent to these materials moving to the inside throughout gastrulation. During the developing gastrula, the germ layers are all recognized. These distinct segments of the embryo develop from these germ tissue layers.

===Polarity and Rotation===

Throughout fertilisation to the beginning of gastrulation, the frog’s egg continues in the original location in relation to its polarity. Subsequent to gastrulation its polarity begins to differentiate. This progression is linked with migration of materials within the gastrula and can be responsible for the alterations of the centre of gravity.

===Closing of Blastopore===

Subsequent to the formation of the gastrula, the blastopore is visible as a tiny round circular filled cavity containing the yolk plug. As it continues to reduce in dimension, it represented as a pear-shaped outline through the mutual approach of its lateral lips. Through it final progression these fuse entirely to produce a longitudinal groove, the streak which continue dorsally and ventrally in a small aperture. The inferior aperture closes, resulting in a depression called the anal pit. The superior region remains open for some period and begins to as the neural groove is laid down.

===Post Gastrulation or Organogenesis===

Throughout the duration of pre-gastrulation, all tissues for different organs vanish from the surface of blastula and migrate inside to take their final arrangement in the embryo structure where organs are developed from their potential regions. Consequently organogenesis transfers an embryo into free larva structure.

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==Germ-layer origin of various body tissues==
[[Image: Development Models of Frog.jpg|thumb|right|Figure 13 Image details:Vertebrate Structure and Development.jpg]]

Ectoderm will give raise to structures such as skin, brain, spinal cord, neurons and sense receptors.
Mesoderm will give raise to structrues such as notochord, muscles, blood, bone and sex organs.
Endoderm will give raise to sturctures such as inner lining of gut, liver, pancreas, lungs and bladder, thyroid and parathyroid glands and thymus.

== Structures derived from Germ-layers of frog species ==

[[Image:Development of Frog Layers.jpg|thumb|left|Development of Frog Layers Primary source[http://www.bio.miami.edu/~cmallery/150/physiol/sf19x11b.jpg]Image details:J,Nassif 2009.jpg]]

[[Image:Development of frog layers.jpg|thumb|left|Development of Frog Layers Primary source [http://www.bio.miami.edu/~cmallery/150/physiol/sf19x11b.jpg]Image details:J,Nassif 2009.jpg]]

'''Ectoderm '''

''Establishes the epidermal segments and its derivatives, to the frog’s nervous system. The ectoderm also contributes to :''

1. The olfactory and auditory epithelium.

2. The retina and lens of the eye.

3. Sensory organs.

4. The epithelial lining of the oral cavity and the anus.

5. The pineal and pituitary body.

'''Mesoderm'''

''Mesoderm originates:''

1. Connective tissue.

2. Muscles, except the notochord.

3. Blood vessels.

4. Lymphatics.

5. The peritoneum and the urinary and reproductive system.

6. The dermis, parts of the eye excluding lens, cornea, and conjunctiva.

'''Endoderm'''

''From the endoderm arises:''

1. The epithelial lining to the gut and oesophagus, stomach, intestine, bile duct.

2. The hepatic cells of the liver, respiratory tract, larynx, trachea and lungs.

3. The lining of the urinary bladder, pancreas thyroid and thymus.

[The two figures reveal the development of structures deriving from the celluar components of the embryology of the frog].[Structures derived from Germ-layers of frog species ]

==Life cycle of a frog==

'''Fertilization-egg''':

The female lays eggs in the spring. A group of fertilized eggs is called spawn;

'''7-10 days''':

Fertilized egg feed on remaining yolk which is in its gut. Their gills, mouth and tail have poorly developed. Begin to swim and feed on algae;

'''10-30 days(4 weeks):'''

A layer of skin grows over gills. Teeth begin to appear. A coiled gut start to develop. This is aid in digestion;

'''30-60 days(6-9 weeks):'''

Legs being to grow and head is more distinct. Start to eat insects. Arms begin to grow;

'''60-80 days(12 weeks):'''

Resemble a frog. Still have remaining tail;

'''80-140 days(20 weeks):'''

Fully developed, spend most of time out of water. Majority of frog live between 4-15 years.

==Timeline of frog development==

Development of egg and embryo at temperature 18 degree celsius.

'''0 hours''' - fertilization of the egg

'''1 hours''' - formation of the gray crescent due to pigment migration

'''3.5 hours''' - early cleavage

'''4.5 hours''' - blastula stage(coeloblastula with eccentric blastocoel

'''26 hours''' - gastrulation

'''26 hours''' -'' early'' - crescent shaped dorsal lip

'''34 hours''' - ''middle''- semicircular blastoporal lip

'''42 hours''' - ''late'' - circular blastoporal lip

'''50 hours''' - neurulation

'''50 hours''' - ''early'' - medullary plate

'''62 hours''' -'' middle''- neural folds converging

'''67 hours''' - ''late'' - neural tube formed and ciliation of embryo

'''84 hours''' - tail bud stage(early organogeny)

'''96 hours''' - muscular response to tactile stimulation

'''118 hours''' - early heart beat, development of gill buds

'''140 hours''' - hatching and gill circulation

'''162 hours''' - mouth opens and cornea becomes transparent

'''192 hours''' - tail fin circulation established

'''216 hours''' - degeneration of external gills, formation of operculum, development of embryonic teeth

'''240 hours''' - opercular fold over brachial chamber except for spiracle and internal gills

'''255 hours''' - prolonged larval stage with refinement of organs

'''270 hours''' - development of hindlimbs, internal development of forelimbs in opercular cavity

'''275 hours''' - projection of forelimbs through operculum, left side first

'''280 hours''' - absorption of the tail and reduction in size of the gut

'''284 hours''' - metamorphosis complete, emergence from water as miniature, air breathing frog

==Stages of frog embryology==
--[[User:S8600021|Mark Hill]] 08:40, 9 October 2009 (EST) [[Talk:2009_Group_Project_5#Constructive_Criticism_of_Coordinator|see my comment on images]]

The rate of development of the egg and embryo will depend upon the temperature at which they are kept. The approximate schedule of development at 23 degree celsius is provided below.

{| border='1px'
|+ Table 1: Stages of frog development
!Stage !!Time since fertilisation (hours)!!Stage Characteristic !!Embryo characteristic !!Image of frog stage
|-
|1
|0.00-1.30
|fertilization of the egg, post fertilization
|animal hemisphere, gray crescent and vegetal hemisphere are present
|[[File:Stage01ventral.jpg|100px]]
|-
|2
|1.30-2.00
|splits into two cells
|appearance of first cleavage furrow
|[[File:Stage02ventral.jpg|100px]]
|-
|3
|2.00-2.15
|becomes four cells
|appearance of second cleavage furrow
|[[File:Stage03dorsolat.jpg|100px]]
|-
|4
|2.15-2.45
|becomes eight cells
|appearance of third cleavage furrow
|[[File:Stage04dorsolat.jpg|100px]]
|-
|5
|2.45-3.00
|becomes sixteen cells
|appearance of fourth cleavage furrow
|[[File:Stage05dorsal.jpg|100px]]
|-
|6
|3.00-3.30
|becomes thirty-two cells
|appearance of fifth cleavage furrow
|[[File:Stage06animal.jpg|100px]]
|-
|6.5
|3.30-4.00
|blastula stage
|Three dorsal folds become visible as a result of endoderm invagination. Pole cells no longer visible on surface
|[[File:Stage065dorsal.jpg|100px]]
|-
|7
|4.00-5.00
|Gastrulation stage
|two primary germ layers. epiblast and endoderm
|[[File:Stage07ventral.jpg|100px]]
|-
|8
|5.00-7.00
|neurulation
|medullary plate, neural folds and neural tube
|[[File:Stage08animal.jpg|100px]]
|-
|9
|7.00-9.00
|germ layer
|complete lip involution encircling yolk
|[[File:Stage09veg.jpg|100px]]
|-
|10
|9.00-11.00
|early gastrula
|two primary germ layers
|[[File:Stage10veg.jpg|100px]]
|-
|10.5
|11.00-11.45
|gastrula
|two germ layers
|[[File:Stage105vegb.jpg|100px]]
|-
|11
|11.45-12.30
|medulla plate
|Yolk sac protrudes dorsally, labium moves to midline on ventral side
|[[File:Stage11veg.jpg|100px]]
|-
|11.5
|12.30-13.15
|continuation of medulla plate
|start closing the plate
|[[File:Stage115veg.jpg|100px]]
|-
|12
|13.15-14.15
|early neurula
|thickened ectoderm give rise to CNS
|[[File:Stage12veg.jpg|100px]]
|-
|12.5
|14.15-14.45
|neural folds
|expansion of cavity
|[[File:Stage125postdors.jpg|100px]]
|-
|13
|14.45-16.15
|neural folds
|continue expanding cavity
|[[File:Stage13postdors.jpg|100px]]
|-
|14
|16.15-17.30
|neural folds
|continuation of cavity
|[[File:Stage14postdors.jpg|100px]]
|-
|15
|17.30-18.15
|tail bud stage
|early organogeny
|[[File:Stage15postdors.jpg|100px]]
|-
|16
|18.15-18.45
|tail bud stage
|posterior ventral view
|[[File:Stage16ant.jpg|100px]]
|-
|17
|18.45-19.45
|tail bud stage
|anterior view
|[[File:Stage17ant.jpg|100px]]
|-
|19
|20.45-21.45
|neural fold close complete
|dorsal view
|[[File:Stage19dorsal.jpg|100px]]
|-
|20
|21.45-22.30
|early tail bud
|anterior view
|[[File:Stage20dorsal.jpg|100px]]
|-
|21
|22.30-24.00
|termination of neural crest
|progress to next stage
|[[File:Stage21ant.jpg|100px]]
|-
|22
|24.00-24.45
|prolonged development
|elongation
|[[File:Stage22lat.jpg|100px]]
|-
|23
|24.45-26.15
|elongation of embryo
|later view
|[[File:Stage23lat.jpg|100px]]
|-
|24
|26.15-27.30
|continuation of elongation of embryo
|dorsal view
|[[File:Stage24latsmall.jpg|50px]]
|-
|25
|27.30-29.30
|organs development
|embryo elongates and develops dorsal thickening
|[[File:Stage25dorsal.jpg|50px]]
|-
|26
|29.30-31.15
|elongation
|dorsally forms neural and brain cavity
|[[File:Stage26lat.jpg|50px]]
|-
|27
|31.15-32.30
|elongation of embryo
|dorsal view
|[[File:Stage27lat.jpg|50px]]
|-
|28
|32.30-35.00
|further development
|lateral view
|[[File:Stage28lat.jpg|50px]]
|-
|29-30
|35.00-37.30
|tail bud
|growth
|[[File:Stage29-30lat.jpg|50px]]
|-
|31
|37.30-40.00
|prolonged development
|bud development
|[[File:Stage31lat.jpg|50px]]
|-
|32
|40.00-44.30
|early muscular development
|elongation
|[[File:Stage32lat.jpg|50px]]
|-
|33-34
|44.30-50.00
|muscular movement
|apparatus for locomotion
|[[File:Stage33-34lat.jpg|50px]]
|-
|35-36
|50.00-53.30
|muscular movement
|apparatus for locomotion
|[[File:Stage35-36lat.jpg|50px]]
|-
|37-38
|53.30-56.30
|heart beat
|develops apparatus
|[[File:Stage37-38lat.jpg|50px]]
|-
|39
|56.30-66.00
|mouth opens
|cornea transparent
|[[File:Stage39latsmall.jpg|50px]]
|-
|40
|66.00-76.00
|gill circulation
|hatching
|[[File:Stage40lat.jpg|50px]]
|-
|41
|76.00-80.00
|tail, fin circulation
|circulation
|[[File:Stage41lat.jpg|50px]]
|-
|42
|80.00-86.00
|internal gills, operculum
|opercular fold, teeth
|[[File:Stage42lat.jpg|50px]]
|-
|43
|86.00-98.00
|operculum complete
|operculum closed on right
|[[File:Stage43lat.jpg|50px]]
|-
|46
|98.00-106.00
|metamorphosis
|emergence from water as miniature, operculum complete|
|[[File:Stage46lat.jpg|50px]]
|-
|}

==Abnormalities of frog==

Abnormalities of frog could be caused by multiple factors. These include change in climate, predators, parasites, bacteria, fungi, viruses or pollution and contaminants such as pesticides, metals and fertilizer.[http://www.fws.gov/contaminants/documents/frogsrefup_septoct_2006.pdf]

The Abnormalities are further classified into different categories. These categories are:

===1. Infectious Diseases:===

'''Perkinsus Symptoms-''' caused by perkinsus-like protozoan organism. Symptoms include swollen viscera that leads to a bloated body and and infected swollen heart

'''Ichthyophonus symptoms-''' cause by parasitic genus, where symptoms include a swollen tail resorption site that matches the surrounding skin in color and translucency.

[[Image:Abnormalities of Frog species.jpg|thumb|left|Figure A Image details[waterwatchadelaide.net.au].jpg]]

===2. Surficial Abnormalities:===

Surficial abnormalities as the one that are visible on the surface of the skin. This includes abnormal pigmentation, , subcutaneous hemorrhaging, wounds due to trauma or from a predator
Edema is a fluid-filled swelling under skin whihc is also a surficial abnormality.

===3. Skeletal Abnormalities:===

This is further classified into three more categories:

'''a. Skeletal Malformations-'''

* Microcephaly (small head or blunt snout)
*Scoliosis (Curved spine in lateral direction)
*Shrunken Limb (Micromelia)
*Amelia (Completely missing limb with no stump)

'''b. Skeletal Abnormalities of Unclear Etiology-'''

This condition arises when a frog has ectromelia (missing limb), brachydactyly (missing digits) or other such condition with no visible trauma or external damage, then this will be classified as the Skeletal abnormality of unclear etiology.

'''c. Skeletal Injuries-'''

Any limb missing or broken due to trauma or other related reason which shows clear evidence of it is classified as skeletal injury

===4. Eye Abnormalities:===

Most common includes-

'''i. Anophthalmia:''' Skin covers the eye socket as there is no eye

'''ii. Abnormal Iris Coloration:''' Reduced pigment in either one eye or both resulting in two different colours of the iris at times

'''iii. Abnormal size or shape:''' Both eyes either deviating from each other or size of pupil or iris is different than the other eye

[http://www.fws.gov/contaminants/Amphibian/pdfs/AbnormalitySOP_woutpics_Jan08.pdf ]

==Genetics==

There are a wide variety of species that differ from each other when it comes to genetics and their functioning.

'''TAXONOMY:''' '''Phylum''' ''Chordata'' / '''Sub Phylum''' ''Vertebrata'' / '''Class''' ''Amphibia'' / '''Order''' ''Anura''

Their are more than two dozen different families of frogs, where suborders are:

'''1. ARCHAEBATRACHIA-''' most primitive frogs

'''2. MESOBATRACHIA-''' linked between the Archaebatrachia and Neobatrachia

'''3. NEOBATRACHIA-''' most modern frogs

{| border='4px'
|+ '''General Info:'''
! !!
|-
| '''Number of frogs' species'''
| 5280
|-
| '''Smallest frog genome size:'''
| 0.95pg, Ornate burrowing frog
|-
| '''Largest frog genome size:'''
| 13.40pg, Ornate horned frog
|-
| '''Mean of frogs' genome'''
| 4.68pg ± 0.13
|-
|}

[http://www.genomesize.com]

*Majority of frogs have only 22 to 26 chromosomes and polyploid is very common where they are almost bisexual.

*Polyploid Amphibians reduce their total cell number such that they acheive the same body size as diploids. One of the most unsual forms of polypoidy in amphibians is the water frog ''Rana esculenta'' from Europe and Western Asia.

* The species with larger genomes have more genes for e.g. the frog genus ''Xenopus'' includes 16 species, with genome sizes ranging from 3.5 x 10^9 bp to 1.6 x 10^10 bp. These differences have arisen by numerous events of polyploidization within the past 40 million years or so. The ancestral chromosome number for the genus seems to have been 18, but there are species with 36, 72 and 105 chromosomes [http://www.xenbase.org/common/]

* Further information on the complete genome sequencing of Xenopus Laevis is provided by '''NCBI Xenopus Genome Resources''' [http://www.ncbi.nlm.nih.gov/nuccore/BC077223?ordinalpos=1&itool=EntrezSystem2.PEntrez.Sequence.Sequence_ResultsPanel.Sequence_RVDocSum]

{| border='4px'
|+ '''Difference within two families'''
! '''SPECIES''' !! ''X.LAEVIS'' !! ''X.TROPICALIS''
|-
| '''PLOIDY'''
| Allotetraploid
| Diploid
|-
| '''NO. OF CHROMOSOMES'''
| 36 chromosomes
| 20 chromosomes
|-
| '''GENOME SIZE'''
| 3.1 x 10^9 bp
| 1.7 x 10^9 bp
|-
| '''EGG SIZE'''
| 1-1.3 mm
| 0.7-0.8 mm
|-
| '''GENERATION TIME'''
| 1-2 years
| 4 months
|-
|}
[http://www.xenbase.org/common/]

===Genome Sequencing===

Since Frog has a huge family with many different species, only few main species that are used widely for the purposes of experiments have their genome sequenced.

''Xenopus tropicalis'' has one of the smallest genomes among amphibians and has the shortest generation time- four to six months and the only diploid genome among the 14 Xenopus species. This means it has no more than two copies of most genes, whereas the other species of Xenopus have four copies of most genes (pseudotetraploid). US Department of Energy's Joint Genome Institute (JGI) in Walnut Creek, California, initiated the X. tropicalis Genome Project, finding 1,700 million base pairs.
[http://www.genome.gov/Pages/Research/Sequencing/BACLibrary/xenopusTropicalis.pdf]

Complete and detailed genome of Xenopus Tropicalis is available from '''NCBI Xenopus Database''' [http://www.ncbi.nlm.nih.gov/nuccore/BC075559?ordinalpos=1&itool=EntrezSystem2.PEntrez.Sequence.Sequence_ResultsPanel.Sequence_RVDocSum]

===Xenopus oocytes===

* The oocytes provide an important expression system for molecular biology.

* By injecting DNA or mRNA into the oocyte or developing embryo, scientists can study the protein products in a controlled system. This allows rapid functional expression of manipulated DNAs (or mRNA). This is particularly useful in electrophysiology, where the ease of recording from the oocyte makes expression of membrane channels attractive.

* One challenge of oocyte work is eliminating native proteins that might confound results, such as membrane channels native to the oocyte.

* Translation of proteins can be blocked or splicing of pre-mRNA can be modified by injection of Morpholino antisense oligos into the oocyte (for distribution throughout the embryo) or early embryo (for distribution only into daughter cells of the injected cell).
[http://www.staff.unibe.ch/sigel/xenopus.html]

===Xenopus Laevis===

* ''Xenopus Laevis'' is an important model organism in developmental biology. X. laevis is tetraploid and reaches sexual maturity in 1 to 2 years. What makes it important in developmental biology is its large and easily manipulable embryo.

* Extracts from the eggs of X. laevis frogs are also commonly used for biochemical studies of DNA replication and repair, as these extracts fully support DNA replication and other related processes in a cell-free environment which allows easier manipulation.

* The Human chorionic gonadotropin hormone (hCG) is present in the urine of the pregnant women in large quantities only. This hormone in the urine induces X.laevis oocyte production which formed the basis of first well-documented method of pregnancy testing X. laevis is also notable for its use as the first well-documented method of pregnancy testing when it was discovered. Today, commercially available HCG is injected into Xenopus males and females to induce mating behavior and breed these frogs in captivity at any time of the year. [http://www.statemaster.com/encyclopedia/Xenopus-laevis]
===Gene cluster===

* The alpha and beta globin genes are closely linked in small cluster of frogs compared to human and chicken

* The similarity of architecture of two clusters found in X.laevis supports the tetraploid origin

* The two loci encoding the muscle specific creatine kinase isoenzymes and have large differences in developmental profile, therefore suggesting that duplicate loci that have not undergone silencing are not simply redundant copies but have acquired specialization.

* Contains twice number of genes for proteins i.e. haemoglobin and sarcomeric actin serum albumin compared with other species

----

==Current Embrology Research==

Currently, a number of fields have benefited from the development of frog embrology. These include cloning, verification of messenger RNA, and Cell cycle.

===Cloning===
[[Image:Robert Briggs.jpg|thumb|left|Figure 16 Image details:Robert Briggs.jpg]]

In 1952, Robert Briggs and Thomas J King cloned northern leopard frogs using a method of nuclear transfer. Briggs and King's experiment was similar to that envisioned - and piloted using salamanders - by Hans Spemann in his 1938 proposal for a 'fantastical experiment'. Later, John Gurdon extended this work and showed that nuclei from differentiated cells could support development, although less well than those from early embryos. [http://genome.wellcome.ac.uk/doc_WTD020799.html]

Lemaitre et a. (2005) from MRC Cancer Cell Unit, Cambridge, U.K. worked on experiments that demonstrated that importance of serial nuclear transplantation for the sucessful cloning of frogs. He demonstrated that exposure of somatic-cell nuclei (erythrocyte nuclei) and sperm nuclei to an extract of mitotic cell extract reorganizes the chromatin into shorter loops and allows replication at much shorter intervals along the DNA. This increases the efficiency of DNA replication in mammalian cell-free systems.

===Transgenesis techniques for functional genomics in Xenopus===

Transgenesis in Xenopus is made possible due to large embryos, a reliable fate map, ease of microinjection, ease of dissection/micromanipulation and existence of the neuroendocrine reflex of background adaptation as a model for activation/inact.

Recently, Hajime Ogino and Haruki Ochi from Nura Institute of Science and Technology in Japan focused on the genomic resources and principles of the transgenesis techniques in Xenopus, and discusses their applications to genome wide network analysis, with emphasis on the use of bioinformatics tools, these studies were undertake in 2009. This is necessary to understand the gene regulatory networks that control vertebrate development. [http://www.ingentaconnect.com/content/bsc/dgd/2009/00000051/00000004/art00001%3Bjsessionid=4ah96rms73gcu.alexandra]

Xenopus used to be a problem in earlier days when it came to transgenesis. Current methods involves isolated sperm nuclei from Xenopus testis that are microinjected into unfertilized eggs. The generated transgenic tadpoles contain 5-35 copies of the integrated plasmid that are expressed in all cells. If desired, expression of the transgene can be directed to the appropriate tissue and at the appropriate time by using specific promoters, mostly the Xenopus POMC gene promoter (isolated from a Xenopus genomic DNA library) to specifically direct expression of green fluorescent protein (GFP) at high levels to the intermediate pituitary cells, which can either be over expressed or inhibited.[http://molanphys.ruhosting.nl/transgenesis.htm]

[[File:Transgenesis.JPG]]

===Verification of messenger RNA===

While the existence and role of messenger RNA (mRNA) was known in bacteria, in the 1960s it was still debated whether it also existed in vertebrates. Taking haemoglobin mRNA from immature red blood cells and injecting it into a Xenopus oocyte, John Gurdon showed that the haemoglobin protein was indeed produced. Producing proteins in Xenopus oocytes has proved to be extremely useful in cell biology, in particular for the study of receptor proteins.[http://genome.wellcome.ac.uk/doc_WTD020799.html]

===Cell Cycle===

As they develop outside the mother, frog eggs are well stocked with the proteins needed to drive the development of the embryo. Studies of these processes has shed considerable light on the processes involved in cell division - termed the cell cycle. [http://genome.wellcome.ac.uk/doc_WTD020799.html]

===Limb development in Xenopus Laevis===

[[Image: Frog Limb development.jpg|thumb|right|From Limb Development Image details:Primary source:[http://images.google.com.au/imgres?imgurl=http://www.sciencedaily.com/images/2006/06/060616130718.jpg&imgrefurl=http://www.sciencedaily.com/releases/2006/06/060616130718.htm&usg=__xliPsPAvheUBME_kjv_q7auiFbo=&h=333&w=300&sz=11&hl=en&start=2&um=1&tbnid=y_ntJtmkRSK7WM:&tbnh=119&tbnw=107&prev=/images%3Fq%3DLimb%2Bdevelopment%2Bin%2BXenopus%2BLaevis%26ndsp%3D18%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

Donald D. Brown (2005),Department of Embryology, Carnegie Institution of Washington demonstrated factors related to limb development of Xenopus Laevis. Thyroid hormone (TH) is found to be required for limb development in this frog. Specific cell types in the growing limb were targeted for expression of a dominant negative form of the TH receptor by sperm-mediated transgenesis. Limb muscle development, the innervation of muscle from the spinal cord, and cartilage growth can be inhibited without affecting patterning of the limb or differentiation of other cell types. Remodeling of the skin occurs late in metamorphosis after the limb has formed. The coordination of these independent programs is affected in part by the control that TH exerts over DNA replication in all cell types of the limb. [http://www.pnas.org/content/102/35/12455.full]

===Growth factor signalling in the pattern of the mesoderm and neuroectoderm of the xenopus===

with current research being undertaken by scientist it has been found that a important factor in the formation of the mesoderm in the xenopus are peptide growth factors. scientist are interested in these peptide growth factors and are trying to understand if they will be able to use them to produce a fully organized embryo. we know that the mesoderm is not fully organized until the gastrula stage, so scientist are focusing on this stage only and trying to understand the different patterns that occur here.

The frog is used in this research because the embryo is well suited for it as the tissues of the frog can be dissected with ease as well as other factors that will help the scientist with their research like isolating the tissues of the frog. there are several methods and tools they use to help them achieve their goal, they can use time lapse video microscopy to see the morphogenetic movements that occur in the gastrula and neurula stages (helps with understand the patterns and signals that occur in the embryo).

An example the scientist have used to study the growth factor signals within the frog at a early stage in development is they inject RNA wild type and mutant growth factors they can produce a cell that secretes growth factors or a cell that is unable to secrete growth factors. this is important because it helps them understand the signals and where they are being produced from as well as transmitted from the mesoderm during the gastrula stage.

The Scientist have also found out that FGF (fibroblast growth factors) signalling is important in these events to produce a fully organized embryo. They made a embryo that has FGF signalling throughout the blastula stage but where the FGF signalling is not acquired through the gastrula stage. This showed that FGF signalling is important if the mesoderm is to stay intact. They came down to a conclusion where embryos that had a mesoderm that had FGF signalling during its induction and that had a compromised FGF signalling during the gastrula stage, the embryo did not form a notochord or any muscles.

----

== Glossary ==

[[Image: Frog species.jpg|thumb|left| Frog Species Image details:Primary source:www.olympus.co.jp/.../080925/large/p02L.jpg].jpg]]

*'''Amphibian:'''

''Relating to or characteristic of animals of the class amphibia.Amphibians are found in the taxonomic class of amphibia, amphibians are capable of both occupying and successfully living in both land and aquatic communities.amphibian''

*'''Augmentation:'''

''Enlargement/Increase in cellular size.''

*'''Autolysis:'''

''breakdown of a part or whole cell or tissue by self-produced enzymes''

*'''Blastomeres:'''

''The undifferentiated cells formed by cleavage of the fertilised ovum. This includes cells in the cleavage, morula, and blastula stages of the embryo''

*'''Carnivorous:'''
''
Flesh-eating; subsisting on animals as food.''

*'''Cleavage:'''

''he repeated division of a fertilised ovum ''

* '''Cleft:'''

''an opening, fissure, or V-shaped indentation made by or as if by splitting''

*'''Chordate:'''

''Members of a diverse phylum of animals that, as embryos, possess a (1) notochord; (2) a dorsal, hollow nerve cord, (3) pharyngeal gill slits; and (4) a post-anal tail''

''The act or state of splitting or dividing of a cell, particularly during the telophase of (animal) cell division.''

*'''Cytoplasm:'''

''The cytoplasm (of both eukaryotes and prokaryotes) is where the functions for cell expansion, growth, metabolism, and replication are carried out''

* '''Epiboly:'''
''The expansion of one cell sheet over other cells, as takes place during gastrulation''

*'''Fertilization:'''

''A process in sexual reproduction that involves the union of male (sperm) and female (ovum) gametes (each with a single, haploid set of chromosomes) to produce a diploid zygote.''

*'''Gamete:'''
''A reproductive cell (male (sperm) or female (egg)) that has only half the usual number of chromosomes''

*'''Gametogenesis:'''

''process leading to the production of gametes. The development and maturation of sex cells through meiosis.Another name for meiosis where a diploid cell is divided into two haploid cells with half the chromosome content of the diploid parent cell.''

*'''Herbivorous:'''

''eating plants; of or pertaining to the herbivora.''

*'''Holoblastic:'''

''The complete division of an isolecithal or microlecithal egg into blastomeres''

*'''Invagination:'''

''One of the methods by which the various germinal layers of the ovum are differentiated.''

*'''Isoenzymes:'''

''Isozymes (also known as isoenzymes) are enzymes that differ in amino acid sequence but catalyze the same chemical reaction.''

*'''Mesentery:'''

'' membranous fold attaching various organs to the body wall.''

*'''Metamorphosis:'''

''A change in the form and often habits of an animal after the embryonic stage during normal development.''

*'''Neuroendocrine:'''

''Neuroendocrine [IPA nʊəroʊˈɛndəkrɪn] cells are cells that release a hormone into the circulating blood in response to a neural stimulus.''

*'''Organogenesis:'''

''The part of embryonic development where the body's main organs develop.''

*'''Peritoneum:'''

''The smooth serous membrane which lines the cavity of the abdomen, or the whole body cavity when there is no diaphragm, and, turning back, surrounds the viscera, forming a closed, or nearly closed, sac.''

*'''Perivitelline space:'''

''The perivitelline space is the space between the zona pellucida and the plasma membrane (sometimes called the vitelline membrane) in a fertilized ovum.''

*'''Polyploidy:'''

''Cells with three or more sets of chromosomes.''

*'''Pronucleus:'''

''the nucleus of the ovum or sperm after fertilization but before they fuse to form the nucleus of the zygote ''

*'''Protoplasm:'''

''The fluid living content of the cell that consists of two major divisions, the cytoplasm and the nucleoplasm (cell nucleus). It is composed mainly of nucleic acids, proteins, lipids, carbohydrates, and inorganic salts''

*'''Segmentation:'''

''division of some metazoan bodies (such as annelida and Arthropoda) into repeated parts, segments. Segmentation can be homomeric (more or less the same) or heteromeric(different from each other).''

*'''Terrestrial:'''

''Of or on the ground, of the habitat of a plant, on land as opposed to in water, or on the ground as opposed to on another plant.''

*'''Transgenesis:'''

''Transgenesis is the process of introducing an exogenous gene - called a transgene - into a living organism so that the organism will exhibit a new property and transmit that property to its offspring.''

*'''Yolk:'''

''nutritive material of an ovum stored for the nutrition of an embryo''

*'''Zygote:'''

''The cell from which an organism develops, that results from the fertilization of the egg by the sperm.''

''Primary Resource "Biology- Online Dictionary''[http://www.biology-online.org/dictionary/Main_Page]

== References - Frog Embryology: ==

[[Image:Frog Research.jpg|thumb|left|Research being done on a Frog Image details:[http://images.google.com.au/imgres?imgurl=http://www.odt.co.nz/files/story/2008/09/university_of_otago_zoology_senior_lecturer_phil_b_3343259744.jpg&imgrefurl=http://www.odt.co.nz/on-campus/university-otago/21670/dunedin-frog-man-wins-zoo-award&usg=__JvJJU5QfOnIwY2bk4xo64UXuJRs=&h=600&w=404&sz=22&hl=en&start=14&um=1&tbnid=AbsP89yWcUiilM:&tbnh=135&tbnw=91&prev=/images%3Fq%3Dfrog%2Bresearch%26hl%3Den%26um%3D1].jpg]]

1. Savage, J. M. (2002). The Amphibians and Reptiles of Costa Rica. University of Chicago Press, Chicago [http://www.springerlink.com/content/vv015277w1746llw/]

2. Ford, L.S.; D.C. Cannatella (1993). "The major clades of frogs". Herpetological Monographs 7: 94–117 [http://digimorph.org/specimens/Xenopus_laevis/]

3. Tyler, M. J. (1994). Australian Frogs A Natural History. Reed Books [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.gracilenta.html]

4. Cogger, H.G.; R.G. Zweifel, and D. Kirschner (2004). Encyclopedia of Reptiles & Amphibians Second Edition. Fog City Press [http://en.wikipedia.org/wiki/Microhylidae]

5. Beltz, Ellin (2005). Frogs: Inside their Remarkable World. Firefly Books [http://unjobs.org/authors/ellin-beltz]

6. Tyler, M. J. (1994). Australian Frogs A Natural History. Reed Books [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

7. Moury JD, Hanken J (1995) Early cranial neural crest migration in the direct-developing frog, Eleutherodactylus coqui. Acta
Anatomica (Basel) 153, 243-253.

8.Raynaud A (1985) Development of limbs and embryonic limb reduction. In Biology of the Reptilia (ed. Gans C, Billett F), pp.
59-148. New York: John Wiley.[http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=9309]

9. Hanken J (1986) Developmental evidence for amphibian origins. In Evolutionary Biology (ed. Hecht MK, Wallace B, Prance GT), 20, pp. 389-417. New York: Plenum Press. [Hanken J (1986) Developmental evidence for amphibian origins. In Evolutionary Biology (ed. Hecht MK, Wallace B, Prance GT), 20, pp. 389-417. New York: Plenum Press.]

10. Elinson RP (1990) Direct development in frogs : wiping the recapitulationist slate clean. Seminars in Developmental Biology
1, 263-270.

11. Beebee, T. J. C. 1996. Ecology and Conservation of Amphibians. Chapman and Hall. London. [http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V5X-3SVHMKH-1X&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=1021245355&_rerunOrigin=google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=825868e10cd178d16a8a0e5ad14dc5ef]

12. Lehtinen, R. M. 2002. The use of screw pines (Pandanus spp.) by amphibians and reptiles in Madagascar. Herpetological Bulletin 2002:20–25.

13. Parris, K. M. and M. A. McCarthy. 1999. What influences the structure of frog assemblages at forest streams. Australian Journal of Ecology 24:495–502. CrossRef

14. Zug, G. R. 1993. Herpetology: An Introductory Biology of Amphibians and Reptiles. Academic Press. San Diego, CA.

15. Slack,J.M.W., Darlington,B.G., Heath,J.K. and Godsave,S.F. (1987)Mesoderm induction in early Xenopus embryos by heparin-binding growth factors. Nature, 326, 197-200.

16. Melton,D.A. (1990) Activins are expressed early in Xenopus embryogenesis and can induce axial mesoderm and anterior structures. Cell, 63, 485-493.

17. Harland,R.M. and Misher,L. (1988) Stability of RNA in developing Xenopus embryos and identification of a destabilizing sequence in TFIIIA RNA. Development, 102, 837-852.

18. Cunliffe,V. and Smith,J.C. (1992) Ectopic mesoderm formation in Xenopus embryos caused by widespread expression of a Brachyury homologue. Nature, 358, 427-430.

19. Kinoshita,K., Bessho,T. and Asashima,M. (1993) Competence prepattern in the animal hemisphere of the 8-cell-stage Xenopus embryo. Devel. Biol., 160, 276-284.

20. LaBonne,C., Burke,B. and Whitman,M. (1995) Role of MAP kinase in mesoderm induction and axial patterning in Xenopus development. Development, 121, 1475-1486.

21. Green,J.B.A., New,H.V. and Smith,J.C. (1992) Responses of embryonic Xenopus cells to activin and FGF are separated by multiple dose thresholds and correspond to distinct axes of the mesoderm. Cell, 71, 731-739.

22. Grainger R., Blumberg B., Harland R., Amemiya C., Importance of Xenopus Tropicalis to biomedical and biological research, Benaroya Research Institute, Virginia Mason Research Center [http://www.genome.gov/Pages/Research/Sequencing/BACLibrary/xenopusTropicalis.pdf ]

23. Gregory, T.R. (2005). Animal Genome Size Database. [http://www.genomesize.com]

24. U.S Fish and Wildlife Services, ABNORMALITY CLASSIFICATION SOP, [http://www.fws.gov/contaminants/Amphibian/pdfs/AbnormalitySOP_woutpics_Jan08.pdf ]

25. Donald D. Brown*, Liquan Cai*, Biswajit Das*, Nicholas Marsh-Armstrong‡, Alexander M. Schreiber*, and Rejeanne Juste*(2005), Thyroid hormone controls multiple independent programs required for limb development in Xenopus laevis metamorphosis [http://www.pnas.org/content/102/35/12455.full]

26. Ogino, Hajime; Ochi, Haruki, Resources and transgenesis techniques for functional genomics in Xenopus, Development Growth & Differentiation, Volume 51, Number 4, May 2009 , pp. 387-401(15) [http://www.ingentaconnect.com/content/bsc/dgd/2009/00000051/00000004/art00001%3Bjsessionid=4ah96rms73gcu.alexandra]

27. Giles Newton (2004) Why the frog? The Human Genome, [http://genome.wellcome.ac.uk/doc_WTD020799.html]

28. NCBI Xenopus Genome Database, ''Xenopus laevis cDNA clone MGC:79055 IMAGE:4679899, complete cds'' [http://www.ncbi.nlm.nih.gov/nuccore/BC077223?ordinalpos=1&itool=EntrezSystem2.PEntrez.Sequence.Sequence_ResultsPanel.Sequence_RVDocSum]

29. NCBI Xenopus Genome Database, ''Xenopus tropicalis cDNA clone MGC:89509 IMAGE:6992565, complete cds'' [http://www.ncbi.nlm.nih.gov/nuccore/BC075559?ordinalpos=1&itool=EntrezSystem2.PEntrez.Sequence.Sequence_ResultsPanel.Sequence_RVDocSum]

28. Xenbase, [http://www.xenbase.org/common/]

29. Donders Center for Neuroscience & Nijmegen Center for Molecular Life Sciences (NCMLS), Beyond the genome (Xenopus transgenesis for functional genomics),Faculty of Science, Radboud University [http://molanphys.ruhosting.nl/transgenesis.htm]

30. Nation Master, [http://www.statemaster.com/encyclopedia/Xenopus-laevis]* (no available year or author)

== External Links ==
[[Image:Frog links.jpg|thumb|left|Smart Frog Image details:[http://images.google.com.au/imgres?imgurl=http://2.bp.blogspot.com/_o93AaY0GzH4/SjY_ZYv0PII/AAAAAAAAAgk/skruNc2yN78/s400/computer%2Bfrog.jpg&imgrefurl=http://hellaheaven-ana.blogspot.com/2009/06/talking-frog-contemporary-fairy-tale.html&usg=__oxji1TGLV2Fi7xe0dnlmuYk8gDo=&h=288&w=288&sz=16&hl=en&start=2&um=1&tbnid=ywZd4zpdxC5plM:&tbnh=115&tbnw=115&prev=/images%3Fq%3Dfrog%2Bon%2Bcomputer%26hl%3Den%26um%3D1].jpg]]

1. Frog embryology [http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/F/FrogEmbryology.html Frog Embryology]

2. Frog cellular materials [http://www.xenbase.org/xenbase/original/cell/cell.html xenbase]

3. The zoology of frog species [http://worms.zoology.wisc.edu/frogs/mainmenu.html zoology frogs]

4. Frog cycle [http://www.bioethics.gov/images/sc_images/frog_dev.gif bioethics frog] Just a little cycle of FROG'S life cycle

5. Frog Embryology [http://embryology.med.unsw.edu.au/OtherEmb/Frog.htm UNSW Embryology]

6. Frog Research [http://apps.carleton.edu/campus/library/now/exhibits/wallcharts/frog/ carleton library exhibit]

{{Template:Projects09}}
[[Category:Frog]]

2009 Group Project 5

2009-10-14T23:30:47Z

Z3258567: /* Transgenesis techniques for functional genomics in Xenopus */

== The Embryology of Frogs ==

== The Frog ==

[[Image: Frog species .jpg|thumb|left|Image details: Wikipedia (2009) Frog species[http://en.wikipedia.org/wiki/Frog#Uses_in_agriculture_and_research].jpg]]

Frogs are scientifically identified by the structure of their long posterior limbs, a petite framework, webbed fingers and feet, budged eyes and the lack of a tail. The majority of frog species are extensively recognized as outstanding jumpers, due to their long, dominant legs, which are adaptations to progress jumping performance during activities. The Frog is one of the most frequently studied species in experimental embryology and most anatomical sciences. ''The Frog is a practically effective model for human embryological development given that the Frog:''

- Comprises of genes which can be effectively manipulated.

- Comprises of similar homogeny with humans species.

- Reproduces a large quantity of offspring in a short period of time.

- Are small species which can be simply sustained.

- Are not extremely luxurious and expensive.

== The History of the uses in agriculture and research ==

[[Image: Frog experiments .jpg|thumb|right|Image details: Scans of chemically cleared and dyed preserved deformed frogs and toads [http://www.sat.qc.ca/upload/residence/frog-04.jpg].jpg]]

There are numerous types of frog species that have been manipulated in many developmental experiments. The frog was traditionally used by countless of the early embryology investigators and presently there are several diverse molecular mechanisms regarding progression of the frog. Theses include:

'''1.''' Food source; frog legs are a delicacy and are eaten in European countries and in many parts of South American regions.

'''2.''' Frogs have the finest biochemical dissection of phenomena that take place in the egg and oocyte. Frogs are the evolutionarily closest to mammals, commonly used as a vertebrate model.

'''3.''' Frogs lay thousands of outsized eggs, from which cell extracts can be readily prepared that is capable of recapitulating most molecular phenomena in a test tube.

'''4.''' Frogs have been commonly used as a laboratory system for a very long period, and have an extensive history of producing crucial observations in countless fields of biology.

'''5.''' Frogs have a important historical connection to the study of epigenetics (John Gurdon-vertebrate cloning and reprogramming) which has been mostly performed on frog species.

'''6.''' Frogs also have very strong evidence of pattern formation and early development, as the embryos are large in size and experimentally manipulative.

'''7.''' Recent research into the biochemistry of chromatin and epigenetics has been performed with frog species and mammalian cultured cells.

'''8.''' The biggest weakness of the Frog model system is the difficulty of performing genetic experiments and analysis, as frogs are allotetraploid, meaning they take approximately a year to fully develop to sexual maturity, and the genome has not been completely sequenced. Nevertheless, biochemical manipulations of cell extracts, such as immunodepletions and application of heterologous DNAs and nuclei can avoid the need for genetic exploitation.

----

== Growth and development of the Frog ==

[[Image: Mature develop frog.jpg|thumb|Image details: Wikipedia (2009) Red Eyed Tree Frog Figure 1 Primary source:[http://en.wikipedia.org/wiki/File:Red-eyed_Tree_Frog_-_Litoria_chloris_edit1].jpg]]

* The frog is a well recognised species, abundant predominantly in ponds, swamps, though various species may also exist in damp or shady environments distant from moist habitats.

* Eggs of specific frogs are easily obtained and may be examined in from the beginning of fertilization onwards. The phases of embryonic development differs in various chordates, yet the typical phases are basically apparent in all frog species. The differences are associated principally to the amount of yolk particles present in an egg.

* The yolk particles offer nourishment of the developing embryo. The process of frog development will be discussed from the phases of gametogenesis to the adult stage.

----

== The Egg ==
[[Image:Development of Poles in frog Fertilization.jpg|thumb|left|Development of Poles in Frog Fertilisation:J,Nassif 2009.jpg]]

- The embryology of a frog egg is a vast cell; its dimensions are approximately 1.4-1.6 million times larger than a typical aquatic species egg cell. Throughout the frog’s embryonic maturation period, the egg will be transformed into a tadpole encompassing millions of cells but still remains with its constant volume of genetic material, the vast prodction of cell have been illusttrated in the figure on the right revealing the production of eggs from female frogs. [http://en.wikipedia.org/wiki/Microhylidae]

- The early embryonic frog structure consists of three main segments the superior hemisphere known as the animal pole which is usually visible as a grey coloured area. The innermost layer appears to be between the outer two sections known as the gray crescent represented in black. Inferiorly, represents the vegetal pole typically lighter than the superior compartment illustrated in gold.

VIDEO RESOURCE: [http://www.youtube.com/watch?v=GO5YN_t1fqw&feature=related]

[[Image:Early Development of Frogs.jpg|thumb|left|Early Development of Frog:J,Nassif 2009.jpg]]

==History of frog embryology use ==

*'''1851''' - ''Henby Nelson''(MD): He identified a remarkable fact through the frog embryo. Henby observed the first cleavage of the yolk, in the egg of the frog. And cleaved structure corresponds in line of direction to the longitudinal axis of the body of the embryo of the frog species.

[[Image:Wilhelm Roux.jpg|thumb|right|Wilhelm Roux[http://images.google.com.au/imgres?imgurl=http://www.todayinsci.com/R/Roux_Wilhelm/RouxWilhelmThm.jpg&imgrefurl=http://www.todayinsci.com/6/6_09.htm&usg=__qRLTEMTHdZpAHxiNX12hWjcm9tA=&h=125&w=100&sz=4&hl=en&start=2&um=1&tbnid=LIKIwZTqCpk7MM:&tbnh=90&tbnw=72&prev=/images%3Fq%3DWilhelm%2BRoux%26gbv%3D2%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

*'''1888''' - ''Wilhelm Roux'': Wilhelm Roux attempted to solve the above observation by damaging one cell of a two-cell frog embryo with a hot needle. The cell stayed in place. However, it did not develop further. Its partner developed into a left or right half-embryo;

*'''1907''' - ''John Hopkins'' hospital: In order to identify the cellular source of neuronal fibres. Scientist placed small portions of frog embryo spinal cords in lymph on a microscope slide and was able to observe clear cut neuronal sprouting.

*'''1951''' - ''Robert Briggs'': Robert Briggs was able to clone a frog embryo by substituting the nucleus of an unfertilized frog egg cell with the nucleus of a frog embryo cell. This process is known as nuclear transplant, has formed the basis for all cloning.

*'''1952''' - ''Robert Briggs and T.J. King'': Robert Briggs and T.J. King used frog for test experiment. Because the size of the eggs in the frogs are enormous compared with those of mammals, which make them easier to manipulate.

*'''1976'''- Using the technique that had been successful in cloning frog embryos, the doctor transferred the nucleus of one cells into a donated egg cell. As an embryo began to develop, it was implanted into the uterus of a young woman.

*'''1997''' - ''Wilmut and Campbell'': Utilizing the cloning technique from frog embryo, Drs. Wilmut and Campbell tried the starvation technique on embryo cells to produce Megan and Morag, the world's first cloned sheep and, until now, the most famous sheep in history.

*'''2000''' - ''Tokyo University'': Scientists at Tokyo University have grown artificial eyeballs. Scientists formed them in tadpoles by using frog embryo cells.

*'''2001''' - ''Advanced Cell Technology'': Scientists from Advanced Cell Technology announced production of a human embryo clone. This is significant as its parthenogenesis has been artificially induced in frogs.

[[Image:John Gurdon .jpg|thumb|right|John Gurdon [http://images.google.com.au/imgres?imgurl=http://www.pnas.org/site/misc/images/gurdon.jpg&imgrefurl=http://www.pnas.org/site/misc/classics4.shtml&usg=__1p-GA1PdOYsxKL-cznMb3RHCm98=&h=526&w=400&sz=223&hl=en&start=1&um=1&tbnid=9k4lhuLssiWCAM:&tbnh=132&tbnw=100&prev=/images%3Fq%3DJohn%2BGurdon%26gbv%3D2%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

*'''2002''' - ''John Gurdon'': John Gurdon from Wellcome Cancer Research Institute in Cambridge experimented on cloned frog embryo.

== Gametogenesis ==

* The sexual reproduction occurs through the fusion of either mature reproductive cells or germ cells known as gametes, which include the sperm from the male frog and ova from female frog species so as to form a single cell, the fertilized zygote. The gametes are typically developed in parents of different sexes . [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

* Males gametes is a spermatozoon , the female frog gamete is an ovum. Each gamete is formed by a process, recognised as maturation or gametogenesis in gonads. The typical male frog gonads are testies in male, while the female gonads are ovaries. The synthesis of both gonads is associated with the process of fertilization. [http://en.wikipedia.org/wiki/Microhylidae]

* The zygote changes into a mature frog through the process of embryology and metamorphosis. Gametogenesis is a progression in which frog gametes are established from germ cells. Initial germ cells are called primordial germ cells, which can be recognised extremely early in the life of frog species.

----

== The Egg & Fertilization ==

[[Image:Fertilized and Unfertilised Eggs.jpg|thumb|left|Fertilized and Unfertilized Eggs:J,Nassif 2009.jpg]]

[[Image:Egg Development.jpg|thumb|left|Egg Development:J,Nassif 2009.jpg]]

- This occurs once the sperm cell has inserted, following the insertion of the sperm cells meiosis II is completed, there is a 30 degree position change of the cytoplasm, gray crescent allows this change to be visible in some amphibians, the gray crescent is able what determines the expect ted outline of how the frog will form. The sperm cell joins with the nuclei of the egg which forms the diploid zygote nucleus. --Sando Rashed 10:09, 24 September 2009 (EST)

- The early phases in the development of the egg is visible, but must be studied in tadpoles throughout maturation. In embryonic tadpoles of about 10 millimetres in length, soon after the opening of the oral cavity, a pair of longitudinal ridge-like thickenings of peritoneum becomes apparent along the posterior surface of the body cavity situated near to the mesentery and along the inner boundaries of the kidneys. Genital ridges are established in all tadpoles of this age, sex is not distinct until a later period. The development of the egg is illustrated in the figure on the left revealing the structure of a developed egg and a mature of egg.

[[Image:Fertilisation life cyle.jpg|thumb|Fertilization of Life cycle:Derived from primary source:[http://en.wikipedia.org/wiki/Frog]]]

== Maturation of the Egg ==

- The eggs have currently accomplished their full size, and develop from the exterior of the ovaries like a small shot, but they still have to pass through the course of maturation before they are prepared to be fertilised. This progression of maturation relates to the nucleus almost completely.

- The nucleus component, containing the nuclear fluid that excludes through the nuclear membrane into the substance of the egg, a great segment of the nuclear reticulum vanishes and becomes degraded into separate globules known as nucleoli, but a extremely small division remains in the midpoint as a slender intricately thread recognised as the nuclear skets.
Relative to the egg getting discharged from the ovary, the follicles shatter allowing the eggs to fall into the abdominal cavity of the frog species, the egg then passes forwards, directly by the contraction of the muscular wall, somewhat by the movement of the cilia of the peritoneum, to the apex of the oviduct, which positioned at the anterior compartment of the body cavity opposite to the roots of the respiratory organs.

- The terminal part of the oviduct establishes a thin-walled pouch capable of great swelling, inside which the eggs gathers in large numbers. In conclusion, the eggs are migrated out through the cloaca into water which the albuminous investments of the eggs rapidly augment to form the gelatinous mass of the frogs spawn.

== Maturation phases ==

'''1. Nuclear skein''', moves from the midpoint of the egg to its outer surface, which it reaches opposite the midpoint of the black pole. The skein, subsequently an unevenly twisted thread, now presumes the specific arrangement of a nuclear spindle, for instance may be visible in the nucleus of an epithelial or additional cell instantly prior to division of the cell occurs.[http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

'''2. The first Polar Body,''' regarding the instance the egg is laid, but prior to its fertilistion, the egg develops a considerably flattened appearance at its upper or black pole, a definite sum of fluid being exuded among the egg and the vitelline membrane. The nuclear spindle currently separate into two identical segments, one of which remains with the egg, and the supplementary is extruded as the first polar body, a small ovoidal white globule, which is situated on the surface of the egg surrounding the exuded peri-vitellline fluid.

'''3. The Second Polar Body''', half of the nuclear spindle that stay behind then splits into two equivalent divisions, one of which remains inside the egg as the female pronucleus, whereas the other segment is extruded as the second polar body, a small white globule extremely related to the first polar body, and like this positioned in the perivitelline fluid on the superior portion of the egg.

'''4. Fertilisation of the egg''', includes the synthesis of the spermatozoon with to egg, specifically, synthesis of the nuclei of these two bodies. The spermatozoa, subsequent to being shed over the seed by the male, distribute vigorously by means of their extended tails, break through the gelatinous investment of the female eggs, bore their way through the vitelline membrane and so go through into the eggs themselves, which they penetrate relative to the superior or black hemispheres.
* Subsequently, an hour following the spermatozoon has entered; a progression may be visible projecting within from the exterior segement of the egg, with a liquid spot in the mid point. This liquid centre is the nucleus of the spermatozoon, and is said to be the male pronucleus, it break through beyond into the female egg, transporting the specialised pigment into it, so that it appears bounded by a pigmented capsule linked with the exterior of the egg by a pigmented stalk.

* By this instance, the second polar body has been established and extruded, and the female pronucleus is merely the only component of the primary egg nucleus still present. Both the male and female pronuceli, which are at initially distance separate to each other, merge and after having enlarged significantly in size then fuse mutually about two and half hours after fertilisation has originated to produce the segmentation nucleus.
* The segmentation nucleus is a huge sphere-shaped vesicle embedded in delicately granular protoplasm, and bounded by a distinct capsule of pigment, its arrangement by the synthesis of the male and female pronuclei completes the action of fertilisation. Specifically female pronucleus may be observe as an imperfect nucleus, and consequently result in the course of fertilisation. The nucleus of the spermatozoon or male pronucleus, replaces the component of the egg- nucleus which has been misplaced as the polar bodies.

'''5. Segmentation of the Egg''', the initial phase of growth consist in constant separation of the egg, whereby it becomes transformed from the unicellular state, which is everlasting only in the lowest species, to muliticelluar state charactertics of all higher species. To these early processes of growth the names segmentation is specified. Shorty subsequent to the competition of fertilisation and arrangement of the segmentation nucleus this later misplaces its sphere-shaped appearance and develops to be spindle-shaped, the yolk granules at the equivalent instance showing a tendency to develop into lines distributing outwards from the distal segment of the spindle.
* The nucleus now split into two halves, which shift away from one another, the yolk granules are likely to combined themselves around the two nuclei, and a slender vertical plate of delicately granular substance is left, dividing the egg.[http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

* Superiorly the eggs depression now becomes visible, initially as a small cavity and then develops as a groove, which almost immediately extends all round, and speedily deepening, splits the egg into two entirely separate halves along a plane equivalent with the vertical plane.

* Shorty after, the two nuclei soon separate again into two, and therefore a second cleft is created in the same state as before, its additionally in the vertical plane, however in a plane at 90 degrees to the initial one, and on its finishing point the egg comprises of four accurately similar segments, each containing a nucleus. The third cleft is horizontal in shape, but not equal, lying closer to the superior than the lower pole, it segregates each of the four cells into, an superior smaller and a inferior larger pole

----

== Cleavage ==

[[Image: Frog Cleavage development.jpg|thumb|left|Cleavage Process details:[http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/F/FrogEmbryology.html].jpg]]

* The egg of the frog is scientifically identified as’ telolecithal’ meaning there is a outsized amount of yolk concentrated at a single pole, in contrast to the concentration of cytoplasm and the site of the nucleus. The cleavage phases are holoblastic, therefore the total and after the second cleavage they are asymmetrical .The initial cleavage stage appears about two and half to three hours after fertilization. It commences as a minor depression in close proximity to the centre of the animal hemisphere. It appears as if some interior force is pushing the surface the egg towards the centre. This small upturned fold steadily continues in the form of a channel until it surrounds the egg. This groove is shallow in the commencement, but develop into deeper eventually separating the fertilized egg into two halves recognised as the blastomeres. [The figure on the left symbolise the development and growth of the frog embryo during cleavage].

* Internally the separation is mitotic, consequently each daughter cell contains a nucleus resulting from the copulation nucleus of the fertilised egg. This cleavage is vertical, the two cells are indistinguishable in respect of cytoplasm, pigment and yolk. The subsequent cleavage appears about an hour after the first. The channel of this cleavage begins at the centre of the animal hemisphere, is at right angles to the first and is vertical. This divides the egg into four blastomeres. The fourth blastomere so produced are not qualitatively equal, since of these only two contain the material from the gray crescent. The cleavage begins about thirty minutes after the second is completed or four hours after fertilisation. the cleavage plane of the third furrow is horizontal and slightly above the equator. Thus the four upper cells are a little smaller than the four lower cells. The smaller blastomeres are called micromeres and the larger blastomeres are called macromeres. The fourth cleavages follow 20 minutes after the third and tend to be vertical. This is usually a double furrow.

* The cleavage rate is accelerated with each of the early divisions and since the blastomeres are of unequal size and have varying amounts of cytoplasm and yolk, synchronous cleavage is lost and there is an obvious overlapping of the division. The upper most cells divide more rapidly than the lowermost cells. From this point onwards perfect symmetry in cleavage and in blastomere is very rare, although the embryo developed perfectly. The fifth cleavage is also doubled, appearing first in the upper hemisphere and then in the lower.

* The cleavage thus far follows the rule that each cleavage plane comes in at right angles to the previous one. The subsequent divisions become so irregular that it is previous one. The subsequent division become so irregular that it is impossible to trace out any plan or procedure. The segmentation continues more rapidly in the pigmented regions, since at that place the protoplasm is most dense, whereas, yolk which is very abundant in the vegetal side delays cell division. The multicelluar embryo at this stage is called morula by some biologists.

----

== Gastrulation ==

[[Image:FROG GASTRULATION .jpg|thumb|left|Frog Gastrulation Image details:[http://www.google.com.au/imgres?imgurl=http://bio1903.nicerweb.com/Locked/media/ch47/47_12FrogGastrulation.jpg&imgrefurl=http://bio1903.nicerweb.com/Locked/media/ch47/gastrulation-frog.html&h=540&w=480&sz=46&tbnid=N78sHjELreGGSM:&tbnh=132&tbnw=117&prev=/images%3Fq%3Dfrog%2B-%2Bgastrulation&hl=en&usg=__4VK9FYLft0W-4lBe6p5EtQAMiaI=&ei=qPy5SurtMJvE6wON8JmdAg&sa=X&oi=image_result&resnum=4&ct=image].jpg]]

''The phase of Blastulation is followed by the unique developmental progression of gastrulation. The process of frog gastrulation involves the following processes.''

'''1. Epiboly Phase'''

The pigmented cellular materials of blastula have the propensity to overgrow the yolk cells within the developing content. This course which is known as epiboly commences gradually in the final blastula and rapidly accelerates with advancing gastrulation development. The cellular matter within the animal pole reproduces and matures on all sides except in area surrounding the dorsal lip of the blastopore has been established.

'''2. Convergence'''

Scientists suggested that the unfolding was thought to result in spreading of the superficial cells over a substrate with suitable absorption properties. Consequently epiboly and convergence are an outcome to this spreading tendency, which is actually increased by a reduction in surface tension of the distributing cells.

'''3. Rotation'''

The epiboly phase is maintained until the region of the dorsal lip has migrated and is a to some extent greater than 90 degrees and the region of the white blastopore is reduced to small circular rings. This section will be positioned away from the developing vegetal pole. Laterally the complete developing gastrula has been rotated to a horizontal axis, allowing it to lie at right angles to the original median plane of the egg. Therefore, the course of rotation is such that the dorsal lip is practically pushed backwards in one direction as rapid or quicker than epiboly moves it forward in the other. The outcome will be that the blastopore produced at roughly the vegetal pole is posterior, and the dorsal and ventral lips are essentially dorsal and ventral. This in addition allows the eggs to form the antero-ventral side of the potential embryo whilst the area marked by the grey crescent is to develop the dorsal segment.

'''4. Invagination'''

Visible is a small fissure- like invagination which is apparent in the middle between the equator and the vegetal segment. The most superior or dorsal border of the cleft produce the dorsal lip of the blastopore. This imput move back and forth on the dorsal plane near the dorsal lip and migrates around the boundaries of the blastocoel in company with the extension of the lateral lips. This adapted invagination is maintained until the blastocoel cavity has been almost abolished; excluding the slender opening separating epiblasts from the hypoblast, the new segment formed is known as the archenteron cavity.

'''5. Involution'''

- Additional to previous course of action a distinct involution also occurs at the blastoporal borders. This is mainly dynamic at the median dorsal lip and gradually more less as it shifts across either side until it reaches the ventral lip where it constant.Throughout this progression, cells positioned beside the superior boundaries of the blastoporal lip migrate over the lip to the interior portion of the lip. These cells are remained within the embryo along the internal edge of the blastopore. This indicates the root of archenteron is composed of involuted cells and beyond this the external layer known as the ectoderm. The base and lateral sides are enclosed mainly of endodermal cellular material, which have been established from larger yolk cells, situated in the vegetal pole of the blastula.

- In the final phases of the gastrula development, the cells contributing to the floor of the archenteron, thin out significantly where they surround the blastocoel.
The hemispherical shaped dorsal lip of blastopore which become visible at the commencement of the gastruation stage carry on to augment, initially becoming semicircular, then transform into a horse shoe shaped and then finally forming into circular band. The band is the accomplished by the blastopore. Various yolk cells of vegetal pole present in the section are crowed into the blastoporal cavity where they form a gathering identified as a yolk plug. Blastopore rapidly reduces in size while the archenteron is still developing and becomes completely formed in the final stage; the yolk plug appears as only a small oval on the gastrula.

==Growth and Modification of Frog Species==

'''1. Changes in habits and habitats:'''

'''a)''' In frogs, metamorphosis is related with or to the modifications and adaptations occuring or taking place as a frog changes environmental habitats from an aquatic to a terrestrial mode. Metamorphosis has modified the adaption of frogs as this alteration it began during the aquatic adaptations in the surface of water to breathe air. Subsequently, it continues the terrestrial surroundings, therefore the frog species become abundant in vegetation area allowing the frog to transform in to amphibious species.

'''b)''' The transition during metamorphosis is linked with a change in food chain. The tadpoles being the embryonic origin of frogs are herbivorous, feeding on algae and green matter, which they collect by the adapted feature such as their teeth surrounding their mouths. Adult frogs, alternatively, are classified as carnivorous feeding on insects and worms. Occasionally, they also consume larger prey, for instance smaller frogs species and even little birds and rodents which they dominant and ingest.

[[Image:Development of frog from sperm to mature structure.jpg|thumb|left|Development of Frog from sperm to mature structure Image details:J,Nassif 2009.jpg]]

'''2. Changes in Morphology'''

These include the decrease or complete absence of specific organs or structures which are essential during development of early frog embryology, but not critical in the mature frog species. The significant alterations of this nature include the following developmental structures.

'''a)''' The long tail of the tadpole alongside the fin folds is absorbed again during metamorphosis and becomes absent at the final stage of the metamorphosis.

'''b) '''The developing gills are resorted, the gill clefts are congested and the branchial cavities start to become absent. The reabsorbtion of gills also takes place by autolysis.

'''c)''' The teeth of the perioral disc additionally the homey lining of the jaws are shed.

'''d)''' The lateral line sense organs within the skin of tadpoles vanish throughout metamorphosis.

'''e)''' The cloacal tube begins to condensed and reduced.

'''f)''' Various blood vessels, together with parts of the aortic arches, are reduced during mature development.

(The figure on the left represents the transformation from a tadpole to a developing structure.)[http://science.jrank.org/pages/2862/Frogs-Adult-morphology.html]

'''3. Progressive or constructive changes'''

This process comprises of the development of specific organs which mature into functional systems only during metamorphosis.

'''a)''' During development the limbs continue to augment in size and differentiation. The forelimbs, which in the tadpole mature under the opercular membrane, which then break through to the exterior. Simultaneously there is a increase in the length and strength of the hind limbs, joints develop in them and the toes become visible.

'''b)''' The middle ear becomes apparent in relation with the first pharyngeal pouch. The tympanic membrane matures. It is bounded by circular tympanic cartilage which allows the frog to retain air.

'''c)''' The visual organs bulge up on the dorsal surface of the head developing the nictitating membrane.

'''d)''' There is augmentation of the tongue and the formation of thevomerina teeth.

[[Image: Growth model.jpg|thumb|Growth Model Image details:J,Nassif2009:]]

'''4. Remodelling of some structures'''

Systematic organs which operate both in the early embryonic larva and the mature adult change their differentiation during metamorphosis so as to meet the requirements of the adult mode of life and due to the habitat adaptations. The figure on the right illustrates structures developing from specic germ cell layers.

'''a)''' The skin of the embryonic tadpole is lined with a double-layered epidermis. The number of layers of cells in the epidermis augments throughout metamorphosis. Superficial surface layers become cornified. Multicellular mucous and serous glands originate in the skin. The pigmentation of the skin continuously changes, new patterns and colour start to form.

'''b)''' There is a lengthening of the mouth gap as a result of rotation of the quadrate cartilage and the true jaws become functional.

'''c)''' The tongue rapidly progresses and becomes larger and more muscular.

'''d)''' The eyes become more specialised.

'''e)''' In early tadpoles, the GIT is extremely long and wound up into a spiral folds. The intestine become greatly lengthened in herbivorous species due to the vegetables food chain.[http://en.wikipedia.org/wiki/Frog]

'''5. Development of the reproductive system'''

(The figure below represents the reproductive and development cycle of a frog as it transform from egg to frog specie.)

In tadpoles, right after the mouth is being formed, two indentation like thickenings of peritoneum begin to appear near the body cavity (dorsal surface), which is nearest to the mesentery which is near the developing kidneys. These appear in all tadpoles.

These indentations appear here because of a change in the endothelial cells, everywhere else they are usually flat looking cells but they undergo a change and in this particular area become somewhat cuboidal/columnar.

Later on the indentations become more obvious due to the epithelial cells replicating numerously to form a thick layer. The posterior two thirds of the indentation for the female is the ovary and for the male it is the testis. The third that is left differentiates and becomes fat for the body.

[[Image: Mature frog life cyle.jpg|thumb|200px|left|Mature from life cycle Image details:Derived from primary source:http://www.scienceclarified.com/images/uesc_01_img0038.jpg]]

[[Image: Developing frog.jpg|thumb|Developing Frog Image details:
[[Image: Mature develop frog.jpg|thumb|Image details: Red eyed tree frog litoria chloris source:[http://en.wikipedia.org/wiki/File:Red-eyed_Tree_Frog_-_Litoria_chloris_edit1.jpg]].jpg]]

===Delamination===

Delamination indicates a mass separating a group of cellular matter from other cellular groups. It has been illustrated that the division of notochord, mesoderm and endoderm tissues from each other to form distinct cellular masses is completed by the progression of delamination, subsequent to these materials moving to the inside throughout gastrulation. During the developing gastrula, the germ layers are all recognized. These distinct segments of the embryo develop from these germ tissue layers.

===Polarity and Rotation===

Throughout fertilisation to the beginning of gastrulation, the frog’s egg continues in the original location in relation to its polarity. Subsequent to gastrulation its polarity begins to differentiate. This progression is linked with migration of materials within the gastrula and can be responsible for the alterations of the centre of gravity.

===Closing of Blastopore===

Subsequent to the formation of the gastrula, the blastopore is visible as a tiny round circular filled cavity containing the yolk plug. As it continues to reduce in dimension, it represented as a pear-shaped outline through the mutual approach of its lateral lips. Through it final progression these fuse entirely to produce a longitudinal groove, the streak which continue dorsally and ventrally in a small aperture. The inferior aperture closes, resulting in a depression called the anal pit. The superior region remains open for some period and begins to as the neural groove is laid down.

===Post Gastrulation or Organogenesis===

Throughout the duration of pre-gastrulation, all tissues for different organs vanish from the surface of blastula and migrate inside to take their final arrangement in the embryo structure where organs are developed from their potential regions. Consequently organogenesis transfers an embryo into free larva structure.

----

==Germ-layer origin of various body tissues==
[[Image: Development Models of Frog.jpg|thumb|right|Figure 13 Image details:Vertebrate Structure and Development.jpg]]

Ectoderm will give raise to structures such as skin, brain, spinal cord, neurons and sense receptors.
Mesoderm will give raise to structrues such as notochord, muscles, blood, bone and sex organs.
Endoderm will give raise to sturctures such as inner lining of gut, liver, pancreas, lungs and bladder, thyroid and parathyroid glands and thymus.

== Structures derived from Germ-layers of frog species ==

[[Image:Development of Frog Layers.jpg|thumb|left|Development of Frog Layers Primary source[http://www.bio.miami.edu/~cmallery/150/physiol/sf19x11b.jpg]Image details:J,Nassif 2009.jpg]]

[[Image:Development of frog layers.jpg|thumb|left|Development of Frog Layers Primary source [http://www.bio.miami.edu/~cmallery/150/physiol/sf19x11b.jpg]Image details:J,Nassif 2009.jpg]]

'''Ectoderm '''

''Establishes the epidermal segments and its derivatives, to the frog’s nervous system. The ectoderm also contributes to :''

1. The olfactory and auditory epithelium.

2. The retina and lens of the eye.

3. Sensory organs.

4. The epithelial lining of the oral cavity and the anus.

5. The pineal and pituitary body.

'''Mesoderm'''

''Mesoderm originates:''

1. Connective tissue.

2. Muscles, except the notochord.

3. Blood vessels.

4. Lymphatics.

5. The peritoneum and the urinary and reproductive system.

6. The dermis, parts of the eye excluding lens, cornea, and conjunctiva.

'''Endoderm'''

''From the endoderm arises:''

1. The epithelial lining to the gut and oesophagus, stomach, intestine, bile duct.

2. The hepatic cells of the liver, respiratory tract, larynx, trachea and lungs.

3. The lining of the urinary bladder, pancreas thyroid and thymus.

[The two figures reveal the development of structures deriving from the celluar components of the embryology of the frog].[Structures derived from Germ-layers of frog species ]

==Life cycle of a frog==

'''Fertilization-egg''':

The female lays eggs in the spring. A group of fertilized eggs is called spawn;

'''7-10 days''':

Fertilized egg feed on remaining yolk which is in its gut. Their gills, mouth and tail have poorly developed. Begin to swim and feed on algae;

'''10-30 days(4 weeks):'''

A layer of skin grows over gills. Teeth begin to appear. A coiled gut start to develop. This is aid in digestion;

'''30-60 days(6-9 weeks):'''

Legs being to grow and head is more distinct. Start to eat insects. Arms begin to grow;

'''60-80 days(12 weeks):'''

Resemble a frog. Still have remaining tail;

'''80-140 days(20 weeks):'''

Fully developed, spend most of time out of water. Majority of frog live between 4-15 years.

==Timeline of frog development==

Development of egg and embryo at temperature 18 degree celsius.

'''0 hours''' - fertilization of the egg

'''1 hours''' - formation of the gray crescent due to pigment migration

'''3.5 hours''' - early cleavage

'''4.5 hours''' - blastula stage(coeloblastula with eccentric blastocoel

'''26 hours''' - gastrulation

'''26 hours''' -'' early'' - crescent shaped dorsal lip

'''34 hours''' - ''middle''- semicircular blastoporal lip

'''42 hours''' - ''late'' - circular blastoporal lip

'''50 hours''' - neurulation

'''50 hours''' - ''early'' - medullary plate

'''62 hours''' -'' middle''- neural folds converging

'''67 hours''' - ''late'' - neural tube formed and ciliation of embryo

'''84 hours''' - tail bud stage(early organogeny)

'''96 hours''' - muscular response to tactile stimulation

'''118 hours''' - early heart beat, development of gill buds

'''140 hours''' - hatching and gill circulation

'''162 hours''' - mouth opens and cornea becomes transparent

'''192 hours''' - tail fin circulation established

'''216 hours''' - degeneration of external gills, formation of operculum, development of embryonic teeth

'''240 hours''' - opercular fold over brachial chamber except for spiracle and internal gills

'''255 hours''' - prolonged larval stage with refinement of organs

'''270 hours''' - development of hindlimbs, internal development of forelimbs in opercular cavity

'''275 hours''' - projection of forelimbs through operculum, left side first

'''280 hours''' - absorption of the tail and reduction in size of the gut

'''284 hours''' - metamorphosis complete, emergence from water as miniature, air breathing frog

==Stages of frog embryology==
--[[User:S8600021|Mark Hill]] 08:40, 9 October 2009 (EST) [[Talk:2009_Group_Project_5#Constructive_Criticism_of_Coordinator|see my comment on images]]

The rate of development of the egg and embryo will depend upon the temperature at which they are kept. The approximate schedule of development at 23 degree celsius is provided below.

{| border='1px'
|+ Table 1: Stages of frog development
!Stage !!Time since fertilisation (hours)!!Stage Characteristic !!Embryo characteristic !!Image of frog stage
|-
|1
|0.00-1.30
|fertilization of the egg, post fertilization
|animal hemisphere, gray crescent and vegetal hemisphere are present
|[[File:Stage01ventral.jpg|100px]]
|-
|2
|1.30-2.00
|splits into two cells
|appearance of first cleavage furrow
|[[File:Stage02ventral.jpg|100px]]
|-
|3
|2.00-2.15
|becomes four cells
|appearance of second cleavage furrow
|[[File:Stage03dorsolat.jpg|100px]]
|-
|4
|2.15-2.45
|becomes eight cells
|appearance of third cleavage furrow
|[[File:Stage04dorsolat.jpg|100px]]
|-
|5
|2.45-3.00
|becomes sixteen cells
|appearance of fourth cleavage furrow
|[[File:Stage05dorsal.jpg|100px]]
|-
|6
|3.00-3.30
|becomes thirty-two cells
|appearance of fifth cleavage furrow
|[[File:Stage06animal.jpg|100px]]
|-
|6.5
|3.30-4.00
|blastula stage
|Three dorsal folds become visible as a result of endoderm invagination. Pole cells no longer visible on surface
|[[File:Stage065dorsal.jpg|100px]]
|-
|7
|4.00-5.00
|Gastrulation stage
|two primary germ layers. epiblast and endoderm
|[[File:Stage07ventral.jpg|100px]]
|-
|8
|5.00-7.00
|neurulation
|medullary plate, neural folds and neural tube
|[[File:Stage08animal.jpg|100px]]
|-
|9
|7.00-9.00
|germ layer
|complete lip involution encircling yolk
|[[File:Stage09veg.jpg|100px]]
|-
|10
|9.00-11.00
|early gastrula
|two primary germ layers
|[[File:Stage10veg.jpg|100px]]
|-
|10.5
|11.00-11.45
|gastrula
|two germ layers
|[[File:Stage105vegb.jpg|100px]]
|-
|11
|11.45-12.30
|medulla plate
|Yolk sac protrudes dorsally, labium moves to midline on ventral side
|[[File:Stage11veg.jpg|100px]]
|-
|11.5
|12.30-13.15
|continuation of medulla plate
|start closing the plate
|[[File:Stage115veg.jpg|100px]]
|-
|12
|13.15-14.15
|early neurula
|thickened ectoderm give rise to CNS
|[[File:Stage12veg.jpg|100px]]
|-
|12.5
|14.15-14.45
|neural folds
|expansion of cavity
|[[File:Stage125postdors.jpg|100px]]
|-
|13
|14.45-16.15
|neural folds
|continue expanding cavity
|[[File:Stage13postdors.jpg|100px]]
|-
|14
|16.15-17.30
|neural folds
|continuation of cavity
|[[File:Stage14postdors.jpg|100px]]
|-
|15
|17.30-18.15
|tail bud stage
|early organogeny
|[[File:Stage15postdors.jpg|100px]]
|-
|16
|18.15-18.45
|tail bud stage
|posterior ventral view
|[[File:Stage16ant.jpg|100px]]
|-
|17
|18.45-19.45
|tail bud stage
|anterior view
|[[File:Stage17ant.jpg|100px]]
|-
|19
|20.45-21.45
|neural fold close complete
|dorsal view
|[[File:Stage19dorsal.jpg|100px]]
|-
|20
|21.45-22.30
|early tail bud
|anterior view
|[[File:Stage20dorsal.jpg|100px]]
|-
|21
|22.30-24.00
|termination of neural crest
|progress to next stage
|[[File:Stage21ant.jpg|100px]]
|-
|22
|24.00-24.45
|prolonged development
|elongation
|[[File:Stage22lat.jpg|100px]]
|-
|23
|24.45-26.15
|elongation of embryo
|later view
|[[File:Stage23lat.jpg|100px]]
|-
|24
|26.15-27.30
|continuation of elongation of embryo
|dorsal view
|[[File:Stage24latsmall.jpg|50px]]
|-
|25
|27.30-29.30
|organs development
|embryo elongates and develops dorsal thickening
|[[File:Stage25dorsal.jpg|50px]]
|-
|26
|29.30-31.15
|elongation
|dorsally forms neural and brain cavity
|[[File:Stage26lat.jpg|50px]]
|-
|27
|31.15-32.30
|elongation of embryo
|dorsal view
|[[File:Stage27lat.jpg|50px]]
|-
|28
|32.30-35.00
|further development
|lateral view
|[[File:Stage28lat.jpg|50px]]
|-
|29-30
|35.00-37.30
|tail bud
|growth
|[[File:Stage29-30lat.jpg|50px]]
|-
|31
|37.30-40.00
|prolonged development
|bud development
|[[File:Stage31lat.jpg|50px]]
|-
|32
|40.00-44.30
|early muscular development
|elongation
|[[File:Stage32lat.jpg|50px]]
|-
|33-34
|44.30-50.00
|muscular movement
|apparatus for locomotion
|[[File:Stage33-34lat.jpg|50px]]
|-
|35-36
|50.00-53.30
|muscular movement
|apparatus for locomotion
|[[File:Stage35-36lat.jpg|50px]]
|-
|37-38
|53.30-56.30
|heart beat
|develops apparatus
|[[File:Stage37-38lat.jpg|50px]]
|-
|39
|56.30-66.00
|mouth opens
|cornea transparent
|[[File:Stage39latsmall.jpg|50px]]
|-
|40
|66.00-76.00
|gill circulation
|hatching
|[[File:Stage40lat.jpg|50px]]
|-
|41
|76.00-80.00
|tail, fin circulation
|circulation
|[[File:Stage41lat.jpg|50px]]
|-
|42
|80.00-86.00
|internal gills, operculum
|opercular fold, teeth
|[[File:Stage42lat.jpg|50px]]
|-
|43
|86.00-98.00
|operculum complete
|operculum closed on right
|[[File:Stage43lat.jpg|50px]]
|-
|46
|98.00-106.00
|metamorphosis
|emergence from water as miniature, operculum complete|
|[[File:Stage46lat.jpg|50px]]
|-
|}

==Abnormalities of frog==

Abnormalities of frog could be caused by multiple factors. These include change in climate, predators, parasites, bacteria, fungi, viruses or pollution and contaminants such as pesticides, metals and fertilizer.[http://www.fws.gov/contaminants/documents/frogsrefup_septoct_2006.pdf]

The Abnormalities are further classified into different categories. These categories are:

===1. Infectious Diseases:===

'''Perkinsus Symptoms-''' caused by perkinsus-like protozoan organism. Symptoms include swollen viscera that leads to a bloated body and and infected swollen heart

'''Ichthyophonus symptoms-''' cause by parasitic genus, where symptoms include a swollen tail resorption site that matches the surrounding skin in color and translucency.

[[Image:Abnormalities of Frog species.jpg|thumb|left|Figure A Image details[waterwatchadelaide.net.au].jpg]]

===2. Surficial Abnormalities:===

Surficial abnormalities as the one that are visible on the surface of the skin. This includes abnormal pigmentation, , subcutaneous hemorrhaging, wounds due to trauma or from a predator
Edema is a fluid-filled swelling under skin whihc is also a surficial abnormality.

===3. Skeletal Abnormalities:===

This is further classified into three more categories:

'''a. Skeletal Malformations-'''

* Microcephaly (small head or blunt snout)
*Scoliosis (Curved spine in lateral direction)
*Shrunken Limb (Micromelia)
*Amelia (Completely missing limb with no stump)

'''b. Skeletal Abnormalities of Unclear Etiology-'''

This condition arises when a frog has ectromelia (missing limb), brachydactyly (missing digits) or other such condition with no visible trauma or external damage, then this will be classified as the Skeletal abnormality of unclear etiology.

'''c. Skeletal Injuries-'''

Any limb missing or broken due to trauma or other related reason which shows clear evidence of it is classified as skeletal injury

===4. Eye Abnormalities:===

Most common includes-

'''i. Anophthalmia:''' Skin covers the eye socket as there is no eye

'''ii. Abnormal Iris Coloration:''' Reduced pigment in either one eye or both resulting in two different colours of the iris at times

'''iii. Abnormal size or shape:''' Both eyes either deviating from each other or size of pupil or iris is different than the other eye

[http://www.fws.gov/contaminants/Amphibian/pdfs/AbnormalitySOP_woutpics_Jan08.pdf ]

==Genetics==

There are a wide variety of species that differ from each other when it comes to genetics and their functioning.

'''TAXONOMY:''' '''Phylum''' ''Chordata'' / '''Sub Phylum''' ''Vertebrata'' / '''Class''' ''Amphibia'' / '''Order''' ''Anura''

Their are more than two dozen different families of frogs, where suborders are:

'''1. ARCHAEBATRACHIA-''' most primitive frogs

'''2. MESOBATRACHIA-''' linked between the Archaebatrachia and Neobatrachia

'''3. NEOBATRACHIA-''' most modern frogs

{| border='4px'
|+ '''General Info:'''
! !!
|-
| '''Number of frogs' species'''
| 5280
|-
| '''Smallest frog genome size:'''
| 0.95pg, Ornate burrowing frog
|-
| '''Largest frog genome size:'''
| 13.40pg, Ornate horned frog
|-
| '''Mean of frogs' genome'''
| 4.68pg ± 0.13
|-
|}

[http://www.genomesize.com]

*Majority of frogs have only 22 to 26 chromosomes and polyploid is very common where they are almost bisexual.

*Polyploid Amphibians reduce their total cell number such that they acheive the same body size as diploids. One of the most unsual forms of polypoidy in amphibians is the water frog ''Rana esculenta'' from Europe and Western Asia.

* The species with larger genomes have more genes for e.g. the frog genus ''Xenopus'' includes 16 species, with genome sizes ranging from 3.5 x 10^9 bp to 1.6 x 10^10 bp. These differences have arisen by numerous events of polyploidization within the past 40 million years or so. The ancestral chromosome number for the genus seems to have been 18, but there are species with 36, 72 and 105 chromosomes [http://www.xenbase.org/common/]

{| border='4px'
|+ '''Difference within two families'''
! '''SPECIES''' !! ''X.LAEVIS'' !! ''X.TROPICALIS''
|-
| '''PLOIDY'''
| Allotetraploid
| Diploid
|-
| '''NO. OF CHROMOSOMES'''
| 36 chromosomes
| 20 chromosomes
|-
| '''GENOME SIZE'''
| 3.1 x 10^9 bp
| 1.7 x 10^9 bp
|-
| '''EGG SIZE'''
| 1-1.3 mm
| 0.7-0.8 mm
|-
| '''GENERATION TIME'''
| 1-2 years
| 4 months
|-
|}
[http://www.xenbase.org/common/]

===Genome Sequencing===

Since Frog has a huge family with many different species, only few main species that are used widely for the purposes of experiments have their genome sequenced.

''Xenopus tropicalis'' has one of the smallest genomes among amphibians and has the shortest generation time- four to six months and the only diploid genome among the 14 Xenopus species. This means it has no more than two copies of most genes, whereas the other species of Xenopus have four copies of most genes (pseudotetraploid). US Department of Energy's Joint Genome Institute (JGI) in Walnut Creek, California, initiated the X. tropicalis Genome Project, finding 1,700 million base pairs.
[http://www.genome.gov/Pages/Research/Sequencing/BACLibrary/xenopusTropicalis.pdf]

===Xenopus oocytes===

* The oocytes provide an important expression system for molecular biology.

* By injecting DNA or mRNA into the oocyte or developing embryo, scientists can study the protein products in a controlled system. This allows rapid functional expression of manipulated DNAs (or mRNA). This is particularly useful in electrophysiology, where the ease of recording from the oocyte makes expression of membrane channels attractive.

* One challenge of oocyte work is eliminating native proteins that might confound results, such as membrane channels native to the oocyte.

* Translation of proteins can be blocked or splicing of pre-mRNA can be modified by injection of Morpholino antisense oligos into the oocyte (for distribution throughout the embryo) or early embryo (for distribution only into daughter cells of the injected cell).
[http://www.staff.unibe.ch/sigel/xenopus.html]

===Xenopus Laevis===

* ''Xenopus Laevis'' is an important model organism in developmental biology. X. laevis is tetraploid and reaches sexual maturity in 1 to 2 years. What makes it important in developmental biology is its large and easily manipulable embryo.

* Extracts from the eggs of X. laevis frogs are also commonly used for biochemical studies of DNA replication and repair, as these extracts fully support DNA replication and other related processes in a cell-free environment which allows easier manipulation.

* The Human chorionic gonadotropin hormone (hCG) is present in the urine of the pregnant women in large quantities only. This hormone in the urine induces X.laevis oocyte production which formed the basis of first well-documented method of pregnancy testing X. laevis is also notable for its use as the first well-documented method of pregnancy testing when it was discovered. Today, commercially available HCG is injected into Xenopus males and females to induce mating behavior and breed these frogs in captivity at any time of the year.

===Gene cluster===

* The alpha and beta globin genes are closely linked in small cluster of frogs compared to human and chicken

* The similarity of architecture of two clusters found in X.laevis supports the tetraploid origin

* The two loci encoding the muscle specific creatine kinase isoenzymes and have large differences in developmental profile, therefore suggesting that duplicate loci that have not undergone silencing are not simply redundant copies but have acquired specialization.

* Contains twice number of genes for proteins i.e. haemoglobin and sarcomeric actin serum albumin compared with other species

----

==Current Embrology Research==

Currently, a number of fields have benefited from the development of frog embrology. These include cloning, verification of messenger RNA, and Cell cycle.

===Cloning===
[[Image:Robert Briggs.jpg|thumb|left|Figure 16 Image details:Robert Briggs.jpg]]

In 1952, Robert Briggs and Thomas J King cloned northern leopard frogs using a method of nuclear transfer. Briggs and King's experiment was similar to that envisioned - and piloted using salamanders - by Hans Spemann in his 1938 proposal for a 'fantastical experiment'. Later, John Gurdon extended this work and showed that nuclei from differentiated cells could support development, although less well than those from early embryos. [http://genome.wellcome.ac.uk/doc_WTD020799.html]

Lemaitre et a. (2005) from MRC Cancer Cell Unit, Cambridge, U.K. worked on experiments that demonstrated that importance of serial nuclear transplantation for the sucessful cloning of frogs. He demonstrated that exposure of somatic-cell nuclei (erythrocyte nuclei) and sperm nuclei to an extract of mitotic cell extract reorganizes the chromatin into shorter loops and allows replication at much shorter intervals along the DNA. This increases the efficiency of DNA replication in mammalian cell-free systems.

===Transgenesis techniques for functional genomics in Xenopus===

Transgenesis in Xenopus is made possible due to large embryos, a reliable fate map, ease of microinjection, ease of dissection/micromanipulation and existence of the neuroendocrine reflex of background adaptation as a model for activation/inact.

Recently, Hajime Ogino and Haruki Ochi from Nura Institute of Science and Technology in Japan focused on the genomic resources and principles of the transgenesis techniques in Xenopus, and discusses their applications to genome wide network analysis, with emphasis on the use of bioinformatics tools, these studies were undertake in 2009. This is necessary to understand the gene regulatory networks that control vertebrate development. [http://www.ingentaconnect.com/content/bsc/dgd/2009/00000051/00000004/art00001%3Bjsessionid=4ah96rms73gcu.alexandra]

Xenopus used to be a problem in earlier days when it came to transgenesis. Current methods involves isolated sperm nuclei from Xenopus testis that are microinjected into unfertilized eggs. The generated transgenic tadpoles contain 5-35 copies of the integrated plasmid that are expressed in all cells. If desired, expression of the transgene can be directed to the appropriate tissue and at the appropriate time by using specific promoters, mostly the Xenopus POMC gene promoter (isolated from a Xenopus genomic DNA library) to specifically direct expression of green fluorescent protein (GFP) at high levels to the intermediate pituitary cells, which can either be over expressed or inhibited.[http://molanphys.ruhosting.nl/transgenesis.htm]

[[File:Transgenesis.JPG]]

===Verification of messenger RNA===

While the existence and role of messenger RNA (mRNA) was known in bacteria, in the 1960s it was still debated whether it also existed in vertebrates. Taking haemoglobin mRNA from immature red blood cells and injecting it into a Xenopus oocyte, John Gurdon showed that the haemoglobin protein was indeed produced. Producing proteins in Xenopus oocytes has proved to be extremely useful in cell biology, in particular for the study of receptor proteins.[http://genome.wellcome.ac.uk/doc_WTD020799.html]

===Cell Cycle===

As they develop outside the mother, frog eggs are well stocked with the proteins needed to drive the development of the embryo. Studies of these processes has shed considerable light on the processes involved in cell division - termed the cell cycle. [http://genome.wellcome.ac.uk/doc_WTD020799.html]

===Limb development in Xenopus Laevis===

[[Image: Frog Limb development.jpg|thumb|right|From Limb Development Image details:Primary source:[http://images.google.com.au/imgres?imgurl=http://www.sciencedaily.com/images/2006/06/060616130718.jpg&imgrefurl=http://www.sciencedaily.com/releases/2006/06/060616130718.htm&usg=__xliPsPAvheUBME_kjv_q7auiFbo=&h=333&w=300&sz=11&hl=en&start=2&um=1&tbnid=y_ntJtmkRSK7WM:&tbnh=119&tbnw=107&prev=/images%3Fq%3DLimb%2Bdevelopment%2Bin%2BXenopus%2BLaevis%26ndsp%3D18%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

Donald D. Brown (2005),Department of Embryology, Carnegie Institution of Washington demonstrated factors related to limb development of Xenopus Laevis. Thyroid hormone (TH) is found to be required for limb development in this frog. Specific cell types in the growing limb were targeted for expression of a dominant negative form of the TH receptor by sperm-mediated transgenesis. Limb muscle development, the innervation of muscle from the spinal cord, and cartilage growth can be inhibited without affecting patterning of the limb or differentiation of other cell types. Remodeling of the skin occurs late in metamorphosis after the limb has formed. The coordination of these independent programs is affected in part by the control that TH exerts over DNA replication in all cell types of the limb. [http://www.pnas.org/content/102/35/12455.full]

----

== Glossary ==

[[Image: Frog species.jpg|thumb|left| Frog Species Image details:Primary source:www.olympus.co.jp/.../080925/large/p02L.jpg].jpg]]

*'''Amphibian:'''

''Relating to or characteristic of animals of the class amphibia.Amphibians are found in the taxonomic class of amphibia, amphibians are capable of both occupying and successfully living in both land and aquatic communities.amphibian''

*'''Augmentation:'''

''Enlargement/Increase in cellular size.''

*'''Autolysis:'''

''breakdown of a part or whole cell or tissue by self-produced enzymes''

*'''Blastomeres:'''

''The undifferentiated cells formed by cleavage of the fertilised ovum. This includes cells in the cleavage, morula, and blastula stages of the embryo''

*'''Carnivorous:'''
''
Flesh-eating; subsisting on animals as food.''

*'''Cleavage:'''

''he repeated division of a fertilised ovum ''

* '''Cleft:'''

''an opening, fissure, or V-shaped indentation made by or as if by splitting''

*'''Chordate:'''

''Members of a diverse phylum of animals that, as embryos, possess a (1) notochord; (2) a dorsal, hollow nerve cord, (3) pharyngeal gill slits; and (4) a post-anal tail''

''The act or state of splitting or dividing of a cell, particularly during the telophase of (animal) cell division.''

*'''Cytoplasm:'''

''The cytoplasm (of both eukaryotes and prokaryotes) is where the functions for cell expansion, growth, metabolism, and replication are carried out''

* '''Epiboly:'''
''The expansion of one cell sheet over other cells, as takes place during gastrulation''

*'''Fertilization:'''

''A process in sexual reproduction that involves the union of male (sperm) and female (ovum) gametes (each with a single, haploid set of chromosomes) to produce a diploid zygote.''

*'''Gamete:'''
''A reproductive cell (male (sperm) or female (egg)) that has only half the usual number of chromosomes''

*'''Gametogenesis:'''

''process leading to the production of gametes. The development and maturation of sex cells through meiosis.Another name for meiosis where a diploid cell is divided into two haploid cells with half the chromosome content of the diploid parent cell.''

*'''Herbivorous:'''

''eating plants; of or pertaining to the herbivora.''

*'''Holoblastic:'''

''The complete division of an isolecithal or microlecithal egg into blastomeres''

*'''Invagination:'''

''One of the methods by which the various germinal layers of the ovum are differentiated.''

*'''Isoenzymes:'''

''Isozymes (also known as isoenzymes) are enzymes that differ in amino acid sequence but catalyze the same chemical reaction.''

*'''Mesentery:'''

'' membranous fold attaching various organs to the body wall.''

*'''Metamorphosis:'''

''A change in the form and often habits of an animal after the embryonic stage during normal development.''

*'''Neuroendocrine:'''

''Neuroendocrine [IPA nʊəroʊˈɛndəkrɪn] cells are cells that release a hormone into the circulating blood in response to a neural stimulus.''

*'''Organogenesis:'''

''The part of embryonic development where the body's main organs develop.''

*'''Peritoneum:'''

''The smooth serous membrane which lines the cavity of the abdomen, or the whole body cavity when there is no diaphragm, and, turning back, surrounds the viscera, forming a closed, or nearly closed, sac.''

*'''Perivitelline space:'''

''The perivitelline space is the space between the zona pellucida and the plasma membrane (sometimes called the vitelline membrane) in a fertilized ovum.''

*'''Polyploidy:'''

''Cells with three or more sets of chromosomes.''

*'''Pronucleus:'''

''the nucleus of the ovum or sperm after fertilization but before they fuse to form the nucleus of the zygote ''

*'''Protoplasm:'''

''The fluid living content of the cell that consists of two major divisions, the cytoplasm and the nucleoplasm (cell nucleus). It is composed mainly of nucleic acids, proteins, lipids, carbohydrates, and inorganic salts''

*'''Segmentation:'''

''division of some metazoan bodies (such as annelida and Arthropoda) into repeated parts, segments. Segmentation can be homomeric (more or less the same) or heteromeric(different from each other).''

*'''Terrestrial:'''

''Of or on the ground, of the habitat of a plant, on land as opposed to in water, or on the ground as opposed to on another plant.''

*'''Transgenesis:'''

''Transgenesis is the process of introducing an exogenous gene - called a transgene - into a living organism so that the organism will exhibit a new property and transmit that property to its offspring.''

*'''Yolk:'''

''nutritive material of an ovum stored for the nutrition of an embryo''

*'''Zygote:'''

''The cell from which an organism develops, that results from the fertilization of the egg by the sperm.''

''Primary Resource "Biology- Online Dictionary''[http://www.biology-online.org/dictionary/Main_Page]

== References - Frog Embryology: ==

[[Image:Frog Research.jpg|thumb|left|Research being done on a Frog Image details:[http://images.google.com.au/imgres?imgurl=http://www.odt.co.nz/files/story/2008/09/university_of_otago_zoology_senior_lecturer_phil_b_3343259744.jpg&imgrefurl=http://www.odt.co.nz/on-campus/university-otago/21670/dunedin-frog-man-wins-zoo-award&usg=__JvJJU5QfOnIwY2bk4xo64UXuJRs=&h=600&w=404&sz=22&hl=en&start=14&um=1&tbnid=AbsP89yWcUiilM:&tbnh=135&tbnw=91&prev=/images%3Fq%3Dfrog%2Bresearch%26hl%3Den%26um%3D1].jpg]]

1. Savage, J. M. (2002). The Amphibians and Reptiles of Costa Rica. University of Chicago Press, Chicago [http://www.springerlink.com/content/vv015277w1746llw/]

2. Ford, L.S.; D.C. Cannatella (1993). "The major clades of frogs". Herpetological Monographs 7: 94–117 [http://digimorph.org/specimens/Xenopus_laevis/]

3. Tyler, M. J. (1994). Australian Frogs A Natural History. Reed Books [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.gracilenta.html]

4. Cogger, H.G.; R.G. Zweifel, and D. Kirschner (2004). Encyclopedia of Reptiles & Amphibians Second Edition. Fog City Press [http://en.wikipedia.org/wiki/Microhylidae]

5. Beltz, Ellin (2005). Frogs: Inside their Remarkable World. Firefly Books [http://unjobs.org/authors/ellin-beltz]

6. Tyler, M. J. (1994). Australian Frogs A Natural History. Reed Books [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

7. Moury JD, Hanken J (1995) Early cranial neural crest migration in the direct-developing frog, Eleutherodactylus coqui. Acta
Anatomica (Basel) 153, 243-253.

8.Raynaud A (1985) Development of limbs and embryonic limb reduction. In Biology of the Reptilia (ed. Gans C, Billett F), pp.
59-148. New York: John Wiley.[http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=9309]

9. Hanken J (1986) Developmental evidence for amphibian origins. In Evolutionary Biology (ed. Hecht MK, Wallace B, Prance GT), 20, pp. 389-417. New York: Plenum Press. [Hanken J (1986) Developmental evidence for amphibian origins. In Evolutionary Biology (ed. Hecht MK, Wallace B, Prance GT), 20, pp. 389-417. New York: Plenum Press.]

10. Elinson RP (1990) Direct development in frogs : wiping the recapitulationist slate clean. Seminars in Developmental Biology
1, 263-270.

11. Beebee, T. J. C. 1996. Ecology and Conservation of Amphibians. Chapman and Hall. London. [http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V5X-3SVHMKH-1X&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=1021245355&_rerunOrigin=google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=825868e10cd178d16a8a0e5ad14dc5ef]

12. Lehtinen, R. M. 2002. The use of screw pines (Pandanus spp.) by amphibians and reptiles in Madagascar. Herpetological Bulletin 2002:20–25.

13. Parris, K. M. and M. A. McCarthy. 1999. What influences the structure of frog assemblages at forest streams. Australian Journal of Ecology 24:495–502. CrossRef

14. Zug, G. R. 1993. Herpetology: An Introductory Biology of Amphibians and Reptiles. Academic Press. San Diego, CA.

15. Slack,J.M.W., Darlington,B.G., Heath,J.K. and Godsave,S.F. (1987)Mesoderm induction in early Xenopus embryos by heparin-binding growth factors. Nature, 326, 197-200.

16. Melton,D.A. (1990) Activins are expressed early in Xenopus embryogenesis and can induce axial mesoderm and anterior structures. Cell, 63, 485-493.

17. Harland,R.M. and Misher,L. (1988) Stability of RNA in developing Xenopus embryos and identification of a destabilizing sequence in TFIIIA RNA. Development, 102, 837-852.

18. Cunliffe,V. and Smith,J.C. (1992) Ectopic mesoderm formation in Xenopus embryos caused by widespread expression of a Brachyury homologue. Nature, 358, 427-430.

19. Kinoshita,K., Bessho,T. and Asashima,M. (1993) Competence prepattern in the animal hemisphere of the 8-cell-stage Xenopus embryo. Devel. Biol., 160, 276-284.

20. LaBonne,C., Burke,B. and Whitman,M. (1995) Role of MAP kinase in mesoderm induction and axial patterning in Xenopus development. Development, 121, 1475-1486.

21. Green,J.B.A., New,H.V. and Smith,J.C. (1992) Responses of embryonic Xenopus cells to activin and FGF are separated by multiple dose thresholds and correspond to distinct axes of the mesoderm. Cell, 71, 731-739.

22. Grainger R., Blumberg B., Harland R., Amemiya C., Importance of Xenopus Tropicalis to biomedical and biological research, Benaroya Research Institute, Virginia Mason Research Center [http://www.genome.gov/Pages/Research/Sequencing/BACLibrary/xenopusTropicalis.pdf ]

23. Gregory, T.R. (2005). Animal Genome Size Database. [http://www.genomesize.com]

24. U.S Fish and Wildlife Services, ABNORMALITY CLASSIFICATION SOP, [http://www.fws.gov/contaminants/Amphibian/pdfs/AbnormalitySOP_woutpics_Jan08.pdf ]

25. Donald D. Brown*, Liquan Cai*, Biswajit Das*, Nicholas Marsh-Armstrong‡, Alexander M. Schreiber*, and Rejeanne Juste*(2005), Thyroid hormone controls multiple independent programs required for limb development in Xenopus laevis metamorphosis [http://www.pnas.org/content/102/35/12455.full]

26. Ogino, Hajime; Ochi, Haruki, Resources and transgenesis techniques for functional genomics in Xenopus, Development Growth & Differentiation, Volume 51, Number 4, May 2009 , pp. 387-401(15) [http://www.ingentaconnect.com/content/bsc/dgd/2009/00000051/00000004/art00001%3Bjsessionid=4ah96rms73gcu.alexandra]

27. Giles Newton (2004) Why the frog? The Human Genome, [http://genome.wellcome.ac.uk/doc_WTD020799.html]

28. Xenbase, [http://www.xenbase.org/common/]

29. Donders Center for Neuroscience & Nijmegen Center for Molecular Life Sciences (NCMLS), Beyond the genome (Xenopus transgenesis for functional genomics),Faculty of Science, Radboud University [http://molanphys.ruhosting.nl/transgenesis.htm]

== External Links ==
[[Image:Frog links.jpg|thumb|left|Smart Frog Image details:[http://images.google.com.au/imgres?imgurl=http://2.bp.blogspot.com/_o93AaY0GzH4/SjY_ZYv0PII/AAAAAAAAAgk/skruNc2yN78/s400/computer%2Bfrog.jpg&imgrefurl=http://hellaheaven-ana.blogspot.com/2009/06/talking-frog-contemporary-fairy-tale.html&usg=__oxji1TGLV2Fi7xe0dnlmuYk8gDo=&h=288&w=288&sz=16&hl=en&start=2&um=1&tbnid=ywZd4zpdxC5plM:&tbnh=115&tbnw=115&prev=/images%3Fq%3Dfrog%2Bon%2Bcomputer%26hl%3Den%26um%3D1].jpg]]

1. Frog embryology [http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/F/FrogEmbryology.html Frog Embryology]

2. Frog cellular materials [http://www.xenbase.org/xenbase/original/cell/cell.html xenbase]

3. The zoology of frog species [http://worms.zoology.wisc.edu/frogs/mainmenu.html zoology frogs]

4. Frog cycle [http://www.bioethics.gov/images/sc_images/frog_dev.gif bioethics frog] Just a little cycle of FROG'S life cycle

5. Frog Embryology [http://embryology.med.unsw.edu.au/OtherEmb/Frog.htm UNSW Embryology]

6. Frog Research [http://apps.carleton.edu/campus/library/now/exhibits/wallcharts/frog/ carleton library exhibit]

{{Template:Projects09}}
[[Category:Frog]]

2009 Group Project 5

2009-10-14T23:21:08Z

Z3258567: /* Growth and Modification of Frog Species */

== The Embryology of Frogs ==

== The Frog ==

[[Image: Frog species .jpg|thumb|left|Image details: Wikipedia (2009) Frog species[http://en.wikipedia.org/wiki/Frog#Uses_in_agriculture_and_research].jpg]]

Frogs are scientifically identified by the structure of their long posterior limbs, a petite framework, webbed fingers and feet, budged eyes and the lack of a tail. The majority of frog species are extensively recognized as outstanding jumpers, due to their long, dominant legs, which are adaptations to progress jumping performance during activities. The Frog is one of the most frequently studied species in experimental embryology and most anatomical sciences. ''The Frog is a practically effective model for human embryological development given that the Frog:''

- Comprises of genes which can be effectively manipulated.

- Comprises of similar homogeny with humans species.

- Reproduces a large quantity of offspring in a short period of time.

- Are small species which can be simply sustained.

- Are not extremely luxurious and expensive.

== The History of the uses in agriculture and research ==

[[Image: Frog experiments .jpg|thumb|right|Image details: Scans of chemically cleared and dyed preserved deformed frogs and toads [http://www.sat.qc.ca/upload/residence/frog-04.jpg].jpg]]

There are numerous types of frog species that have been manipulated in many developmental experiments. The frog was traditionally used by countless of the early embryology investigators and presently there are several diverse molecular mechanisms regarding progression of the frog. Theses include:

'''1.''' Food source; frog legs are a delicacy and are eaten in European countries and in many parts of South American regions.

'''2.''' Frogs have the finest biochemical dissection of phenomena that take place in the egg and oocyte. Frogs are the evolutionarily closest to mammals, commonly used as a vertebrate model.

'''3.''' Frogs lay thousands of outsized eggs, from which cell extracts can be readily prepared that is capable of recapitulating most molecular phenomena in a test tube.

'''4.''' Frogs have been commonly used as a laboratory system for a very long period, and have an extensive history of producing crucial observations in countless fields of biology.

'''5.''' Frogs have a important historical connection to the study of epigenetics (John Gurdon-vertebrate cloning and reprogramming) which has been mostly performed on frog species.

'''6.''' Frogs also have very strong evidence of pattern formation and early development, as the embryos are large in size and experimentally manipulative.

'''7.''' Recent research into the biochemistry of chromatin and epigenetics has been performed with frog species and mammalian cultured cells.

'''8.''' The biggest weakness of the Frog model system is the difficulty of performing genetic experiments and analysis, as frogs are allotetraploid, meaning they take approximately a year to fully develop to sexual maturity, and the genome has not been completely sequenced. Nevertheless, biochemical manipulations of cell extracts, such as immunodepletions and application of heterologous DNAs and nuclei can avoid the need for genetic exploitation.

----

== Growth and development of the Frog ==

[[Image: Mature develop frog.jpg|thumb|Image details: Wikipedia (2009) Red Eyed Tree Frog Figure 1 Primary source:[http://en.wikipedia.org/wiki/File:Red-eyed_Tree_Frog_-_Litoria_chloris_edit1].jpg]]

* The frog is a well recognised species, abundant predominantly in ponds, swamps, though various species may also exist in damp or shady environments distant from moist habitats.

* Eggs of specific frogs are easily obtained and may be examined in from the beginning of fertilization onwards. The phases of embryonic development differs in various chordates, yet the typical phases are basically apparent in all frog species. The differences are associated principally to the amount of yolk particles present in an egg.

* The yolk particles offer nourishment of the developing embryo. The process of frog development will be discussed from the phases of gametogenesis to the adult stage.

----

== The Egg ==
[[Image:Development of Poles in frog Fertilization.jpg|thumb|left|Development of Poles in Frog Fertilisation:J,Nassif 2009.jpg]]

- The embryology of a frog egg is a vast cell; its dimensions are approximately 1.4-1.6 million times larger than a typical aquatic species egg cell. Throughout the frog’s embryonic maturation period, the egg will be transformed into a tadpole encompassing millions of cells but still remains with its constant volume of genetic material, the vast prodction of cell have been illusttrated in the figure on the right revealing the production of eggs from female frogs. [http://en.wikipedia.org/wiki/Microhylidae]

- The early embryonic frog structure consists of three main segments the superior hemisphere known as the animal pole which is usually visible as a grey coloured area. The innermost layer appears to be between the outer two sections known as the gray crescent represented in black. Inferiorly, represents the vegetal pole typically lighter than the superior compartment illustrated in gold.

VIDEO RESOURCE: [http://www.youtube.com/watch?v=GO5YN_t1fqw&feature=related]

[[Image:Early Development of Frogs.jpg|thumb|left|Early Development of Frog:J,Nassif 2009.jpg]]

==History of frog embryology use ==

*'''1851''' - ''Henby Nelson''(MD): He identified a remarkable fact through the frog embryo. Henby observed the first cleavage of the yolk, in the egg of the frog. And cleaved structure corresponds in line of direction to the longitudinal axis of the body of the embryo of the frog species.

[[Image:Wilhelm Roux.jpg|thumb|right|Wilhelm Roux[http://images.google.com.au/imgres?imgurl=http://www.todayinsci.com/R/Roux_Wilhelm/RouxWilhelmThm.jpg&imgrefurl=http://www.todayinsci.com/6/6_09.htm&usg=__qRLTEMTHdZpAHxiNX12hWjcm9tA=&h=125&w=100&sz=4&hl=en&start=2&um=1&tbnid=LIKIwZTqCpk7MM:&tbnh=90&tbnw=72&prev=/images%3Fq%3DWilhelm%2BRoux%26gbv%3D2%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

*'''1888''' - ''Wilhelm Roux'': Wilhelm Roux attempted to solve the above observation by damaging one cell of a two-cell frog embryo with a hot needle. The cell stayed in place. However, it did not develop further. Its partner developed into a left or right half-embryo;

*'''1907''' - ''John Hopkins'' hospital: In order to identify the cellular source of neuronal fibres. Scientist placed small portions of frog embryo spinal cords in lymph on a microscope slide and was able to observe clear cut neuronal sprouting.

*'''1951''' - ''Robert Briggs'': Robert Briggs was able to clone a frog embryo by substituting the nucleus of an unfertilized frog egg cell with the nucleus of a frog embryo cell. This process is known as nuclear transplant, has formed the basis for all cloning.

*'''1952''' - ''Robert Briggs and T.J. King'': Robert Briggs and T.J. King used frog for test experiment. Because the size of the eggs in the frogs are enormous compared with those of mammals, which make them easier to manipulate.

*'''1976'''- Using the technique that had been successful in cloning frog embryos, the doctor transferred the nucleus of one cells into a donated egg cell. As an embryo began to develop, it was implanted into the uterus of a young woman.

*'''1997''' - ''Wilmut and Campbell'': Utilizing the cloning technique from frog embryo, Drs. Wilmut and Campbell tried the starvation technique on embryo cells to produce Megan and Morag, the world's first cloned sheep and, until now, the most famous sheep in history.

*'''2000''' - ''Tokyo University'': Scientists at Tokyo University have grown artificial eyeballs. Scientists formed them in tadpoles by using frog embryo cells.

*'''2001''' - ''Advanced Cell Technology'': Scientists from Advanced Cell Technology announced production of a human embryo clone. This is significant as its parthenogenesis has been artificially induced in frogs.

[[Image:John Gurdon .jpg|thumb|right|John Gurdon [http://images.google.com.au/imgres?imgurl=http://www.pnas.org/site/misc/images/gurdon.jpg&imgrefurl=http://www.pnas.org/site/misc/classics4.shtml&usg=__1p-GA1PdOYsxKL-cznMb3RHCm98=&h=526&w=400&sz=223&hl=en&start=1&um=1&tbnid=9k4lhuLssiWCAM:&tbnh=132&tbnw=100&prev=/images%3Fq%3DJohn%2BGurdon%26gbv%3D2%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

*'''2002''' - ''John Gurdon'': John Gurdon from Wellcome Cancer Research Institute in Cambridge experimented on cloned frog embryo.

== Gametogenesis ==

* The sexual reproduction occurs through the fusion of either mature reproductive cells or germ cells known as gametes, which include the sperm from the male frog and ova from female frog species so as to form a single cell, the fertilized zygote. The gametes are typically developed in parents of different sexes . [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

* Males gametes is a spermatozoon , the female frog gamete is an ovum. Each gamete is formed by a process, recognised as maturation or gametogenesis in gonads. The typical male frog gonads are testies in male, while the female gonads are ovaries. The synthesis of both gonads is associated with the process of fertilization. [http://en.wikipedia.org/wiki/Microhylidae]

* The zygote changes into a mature frog through the process of embryology and metamorphosis. Gametogenesis is a progression in which frog gametes are established from germ cells. Initial germ cells are called primordial germ cells, which can be recognised extremely early in the life of frog species.

----

== The Egg & Fertilization ==

[[Image:Fertilized and Unfertilised Eggs.jpg|thumb|left|Fertilized and Unfertilized Eggs:J,Nassif 2009.jpg]]

[[Image:Egg Development.jpg|thumb|left|Egg Development:J,Nassif 2009.jpg]]

- This occurs once the sperm cell has inserted, following the insertion of the sperm cells meiosis II is completed, there is a 30 degree position change of the cytoplasm, gray crescent allows this change to be visible in some amphibians, the gray crescent is able what determines the expect ted outline of how the frog will form. The sperm cell joins with the nuclei of the egg which forms the diploid zygote nucleus. --Sando Rashed 10:09, 24 September 2009 (EST)

- The early phases in the development of the egg is visible, but must be studied in tadpoles throughout maturation. In embryonic tadpoles of about 10 millimetres in length, soon after the opening of the oral cavity, a pair of longitudinal ridge-like thickenings of peritoneum becomes apparent along the posterior surface of the body cavity situated near to the mesentery and along the inner boundaries of the kidneys. Genital ridges are established in all tadpoles of this age, sex is not distinct until a later period. The development of the egg is illustrated in the figure on the left revealing the structure of a developed egg and a mature of egg.

[[Image:Fertilisation life cyle.jpg|thumb|Fertilization of Life cycle:Derived from primary source:[http://en.wikipedia.org/wiki/Frog]]]

== Maturation of the Egg ==

- The eggs have currently accomplished their full size, and develop from the exterior of the ovaries like a small shot, but they still have to pass through the course of maturation before they are prepared to be fertilised. This progression of maturation relates to the nucleus almost completely.

- The nucleus component, containing the nuclear fluid that excludes through the nuclear membrane into the substance of the egg, a great segment of the nuclear reticulum vanishes and becomes degraded into separate globules known as nucleoli, but a extremely small division remains in the midpoint as a slender intricately thread recognised as the nuclear skets.
Relative to the egg getting discharged from the ovary, the follicles shatter allowing the eggs to fall into the abdominal cavity of the frog species, the egg then passes forwards, directly by the contraction of the muscular wall, somewhat by the movement of the cilia of the peritoneum, to the apex of the oviduct, which positioned at the anterior compartment of the body cavity opposite to the roots of the respiratory organs.

- The terminal part of the oviduct establishes a thin-walled pouch capable of great swelling, inside which the eggs gathers in large numbers. In conclusion, the eggs are migrated out through the cloaca into water which the albuminous investments of the eggs rapidly augment to form the gelatinous mass of the frogs spawn.

== Maturation phases ==

'''1. Nuclear skein''', moves from the midpoint of the egg to its outer surface, which it reaches opposite the midpoint of the black pole. The skein, subsequently an unevenly twisted thread, now presumes the specific arrangement of a nuclear spindle, for instance may be visible in the nucleus of an epithelial or additional cell instantly prior to division of the cell occurs.[http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

'''2. The first Polar Body,''' regarding the instance the egg is laid, but prior to its fertilistion, the egg develops a considerably flattened appearance at its upper or black pole, a definite sum of fluid being exuded among the egg and the vitelline membrane. The nuclear spindle currently separate into two identical segments, one of which remains with the egg, and the supplementary is extruded as the first polar body, a small ovoidal white globule, which is situated on the surface of the egg surrounding the exuded peri-vitellline fluid.

'''3. The Second Polar Body''', half of the nuclear spindle that stay behind then splits into two equivalent divisions, one of which remains inside the egg as the female pronucleus, whereas the other segment is extruded as the second polar body, a small white globule extremely related to the first polar body, and like this positioned in the perivitelline fluid on the superior portion of the egg.

'''4. Fertilisation of the egg''', includes the synthesis of the spermatozoon with to egg, specifically, synthesis of the nuclei of these two bodies. The spermatozoa, subsequent to being shed over the seed by the male, distribute vigorously by means of their extended tails, break through the gelatinous investment of the female eggs, bore their way through the vitelline membrane and so go through into the eggs themselves, which they penetrate relative to the superior or black hemispheres.
* Subsequently, an hour following the spermatozoon has entered; a progression may be visible projecting within from the exterior segement of the egg, with a liquid spot in the mid point. This liquid centre is the nucleus of the spermatozoon, and is said to be the male pronucleus, it break through beyond into the female egg, transporting the specialised pigment into it, so that it appears bounded by a pigmented capsule linked with the exterior of the egg by a pigmented stalk.

* By this instance, the second polar body has been established and extruded, and the female pronucleus is merely the only component of the primary egg nucleus still present. Both the male and female pronuceli, which are at initially distance separate to each other, merge and after having enlarged significantly in size then fuse mutually about two and half hours after fertilisation has originated to produce the segmentation nucleus.
* The segmentation nucleus is a huge sphere-shaped vesicle embedded in delicately granular protoplasm, and bounded by a distinct capsule of pigment, its arrangement by the synthesis of the male and female pronuclei completes the action of fertilisation. Specifically female pronucleus may be observe as an imperfect nucleus, and consequently result in the course of fertilisation. The nucleus of the spermatozoon or male pronucleus, replaces the component of the egg- nucleus which has been misplaced as the polar bodies.

'''5. Segmentation of the Egg''', the initial phase of growth consist in constant separation of the egg, whereby it becomes transformed from the unicellular state, which is everlasting only in the lowest species, to muliticelluar state charactertics of all higher species. To these early processes of growth the names segmentation is specified. Shorty subsequent to the competition of fertilisation and arrangement of the segmentation nucleus this later misplaces its sphere-shaped appearance and develops to be spindle-shaped, the yolk granules at the equivalent instance showing a tendency to develop into lines distributing outwards from the distal segment of the spindle.
* The nucleus now split into two halves, which shift away from one another, the yolk granules are likely to combined themselves around the two nuclei, and a slender vertical plate of delicately granular substance is left, dividing the egg.[http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

* Superiorly the eggs depression now becomes visible, initially as a small cavity and then develops as a groove, which almost immediately extends all round, and speedily deepening, splits the egg into two entirely separate halves along a plane equivalent with the vertical plane.

* Shorty after, the two nuclei soon separate again into two, and therefore a second cleft is created in the same state as before, its additionally in the vertical plane, however in a plane at 90 degrees to the initial one, and on its finishing point the egg comprises of four accurately similar segments, each containing a nucleus. The third cleft is horizontal in shape, but not equal, lying closer to the superior than the lower pole, it segregates each of the four cells into, an superior smaller and a inferior larger pole

----

== Cleavage ==

[[Image: Frog Cleavage development.jpg|thumb|left|Cleavage Process details:[http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/F/FrogEmbryology.html].jpg]]

* The egg of the frog is scientifically identified as’ telolecithal’ meaning there is a outsized amount of yolk concentrated at a single pole, in contrast to the concentration of cytoplasm and the site of the nucleus. The cleavage phases are holoblastic, therefore the total and after the second cleavage they are asymmetrical .The initial cleavage stage appears about two and half to three hours after fertilization. It commences as a minor depression in close proximity to the centre of the animal hemisphere. It appears as if some interior force is pushing the surface the egg towards the centre. This small upturned fold steadily continues in the form of a channel until it surrounds the egg. This groove is shallow in the commencement, but develop into deeper eventually separating the fertilized egg into two halves recognised as the blastomeres. [The figure on the left symbolise the development and growth of the frog embryo during cleavage].

* Internally the separation is mitotic, consequently each daughter cell contains a nucleus resulting from the copulation nucleus of the fertilised egg. This cleavage is vertical, the two cells are indistinguishable in respect of cytoplasm, pigment and yolk. The subsequent cleavage appears about an hour after the first. The channel of this cleavage begins at the centre of the animal hemisphere, is at right angles to the first and is vertical. This divides the egg into four blastomeres. The fourth blastomere so produced are not qualitatively equal, since of these only two contain the material from the gray crescent. The cleavage begins about thirty minutes after the second is completed or four hours after fertilisation. the cleavage plane of the third furrow is horizontal and slightly above the equator. Thus the four upper cells are a little smaller than the four lower cells. The smaller blastomeres are called micromeres and the larger blastomeres are called macromeres. The fourth cleavages follow 20 minutes after the third and tend to be vertical. This is usually a double furrow.

* The cleavage rate is accelerated with each of the early divisions and since the blastomeres are of unequal size and have varying amounts of cytoplasm and yolk, synchronous cleavage is lost and there is an obvious overlapping of the division. The upper most cells divide more rapidly than the lowermost cells. From this point onwards perfect symmetry in cleavage and in blastomere is very rare, although the embryo developed perfectly. The fifth cleavage is also doubled, appearing first in the upper hemisphere and then in the lower.

* The cleavage thus far follows the rule that each cleavage plane comes in at right angles to the previous one. The subsequent divisions become so irregular that it is previous one. The subsequent division become so irregular that it is impossible to trace out any plan or procedure. The segmentation continues more rapidly in the pigmented regions, since at that place the protoplasm is most dense, whereas, yolk which is very abundant in the vegetal side delays cell division. The multicelluar embryo at this stage is called morula by some biologists.

----

== Gastrulation ==

[[Image:FROG GASTRULATION .jpg|thumb|left|Frog Gastrulation Image details:[http://www.google.com.au/imgres?imgurl=http://bio1903.nicerweb.com/Locked/media/ch47/47_12FrogGastrulation.jpg&imgrefurl=http://bio1903.nicerweb.com/Locked/media/ch47/gastrulation-frog.html&h=540&w=480&sz=46&tbnid=N78sHjELreGGSM:&tbnh=132&tbnw=117&prev=/images%3Fq%3Dfrog%2B-%2Bgastrulation&hl=en&usg=__4VK9FYLft0W-4lBe6p5EtQAMiaI=&ei=qPy5SurtMJvE6wON8JmdAg&sa=X&oi=image_result&resnum=4&ct=image].jpg]]

''The phase of Blastulation is followed by the unique developmental progression of gastrulation. The process of frog gastrulation involves the following processes.''

'''1. Epiboly Phase'''

The pigmented cellular materials of blastula have the propensity to overgrow the yolk cells within the developing content. This course which is known as epiboly commences gradually in the final blastula and rapidly accelerates with advancing gastrulation development. The cellular matter within the animal pole reproduces and matures on all sides except in area surrounding the dorsal lip of the blastopore has been established.

'''2. Convergence'''

Scientists suggested that the unfolding was thought to result in spreading of the superficial cells over a substrate with suitable absorption properties. Consequently epiboly and convergence are an outcome to this spreading tendency, which is actually increased by a reduction in surface tension of the distributing cells.

'''3. Rotation'''

The epiboly phase is maintained until the region of the dorsal lip has migrated and is a to some extent greater than 90 degrees and the region of the white blastopore is reduced to small circular rings. This section will be positioned away from the developing vegetal pole. Laterally the complete developing gastrula has been rotated to a horizontal axis, allowing it to lie at right angles to the original median plane of the egg. Therefore, the course of rotation is such that the dorsal lip is practically pushed backwards in one direction as rapid or quicker than epiboly moves it forward in the other. The outcome will be that the blastopore produced at roughly the vegetal pole is posterior, and the dorsal and ventral lips are essentially dorsal and ventral. This in addition allows the eggs to form the antero-ventral side of the potential embryo whilst the area marked by the grey crescent is to develop the dorsal segment.

'''4. Invagination'''

Visible is a small fissure- like invagination which is apparent in the middle between the equator and the vegetal segment. The most superior or dorsal border of the cleft produce the dorsal lip of the blastopore. This imput move back and forth on the dorsal plane near the dorsal lip and migrates around the boundaries of the blastocoel in company with the extension of the lateral lips. This adapted invagination is maintained until the blastocoel cavity has been almost abolished; excluding the slender opening separating epiblasts from the hypoblast, the new segment formed is known as the archenteron cavity.

'''5. Involution'''

- Additional to previous course of action a distinct involution also occurs at the blastoporal borders. This is mainly dynamic at the median dorsal lip and gradually more less as it shifts across either side until it reaches the ventral lip where it constant.Throughout this progression, cells positioned beside the superior boundaries of the blastoporal lip migrate over the lip to the interior portion of the lip. These cells are remained within the embryo along the internal edge of the blastopore. This indicates the root of archenteron is composed of involuted cells and beyond this the external layer known as the ectoderm. The base and lateral sides are enclosed mainly of endodermal cellular material, which have been established from larger yolk cells, situated in the vegetal pole of the blastula.

- In the final phases of the gastrula development, the cells contributing to the floor of the archenteron, thin out significantly where they surround the blastocoel.
The hemispherical shaped dorsal lip of blastopore which become visible at the commencement of the gastruation stage carry on to augment, initially becoming semicircular, then transform into a horse shoe shaped and then finally forming into circular band. The band is the accomplished by the blastopore. Various yolk cells of vegetal pole present in the section are crowed into the blastoporal cavity where they form a gathering identified as a yolk plug. Blastopore rapidly reduces in size while the archenteron is still developing and becomes completely formed in the final stage; the yolk plug appears as only a small oval on the gastrula.

==Growth and Modification of Frog Species==

'''1. Changes in habits and habitats:'''

'''a)''' In frogs, metamorphosis is related with or to the modifications and adaptations occuring or taking place as a frog changes environmental habitats from an aquatic to a terrestrial mode. Metamorphosis has modified the adaption of frogs as this alteration it began during the aquatic adaptations in the surface of water to breathe air. Subsequently, it continues the terrestrial surroundings, therefore the frog species become abundant in vegetation area allowing the frog to transform in to amphibious species.

'''b)''' The transition during metamorphosis is linked with a change in food chain. The tadpoles being the embryonic origin of frogs are herbivorous, feeding on algae and green matter, which they collect by the adapted feature such as their teeth surrounding their mouths. Adult frogs, alternatively, are classified as carnivorous feeding on insects and worms. Occasionally, they also consume larger prey, for instance smaller frogs species and even little birds and rodents which they dominant and ingest.

[[Image:Development of frog from sperm to mature structure.jpg|thumb|left|Development of Frog from sperm to mature structure Image details:J,Nassif 2009.jpg]]

'''2. Changes in Morphology'''

These include the decrease or complete absence of specific organs or structures which are essential during development of early frog embryology, but not critical in the mature frog species. The significant alterations of this nature include the following developmental structures.

'''a)''' The long tail of the tadpole alongside the fin folds is absorbed again during metamorphosis and becomes absent at the final stage of the metamorphosis.

'''b) '''The developing gills are resorted, the gill clefts are congested and the branchial cavities start to become absent. The reabsorbtion of gills also takes place by autolysis.

'''c)''' The teeth of the perioral disc additionally the homey lining of the jaws are shed.

'''d)''' The lateral line sense organs within the skin of tadpoles vanish throughout metamorphosis.

'''e)''' The cloacal tube begins to condensed and reduced.

'''f)''' Various blood vessels, together with parts of the aortic arches, are reduced during mature development.

(The figure on the left represents the transformation from a tadpole to a developing structure.)[http://science.jrank.org/pages/2862/Frogs-Adult-morphology.html]

'''3. Progressive or constructive changes'''

This process comprises of the development of specific organs which mature into functional systems only during metamorphosis.

'''a)''' During development the limbs continue to augment in size and differentiation. The forelimbs, which in the tadpole mature under the opercular membrane, which then break through to the exterior. Simultaneously there is a increase in the length and strength of the hind limbs, joints develop in them and the toes become visible.

'''b)''' The middle ear becomes apparent in relation with the first pharyngeal pouch. The tympanic membrane matures. It is bounded by circular tympanic cartilage which allows the frog to retain air.

'''c)''' The visual organs bulge up on the dorsal surface of the head developing the nictitating membrane.

'''d)''' There is augmentation of the tongue and the formation of thevomerina teeth.

[[Image: Growth model.jpg|thumb|Growth Model Image details:J,Nassif2009:]]

'''4. Remodelling of some structures'''

Systematic organs which operate both in the early embryonic larva and the mature adult change their differentiation during metamorphosis so as to meet the requirements of the adult mode of life and due to the habitat adaptations. The figure on the right illustrates structures developing from specic germ cell layers.

'''a)''' The skin of the embryonic tadpole is lined with a double-layered epidermis. The number of layers of cells in the epidermis augments throughout metamorphosis. Superficial surface layers become cornified. Multicellular mucous and serous glands originate in the skin. The pigmentation of the skin continuously changes, new patterns and colour start to form.

'''b)''' There is a lengthening of the mouth gap as a result of rotation of the quadrate cartilage and the true jaws become functional.

'''c)''' The tongue rapidly progresses and becomes larger and more muscular.

'''d)''' The eyes become more specialised.

'''e)''' In early tadpoles, the GIT is extremely long and wound up into a spiral folds. The intestine become greatly lengthened in herbivorous species due to the vegetables food chain.[http://en.wikipedia.org/wiki/Frog]

'''5. Development of the reproductive system'''

(The figure below represents the reproductive and development cycle of a frog as it transform from egg to frog specie.)

In tadpoles, right after the mouth is being formed, two indentation like thickenings of peritoneum begin to appear near the body cavity (dorsal surface), which is nearest to the mesentery which is near the developing kidneys. These appear in all tadpoles.

These indentations appear here because of a change in the endothelial cells, everywhere else they are usually flat looking cells but they undergo a change and in this particular area become somewhat cuboidal/columnar.

Later on the indentations become more obvious due to the epithelial cells replicating numerously to form a thick layer. The posterior two thirds of the indentation for the female is the ovary and for the male it is the testis. The third that is left differentiates and becomes fat for the body.

[[Image: Mature frog life cyle.jpg|thumb|200px|left|Mature from life cycle Image details:Derived from primary source:http://www.scienceclarified.com/images/uesc_01_img0038.jpg]]

[[Image: Developing frog.jpg|thumb|Developing Frog Image details:
[[Image: Mature develop frog.jpg|thumb|Image details: Red eyed tree frog litoria chloris source:[http://en.wikipedia.org/wiki/File:Red-eyed_Tree_Frog_-_Litoria_chloris_edit1.jpg]].jpg]]

===Delamination===

Delamination indicates a mass separating a group of cellular matter from other cellular groups. It has been illustrated that the division of notochord, mesoderm and endoderm tissues from each other to form distinct cellular masses is completed by the progression of delamination, subsequent to these materials moving to the inside throughout gastrulation. During the developing gastrula, the germ layers are all recognized. These distinct segments of the embryo develop from these germ tissue layers.

===Polarity and Rotation===

Throughout fertilisation to the beginning of gastrulation, the frog’s egg continues in the original location in relation to its polarity. Subsequent to gastrulation its polarity begins to differentiate. This progression is linked with migration of materials within the gastrula and can be responsible for the alterations of the centre of gravity.

===Closing of Blastopore===

Subsequent to the formation of the gastrula, the blastopore is visible as a tiny round circular filled cavity containing the yolk plug. As it continues to reduce in dimension, it represented as a pear-shaped outline through the mutual approach of its lateral lips. Through it final progression these fuse entirely to produce a longitudinal groove, the streak which continue dorsally and ventrally in a small aperture. The inferior aperture closes, resulting in a depression called the anal pit. The superior region remains open for some period and begins to as the neural groove is laid down.

===Post Gastrulation or Organogenesis===

Throughout the duration of pre-gastrulation, all tissues for different organs vanish from the surface of blastula and migrate inside to take their final arrangement in the embryo structure where organs are developed from their potential regions. Consequently organogenesis transfers an embryo into free larva structure.

----

==Germ-layer origin of various body tissues==
[[Image: Development Models of Frog.jpg|thumb|right|Figure 13 Image details:Vertebrate Structure and Development.jpg]]

Ectoderm will give raise to structures such as skin, brain, spinal cord, neurons and sense receptors.
Mesoderm will give raise to structrues such as notochord, muscles, blood, bone and sex organs.
Endoderm will give raise to sturctures such as inner lining of gut, liver, pancreas, lungs and bladder, thyroid and parathyroid glands and thymus.

== Structures derived from Germ-layers of frog species ==

[[Image:Development of Frog Layers.jpg|thumb|left|Development of Frog Layers Primary source[http://www.bio.miami.edu/~cmallery/150/physiol/sf19x11b.jpg]Image details:J,Nassif 2009.jpg]]

[[Image:Development of frog layers.jpg|thumb|left|Development of Frog Layers Primary source [http://www.bio.miami.edu/~cmallery/150/physiol/sf19x11b.jpg]Image details:J,Nassif 2009.jpg]]

'''Ectoderm '''

''Establishes the epidermal segments and its derivatives, to the frog’s nervous system. The ectoderm also contributes to :''

1. The olfactory and auditory epithelium.

2. The retina and lens of the eye.

3. Sensory organs.

4. The epithelial lining of the oral cavity and the anus.

5. The pineal and pituitary body.

'''Mesoderm'''

''Mesoderm originates:''

1. Connective tissue.

2. Muscles, except the notochord.

3. Blood vessels.

4. Lymphatics.

5. The peritoneum and the urinary and reproductive system.

6. The dermis, parts of the eye excluding lens, cornea, and conjunctiva.

'''Endoderm'''

''From the endoderm arises:''

1. The epithelial lining to the gut and oesophagus, stomach, intestine, bile duct.

2. The hepatic cells of the liver, respiratory tract, larynx, trachea and lungs.

3. The lining of the urinary bladder, pancreas thyroid and thymus.

[The two figures reveal the development of structures deriving from the celluar components of the embryology of the frog].[Structures derived from Germ-layers of frog species ]

==Life cycle of a frog==

'''Fertilization-egg''':

The female lays eggs in the spring. A group of fertilized eggs is called spawn;

'''7-10 days''':

Fertilized egg feed on remaining yolk which is in its gut. Their gills, mouth and tail have poorly developed. Begin to swim and feed on algae;

'''10-30 days(4 weeks):'''

A layer of skin grows over gills. Teeth begin to appear. A coiled gut start to develop. This is aid in digestion;

'''30-60 days(6-9 weeks):'''

Legs being to grow and head is more distinct. Start to eat insects. Arms begin to grow;

'''60-80 days(12 weeks):'''

Resemble a frog. Still have remaining tail;

'''80-140 days(20 weeks):'''

Fully developed, spend most of time out of water. Majority of frog live between 4-15 years.

==Timeline of frog development==

Development of egg and embryo at temperature 18 degree celsius.

'''0 hours''' - fertilization of the egg

'''1 hours''' - formation of the gray crescent due to pigment migration

'''3.5 hours''' - early cleavage

'''4.5 hours''' - blastula stage(coeloblastula with eccentric blastocoel

'''26 hours''' - gastrulation

'''26 hours''' -'' early'' - crescent shaped dorsal lip

'''34 hours''' - ''middle''- semicircular blastoporal lip

'''42 hours''' - ''late'' - circular blastoporal lip

'''50 hours''' - neurulation

'''50 hours''' - ''early'' - medullary plate

'''62 hours''' -'' middle''- neural folds converging

'''67 hours''' - ''late'' - neural tube formed and ciliation of embryo

'''84 hours''' - tail bud stage(early organogeny)

'''96 hours''' - muscular response to tactile stimulation

'''118 hours''' - early heart beat, development of gill buds

'''140 hours''' - hatching and gill circulation

'''162 hours''' - mouth opens and cornea becomes transparent

'''192 hours''' - tail fin circulation established

'''216 hours''' - degeneration of external gills, formation of operculum, development of embryonic teeth

'''240 hours''' - opercular fold over brachial chamber except for spiracle and internal gills

'''255 hours''' - prolonged larval stage with refinement of organs

'''270 hours''' - development of hindlimbs, internal development of forelimbs in opercular cavity

'''275 hours''' - projection of forelimbs through operculum, left side first

'''280 hours''' - absorption of the tail and reduction in size of the gut

'''284 hours''' - metamorphosis complete, emergence from water as miniature, air breathing frog

==Stages of frog embryology==
--[[User:S8600021|Mark Hill]] 08:40, 9 October 2009 (EST) [[Talk:2009_Group_Project_5#Constructive_Criticism_of_Coordinator|see my comment on images]]

The rate of development of the egg and embryo will depend upon the temperature at which they are kept. The approximate schedule of development at 23 degree celsius is provided below.

{| border='1px'
|+ Table 1: Stages of frog development
!Stage !!Time since fertilisation (hours)!!Stage Characteristic !!Embryo characteristic !!Image of frog stage
|-
|1
|0.00-1.30
|fertilization of the egg, post fertilization
|animal hemisphere, gray crescent and vegetal hemisphere are present
|[[File:Stage01ventral.jpg|100px]]
|-
|2
|1.30-2.00
|splits into two cells
|appearance of first cleavage furrow
|[[File:Stage02ventral.jpg|100px]]
|-
|3
|2.00-2.15
|becomes four cells
|appearance of second cleavage furrow
|[[File:Stage03dorsolat.jpg|100px]]
|-
|4
|2.15-2.45
|becomes eight cells
|appearance of third cleavage furrow
|[[File:Stage04dorsolat.jpg|100px]]
|-
|5
|2.45-3.00
|becomes sixteen cells
|appearance of fourth cleavage furrow
|[[File:Stage05dorsal.jpg|100px]]
|-
|6
|3.00-3.30
|becomes thirty-two cells
|appearance of fifth cleavage furrow
|[[File:Stage06animal.jpg|100px]]
|-
|6.5
|3.30-4.00
|blastula stage
|Three dorsal folds become visible as a result of endoderm invagination. Pole cells no longer visible on surface
|[[File:Stage065dorsal.jpg|100px]]
|-
|7
|4.00-5.00
|Gastrulation stage
|two primary germ layers. epiblast and endoderm
|[[File:Stage07ventral.jpg|100px]]
|-
|8
|5.00-7.00
|neurulation
|medullary plate, neural folds and neural tube
|[[File:Stage08animal.jpg|100px]]
|-
|9
|7.00-9.00
|germ layer
|complete lip involution encircling yolk
|[[File:Stage09veg.jpg|100px]]
|-
|10
|9.00-11.00
|early gastrula
|two primary germ layers
|[[File:Stage10veg.jpg|100px]]
|-
|10.5
|11.00-11.45
|gastrula
|two germ layers
|[[File:Stage105vegb.jpg|100px]]
|-
|11
|11.45-12.30
|medulla plate
|Yolk sac protrudes dorsally, labium moves to midline on ventral side
|[[File:Stage11veg.jpg|100px]]
|-
|11.5
|12.30-13.15
|continuation of medulla plate
|start closing the plate
|[[File:Stage115veg.jpg|100px]]
|-
|12
|13.15-14.15
|early neurula
|thickened ectoderm give rise to CNS
|[[File:Stage12veg.jpg|100px]]
|-
|12.5
|14.15-14.45
|neural folds
|expansion of cavity
|[[File:Stage125postdors.jpg|100px]]
|-
|13
|14.45-16.15
|neural folds
|continue expanding cavity
|[[File:Stage13postdors.jpg|100px]]
|-
|14
|16.15-17.30
|neural folds
|continuation of cavity
|[[File:Stage14postdors.jpg|100px]]
|-
|15
|17.30-18.15
|tail bud stage
|early organogeny
|[[File:Stage15postdors.jpg|100px]]
|-
|16
|18.15-18.45
|tail bud stage
|posterior ventral view
|[[File:Stage16ant.jpg|100px]]
|-
|17
|18.45-19.45
|tail bud stage
|anterior view
|[[File:Stage17ant.jpg|100px]]
|-
|19
|20.45-21.45
|neural fold close complete
|dorsal view
|[[File:Stage19dorsal.jpg|100px]]
|-
|20
|21.45-22.30
|early tail bud
|anterior view
|[[File:Stage20dorsal.jpg|100px]]
|-
|21
|22.30-24.00
|termination of neural crest
|progress to next stage
|[[File:Stage21ant.jpg|100px]]
|-
|22
|24.00-24.45
|prolonged development
|elongation
|[[File:Stage22lat.jpg|100px]]
|-
|23
|24.45-26.15
|elongation of embryo
|later view
|[[File:Stage23lat.jpg|100px]]
|-
|24
|26.15-27.30
|continuation of elongation of embryo
|dorsal view
|[[File:Stage24latsmall.jpg|50px]]
|-
|25
|27.30-29.30
|organs development
|embryo elongates and develops dorsal thickening
|[[File:Stage25dorsal.jpg|50px]]
|-
|26
|29.30-31.15
|elongation
|dorsally forms neural and brain cavity
|[[File:Stage26lat.jpg|50px]]
|-
|27
|31.15-32.30
|elongation of embryo
|dorsal view
|[[File:Stage27lat.jpg|50px]]
|-
|28
|32.30-35.00
|further development
|lateral view
|[[File:Stage28lat.jpg|50px]]
|-
|29-30
|35.00-37.30
|tail bud
|growth
|[[File:Stage29-30lat.jpg|50px]]
|-
|31
|37.30-40.00
|prolonged development
|bud development
|[[File:Stage31lat.jpg|50px]]
|-
|32
|40.00-44.30
|early muscular development
|elongation
|[[File:Stage32lat.jpg|50px]]
|-
|33-34
|44.30-50.00
|muscular movement
|apparatus for locomotion
|[[File:Stage33-34lat.jpg|50px]]
|-
|35-36
|50.00-53.30
|muscular movement
|apparatus for locomotion
|[[File:Stage35-36lat.jpg|50px]]
|-
|37-38
|53.30-56.30
|heart beat
|develops apparatus
|[[File:Stage37-38lat.jpg|50px]]
|-
|39
|56.30-66.00
|mouth opens
|cornea transparent
|[[File:Stage39latsmall.jpg|50px]]
|-
|40
|66.00-76.00
|gill circulation
|hatching
|[[File:Stage40lat.jpg|50px]]
|-
|41
|76.00-80.00
|tail, fin circulation
|circulation
|[[File:Stage41lat.jpg|50px]]
|-
|42
|80.00-86.00
|internal gills, operculum
|opercular fold, teeth
|[[File:Stage42lat.jpg|50px]]
|-
|43
|86.00-98.00
|operculum complete
|operculum closed on right
|[[File:Stage43lat.jpg|50px]]
|-
|46
|98.00-106.00
|metamorphosis
|emergence from water as miniature, operculum complete|
|[[File:Stage46lat.jpg|50px]]
|-
|}

==Abnormalities of frog==

Abnormalities of frog could be caused by multiple factors. These include change in climate, predators, parasites, bacteria, fungi, viruses or pollution and contaminants such as pesticides, metals and fertilizer.[http://www.fws.gov/contaminants/documents/frogsrefup_septoct_2006.pdf]

The Abnormalities are further classified into different categories. These categories are:

===1. Infectious Diseases:===

'''Perkinsus Symptoms-''' caused by perkinsus-like protozoan organism. Symptoms include swollen viscera that leads to a bloated body and and infected swollen heart

'''Ichthyophonus symptoms-''' cause by parasitic genus, where symptoms include a swollen tail resorption site that matches the surrounding skin in color and translucency.

[[Image:Abnormalities of Frog species.jpg|thumb|left|Figure A Image details[waterwatchadelaide.net.au].jpg]]

===2. Surficial Abnormalities:===

Surficial abnormalities as the one that are visible on the surface of the skin. This includes abnormal pigmentation, , subcutaneous hemorrhaging, wounds due to trauma or from a predator
Edema is a fluid-filled swelling under skin whihc is also a surficial abnormality.

===3. Skeletal Abnormalities:===

This is further classified into three more categories:

'''a. Skeletal Malformations-'''

* Microcephaly (small head or blunt snout)
*Scoliosis (Curved spine in lateral direction)
*Shrunken Limb (Micromelia)
*Amelia (Completely missing limb with no stump)

'''b. Skeletal Abnormalities of Unclear Etiology-'''

This condition arises when a frog has ectromelia (missing limb), brachydactyly (missing digits) or other such condition with no visible trauma or external damage, then this will be classified as the Skeletal abnormality of unclear etiology.

'''c. Skeletal Injuries-'''

Any limb missing or broken due to trauma or other related reason which shows clear evidence of it is classified as skeletal injury

===4. Eye Abnormalities:===

Most common includes-

'''i. Anophthalmia:''' Skin covers the eye socket as there is no eye

'''ii. Abnormal Iris Coloration:''' Reduced pigment in either one eye or both resulting in two different colours of the iris at times

'''iii. Abnormal size or shape:''' Both eyes either deviating from each other or size of pupil or iris is different than the other eye

[http://www.fws.gov/contaminants/Amphibian/pdfs/AbnormalitySOP_woutpics_Jan08.pdf ]

==Genetics==

There are a wide variety of species that differ from each other when it comes to genetics and their functioning.

'''TAXONOMY:''' '''Phylum''' ''Chordata'' / '''Sub Phylum''' ''Vertebrata'' / '''Class''' ''Amphibia'' / '''Order''' ''Anura''

Their are more than two dozen different families of frogs, where suborders are:

'''1. ARCHAEBATRACHIA-''' most primitive frogs

'''2. MESOBATRACHIA-''' linked between the Archaebatrachia and Neobatrachia

'''3. NEOBATRACHIA-''' most modern frogs

{| border='4px'
|+ '''General Info:'''
! !!
|-
| '''Number of frogs' species'''
| 5280
|-
| '''Smallest frog genome size:'''
| 0.95pg, Ornate burrowing frog
|-
| '''Largest frog genome size:'''
| 13.40pg, Ornate horned frog
|-
| '''Mean of frogs' genome'''
| 4.68pg ± 0.13
|-
|}

[http://www.genomesize.com]

*Majority of frogs have only 22 to 26 chromosomes and polyploid is very common where they are almost bisexual.

*Polyploid Amphibians reduce their total cell number such that they acheive the same body size as diploids. One of the most unsual forms of polypoidy in amphibians is the water frog ''Rana esculenta'' from Europe and Western Asia.

* The species with larger genomes have more genes for e.g. the frog genus ''Xenopus'' includes 16 species, with genome sizes ranging from 3.5 x 10^9 bp to 1.6 x 10^10 bp. These differences have arisen by numerous events of polyploidization within the past 40 million years or so. The ancestral chromosome number for the genus seems to have been 18, but there are species with 36, 72 and 105 chromosomes [http://www.xenbase.org/common/]

{| border='4px'
|+ '''Difference within two families'''
! '''SPECIES''' !! ''X.LAEVIS'' !! ''X.TROPICALIS''
|-
| '''PLOIDY'''
| Allotetraploid
| Diploid
|-
| '''NO. OF CHROMOSOMES'''
| 36 chromosomes
| 20 chromosomes
|-
| '''GENOME SIZE'''
| 3.1 x 10^9 bp
| 1.7 x 10^9 bp
|-
| '''EGG SIZE'''
| 1-1.3 mm
| 0.7-0.8 mm
|-
| '''GENERATION TIME'''
| 1-2 years
| 4 months
|-
|}
[http://www.xenbase.org/common/]

===Genome Sequencing===

Since Frog has a huge family with many different species, only few main species that are used widely for the purposes of experiments have their genome sequenced.

''Xenopus tropicalis'' has one of the smallest genomes among amphibians and has the shortest generation time- four to six months and the only diploid genome among the 14 Xenopus species. This means it has no more than two copies of most genes, whereas the other species of Xenopus have four copies of most genes (pseudotetraploid). US Department of Energy's Joint Genome Institute (JGI) in Walnut Creek, California, initiated the X. tropicalis Genome Project, finding 1,700 million base pairs.
[http://www.genome.gov/Pages/Research/Sequencing/BACLibrary/xenopusTropicalis.pdf]

===Xenopus oocytes===

* The oocytes provide an important expression system for molecular biology.

* By injecting DNA or mRNA into the oocyte or developing embryo, scientists can study the protein products in a controlled system. This allows rapid functional expression of manipulated DNAs (or mRNA). This is particularly useful in electrophysiology, where the ease of recording from the oocyte makes expression of membrane channels attractive.

* One challenge of oocyte work is eliminating native proteins that might confound results, such as membrane channels native to the oocyte.

* Translation of proteins can be blocked or splicing of pre-mRNA can be modified by injection of Morpholino antisense oligos into the oocyte (for distribution throughout the embryo) or early embryo (for distribution only into daughter cells of the injected cell).
[http://www.staff.unibe.ch/sigel/xenopus.html]

===Xenopus Laevis===

* ''Xenopus Laevis'' is an important model organism in developmental biology. X. laevis is tetraploid and reaches sexual maturity in 1 to 2 years. What makes it important in developmental biology is its large and easily manipulable embryo.

* Extracts from the eggs of X. laevis frogs are also commonly used for biochemical studies of DNA replication and repair, as these extracts fully support DNA replication and other related processes in a cell-free environment which allows easier manipulation.

* The Human chorionic gonadotropin hormone (hCG) is present in the urine of the pregnant women in large quantities only. This hormone in the urine induces X.laevis oocyte production which formed the basis of first well-documented method of pregnancy testing X. laevis is also notable for its use as the first well-documented method of pregnancy testing when it was discovered. Today, commercially available HCG is injected into Xenopus males and females to induce mating behavior and breed these frogs in captivity at any time of the year.

===Gene cluster===

* The alpha and beta globin genes are closely linked in small cluster of frogs compared to human and chicken

* The similarity of architecture of two clusters found in X.laevis supports the tetraploid origin

* The two loci encoding the muscle specific creatine kinase isoenzymes and have large differences in developmental profile, therefore suggesting that duplicate loci that have not undergone silencing are not simply redundant copies but have acquired specialization.

* Contains twice number of genes for proteins i.e. haemoglobin and sarcomeric actin serum albumin compared with other species

----

==Current Embrology Research==

Currently, a number of fields have benefited from the development of frog embrology. These include cloning, verification of messenger RNA, and Cell cycle.

===Cloning===
[[Image:Robert Briggs.jpg|thumb|left|Figure 16 Image details:Robert Briggs.jpg]]

In 1952, Robert Briggs and Thomas J King cloned northern leopard frogs using a method of nuclear transfer. Briggs and King's experiment was similar to that envisioned - and piloted using salamanders - by Hans Spemann in his 1938 proposal for a 'fantastical experiment'. Later, John Gurdon extended this work and showed that nuclei from differentiated cells could support development, although less well than those from early embryos. [http://genome.wellcome.ac.uk/doc_WTD020799.html]

Lemaitre et a. (2005) from MRC Cancer Cell Unit, Cambridge, U.K. worked on experiments that demonstrated that importance of serial nuclear transplantation for the sucessful cloning of frogs. He demonstrated that exposure of somatic-cell nuclei (erythrocyte nuclei) and sperm nuclei to an extract of mitotic cell extract reorganizes the chromatin into shorter loops and allows replication at much shorter intervals along the DNA. This increases the efficiency of DNA replication in mammalian cell-free systems.

===Transgenesis techniques for functional genomics in Xenopus===

Transgenesis in Xenopus is made possible due to large embryos, a reliable fate map, ease of microinjection, ease of dissection/micromanipulation and existence of the neuroendocrine reflex of background adaptation as a model for activation/inact.

Recently, Hajime Ogino and Haruki Ochi from Nura Institute of Science and Technology in Japan focused on the genomic resources and principles of the transgenesis techniques in Xenopus, and discusses their applications to genome wide network analysis, with emphasis on the use of bioinformatics tools. This is will to understand the gene regulatory networks that control vertebrate development. [http://www.ingentaconnect.com/content/bsc/dgd/2009/00000051/00000004/art00001%3Bjsessionid=4ah96rms73gcu.alexandra]

Xenopus used to be a problem in earlier days when it came to transgenesis. Current methods involves isolated sperm nuclei from Xenopus testis that are microinjected into unfertilized eggs. The generated transgenic tadpoles contain 5-35 copies of the integrated plasmid that are expressed in all cells. If desired, expression of the transgene can be directed to the appropriate tissue and at the appropriate time by using specific promoters, mostly the Xenopus POMC gene promoter (isolated from a Xenopus genomic DNA library) to specifically direct expression of green fluorescent protein (GFP) at high levels to the intermediate pituitary cells, which can either be over expressed or inhibited.[http://molanphys.ruhosting.nl/transgenesis.htm]

[[File:Transgenesis.JPG]]

===Verification of messenger RNA===

While the existence and role of messenger RNA (mRNA) was known in bacteria, in the 1960s it was still debated whether it also existed in vertebrates. Taking haemoglobin mRNA from immature red blood cells and injecting it into a Xenopus oocyte, John Gurdon showed that the haemoglobin protein was indeed produced. Producing proteins in Xenopus oocytes has proved to be extremely useful in cell biology, in particular for the study of receptor proteins.[http://genome.wellcome.ac.uk/doc_WTD020799.html]

===Cell Cycle===

As they develop outside the mother, frog eggs are well stocked with the proteins needed to drive the development of the embryo. Studies of these processes has shed considerable light on the processes involved in cell division - termed the cell cycle. [http://genome.wellcome.ac.uk/doc_WTD020799.html]

===Limb development in Xenopus Laevis===

[[Image: Frog Limb development.jpg|thumb|right|From Limb Development Image details:Primary source:[http://images.google.com.au/imgres?imgurl=http://www.sciencedaily.com/images/2006/06/060616130718.jpg&imgrefurl=http://www.sciencedaily.com/releases/2006/06/060616130718.htm&usg=__xliPsPAvheUBME_kjv_q7auiFbo=&h=333&w=300&sz=11&hl=en&start=2&um=1&tbnid=y_ntJtmkRSK7WM:&tbnh=119&tbnw=107&prev=/images%3Fq%3DLimb%2Bdevelopment%2Bin%2BXenopus%2BLaevis%26ndsp%3D18%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

Donald D. Brown (2005),Department of Embryology, Carnegie Institution of Washington demonstrated factors related to limb development of Xenopus Laevis. Thyroid hormone (TH) is found to be required for limb development in this frog. Specific cell types in the growing limb were targeted for expression of a dominant negative form of the TH receptor by sperm-mediated transgenesis. Limb muscle development, the innervation of muscle from the spinal cord, and cartilage growth can be inhibited without affecting patterning of the limb or differentiation of other cell types. Remodeling of the skin occurs late in metamorphosis after the limb has formed. The coordination of these independent programs is affected in part by the control that TH exerts over DNA replication in all cell types of the limb. [http://www.pnas.org/content/102/35/12455.full]

----

== Glossary ==

[[Image: Frog species.jpg|thumb|left| Frog Species Image details:Primary source:www.olympus.co.jp/.../080925/large/p02L.jpg].jpg]]

*'''Amphibian:'''

''Relating to or characteristic of animals of the class amphibia.Amphibians are found in the taxonomic class of amphibia, amphibians are capable of both occupying and successfully living in both land and aquatic communities.amphibian''

*'''Augmentation:'''

''Enlargement/Increase in cellular size.''

*'''Autolysis:'''

''breakdown of a part or whole cell or tissue by self-produced enzymes''

*'''Blastomeres:'''

''The undifferentiated cells formed by cleavage of the fertilised ovum. This includes cells in the cleavage, morula, and blastula stages of the embryo''

*'''Carnivorous:'''
''
Flesh-eating; subsisting on animals as food.''

*'''Cleavage:'''

''he repeated division of a fertilised ovum ''

* '''Cleft:'''

''an opening, fissure, or V-shaped indentation made by or as if by splitting''

*'''Chordate:'''

''Members of a diverse phylum of animals that, as embryos, possess a (1) notochord; (2) a dorsal, hollow nerve cord, (3) pharyngeal gill slits; and (4) a post-anal tail''

''The act or state of splitting or dividing of a cell, particularly during the telophase of (animal) cell division.''

*'''Cytoplasm:'''

''The cytoplasm (of both eukaryotes and prokaryotes) is where the functions for cell expansion, growth, metabolism, and replication are carried out''

* '''Epiboly:'''
''The expansion of one cell sheet over other cells, as takes place during gastrulation''

*'''Fertilization:'''

''A process in sexual reproduction that involves the union of male (sperm) and female (ovum) gametes (each with a single, haploid set of chromosomes) to produce a diploid zygote.''

*'''Gamete:'''
''A reproductive cell (male (sperm) or female (egg)) that has only half the usual number of chromosomes''

*'''Gametogenesis:'''

''process leading to the production of gametes. The development and maturation of sex cells through meiosis.Another name for meiosis where a diploid cell is divided into two haploid cells with half the chromosome content of the diploid parent cell.''

*'''Herbivorous:'''

''eating plants; of or pertaining to the herbivora.''

*'''Holoblastic:'''

''The complete division of an isolecithal or microlecithal egg into blastomeres''

*'''Invagination:'''

''One of the methods by which the various germinal layers of the ovum are differentiated.''

*'''Isoenzymes:'''

''Isozymes (also known as isoenzymes) are enzymes that differ in amino acid sequence but catalyze the same chemical reaction.''

*'''Mesentery:'''

'' membranous fold attaching various organs to the body wall.''

*'''Metamorphosis:'''

''A change in the form and often habits of an animal after the embryonic stage during normal development.''

*'''Neuroendocrine:'''

''Neuroendocrine [IPA nʊəroʊˈɛndəkrɪn] cells are cells that release a hormone into the circulating blood in response to a neural stimulus.''

*'''Organogenesis:'''

''The part of embryonic development where the body's main organs develop.''

*'''Peritoneum:'''

''The smooth serous membrane which lines the cavity of the abdomen, or the whole body cavity when there is no diaphragm, and, turning back, surrounds the viscera, forming a closed, or nearly closed, sac.''

*'''Perivitelline space:'''

''The perivitelline space is the space between the zona pellucida and the plasma membrane (sometimes called the vitelline membrane) in a fertilized ovum.''

*'''Polyploidy:'''

''Cells with three or more sets of chromosomes.''

*'''Pronucleus:'''

''the nucleus of the ovum or sperm after fertilization but before they fuse to form the nucleus of the zygote ''

*'''Protoplasm:'''

''The fluid living content of the cell that consists of two major divisions, the cytoplasm and the nucleoplasm (cell nucleus). It is composed mainly of nucleic acids, proteins, lipids, carbohydrates, and inorganic salts''

*'''Segmentation:'''

''division of some metazoan bodies (such as annelida and Arthropoda) into repeated parts, segments. Segmentation can be homomeric (more or less the same) or heteromeric(different from each other).''

*'''Terrestrial:'''

''Of or on the ground, of the habitat of a plant, on land as opposed to in water, or on the ground as opposed to on another plant.''

*'''Transgenesis:'''

''Transgenesis is the process of introducing an exogenous gene - called a transgene - into a living organism so that the organism will exhibit a new property and transmit that property to its offspring.''

*'''Yolk:'''

''nutritive material of an ovum stored for the nutrition of an embryo''

*'''Zygote:'''

''The cell from which an organism develops, that results from the fertilization of the egg by the sperm.''

''Primary Resource "Biology- Online Dictionary''[http://www.biology-online.org/dictionary/Main_Page]

== References - Frog Embryology: ==

[[Image:Frog Research.jpg|thumb|left|Research being done on a Frog Image details:[http://images.google.com.au/imgres?imgurl=http://www.odt.co.nz/files/story/2008/09/university_of_otago_zoology_senior_lecturer_phil_b_3343259744.jpg&imgrefurl=http://www.odt.co.nz/on-campus/university-otago/21670/dunedin-frog-man-wins-zoo-award&usg=__JvJJU5QfOnIwY2bk4xo64UXuJRs=&h=600&w=404&sz=22&hl=en&start=14&um=1&tbnid=AbsP89yWcUiilM:&tbnh=135&tbnw=91&prev=/images%3Fq%3Dfrog%2Bresearch%26hl%3Den%26um%3D1].jpg]]

1. Savage, J. M. (2002). The Amphibians and Reptiles of Costa Rica. University of Chicago Press, Chicago [http://www.springerlink.com/content/vv015277w1746llw/]

2. Ford, L.S.; D.C. Cannatella (1993). "The major clades of frogs". Herpetological Monographs 7: 94–117 [http://digimorph.org/specimens/Xenopus_laevis/]

3. Tyler, M. J. (1994). Australian Frogs A Natural History. Reed Books [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.gracilenta.html]

4. Cogger, H.G.; R.G. Zweifel, and D. Kirschner (2004). Encyclopedia of Reptiles & Amphibians Second Edition. Fog City Press [http://en.wikipedia.org/wiki/Microhylidae]

5. Beltz, Ellin (2005). Frogs: Inside their Remarkable World. Firefly Books [http://unjobs.org/authors/ellin-beltz]

6. Tyler, M. J. (1994). Australian Frogs A Natural History. Reed Books [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

7. Moury JD, Hanken J (1995) Early cranial neural crest migration in the direct-developing frog, Eleutherodactylus coqui. Acta
Anatomica (Basel) 153, 243-253.

8.Raynaud A (1985) Development of limbs and embryonic limb reduction. In Biology of the Reptilia (ed. Gans C, Billett F), pp.
59-148. New York: John Wiley.[http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=9309]

9. Hanken J (1986) Developmental evidence for amphibian origins. In Evolutionary Biology (ed. Hecht MK, Wallace B, Prance GT), 20, pp. 389-417. New York: Plenum Press. [Hanken J (1986) Developmental evidence for amphibian origins. In Evolutionary Biology (ed. Hecht MK, Wallace B, Prance GT), 20, pp. 389-417. New York: Plenum Press.]

10. Elinson RP (1990) Direct development in frogs : wiping the recapitulationist slate clean. Seminars in Developmental Biology
1, 263-270.

11. Beebee, T. J. C. 1996. Ecology and Conservation of Amphibians. Chapman and Hall. London. [http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V5X-3SVHMKH-1X&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=1021245355&_rerunOrigin=google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=825868e10cd178d16a8a0e5ad14dc5ef]

12. Lehtinen, R. M. 2002. The use of screw pines (Pandanus spp.) by amphibians and reptiles in Madagascar. Herpetological Bulletin 2002:20–25.

13. Parris, K. M. and M. A. McCarthy. 1999. What influences the structure of frog assemblages at forest streams. Australian Journal of Ecology 24:495–502. CrossRef

14. Zug, G. R. 1993. Herpetology: An Introductory Biology of Amphibians and Reptiles. Academic Press. San Diego, CA.

15. Slack,J.M.W., Darlington,B.G., Heath,J.K. and Godsave,S.F. (1987)Mesoderm induction in early Xenopus embryos by heparin-binding growth factors. Nature, 326, 197-200.

16. Melton,D.A. (1990) Activins are expressed early in Xenopus embryogenesis and can induce axial mesoderm and anterior structures. Cell, 63, 485-493.

17. Harland,R.M. and Misher,L. (1988) Stability of RNA in developing Xenopus embryos and identification of a destabilizing sequence in TFIIIA RNA. Development, 102, 837-852.

18. Cunliffe,V. and Smith,J.C. (1992) Ectopic mesoderm formation in Xenopus embryos caused by widespread expression of a Brachyury homologue. Nature, 358, 427-430.

19. Kinoshita,K., Bessho,T. and Asashima,M. (1993) Competence prepattern in the animal hemisphere of the 8-cell-stage Xenopus embryo. Devel. Biol., 160, 276-284.

20. LaBonne,C., Burke,B. and Whitman,M. (1995) Role of MAP kinase in mesoderm induction and axial patterning in Xenopus development. Development, 121, 1475-1486.

21. Green,J.B.A., New,H.V. and Smith,J.C. (1992) Responses of embryonic Xenopus cells to activin and FGF are separated by multiple dose thresholds and correspond to distinct axes of the mesoderm. Cell, 71, 731-739.

22. Grainger R., Blumberg B., Harland R., Amemiya C., Importance of Xenopus Tropicalis to biomedical and biological research, Benaroya Research Institute, Virginia Mason Research Center [http://www.genome.gov/Pages/Research/Sequencing/BACLibrary/xenopusTropicalis.pdf ]

23. Gregory, T.R. (2005). Animal Genome Size Database. [http://www.genomesize.com]

24. U.S Fish and Wildlife Services, ABNORMALITY CLASSIFICATION SOP, [http://www.fws.gov/contaminants/Amphibian/pdfs/AbnormalitySOP_woutpics_Jan08.pdf ]

25. Donald D. Brown*, Liquan Cai*, Biswajit Das*, Nicholas Marsh-Armstrong‡, Alexander M. Schreiber*, and Rejeanne Juste*(2005), Thyroid hormone controls multiple independent programs required for limb development in Xenopus laevis metamorphosis [http://www.pnas.org/content/102/35/12455.full]

26. Ogino, Hajime; Ochi, Haruki, Resources and transgenesis techniques for functional genomics in Xenopus, Development Growth & Differentiation, Volume 51, Number 4, May 2009 , pp. 387-401(15) [http://www.ingentaconnect.com/content/bsc/dgd/2009/00000051/00000004/art00001%3Bjsessionid=4ah96rms73gcu.alexandra]

27. Giles Newton (2004) Why the frog? The Human Genome, [http://genome.wellcome.ac.uk/doc_WTD020799.html]

28. Xenbase, [http://www.xenbase.org/common/]

29. Donders Center for Neuroscience & Nijmegen Center for Molecular Life Sciences (NCMLS), Beyond the genome (Xenopus transgenesis for functional genomics),Faculty of Science, Radboud University [http://molanphys.ruhosting.nl/transgenesis.htm]

== External Links ==
[[Image:Frog links.jpg|thumb|left|Smart Frog Image details:[http://images.google.com.au/imgres?imgurl=http://2.bp.blogspot.com/_o93AaY0GzH4/SjY_ZYv0PII/AAAAAAAAAgk/skruNc2yN78/s400/computer%2Bfrog.jpg&imgrefurl=http://hellaheaven-ana.blogspot.com/2009/06/talking-frog-contemporary-fairy-tale.html&usg=__oxji1TGLV2Fi7xe0dnlmuYk8gDo=&h=288&w=288&sz=16&hl=en&start=2&um=1&tbnid=ywZd4zpdxC5plM:&tbnh=115&tbnw=115&prev=/images%3Fq%3Dfrog%2Bon%2Bcomputer%26hl%3Den%26um%3D1].jpg]]

1. Frog embryology [http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/F/FrogEmbryology.html Frog Embryology]

2. Frog cellular materials [http://www.xenbase.org/xenbase/original/cell/cell.html xenbase]

3. The zoology of frog species [http://worms.zoology.wisc.edu/frogs/mainmenu.html zoology frogs]

4. Frog cycle [http://www.bioethics.gov/images/sc_images/frog_dev.gif bioethics frog] Just a little cycle of FROG'S life cycle

5. Frog Embryology [http://embryology.med.unsw.edu.au/OtherEmb/Frog.htm UNSW Embryology]

6. Frog Research [http://apps.carleton.edu/campus/library/now/exhibits/wallcharts/frog/ carleton library exhibit]

{{Template:Projects09}}
[[Category:Frog]]

2009 Group Project 5

2009-10-14T23:18:01Z

Z3258567: /* Gametogenesis */

== The Embryology of Frogs ==

== The Frog ==

[[Image: Frog species .jpg|thumb|left|Image details: Wikipedia (2009) Frog species[http://en.wikipedia.org/wiki/Frog#Uses_in_agriculture_and_research].jpg]]

Frogs are scientifically identified by the structure of their long posterior limbs, a petite framework, webbed fingers and feet, budged eyes and the lack of a tail. The majority of frog species are extensively recognized as outstanding jumpers, due to their long, dominant legs, which are adaptations to progress jumping performance during activities. The Frog is one of the most frequently studied species in experimental embryology and most anatomical sciences. ''The Frog is a practically effective model for human embryological development given that the Frog:''

- Comprises of genes which can be effectively manipulated.

- Comprises of similar homogeny with humans species.

- Reproduces a large quantity of offspring in a short period of time.

- Are small species which can be simply sustained.

- Are not extremely luxurious and expensive.

== The History of the uses in agriculture and research ==

[[Image: Frog experiments .jpg|thumb|right|Image details: Scans of chemically cleared and dyed preserved deformed frogs and toads [http://www.sat.qc.ca/upload/residence/frog-04.jpg].jpg]]

There are numerous types of frog species that have been manipulated in many developmental experiments. The frog was traditionally used by countless of the early embryology investigators and presently there are several diverse molecular mechanisms regarding progression of the frog. Theses include:

'''1.''' Food source; frog legs are a delicacy and are eaten in European countries and in many parts of South American regions.

'''2.''' Frogs have the finest biochemical dissection of phenomena that take place in the egg and oocyte. Frogs are the evolutionarily closest to mammals, commonly used as a vertebrate model.

'''3.''' Frogs lay thousands of outsized eggs, from which cell extracts can be readily prepared that is capable of recapitulating most molecular phenomena in a test tube.

'''4.''' Frogs have been commonly used as a laboratory system for a very long period, and have an extensive history of producing crucial observations in countless fields of biology.

'''5.''' Frogs have a important historical connection to the study of epigenetics (John Gurdon-vertebrate cloning and reprogramming) which has been mostly performed on frog species.

'''6.''' Frogs also have very strong evidence of pattern formation and early development, as the embryos are large in size and experimentally manipulative.

'''7.''' Recent research into the biochemistry of chromatin and epigenetics has been performed with frog species and mammalian cultured cells.

'''8.''' The biggest weakness of the Frog model system is the difficulty of performing genetic experiments and analysis, as frogs are allotetraploid, meaning they take approximately a year to fully develop to sexual maturity, and the genome has not been completely sequenced. Nevertheless, biochemical manipulations of cell extracts, such as immunodepletions and application of heterologous DNAs and nuclei can avoid the need for genetic exploitation.

----

== Growth and development of the Frog ==

[[Image: Mature develop frog.jpg|thumb|Image details: Wikipedia (2009) Red Eyed Tree Frog Figure 1 Primary source:[http://en.wikipedia.org/wiki/File:Red-eyed_Tree_Frog_-_Litoria_chloris_edit1].jpg]]

* The frog is a well recognised species, abundant predominantly in ponds, swamps, though various species may also exist in damp or shady environments distant from moist habitats.

* Eggs of specific frogs are easily obtained and may be examined in from the beginning of fertilization onwards. The phases of embryonic development differs in various chordates, yet the typical phases are basically apparent in all frog species. The differences are associated principally to the amount of yolk particles present in an egg.

* The yolk particles offer nourishment of the developing embryo. The process of frog development will be discussed from the phases of gametogenesis to the adult stage.

----

== The Egg ==
[[Image:Development of Poles in frog Fertilization.jpg|thumb|left|Development of Poles in Frog Fertilisation:J,Nassif 2009.jpg]]

- The embryology of a frog egg is a vast cell; its dimensions are approximately 1.4-1.6 million times larger than a typical aquatic species egg cell. Throughout the frog’s embryonic maturation period, the egg will be transformed into a tadpole encompassing millions of cells but still remains with its constant volume of genetic material, the vast prodction of cell have been illusttrated in the figure on the right revealing the production of eggs from female frogs. [http://en.wikipedia.org/wiki/Microhylidae]

- The early embryonic frog structure consists of three main segments the superior hemisphere known as the animal pole which is usually visible as a grey coloured area. The innermost layer appears to be between the outer two sections known as the gray crescent represented in black. Inferiorly, represents the vegetal pole typically lighter than the superior compartment illustrated in gold.

VIDEO RESOURCE: [http://www.youtube.com/watch?v=GO5YN_t1fqw&feature=related]

[[Image:Early Development of Frogs.jpg|thumb|left|Early Development of Frog:J,Nassif 2009.jpg]]

==History of frog embryology use ==

*'''1851''' - ''Henby Nelson''(MD): He identified a remarkable fact through the frog embryo. Henby observed the first cleavage of the yolk, in the egg of the frog. And cleaved structure corresponds in line of direction to the longitudinal axis of the body of the embryo of the frog species.

[[Image:Wilhelm Roux.jpg|thumb|right|Wilhelm Roux[http://images.google.com.au/imgres?imgurl=http://www.todayinsci.com/R/Roux_Wilhelm/RouxWilhelmThm.jpg&imgrefurl=http://www.todayinsci.com/6/6_09.htm&usg=__qRLTEMTHdZpAHxiNX12hWjcm9tA=&h=125&w=100&sz=4&hl=en&start=2&um=1&tbnid=LIKIwZTqCpk7MM:&tbnh=90&tbnw=72&prev=/images%3Fq%3DWilhelm%2BRoux%26gbv%3D2%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

*'''1888''' - ''Wilhelm Roux'': Wilhelm Roux attempted to solve the above observation by damaging one cell of a two-cell frog embryo with a hot needle. The cell stayed in place. However, it did not develop further. Its partner developed into a left or right half-embryo;

*'''1907''' - ''John Hopkins'' hospital: In order to identify the cellular source of neuronal fibres. Scientist placed small portions of frog embryo spinal cords in lymph on a microscope slide and was able to observe clear cut neuronal sprouting.

*'''1951''' - ''Robert Briggs'': Robert Briggs was able to clone a frog embryo by substituting the nucleus of an unfertilized frog egg cell with the nucleus of a frog embryo cell. This process is known as nuclear transplant, has formed the basis for all cloning.

*'''1952''' - ''Robert Briggs and T.J. King'': Robert Briggs and T.J. King used frog for test experiment. Because the size of the eggs in the frogs are enormous compared with those of mammals, which make them easier to manipulate.

*'''1976'''- Using the technique that had been successful in cloning frog embryos, the doctor transferred the nucleus of one cells into a donated egg cell. As an embryo began to develop, it was implanted into the uterus of a young woman.

*'''1997''' - ''Wilmut and Campbell'': Utilizing the cloning technique from frog embryo, Drs. Wilmut and Campbell tried the starvation technique on embryo cells to produce Megan and Morag, the world's first cloned sheep and, until now, the most famous sheep in history.

*'''2000''' - ''Tokyo University'': Scientists at Tokyo University have grown artificial eyeballs. Scientists formed them in tadpoles by using frog embryo cells.

*'''2001''' - ''Advanced Cell Technology'': Scientists from Advanced Cell Technology announced production of a human embryo clone. This is significant as its parthenogenesis has been artificially induced in frogs.

[[Image:John Gurdon .jpg|thumb|right|John Gurdon [http://images.google.com.au/imgres?imgurl=http://www.pnas.org/site/misc/images/gurdon.jpg&imgrefurl=http://www.pnas.org/site/misc/classics4.shtml&usg=__1p-GA1PdOYsxKL-cznMb3RHCm98=&h=526&w=400&sz=223&hl=en&start=1&um=1&tbnid=9k4lhuLssiWCAM:&tbnh=132&tbnw=100&prev=/images%3Fq%3DJohn%2BGurdon%26gbv%3D2%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

*'''2002''' - ''John Gurdon'': John Gurdon from Wellcome Cancer Research Institute in Cambridge experimented on cloned frog embryo.

== Gametogenesis ==

* The sexual reproduction occurs through the fusion of either mature reproductive cells or germ cells known as gametes, which include the sperm from the male frog and ova from female frog species so as to form a single cell, the fertilized zygote. The gametes are typically developed in parents of different sexes . [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

* Males gametes is a spermatozoon , the female frog gamete is an ovum. Each gamete is formed by a process, recognised as maturation or gametogenesis in gonads. The typical male frog gonads are testies in male, while the female gonads are ovaries. The synthesis of both gonads is associated with the process of fertilization. [http://en.wikipedia.org/wiki/Microhylidae]

* The zygote changes into a mature frog through the process of embryology and metamorphosis. Gametogenesis is a progression in which frog gametes are established from germ cells. Initial germ cells are called primordial germ cells, which can be recognised extremely early in the life of frog species.

----

== The Egg & Fertilization ==

[[Image:Fertilized and Unfertilised Eggs.jpg|thumb|left|Fertilized and Unfertilized Eggs:J,Nassif 2009.jpg]]

[[Image:Egg Development.jpg|thumb|left|Egg Development:J,Nassif 2009.jpg]]

- This occurs once the sperm cell has inserted, following the insertion of the sperm cells meiosis II is completed, there is a 30 degree position change of the cytoplasm, gray crescent allows this change to be visible in some amphibians, the gray crescent is able what determines the expect ted outline of how the frog will form. The sperm cell joins with the nuclei of the egg which forms the diploid zygote nucleus. --Sando Rashed 10:09, 24 September 2009 (EST)

- The early phases in the development of the egg is visible, but must be studied in tadpoles throughout maturation. In embryonic tadpoles of about 10 millimetres in length, soon after the opening of the oral cavity, a pair of longitudinal ridge-like thickenings of peritoneum becomes apparent along the posterior surface of the body cavity situated near to the mesentery and along the inner boundaries of the kidneys. Genital ridges are established in all tadpoles of this age, sex is not distinct until a later period. The development of the egg is illustrated in the figure on the left revealing the structure of a developed egg and a mature of egg.

[[Image:Fertilisation life cyle.jpg|thumb|Fertilization of Life cycle:Derived from primary source:[http://en.wikipedia.org/wiki/Frog]]]

== Maturation of the Egg ==

- The eggs have currently accomplished their full size, and develop from the exterior of the ovaries like a small shot, but they still have to pass through the course of maturation before they are prepared to be fertilised. This progression of maturation relates to the nucleus almost completely.

- The nucleus component, containing the nuclear fluid that excludes through the nuclear membrane into the substance of the egg, a great segment of the nuclear reticulum vanishes and becomes degraded into separate globules known as nucleoli, but a extremely small division remains in the midpoint as a slender intricately thread recognised as the nuclear skets.
Relative to the egg getting discharged from the ovary, the follicles shatter allowing the eggs to fall into the abdominal cavity of the frog species, the egg then passes forwards, directly by the contraction of the muscular wall, somewhat by the movement of the cilia of the peritoneum, to the apex of the oviduct, which positioned at the anterior compartment of the body cavity opposite to the roots of the respiratory organs.

- The terminal part of the oviduct establishes a thin-walled pouch capable of great swelling, inside which the eggs gathers in large numbers. In conclusion, the eggs are migrated out through the cloaca into water which the albuminous investments of the eggs rapidly augment to form the gelatinous mass of the frogs spawn.

== Maturation phases ==

'''1. Nuclear skein''', moves from the midpoint of the egg to its outer surface, which it reaches opposite the midpoint of the black pole. The skein, subsequently an unevenly twisted thread, now presumes the specific arrangement of a nuclear spindle, for instance may be visible in the nucleus of an epithelial or additional cell instantly prior to division of the cell occurs.[http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

'''2. The first Polar Body,''' regarding the instance the egg is laid, but prior to its fertilistion, the egg develops a considerably flattened appearance at its upper or black pole, a definite sum of fluid being exuded among the egg and the vitelline membrane. The nuclear spindle currently separate into two identical segments, one of which remains with the egg, and the supplementary is extruded as the first polar body, a small ovoidal white globule, which is situated on the surface of the egg surrounding the exuded peri-vitellline fluid.

'''3. The Second Polar Body''', half of the nuclear spindle that stay behind then splits into two equivalent divisions, one of which remains inside the egg as the female pronucleus, whereas the other segment is extruded as the second polar body, a small white globule extremely related to the first polar body, and like this positioned in the perivitelline fluid on the superior portion of the egg.

'''4. Fertilisation of the egg''', includes the synthesis of the spermatozoon with to egg, specifically, synthesis of the nuclei of these two bodies. The spermatozoa, subsequent to being shed over the seed by the male, distribute vigorously by means of their extended tails, break through the gelatinous investment of the female eggs, bore their way through the vitelline membrane and so go through into the eggs themselves, which they penetrate relative to the superior or black hemispheres.
* Subsequently, an hour following the spermatozoon has entered; a progression may be visible projecting within from the exterior segement of the egg, with a liquid spot in the mid point. This liquid centre is the nucleus of the spermatozoon, and is said to be the male pronucleus, it break through beyond into the female egg, transporting the specialised pigment into it, so that it appears bounded by a pigmented capsule linked with the exterior of the egg by a pigmented stalk.

* By this instance, the second polar body has been established and extruded, and the female pronucleus is merely the only component of the primary egg nucleus still present. Both the male and female pronuceli, which are at initially distance separate to each other, merge and after having enlarged significantly in size then fuse mutually about two and half hours after fertilisation has originated to produce the segmentation nucleus.
* The segmentation nucleus is a huge sphere-shaped vesicle embedded in delicately granular protoplasm, and bounded by a distinct capsule of pigment, its arrangement by the synthesis of the male and female pronuclei completes the action of fertilisation. Specifically female pronucleus may be observe as an imperfect nucleus, and consequently result in the course of fertilisation. The nucleus of the spermatozoon or male pronucleus, replaces the component of the egg- nucleus which has been misplaced as the polar bodies.

'''5. Segmentation of the Egg''', the initial phase of growth consist in constant separation of the egg, whereby it becomes transformed from the unicellular state, which is everlasting only in the lowest species, to muliticelluar state charactertics of all higher species. To these early processes of growth the names segmentation is specified. Shorty subsequent to the competition of fertilisation and arrangement of the segmentation nucleus this later misplaces its sphere-shaped appearance and develops to be spindle-shaped, the yolk granules at the equivalent instance showing a tendency to develop into lines distributing outwards from the distal segment of the spindle.
* The nucleus now split into two halves, which shift away from one another, the yolk granules are likely to combined themselves around the two nuclei, and a slender vertical plate of delicately granular substance is left, dividing the egg.[http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

* Superiorly the eggs depression now becomes visible, initially as a small cavity and then develops as a groove, which almost immediately extends all round, and speedily deepening, splits the egg into two entirely separate halves along a plane equivalent with the vertical plane.

* Shorty after, the two nuclei soon separate again into two, and therefore a second cleft is created in the same state as before, its additionally in the vertical plane, however in a plane at 90 degrees to the initial one, and on its finishing point the egg comprises of four accurately similar segments, each containing a nucleus. The third cleft is horizontal in shape, but not equal, lying closer to the superior than the lower pole, it segregates each of the four cells into, an superior smaller and a inferior larger pole

----

== Cleavage ==

[[Image: Frog Cleavage development.jpg|thumb|left|Cleavage Process details:[http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/F/FrogEmbryology.html].jpg]]

* The egg of the frog is scientifically identified as’ telolecithal’ meaning there is a outsized amount of yolk concentrated at a single pole, in contrast to the concentration of cytoplasm and the site of the nucleus. The cleavage phases are holoblastic, therefore the total and after the second cleavage they are asymmetrical .The initial cleavage stage appears about two and half to three hours after fertilization. It commences as a minor depression in close proximity to the centre of the animal hemisphere. It appears as if some interior force is pushing the surface the egg towards the centre. This small upturned fold steadily continues in the form of a channel until it surrounds the egg. This groove is shallow in the commencement, but develop into deeper eventually separating the fertilized egg into two halves recognised as the blastomeres. [The figure on the left symbolise the development and growth of the frog embryo during cleavage].

* Internally the separation is mitotic, consequently each daughter cell contains a nucleus resulting from the copulation nucleus of the fertilised egg. This cleavage is vertical, the two cells are indistinguishable in respect of cytoplasm, pigment and yolk. The subsequent cleavage appears about an hour after the first. The channel of this cleavage begins at the centre of the animal hemisphere, is at right angles to the first and is vertical. This divides the egg into four blastomeres. The fourth blastomere so produced are not qualitatively equal, since of these only two contain the material from the gray crescent. The cleavage begins about thirty minutes after the second is completed or four hours after fertilisation. the cleavage plane of the third furrow is horizontal and slightly above the equator. Thus the four upper cells are a little smaller than the four lower cells. The smaller blastomeres are called micromeres and the larger blastomeres are called macromeres. The fourth cleavages follow 20 minutes after the third and tend to be vertical. This is usually a double furrow.

* The cleavage rate is accelerated with each of the early divisions and since the blastomeres are of unequal size and have varying amounts of cytoplasm and yolk, synchronous cleavage is lost and there is an obvious overlapping of the division. The upper most cells divide more rapidly than the lowermost cells. From this point onwards perfect symmetry in cleavage and in blastomere is very rare, although the embryo developed perfectly. The fifth cleavage is also doubled, appearing first in the upper hemisphere and then in the lower.

* The cleavage thus far follows the rule that each cleavage plane comes in at right angles to the previous one. The subsequent divisions become so irregular that it is previous one. The subsequent division become so irregular that it is impossible to trace out any plan or procedure. The segmentation continues more rapidly in the pigmented regions, since at that place the protoplasm is most dense, whereas, yolk which is very abundant in the vegetal side delays cell division. The multicelluar embryo at this stage is called morula by some biologists.

----

== Gastrulation ==

[[Image:FROG GASTRULATION .jpg|thumb|left|Frog Gastrulation Image details:[http://www.google.com.au/imgres?imgurl=http://bio1903.nicerweb.com/Locked/media/ch47/47_12FrogGastrulation.jpg&imgrefurl=http://bio1903.nicerweb.com/Locked/media/ch47/gastrulation-frog.html&h=540&w=480&sz=46&tbnid=N78sHjELreGGSM:&tbnh=132&tbnw=117&prev=/images%3Fq%3Dfrog%2B-%2Bgastrulation&hl=en&usg=__4VK9FYLft0W-4lBe6p5EtQAMiaI=&ei=qPy5SurtMJvE6wON8JmdAg&sa=X&oi=image_result&resnum=4&ct=image].jpg]]

''The phase of Blastulation is followed by the unique developmental progression of gastrulation. The process of frog gastrulation involves the following processes.''

'''1. Epiboly Phase'''

The pigmented cellular materials of blastula have the propensity to overgrow the yolk cells within the developing content. This course which is known as epiboly commences gradually in the final blastula and rapidly accelerates with advancing gastrulation development. The cellular matter within the animal pole reproduces and matures on all sides except in area surrounding the dorsal lip of the blastopore has been established.

'''2. Convergence'''

Scientists suggested that the unfolding was thought to result in spreading of the superficial cells over a substrate with suitable absorption properties. Consequently epiboly and convergence are an outcome to this spreading tendency, which is actually increased by a reduction in surface tension of the distributing cells.

'''3. Rotation'''

The epiboly phase is maintained until the region of the dorsal lip has migrated and is a to some extent greater than 90 degrees and the region of the white blastopore is reduced to small circular rings. This section will be positioned away from the developing vegetal pole. Laterally the complete developing gastrula has been rotated to a horizontal axis, allowing it to lie at right angles to the original median plane of the egg. Therefore, the course of rotation is such that the dorsal lip is practically pushed backwards in one direction as rapid or quicker than epiboly moves it forward in the other. The outcome will be that the blastopore produced at roughly the vegetal pole is posterior, and the dorsal and ventral lips are essentially dorsal and ventral. This in addition allows the eggs to form the antero-ventral side of the potential embryo whilst the area marked by the grey crescent is to develop the dorsal segment.

'''4. Invagination'''

Visible is a small fissure- like invagination which is apparent in the middle between the equator and the vegetal segment. The most superior or dorsal border of the cleft produce the dorsal lip of the blastopore. This imput move back and forth on the dorsal plane near the dorsal lip and migrates around the boundaries of the blastocoel in company with the extension of the lateral lips. This adapted invagination is maintained until the blastocoel cavity has been almost abolished; excluding the slender opening separating epiblasts from the hypoblast, the new segment formed is known as the archenteron cavity.

'''5. Involution'''

- Additional to previous course of action a distinct involution also occurs at the blastoporal borders. This is mainly dynamic at the median dorsal lip and gradually more less as it shifts across either side until it reaches the ventral lip where it constant.Throughout this progression, cells positioned beside the superior boundaries of the blastoporal lip migrate over the lip to the interior portion of the lip. These cells are remained within the embryo along the internal edge of the blastopore. This indicates the root of archenteron is composed of involuted cells and beyond this the external layer known as the ectoderm. The base and lateral sides are enclosed mainly of endodermal cellular material, which have been established from larger yolk cells, situated in the vegetal pole of the blastula.

- In the final phases of the gastrula development, the cells contributing to the floor of the archenteron, thin out significantly where they surround the blastocoel.
The hemispherical shaped dorsal lip of blastopore which become visible at the commencement of the gastruation stage carry on to augment, initially becoming semicircular, then transform into a horse shoe shaped and then finally forming into circular band. The band is the accomplished by the blastopore. Various yolk cells of vegetal pole present in the section are crowed into the blastoporal cavity where they form a gathering identified as a yolk plug. Blastopore rapidly reduces in size while the archenteron is still developing and becomes completely formed in the final stage; the yolk plug appears as only a small oval on the gastrula.

==Growth and Modification of Frog Species==

'''1. Changes in habits and habitats:'''

'''a)''' In frogs, metamorphosis is related with to the modifications and adaptations as a frog changes environmental habitats from an aquatic to a terrestrial mode. Metamorphosis has modified the adaption of frogs as this alteration it began during the aquatic adaptations in the surface of water to breathe air. Subsequently, it continues the terrestrial surroundings, therefore the frog species become abundant in vegetation area allowing the frog to transform in to amphibious species.

'''b)''' The transition during metamorphosis is linked with a change in food chain. The tadpoles being the embryonic origin of frogs are herbivorous, feeding on algae and green matter, which they collect by the adapted feature such as their teeth surrounding their mouths. Adult frogs, alternatively, are classified as carnivorous feeding on insects and worms. Occasionally, they also consume larger prey, for instance smaller frogs species and even little birds and rodents which they dominant and ingest.

[[Image:Development of frog from sperm to mature structure.jpg|thumb|left|Development of Frog from sperm to mature structure Image details:J,Nassif 2009.jpg]]

'''2. Changes in Morphology'''

These include the decrease or complete absence of specific organs or structures which are essential during development of early frog embryology, but not critical in the mature frog species. The significant alterations of this nature include the following developmental structures.

'''a)''' The long tail of the tadpole alongside the fin folds is absorbed again during metamorphosis and becomes absent at the final stage of the metamorphosis.

'''b) '''The developing gills are resorted, the gill clefts are congested and the branchial cavities start to become absent. The reabsorbtion of gills also takes place by autolysis.

'''c)''' The teeth of the perioral disc additionally the homey lining of the jaws are shed.

'''d)''' The lateral line sense organs within the skin of tadpoles vanish throughout metamorphosis.

'''e)''' The cloacal tube begins to condensed and reduced.

'''f)''' Various blood vessels, together with parts of the aortic arches, are reduced during mature development.

(The figure on the left represents the transformation from a tadpole to a developing structure.)[http://science.jrank.org/pages/2862/Frogs-Adult-morphology.html]

'''3. Progressive or constructive changes'''

This process comprises of the development of specific organs which mature into functional systems only during metamorphosis.

'''a)''' During development the limbs continue to augment in size and differentiation. The forelimbs, which in the tadpole mature under the opercular membrane, which then break through to the exterior. Simultaneously there is a increase in the length and strength of the hind limbs, joints develop in them and the toes become visible.

'''b)''' The middle ear becomes apparent in relation with the first pharyngeal pouch. The tympanic membrane matures. It is bounded by circular tympanic cartilage which allows the frog to retain air.

'''c)''' The visual organs bulge up on the dorsal surface of the head developing the nictitating membrane.

'''d)''' There is augmentation of the tongue and the formation of thevomerina teeth.

[[Image: Growth model.jpg|thumb|Growth Model Image details:J,Nassif2009:]]

'''4. Remodelling of some structures'''

Systematic organs which operate both in the early embryonic larva and the mature adult change their differentiation during metamorphosis so as to meet the requirements of the adult mode of life and due to the habitat adaptations. The figure on the right illustrates structures developing from specic germ cell layers.

'''a)''' The skin of the embryonic tadpole is lined with a double-layered epidermis. The number of layers of cells in the epidermis augments throughout metamorphosis. Superficial surface layers become cornified. Multicellular mucous and serous glands originate in the skin. The pigmentation of the skin continuously changes, new patterns and colour start to form.

'''b)''' There is a lengthening of the mouth gap as a result of rotation of the quadrate cartilage and the true jaws become functional.

'''c)''' The tongue rapidly progresses and becomes larger and more muscular.

'''d)''' The eyes become more specialised.

'''e)''' In early tadpoles, the GIT is extremely long and wound up into a spiral folds. The intestine become greatly lengthened in herbivorous species due to the vegetables food chain.[http://en.wikipedia.org/wiki/Frog]

'''5. Development of the reproductive system'''

(The figure below represents the reproductive and development cycle of a frog as it transform from egg to frog specie.)

In tadpoles, right after the mouth is being formed, two indentation like thickenings of peritoneum begin to appear near the body cavity (dorsal surface), which is nearest to the mesentery which is near the developing kidneys. These appear in all tadpoles.

These indentations appear here because of a change in the endothelial cells, everywhere else they are usually flat looking cells but they undergo a change and in this particular area become somewhat cuboidal/columnar.

Later on the indentations become more obvious due to the epithelial cells replicating numerously to form a thick layer. The posterior two thirds of the indentation for the female is the ovary and for the male it is the testis. The third that is left differentiates and becomes fat for the body.

[[Image: Mature frog life cyle.jpg|thumb|200px|left|Mature from life cycle Image details:Derived from primary source:http://www.scienceclarified.com/images/uesc_01_img0038.jpg]]

[[Image: Developing frog.jpg|thumb|Developing Frog Image details:
[[Image: Mature develop frog.jpg|thumb|Image details: Red eyed tree frog litoria chloris source:[http://en.wikipedia.org/wiki/File:Red-eyed_Tree_Frog_-_Litoria_chloris_edit1.jpg]].jpg]]

===Delamination===

Delamination indicates a mass separating a group of cellular matter from other cellular groups. It has been illustrated that the division of notochord, mesoderm and endoderm tissues from each other to form distinct cellular masses is completed by the progression of delamination, subsequent to these materials moving to the inside throughout gastrulation. During the developing gastrula, the germ layers are all recognized. These distinct segments of the embryo develop from these germ tissue layers.

===Polarity and Rotation===

Throughout fertilisation to the beginning of gastrulation, the frog’s egg continues in the original location in relation to its polarity. Subsequent to gastrulation its polarity begins to differentiate. This progression is linked with migration of materials within the gastrula and can be responsible for the alterations of the centre of gravity.

===Closing of Blastopore===

Subsequent to the formation of the gastrula, the blastopore is visible as a tiny round circular filled cavity containing the yolk plug. As it continues to reduce in dimension, it represented as a pear-shaped outline through the mutual approach of its lateral lips. Through it final progression these fuse entirely to produce a longitudinal groove, the streak which continue dorsally and ventrally in a small aperture. The inferior aperture closes, resulting in a depression called the anal pit. The superior region remains open for some period and begins to as the neural groove is laid down.

===Post Gastrulation or Organogenesis===

Throughout the duration of pre-gastrulation, all tissues for different organs vanish from the surface of blastula and migrate inside to take their final arrangement in the embryo structure where organs are developed from their potential regions. Consequently organogenesis transfers an embryo into free larva structure.

----

==Germ-layer origin of various body tissues==
[[Image: Development Models of Frog.jpg|thumb|right|Figure 13 Image details:Vertebrate Structure and Development.jpg]]

Ectoderm will give raise to structures such as skin, brain, spinal cord, neurons and sense receptors.
Mesoderm will give raise to structrues such as notochord, muscles, blood, bone and sex organs.
Endoderm will give raise to sturctures such as inner lining of gut, liver, pancreas, lungs and bladder, thyroid and parathyroid glands and thymus.

== Structures derived from Germ-layers of frog species ==

[[Image:Development of Frog Layers.jpg|thumb|left|Development of Frog Layers Primary source[http://www.bio.miami.edu/~cmallery/150/physiol/sf19x11b.jpg]Image details:J,Nassif 2009.jpg]]

[[Image:Development of frog layers.jpg|thumb|left|Development of Frog Layers Primary source [http://www.bio.miami.edu/~cmallery/150/physiol/sf19x11b.jpg]Image details:J,Nassif 2009.jpg]]

'''Ectoderm '''

''Establishes the epidermal segments and its derivatives, to the frog’s nervous system. The ectoderm also contributes to :''

1. The olfactory and auditory epithelium.

2. The retina and lens of the eye.

3. Sensory organs.

4. The epithelial lining of the oral cavity and the anus.

5. The pineal and pituitary body.

'''Mesoderm'''

''Mesoderm originates:''

1. Connective tissue.

2. Muscles, except the notochord.

3. Blood vessels.

4. Lymphatics.

5. The peritoneum and the urinary and reproductive system.

6. The dermis, parts of the eye excluding lens, cornea, and conjunctiva.

'''Endoderm'''

''From the endoderm arises:''

1. The epithelial lining to the gut and oesophagus, stomach, intestine, bile duct.

2. The hepatic cells of the liver, respiratory tract, larynx, trachea and lungs.

3. The lining of the urinary bladder, pancreas thyroid and thymus.

[The two figures reveal the development of structures deriving from the celluar components of the embryology of the frog].[Structures derived from Germ-layers of frog species ]

==Life cycle of a frog==

'''Fertilization-egg''':

The female lays eggs in the spring. A group of fertilized eggs is called spawn;

'''7-10 days''':

Fertilized egg feed on remaining yolk which is in its gut. Their gills, mouth and tail have poorly developed. Begin to swim and feed on algae;

'''10-30 days(4 weeks):'''

A layer of skin grows over gills. Teeth begin to appear. A coiled gut start to develop. This is aid in digestion;

'''30-60 days(6-9 weeks):'''

Legs being to grow and head is more distinct. Start to eat insects. Arms begin to grow;

'''60-80 days(12 weeks):'''

Resemble a frog. Still have remaining tail;

'''80-140 days(20 weeks):'''

Fully developed, spend most of time out of water. Majority of frog live between 4-15 years.

==Timeline of frog development==

Development of egg and embryo at temperature 18 degree celsius.

'''0 hours''' - fertilization of the egg

'''1 hours''' - formation of the gray crescent due to pigment migration

'''3.5 hours''' - early cleavage

'''4.5 hours''' - blastula stage(coeloblastula with eccentric blastocoel

'''26 hours''' - gastrulation

'''26 hours''' -'' early'' - crescent shaped dorsal lip

'''34 hours''' - ''middle''- semicircular blastoporal lip

'''42 hours''' - ''late'' - circular blastoporal lip

'''50 hours''' - neurulation

'''50 hours''' - ''early'' - medullary plate

'''62 hours''' -'' middle''- neural folds converging

'''67 hours''' - ''late'' - neural tube formed and ciliation of embryo

'''84 hours''' - tail bud stage(early organogeny)

'''96 hours''' - muscular response to tactile stimulation

'''118 hours''' - early heart beat, development of gill buds

'''140 hours''' - hatching and gill circulation

'''162 hours''' - mouth opens and cornea becomes transparent

'''192 hours''' - tail fin circulation established

'''216 hours''' - degeneration of external gills, formation of operculum, development of embryonic teeth

'''240 hours''' - opercular fold over brachial chamber except for spiracle and internal gills

'''255 hours''' - prolonged larval stage with refinement of organs

'''270 hours''' - development of hindlimbs, internal development of forelimbs in opercular cavity

'''275 hours''' - projection of forelimbs through operculum, left side first

'''280 hours''' - absorption of the tail and reduction in size of the gut

'''284 hours''' - metamorphosis complete, emergence from water as miniature, air breathing frog

==Stages of frog embryology==
--[[User:S8600021|Mark Hill]] 08:40, 9 October 2009 (EST) [[Talk:2009_Group_Project_5#Constructive_Criticism_of_Coordinator|see my comment on images]]

The rate of development of the egg and embryo will depend upon the temperature at which they are kept. The approximate schedule of development at 23 degree celsius is provided below.

{| border='1px'
|+ Table 1: Stages of frog development
!Stage !!Time since fertilisation (hours)!!Stage Characteristic !!Embryo characteristic !!Image of frog stage
|-
|1
|0.00-1.30
|fertilization of the egg, post fertilization
|animal hemisphere, gray crescent and vegetal hemisphere are present
|[[File:Stage01ventral.jpg|100px]]
|-
|2
|1.30-2.00
|splits into two cells
|appearance of first cleavage furrow
|[[File:Stage02ventral.jpg|100px]]
|-
|3
|2.00-2.15
|becomes four cells
|appearance of second cleavage furrow
|[[File:Stage03dorsolat.jpg|100px]]
|-
|4
|2.15-2.45
|becomes eight cells
|appearance of third cleavage furrow
|[[File:Stage04dorsolat.jpg|100px]]
|-
|5
|2.45-3.00
|becomes sixteen cells
|appearance of fourth cleavage furrow
|[[File:Stage05dorsal.jpg|100px]]
|-
|6
|3.00-3.30
|becomes thirty-two cells
|appearance of fifth cleavage furrow
|[[File:Stage06animal.jpg|100px]]
|-
|6.5
|3.30-4.00
|blastula stage
|Three dorsal folds become visible as a result of endoderm invagination. Pole cells no longer visible on surface
|[[File:Stage065dorsal.jpg|100px]]
|-
|7
|4.00-5.00
|Gastrulation stage
|two primary germ layers. epiblast and endoderm
|[[File:Stage07ventral.jpg|100px]]
|-
|8
|5.00-7.00
|neurulation
|medullary plate, neural folds and neural tube
|[[File:Stage08animal.jpg|100px]]
|-
|9
|7.00-9.00
|germ layer
|complete lip involution encircling yolk
|[[File:Stage09veg.jpg|100px]]
|-
|10
|9.00-11.00
|early gastrula
|two primary germ layers
|[[File:Stage10veg.jpg|100px]]
|-
|10.5
|11.00-11.45
|gastrula
|two germ layers
|[[File:Stage105vegb.jpg|100px]]
|-
|11
|11.45-12.30
|medulla plate
|Yolk sac protrudes dorsally, labium moves to midline on ventral side
|[[File:Stage11veg.jpg|100px]]
|-
|11.5
|12.30-13.15
|continuation of medulla plate
|start closing the plate
|[[File:Stage115veg.jpg|100px]]
|-
|12
|13.15-14.15
|early neurula
|thickened ectoderm give rise to CNS
|[[File:Stage12veg.jpg|100px]]
|-
|12.5
|14.15-14.45
|neural folds
|expansion of cavity
|[[File:Stage125postdors.jpg|100px]]
|-
|13
|14.45-16.15
|neural folds
|continue expanding cavity
|[[File:Stage13postdors.jpg|100px]]
|-
|14
|16.15-17.30
|neural folds
|continuation of cavity
|[[File:Stage14postdors.jpg|100px]]
|-
|15
|17.30-18.15
|tail bud stage
|early organogeny
|[[File:Stage15postdors.jpg|100px]]
|-
|16
|18.15-18.45
|tail bud stage
|posterior ventral view
|[[File:Stage16ant.jpg|100px]]
|-
|17
|18.45-19.45
|tail bud stage
|anterior view
|[[File:Stage17ant.jpg|100px]]
|-
|19
|20.45-21.45
|neural fold close complete
|dorsal view
|[[File:Stage19dorsal.jpg|100px]]
|-
|20
|21.45-22.30
|early tail bud
|anterior view
|[[File:Stage20dorsal.jpg|100px]]
|-
|21
|22.30-24.00
|termination of neural crest
|progress to next stage
|[[File:Stage21ant.jpg|100px]]
|-
|22
|24.00-24.45
|prolonged development
|elongation
|[[File:Stage22lat.jpg|100px]]
|-
|23
|24.45-26.15
|elongation of embryo
|later view
|[[File:Stage23lat.jpg|100px]]
|-
|24
|26.15-27.30
|continuation of elongation of embryo
|dorsal view
|[[File:Stage24latsmall.jpg|50px]]
|-
|25
|27.30-29.30
|organs development
|embryo elongates and develops dorsal thickening
|[[File:Stage25dorsal.jpg|50px]]
|-
|26
|29.30-31.15
|elongation
|dorsally forms neural and brain cavity
|[[File:Stage26lat.jpg|50px]]
|-
|27
|31.15-32.30
|elongation of embryo
|dorsal view
|[[File:Stage27lat.jpg|50px]]
|-
|28
|32.30-35.00
|further development
|lateral view
|[[File:Stage28lat.jpg|50px]]
|-
|29-30
|35.00-37.30
|tail bud
|growth
|[[File:Stage29-30lat.jpg|50px]]
|-
|31
|37.30-40.00
|prolonged development
|bud development
|[[File:Stage31lat.jpg|50px]]
|-
|32
|40.00-44.30
|early muscular development
|elongation
|[[File:Stage32lat.jpg|50px]]
|-
|33-34
|44.30-50.00
|muscular movement
|apparatus for locomotion
|[[File:Stage33-34lat.jpg|50px]]
|-
|35-36
|50.00-53.30
|muscular movement
|apparatus for locomotion
|[[File:Stage35-36lat.jpg|50px]]
|-
|37-38
|53.30-56.30
|heart beat
|develops apparatus
|[[File:Stage37-38lat.jpg|50px]]
|-
|39
|56.30-66.00
|mouth opens
|cornea transparent
|[[File:Stage39latsmall.jpg|50px]]
|-
|40
|66.00-76.00
|gill circulation
|hatching
|[[File:Stage40lat.jpg|50px]]
|-
|41
|76.00-80.00
|tail, fin circulation
|circulation
|[[File:Stage41lat.jpg|50px]]
|-
|42
|80.00-86.00
|internal gills, operculum
|opercular fold, teeth
|[[File:Stage42lat.jpg|50px]]
|-
|43
|86.00-98.00
|operculum complete
|operculum closed on right
|[[File:Stage43lat.jpg|50px]]
|-
|46
|98.00-106.00
|metamorphosis
|emergence from water as miniature, operculum complete|
|[[File:Stage46lat.jpg|50px]]
|-
|}

==Abnormalities of frog==

Abnormalities of frog could be caused by multiple factors. These include change in climate, predators, parasites, bacteria, fungi, viruses or pollution and contaminants such as pesticides, metals and fertilizer.[http://www.fws.gov/contaminants/documents/frogsrefup_septoct_2006.pdf]

The Abnormalities are further classified into different categories. These categories are:

===1. Infectious Diseases:===

'''Perkinsus Symptoms-''' caused by perkinsus-like protozoan organism. Symptoms include swollen viscera that leads to a bloated body and and infected swollen heart

'''Ichthyophonus symptoms-''' cause by parasitic genus, where symptoms include a swollen tail resorption site that matches the surrounding skin in color and translucency.

[[Image:Abnormalities of Frog species.jpg|thumb|left|Figure A Image details[waterwatchadelaide.net.au].jpg]]

===2. Surficial Abnormalities:===

Surficial abnormalities as the one that are visible on the surface of the skin. This includes abnormal pigmentation, , subcutaneous hemorrhaging, wounds due to trauma or from a predator
Edema is a fluid-filled swelling under skin whihc is also a surficial abnormality.

===3. Skeletal Abnormalities:===

This is further classified into three more categories:

'''a. Skeletal Malformations-'''

* Microcephaly (small head or blunt snout)
*Scoliosis (Curved spine in lateral direction)
*Shrunken Limb (Micromelia)
*Amelia (Completely missing limb with no stump)

'''b. Skeletal Abnormalities of Unclear Etiology-'''

This condition arises when a frog has ectromelia (missing limb), brachydactyly (missing digits) or other such condition with no visible trauma or external damage, then this will be classified as the Skeletal abnormality of unclear etiology.

'''c. Skeletal Injuries-'''

Any limb missing or broken due to trauma or other related reason which shows clear evidence of it is classified as skeletal injury

===4. Eye Abnormalities:===

Most common includes-

'''i. Anophthalmia:''' Skin covers the eye socket as there is no eye

'''ii. Abnormal Iris Coloration:''' Reduced pigment in either one eye or both resulting in two different colours of the iris at times

'''iii. Abnormal size or shape:''' Both eyes either deviating from each other or size of pupil or iris is different than the other eye

[http://www.fws.gov/contaminants/Amphibian/pdfs/AbnormalitySOP_woutpics_Jan08.pdf ]

==Genetics==

There are a wide variety of species that differ from each other when it comes to genetics and their functioning.

'''TAXONOMY:''' '''Phylum''' ''Chordata'' / '''Sub Phylum''' ''Vertebrata'' / '''Class''' ''Amphibia'' / '''Order''' ''Anura''

Their are more than two dozen different families of frogs, where suborders are:

'''1. ARCHAEBATRACHIA-''' most primitive frogs

'''2. MESOBATRACHIA-''' linked between the Archaebatrachia and Neobatrachia

'''3. NEOBATRACHIA-''' most modern frogs

{| border='4px'
|+ '''General Info:'''
! !!
|-
| '''Number of frogs' species'''
| 5280
|-
| '''Smallest frog genome size:'''
| 0.95pg, Ornate burrowing frog
|-
| '''Largest frog genome size:'''
| 13.40pg, Ornate horned frog
|-
| '''Mean of frogs' genome'''
| 4.68pg ± 0.13
|-
|}

[http://www.genomesize.com]

*Majority of frogs have only 22 to 26 chromosomes and polyploid is very common where they are almost bisexual.

*Polyploid Amphibians reduce their total cell number such that they acheive the same body size as diploids. One of the most unsual forms of polypoidy in amphibians is the water frog ''Rana esculenta'' from Europe and Western Asia.

* The species with larger genomes have more genes for e.g. the frog genus ''Xenopus'' includes 16 species, with genome sizes ranging from 3.5 x 10^9 bp to 1.6 x 10^10 bp. These differences have arisen by numerous events of polyploidization within the past 40 million years or so. The ancestral chromosome number for the genus seems to have been 18, but there are species with 36, 72 and 105 chromosomes [http://www.xenbase.org/common/]

{| border='4px'
|+ '''Difference within two families'''
! '''SPECIES''' !! ''X.LAEVIS'' !! ''X.TROPICALIS''
|-
| '''PLOIDY'''
| Allotetraploid
| Diploid
|-
| '''NO. OF CHROMOSOMES'''
| 36 chromosomes
| 20 chromosomes
|-
| '''GENOME SIZE'''
| 3.1 x 10^9 bp
| 1.7 x 10^9 bp
|-
| '''EGG SIZE'''
| 1-1.3 mm
| 0.7-0.8 mm
|-
| '''GENERATION TIME'''
| 1-2 years
| 4 months
|-
|}
[http://www.xenbase.org/common/]

===Genome Sequencing===

Since Frog has a huge family with many different species, only few main species that are used widely for the purposes of experiments have their genome sequenced.

''Xenopus tropicalis'' has one of the smallest genomes among amphibians and has the shortest generation time- four to six months and the only diploid genome among the 14 Xenopus species. This means it has no more than two copies of most genes, whereas the other species of Xenopus have four copies of most genes (pseudotetraploid). US Department of Energy's Joint Genome Institute (JGI) in Walnut Creek, California, initiated the X. tropicalis Genome Project, finding 1,700 million base pairs.
[http://www.genome.gov/Pages/Research/Sequencing/BACLibrary/xenopusTropicalis.pdf]

===Xenopus oocytes===

* The oocytes provide an important expression system for molecular biology.

* By injecting DNA or mRNA into the oocyte or developing embryo, scientists can study the protein products in a controlled system. This allows rapid functional expression of manipulated DNAs (or mRNA). This is particularly useful in electrophysiology, where the ease of recording from the oocyte makes expression of membrane channels attractive.

* One challenge of oocyte work is eliminating native proteins that might confound results, such as membrane channels native to the oocyte.

* Translation of proteins can be blocked or splicing of pre-mRNA can be modified by injection of Morpholino antisense oligos into the oocyte (for distribution throughout the embryo) or early embryo (for distribution only into daughter cells of the injected cell).
[http://www.staff.unibe.ch/sigel/xenopus.html]

===Xenopus Laevis===

* ''Xenopus Laevis'' is an important model organism in developmental biology. X. laevis is tetraploid and reaches sexual maturity in 1 to 2 years. What makes it important in developmental biology is its large and easily manipulable embryo.

* Extracts from the eggs of X. laevis frogs are also commonly used for biochemical studies of DNA replication and repair, as these extracts fully support DNA replication and other related processes in a cell-free environment which allows easier manipulation.

* The Human chorionic gonadotropin hormone (hCG) is present in the urine of the pregnant women in large quantities only. This hormone in the urine induces X.laevis oocyte production which formed the basis of first well-documented method of pregnancy testing X. laevis is also notable for its use as the first well-documented method of pregnancy testing when it was discovered. Today, commercially available HCG is injected into Xenopus males and females to induce mating behavior and breed these frogs in captivity at any time of the year.

===Gene cluster===

* The alpha and beta globin genes are closely linked in small cluster of frogs compared to human and chicken

* The similarity of architecture of two clusters found in X.laevis supports the tetraploid origin

* The two loci encoding the muscle specific creatine kinase isoenzymes and have large differences in developmental profile, therefore suggesting that duplicate loci that have not undergone silencing are not simply redundant copies but have acquired specialization.

* Contains twice number of genes for proteins i.e. haemoglobin and sarcomeric actin serum albumin compared with other species

----

==Current Embrology Research==

Currently, a number of fields have benefited from the development of frog embrology. These include cloning, verification of messenger RNA, and Cell cycle.

===Cloning===
[[Image:Robert Briggs.jpg|thumb|left|Figure 16 Image details:Robert Briggs.jpg]]

In 1952, Robert Briggs and Thomas J King cloned northern leopard frogs using a method of nuclear transfer. Briggs and King's experiment was similar to that envisioned - and piloted using salamanders - by Hans Spemann in his 1938 proposal for a 'fantastical experiment'. Later, John Gurdon extended this work and showed that nuclei from differentiated cells could support development, although less well than those from early embryos. [http://genome.wellcome.ac.uk/doc_WTD020799.html]

Lemaitre et a. (2005) from MRC Cancer Cell Unit, Cambridge, U.K. worked on experiments that demonstrated that importance of serial nuclear transplantation for the sucessful cloning of frogs. He demonstrated that exposure of somatic-cell nuclei (erythrocyte nuclei) and sperm nuclei to an extract of mitotic cell extract reorganizes the chromatin into shorter loops and allows replication at much shorter intervals along the DNA. This increases the efficiency of DNA replication in mammalian cell-free systems.

===Transgenesis techniques for functional genomics in Xenopus===

Transgenesis in Xenopus is made possible due to large embryos, a reliable fate map, ease of microinjection, ease of dissection/micromanipulation and existence of the neuroendocrine reflex of background adaptation as a model for activation/inact.

Recently, Hajime Ogino and Haruki Ochi from Nura Institute of Science and Technology in Japan focused on the genomic resources and principles of the transgenesis techniques in Xenopus, and discusses their applications to genome wide network analysis, with emphasis on the use of bioinformatics tools. This is will to understand the gene regulatory networks that control vertebrate development. [http://www.ingentaconnect.com/content/bsc/dgd/2009/00000051/00000004/art00001%3Bjsessionid=4ah96rms73gcu.alexandra]

Xenopus used to be a problem in earlier days when it came to transgenesis. Current methods involves isolated sperm nuclei from Xenopus testis that are microinjected into unfertilized eggs. The generated transgenic tadpoles contain 5-35 copies of the integrated plasmid that are expressed in all cells. If desired, expression of the transgene can be directed to the appropriate tissue and at the appropriate time by using specific promoters, mostly the Xenopus POMC gene promoter (isolated from a Xenopus genomic DNA library) to specifically direct expression of green fluorescent protein (GFP) at high levels to the intermediate pituitary cells, which can either be over expressed or inhibited.[http://molanphys.ruhosting.nl/transgenesis.htm]

[[File:Transgenesis.JPG]]

===Verification of messenger RNA===

While the existence and role of messenger RNA (mRNA) was known in bacteria, in the 1960s it was still debated whether it also existed in vertebrates. Taking haemoglobin mRNA from immature red blood cells and injecting it into a Xenopus oocyte, John Gurdon showed that the haemoglobin protein was indeed produced. Producing proteins in Xenopus oocytes has proved to be extremely useful in cell biology, in particular for the study of receptor proteins.[http://genome.wellcome.ac.uk/doc_WTD020799.html]

===Cell Cycle===

As they develop outside the mother, frog eggs are well stocked with the proteins needed to drive the development of the embryo. Studies of these processes has shed considerable light on the processes involved in cell division - termed the cell cycle. [http://genome.wellcome.ac.uk/doc_WTD020799.html]

===Limb development in Xenopus Laevis===

[[Image: Frog Limb development.jpg|thumb|right|From Limb Development Image details:Primary source:[http://images.google.com.au/imgres?imgurl=http://www.sciencedaily.com/images/2006/06/060616130718.jpg&imgrefurl=http://www.sciencedaily.com/releases/2006/06/060616130718.htm&usg=__xliPsPAvheUBME_kjv_q7auiFbo=&h=333&w=300&sz=11&hl=en&start=2&um=1&tbnid=y_ntJtmkRSK7WM:&tbnh=119&tbnw=107&prev=/images%3Fq%3DLimb%2Bdevelopment%2Bin%2BXenopus%2BLaevis%26ndsp%3D18%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

Donald D. Brown (2005),Department of Embryology, Carnegie Institution of Washington demonstrated factors related to limb development of Xenopus Laevis. Thyroid hormone (TH) is found to be required for limb development in this frog. Specific cell types in the growing limb were targeted for expression of a dominant negative form of the TH receptor by sperm-mediated transgenesis. Limb muscle development, the innervation of muscle from the spinal cord, and cartilage growth can be inhibited without affecting patterning of the limb or differentiation of other cell types. Remodeling of the skin occurs late in metamorphosis after the limb has formed. The coordination of these independent programs is affected in part by the control that TH exerts over DNA replication in all cell types of the limb. [http://www.pnas.org/content/102/35/12455.full]

----

== Glossary ==

[[Image: Frog species.jpg|thumb|left| Frog Species Image details:Primary source:www.olympus.co.jp/.../080925/large/p02L.jpg].jpg]]

*'''Amphibian:'''

''Relating to or characteristic of animals of the class amphibia.Amphibians are found in the taxonomic class of amphibia, amphibians are capable of both occupying and successfully living in both land and aquatic communities.amphibian''

*'''Augmentation:'''

''Enlargement/Increase in cellular size.''

*'''Autolysis:'''

''breakdown of a part or whole cell or tissue by self-produced enzymes''

*'''Blastomeres:'''

''The undifferentiated cells formed by cleavage of the fertilised ovum. This includes cells in the cleavage, morula, and blastula stages of the embryo''

*'''Carnivorous:'''
''
Flesh-eating; subsisting on animals as food.''

*'''Cleavage:'''

''he repeated division of a fertilised ovum ''

* '''Cleft:'''

''an opening, fissure, or V-shaped indentation made by or as if by splitting''

*'''Chordate:'''

''Members of a diverse phylum of animals that, as embryos, possess a (1) notochord; (2) a dorsal, hollow nerve cord, (3) pharyngeal gill slits; and (4) a post-anal tail''

''The act or state of splitting or dividing of a cell, particularly during the telophase of (animal) cell division.''

*'''Cytoplasm:'''

''The cytoplasm (of both eukaryotes and prokaryotes) is where the functions for cell expansion, growth, metabolism, and replication are carried out''

* '''Epiboly:'''
''The expansion of one cell sheet over other cells, as takes place during gastrulation''

*'''Fertilization:'''

''A process in sexual reproduction that involves the union of male (sperm) and female (ovum) gametes (each with a single, haploid set of chromosomes) to produce a diploid zygote.''

*'''Gamete:'''
''A reproductive cell (male (sperm) or female (egg)) that has only half the usual number of chromosomes''

*'''Gametogenesis:'''

''process leading to the production of gametes. The development and maturation of sex cells through meiosis.Another name for meiosis where a diploid cell is divided into two haploid cells with half the chromosome content of the diploid parent cell.''

*'''Herbivorous:'''

''eating plants; of or pertaining to the herbivora.''

*'''Holoblastic:'''

''The complete division of an isolecithal or microlecithal egg into blastomeres''

*'''Invagination:'''

''One of the methods by which the various germinal layers of the ovum are differentiated.''

*'''Isoenzymes:'''

''Isozymes (also known as isoenzymes) are enzymes that differ in amino acid sequence but catalyze the same chemical reaction.''

*'''Mesentery:'''

'' membranous fold attaching various organs to the body wall.''

*'''Metamorphosis:'''

''A change in the form and often habits of an animal after the embryonic stage during normal development.''

*'''Neuroendocrine:'''

''Neuroendocrine [IPA nʊəroʊˈɛndəkrɪn] cells are cells that release a hormone into the circulating blood in response to a neural stimulus.''

*'''Organogenesis:'''

''The part of embryonic development where the body's main organs develop.''

*'''Peritoneum:'''

''The smooth serous membrane which lines the cavity of the abdomen, or the whole body cavity when there is no diaphragm, and, turning back, surrounds the viscera, forming a closed, or nearly closed, sac.''

*'''Perivitelline space:'''

''The perivitelline space is the space between the zona pellucida and the plasma membrane (sometimes called the vitelline membrane) in a fertilized ovum.''

*'''Polyploidy:'''

''Cells with three or more sets of chromosomes.''

*'''Pronucleus:'''

''the nucleus of the ovum or sperm after fertilization but before they fuse to form the nucleus of the zygote ''

*'''Protoplasm:'''

''The fluid living content of the cell that consists of two major divisions, the cytoplasm and the nucleoplasm (cell nucleus). It is composed mainly of nucleic acids, proteins, lipids, carbohydrates, and inorganic salts''

*'''Segmentation:'''

''division of some metazoan bodies (such as annelida and Arthropoda) into repeated parts, segments. Segmentation can be homomeric (more or less the same) or heteromeric(different from each other).''

*'''Terrestrial:'''

''Of or on the ground, of the habitat of a plant, on land as opposed to in water, or on the ground as opposed to on another plant.''

*'''Transgenesis:'''

''Transgenesis is the process of introducing an exogenous gene - called a transgene - into a living organism so that the organism will exhibit a new property and transmit that property to its offspring.''

*'''Yolk:'''

''nutritive material of an ovum stored for the nutrition of an embryo''

*'''Zygote:'''

''The cell from which an organism develops, that results from the fertilization of the egg by the sperm.''

''Primary Resource "Biology- Online Dictionary''[http://www.biology-online.org/dictionary/Main_Page]

== References - Frog Embryology: ==

[[Image:Frog Research.jpg|thumb|left|Research being done on a Frog Image details:[http://images.google.com.au/imgres?imgurl=http://www.odt.co.nz/files/story/2008/09/university_of_otago_zoology_senior_lecturer_phil_b_3343259744.jpg&imgrefurl=http://www.odt.co.nz/on-campus/university-otago/21670/dunedin-frog-man-wins-zoo-award&usg=__JvJJU5QfOnIwY2bk4xo64UXuJRs=&h=600&w=404&sz=22&hl=en&start=14&um=1&tbnid=AbsP89yWcUiilM:&tbnh=135&tbnw=91&prev=/images%3Fq%3Dfrog%2Bresearch%26hl%3Den%26um%3D1].jpg]]

1. Savage, J. M. (2002). The Amphibians and Reptiles of Costa Rica. University of Chicago Press, Chicago [http://www.springerlink.com/content/vv015277w1746llw/]

2. Ford, L.S.; D.C. Cannatella (1993). "The major clades of frogs". Herpetological Monographs 7: 94–117 [http://digimorph.org/specimens/Xenopus_laevis/]

3. Tyler, M. J. (1994). Australian Frogs A Natural History. Reed Books [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.gracilenta.html]

4. Cogger, H.G.; R.G. Zweifel, and D. Kirschner (2004). Encyclopedia of Reptiles & Amphibians Second Edition. Fog City Press [http://en.wikipedia.org/wiki/Microhylidae]

5. Beltz, Ellin (2005). Frogs: Inside their Remarkable World. Firefly Books [http://unjobs.org/authors/ellin-beltz]

6. Tyler, M. J. (1994). Australian Frogs A Natural History. Reed Books [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

7. Moury JD, Hanken J (1995) Early cranial neural crest migration in the direct-developing frog, Eleutherodactylus coqui. Acta
Anatomica (Basel) 153, 243-253.

8.Raynaud A (1985) Development of limbs and embryonic limb reduction. In Biology of the Reptilia (ed. Gans C, Billett F), pp.
59-148. New York: John Wiley.[http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=9309]

9. Hanken J (1986) Developmental evidence for amphibian origins. In Evolutionary Biology (ed. Hecht MK, Wallace B, Prance GT), 20, pp. 389-417. New York: Plenum Press. [Hanken J (1986) Developmental evidence for amphibian origins. In Evolutionary Biology (ed. Hecht MK, Wallace B, Prance GT), 20, pp. 389-417. New York: Plenum Press.]

10. Elinson RP (1990) Direct development in frogs : wiping the recapitulationist slate clean. Seminars in Developmental Biology
1, 263-270.

11. Beebee, T. J. C. 1996. Ecology and Conservation of Amphibians. Chapman and Hall. London. [http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V5X-3SVHMKH-1X&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=1021245355&_rerunOrigin=google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=825868e10cd178d16a8a0e5ad14dc5ef]

12. Lehtinen, R. M. 2002. The use of screw pines (Pandanus spp.) by amphibians and reptiles in Madagascar. Herpetological Bulletin 2002:20–25.

13. Parris, K. M. and M. A. McCarthy. 1999. What influences the structure of frog assemblages at forest streams. Australian Journal of Ecology 24:495–502. CrossRef

14. Zug, G. R. 1993. Herpetology: An Introductory Biology of Amphibians and Reptiles. Academic Press. San Diego, CA.

15. Slack,J.M.W., Darlington,B.G., Heath,J.K. and Godsave,S.F. (1987)Mesoderm induction in early Xenopus embryos by heparin-binding growth factors. Nature, 326, 197-200.

16. Melton,D.A. (1990) Activins are expressed early in Xenopus embryogenesis and can induce axial mesoderm and anterior structures. Cell, 63, 485-493.

17. Harland,R.M. and Misher,L. (1988) Stability of RNA in developing Xenopus embryos and identification of a destabilizing sequence in TFIIIA RNA. Development, 102, 837-852.

18. Cunliffe,V. and Smith,J.C. (1992) Ectopic mesoderm formation in Xenopus embryos caused by widespread expression of a Brachyury homologue. Nature, 358, 427-430.

19. Kinoshita,K., Bessho,T. and Asashima,M. (1993) Competence prepattern in the animal hemisphere of the 8-cell-stage Xenopus embryo. Devel. Biol., 160, 276-284.

20. LaBonne,C., Burke,B. and Whitman,M. (1995) Role of MAP kinase in mesoderm induction and axial patterning in Xenopus development. Development, 121, 1475-1486.

21. Green,J.B.A., New,H.V. and Smith,J.C. (1992) Responses of embryonic Xenopus cells to activin and FGF are separated by multiple dose thresholds and correspond to distinct axes of the mesoderm. Cell, 71, 731-739.

22. Grainger R., Blumberg B., Harland R., Amemiya C., Importance of Xenopus Tropicalis to biomedical and biological research, Benaroya Research Institute, Virginia Mason Research Center [http://www.genome.gov/Pages/Research/Sequencing/BACLibrary/xenopusTropicalis.pdf ]

23. Gregory, T.R. (2005). Animal Genome Size Database. [http://www.genomesize.com]

24. U.S Fish and Wildlife Services, ABNORMALITY CLASSIFICATION SOP, [http://www.fws.gov/contaminants/Amphibian/pdfs/AbnormalitySOP_woutpics_Jan08.pdf ]

25. Donald D. Brown*, Liquan Cai*, Biswajit Das*, Nicholas Marsh-Armstrong‡, Alexander M. Schreiber*, and Rejeanne Juste*(2005), Thyroid hormone controls multiple independent programs required for limb development in Xenopus laevis metamorphosis [http://www.pnas.org/content/102/35/12455.full]

26. Ogino, Hajime; Ochi, Haruki, Resources and transgenesis techniques for functional genomics in Xenopus, Development Growth & Differentiation, Volume 51, Number 4, May 2009 , pp. 387-401(15) [http://www.ingentaconnect.com/content/bsc/dgd/2009/00000051/00000004/art00001%3Bjsessionid=4ah96rms73gcu.alexandra]

27. Giles Newton (2004) Why the frog? The Human Genome, [http://genome.wellcome.ac.uk/doc_WTD020799.html]

28. Xenbase, [http://www.xenbase.org/common/]

29. Donders Center for Neuroscience & Nijmegen Center for Molecular Life Sciences (NCMLS), Beyond the genome (Xenopus transgenesis for functional genomics),Faculty of Science, Radboud University [http://molanphys.ruhosting.nl/transgenesis.htm]

== External Links ==
[[Image:Frog links.jpg|thumb|left|Smart Frog Image details:[http://images.google.com.au/imgres?imgurl=http://2.bp.blogspot.com/_o93AaY0GzH4/SjY_ZYv0PII/AAAAAAAAAgk/skruNc2yN78/s400/computer%2Bfrog.jpg&imgrefurl=http://hellaheaven-ana.blogspot.com/2009/06/talking-frog-contemporary-fairy-tale.html&usg=__oxji1TGLV2Fi7xe0dnlmuYk8gDo=&h=288&w=288&sz=16&hl=en&start=2&um=1&tbnid=ywZd4zpdxC5plM:&tbnh=115&tbnw=115&prev=/images%3Fq%3Dfrog%2Bon%2Bcomputer%26hl%3Den%26um%3D1].jpg]]

1. Frog embryology [http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/F/FrogEmbryology.html Frog Embryology]

2. Frog cellular materials [http://www.xenbase.org/xenbase/original/cell/cell.html xenbase]

3. The zoology of frog species [http://worms.zoology.wisc.edu/frogs/mainmenu.html zoology frogs]

4. Frog cycle [http://www.bioethics.gov/images/sc_images/frog_dev.gif bioethics frog] Just a little cycle of FROG'S life cycle

5. Frog Embryology [http://embryology.med.unsw.edu.au/OtherEmb/Frog.htm UNSW Embryology]

6. Frog Research [http://apps.carleton.edu/campus/library/now/exhibits/wallcharts/frog/ carleton library exhibit]

{{Template:Projects09}}
[[Category:Frog]]

Talk:2009 Group Project 5

2009-10-14T22:51:15Z

Z3258567: /* Evaluation/ Alterations After Peer Review */

== Evaluation/ Alterations After Peer Review ==

--[[User:Z3295026|Joe Nassif]] 12:47, 14 October 2009 (EST)

• Edited structure of table of stages

• Corrected introduction " added a brief overview about frog and usage"

• In changed size of images to 200px and moved to the left to suit page

• Removed spaces and gaps between specific sections

• Formatted intro section to look neater and to flow more better

• Deleted the links and added proper reference

• Added to glossary of terms

• Added in text citations to the developments section

• Enhanced and added more definitions

• Changed reference list and changed the format it into APA format

• re-uploaded information and reference for images as stated by Mark Hill

• Added information below images for a description.

• Added links to source below images about the germa layer of frogs.

• Deleted image -unable to find copyright license in gastrualtion

• Changed to APA, had to look up dates and authors for incomplete references added by other students.

• Finished the glossary of terms

• Worked on current research about Frogs. Added relevant info about usage through history

• Proof read. Added in sentences to make the transition from history of use .

• Read through and edited spelling of development and stages

• Edit all information bout images.
--[[User:Z3295026|Joe Nassif]] 12:47, 14 October 2009 (EST)

--[[User:Z3258567|Sando Rashed]] 09:51, 15 October 2009 (EST) edited all the image names to appropriate titles

== Group Project Updates ==
--[[User:Z3258567|Sando Rashed]] 00:08, 13 October 2009 (EST) i got rid of a few more individual signatures
--[[User:Z3126345|Gang Liu]] 14:42, 8 October 2009 (EST)Hi group, one of the peer comments is to delete individual signature, so i got rid of all the signatures on the page.

--[[User:S8600021|Mark Hill]] 10:08, 10 October 2009 (EST) The [[2009_Group_Project_5#Stages_of_frog_embryology|stage images]] you have begun to add to your project are from [http://www.xenbase.org/anatomy/alldev.do? Xenbase - stages] it is incorrect to give UNSW Embryology as the source as my page just provides links to this external site. "Digitized images and developmental data from Nieuwkoop and Faber (1994) Normal Table of Xenopus laevis (Daudin). Garland Publishing Inc, New York ISBN 0-8153-1896-0." you will need to get permission to use these images in your project.

--[[User:Z3126345|Gang Liu]] 22:22, 11 October 2009 (EST)Thank you Dr Hill. I've just realised. Yes, i will try to get permission from authors.

--[[User:Z3126345|Gang Liu]] 09:22, 14 October 2009 (EST)Hello, Dr Hill. I have tried to contact the publisher regarding permission to reproduce their images on my group project page. So far, i have not received any replies. Could i use your images on unsw embryology?

--[[User:Z3126345|Gang Liu]] 10:12, 14 October 2009 (EST) Hello, Dr Hill I just got the permission to reproduce those images on my page.

== Project Updates ==
--[[User:Z3283499|Antonio Lee]] 10:57, 2 October 2009 (EST) Hi everyone, I will be working with you during the Lab10 Tutorial and here is the news link and PDF of the manuscript for your group exercise. I encourage you to read the paper before the tutorial. Also, please indicate next to the questions below (using either your initials or student number) which one of the four questions you wish to address.
:'''Group 5 :''' [http://www.sciencedaily.com/releases/2009/09/090918111056.htm '''Human Induced Pluripotent Stem Cells Retain Some Gene Expression Of Donor Cells'''] in Science Daily Published online 19 September 2009 [[Media:ANAT2341_Lab10_2009_Group 5 Reading.pdf|Manuscript (PDF): Transcriptional Signature and Memory Retention of Human-Induced Pluripotent Stem Cells]]

----

:'''Question 1. What is the background to the existing problem / disease condition? (z3295026)- JOE NASSIF'''
''

The discovery of neural stem cells, has lead to the exposure that a single cellular factor can be carried out to re-program and stimulate a human cellular component into a pluripotent form, allow the cell to have the ability to distinguish any category of cellular material in the human body. The ability of this process will allow the identification of common cellular material and what is not common for instance abnormal tumour cell or cancer cells, this process of iPSCs is an advantage in recognising normal and abnormal cellular matter extrinistically as the stem cell will recognise what it going to develop into, through signalling and programming. These stem cells are extremely useful in therapeutic uses, muscular dystrophies and replacement of cell into the specific regions of the human body needed to be replaced or repaired.

An arrangement of four particular factors was experimented to generate iPSCs, using knowledge involving viral vectors including viruses with the possibility to influence the transcriptional configuration of the cellular material, at times inducing the cell death process and trying to destroy cancerous material in specific regions of the body.

The mouse and human genetics in relations to iPSCs have revealed to be comparable to embryonic stem cells in relation to the cellular behaviour, gene expression and their potential to make a distinction between different types of cells.

Sequentially in regard to the advantage of reprogramming specific genetic materials, it is necessary to model processes to encourage pluripotency in the alterations of the genome, and it structures. By reprogramming neural cellular materials with the human body and creating iPSCs from human neural stem cells lacking the presence of specific viruses, the scientists developed new understanding of the function of iPSCs.'' --[[User:Z3295026|Joe Nassif]] 13:33, 8 October 2009 (EST)

----

:Question 2. What approach / method did the research team take to tackle / improve the problem? (z3255007)- Sadaf Masood

''Introduction of Viral-free, integration free reprogramming approach, where pluripotent factors Oct4 and Nanog were cloned and transferred into human fetal neural progenitor cells under high frequency, which when expressed itself, became human iPSCs. This is also considered a safe approach in clinical terms as virus will not be affecting the genome.''

:Question 3. What was the breakthrough / major advancement OR failure / drawback? and why might this be of significance?(z3126345) Gary Liu

while both mouse and human iPSCs have been shown to be similar to embryonic stem cells in terms of cell behavior, gene expression and their potential to differentiate into different types of cells, researchers had not achieved a comprehensive analysis to compare iPSCs and embryonic stem cells.

"One reason is that previous methodologies used to derive iPSCs weren't 'footprint free,'" Muotri explained. "Viruses could integrate into the genome of the cell, possibly affecting or disrupting genes."

"In order to take full advantage of reprogramming, it is essential to develop methods to induce pluripotency in the absence of permanent changes in the genome," added Fred H. Gage, PhD, a professor in the Laboratory for Genetics at the Salk Institute and the Vi and John Adler Chair for Research on Age-Related Neurodegenerative Diseases.

:Question 4. What are the next steps in moving forward? What are the next or new hurdles to overcome? --[[User:Z3258567|Sando Rashed]] 14:15, 8 October 2009 (EST)
they have been able to find out that there is a safe way to create induced pluripotent stem cells, but what they are able to research now is that do these cells they have created have a issue with there memories is it affected by using a viral free method.

==Constructive Criticism of Coordinator==
--[[User:S8600021|Mark Hill]] 08:07, 8 October 2009 (EST) The following comments are general in nature in no specific order, as it would be inappropriate to suggest specific changes and then assess the final project. Comments will be added during this week and you still have one week before final submission.

* [[:File:Fertilized_and_Unfertilised_Eggs.jpg]] [[:File:Egg_Development.jpg]] what is the original source that these images are based upon? There is no description on the image page when it opens of what the images are showing.
* Some figure legend titles could be tidier.
* There is no list of changes that have been made in response to peer review process.
* The [[2009_Group_Project_5#Stages_of_frog_embryology|stage images]] you have begun to add to your project are from [http://www.xenbase.org/anatomy/alldev.do? Xenbase - stages] it is incorrect to give UNSW Embryology as the source as my page just provides links to this external site. "Digitized images and developmental data from Nieuwkoop and Faber (1994) Normal Table of Xenopus laevis (Daudin). Garland Publishing Inc, New York ISBN 0-8153-1896-0." you will need to get permission to use these images in your project.

==Constructive Criticism of Peers==

--[[User:Z3218657|Sally Clarke]] 10:12, 1 October 2009 (EST)
Great Assignments guys

- Great use of images

- It jumps straight into the information which can be either a good and bad thing depending on what you are trying to achieve, maybe add in an introductory section which leads the reader on to the next bits of information

- is the anatomy section of the Frog Necessary - remember what we are studying here!!!

- The staging section is good except that you only link to the images - would you be able to have thumbnails of each of them in the table - it would help the information

- Wiki Pages??? Maybe not

- Try to make your information a little more succinct as you repeat information in the timeline and staging sections and remember formatting - history section etc.

- Include the information on why this model is used - advantages and disadvantages of this model maybe

- Current research is good but you should probably include some info on the genome - or a link to find out information about it

Overall its a great project!

--[[User:Z3223194|Bronwyn Lewis-Jones]] 09:06, 1 October 2009 (EST) This is a great assignment. Congratulations. Well set out and good use of applicable images. I think the most important change to make is to include an introduction which gives the reader a brief understanding about the frog (the anatomy section does a good job of this but maybe include a few sentences in an intro) and why it is used in embryology research. Also you could be more specific with your image labels (e.g. "Typical Frog" - why not give us it's biological name if possible). I think you could also cut back on some unnecessary information in the timing/staging section(s). Also it might be a good idea to remove the signatures to allow the reader to focus on the information. Hope you find this helpful. :)

--[[User:Z3218146|Julianna Lam]] 01:39, 1 October 2009 (EST) great work guys.

- history section is lacking information

- the maturation phases are too detailed and i dont think that much detail is required.

- staging and timeline is excellent. it could look better if there were more pictures added into the staging part.

- the glossary is very helpful

--[[User:Z3254857|Begum Sonmez]] 22:49, 30 September 2009 (EST)
Hello Group 5. I'd like to start off by saying that the effort you all have put into you page is impressive. The first thing I noticed was the background information on the frog such as the embryology, growth and development, anatomy, and the egg of the frog. I found this extra information informative, interesting, and due to the lack of text,easy-to-read and engaging. The video under 'The Egg' depicting Early cleavage was an interesting video. I like how it wasn't placed under timeline or stages. The reason is because timeline and stages already has enough images, and this short and simple video provides an introduction to development.

*You all might have noticed there is a problem with the formatting of the History section (the text needs to be 'pulled down' below the image 'Early Development of Frogs'. The same problem is found under the sections 'Abnormalities of the Frog', and 'Current Research'.
*I think the sentence strucutre, and punctuation of the History section should be looked at. For example, '1851 - Henby Nelson(MD): He identified a remarkable fact through frog embryo. Henby observed the first cleavage of the yolk, in the egg of the frog. And corresponds in its line of direction to the longitudinal axis of the body of the embryo of those animals;' should read:
'1851 - Henby Nelson(MD): He identified a remarkable fact through '''the''' frog embryo. Henby observed the first cleavage of the yolk in the egg of the frog. And ('''what? The Yolk?''') corresponds in its line of direction to the longitudinal axis of the body of the embryo of those animals ('''of what animals?'''). This is just something small that should be worked on just to make more sense, but the amount of text you included is good.
*Under Gametogenesis, the sentence 'Gametogenesis is a progression which frog gametes are established from cells, called germ cells.' should read 'Gametogenesis is a progression '''in''' which frog gametes are established from '''germ cells'''.' Again, this is just a small amendment, but it will still be effective.
*Good pictures under 'Egg and Fertilisation' and under 'Gastrulation'.
*Under Gastrulation, the sentence 'In frogs, metamorphosis is related with to the modifications and adaptations as a frog changes environmental habitats from an aquatic to a terrestrial mode.' should read 'In frogs, metamorphosis is related '''with or to''' the modifications and adaptations '''occuring or taking place''' as a frog changes environmental habitats from an aquatic to a terrestrial mode.'
*Too much unnecessary text under 'Maturation phases'. Try condensing the text under '4. Fertilisation of the egg' and '5.Segmentation of the Egg'.
*There is a good amount of information under the 'Structures derived from Germ-layers of frog species' section. It can be improved by listing (in dot form or numbering) the structures instead of including them all in a paragraph. I really liked this section. To the artist of the drawings: great work. I found them really helpful and relevant.
*Under 'Current Research', try to include dates for 'Transgenesis techniques for functional genomics in Xenopus' and 'Verification of messenger RNA'. Also, is there a specific example of a current research under the sub-heading 'Cell Cycle'. This would be more resourceful for the reader.
*The glossary was helpful.
Overall, well done on your efforts Group 5. The pictures are a great asset to this page.

--[[User:Z3252231|Angama Yaquobi]] 22:01, 30 September 2009 (EST)
Congratulation all the team members of group 5, the page looks amazing. Very well researched. So far one of the best looking
page with alot of informative content.Great images used throughout the entire page especially in the section of the growth and modification of frog species.However i suggest few changes can make the page look even better

* Lack of information in the section of history.

* There is too much information in the maturation phase which can be concised to make it much more easy for the readers to acquire the important information.

* For the section of current research more information is needed to give readers a more in-depth knowledge of the current research done on the model.

Overall well researched page. Well done guys. cheers.

--[[User:Z3186093|Jenny Guy]] 19:01, 30 September 2009 (EST)

Improvements:
* The frog...is a specific breed of frog used? Or are many types used for embryological research? This should be stated in the introduction. The image youve used from wiki is fine except its a "typical frog"...what is this? are you forming your page based on this frog?
* I dont believe the anatomy of the frog needs to be stated. We're researching the embryology, and yes this is going to be different to the human, so state the differences that cause embryology problems. Obviously we're going to be different but if you want to state that the frog only has 3 chambers, state that heart research wouldnt use a frog model since its not similar.
* Need to do some formatting - history heading is misplaced, i almost missed it.
* There is a hell of a lot of information to digest for the fertilisation. Would it be possible to cut some of this down? Select the best parts?
* Stages is very plain. Enough said.
* The image of the frog abnormalities...is it in the wrong spot? Shouldn't it be put close to the skeletal abnormalities paragraph - and refer to the image, and not the infectious diseases section.
* In genetics, can you explain why frogs have different numbers of chromosomes. Does this mean that some breeds of frogs can mate because they would have ill adapting chromosomes? How does the chromosomes it does have relate to human chromosomes??
* i got very confused with the subtypes of families of frogs...is the embryological research affected with modern or primative frogs?
* Has the genome been sequenced? Apparently so? Some of the english here needs to be editted. Grammar isnt good, some sentences dont make too much sense.
* Have you listed "links to related resources/research laboratories?" like Mark asked for in the marking criteria?? nope.

--[[User:Z3218792|Gabriela Pinget]] 14:36, 30 September 2009 (EST) Hello! Nice page! Mind if I criticise?

- I like the use of the anatomy of the frog to better orientate the reader. Although it is slightly superflous, it does not contain too much information to look out of place,so it looks good

-Maybe in the intro you should add a little info on why it is a model for embryological studies i.e. its advantages over the others

- I like the clear structure of the history section. It makes it very easy to read and understand.Although, the poor grammar makes it a little hard to understand (e.g. you may want to re-word what you wrote for 1976, it reads as though a woman was impregnated with a frog)

-perhaps there is a little too much detail on the growth and development of the frog. It's a little overwhelming- also quite a bit of repetition in this section

--[[User:Z3217015|Mitchell Mathieson]] 09:32, 25 September 2009 (EST) I think the looks good. However, the information is very spread out all over the place, and there is a bit of irrelevant information, such as the anatomy of the frog. There also seems to be repeated information in the stages and timelines; such as having tables and text to say the same thing. There was a heavy emphasis on the stages of development (it pretty much takes up 3/4 of the page) which probably could have been done more succinctly. The formatting needs a bit of fine tuning (heading separated from their text, and gaps everywhere), but in general it is good; the information is quite useful and well written.

--[[User:Z3224449|Elide Newton]] 14:57, 26 September 2009 (EST)HELLO GROUP 5: Well done on your assignment. my one piece of advice on your assignment is all about improving the flow and purpose of your assignment. Firstly There needs to be a introduction to the frog. why the frog is used as a model for embryology? By understanding the stages of development and timeline of the frog we can study the frog as a model. Why it is a good model and our understanding can be linked to why is has been used in the past and why it is being used currently in the future. hopefully this introduction clarifies the purpose of your information, and gives an outline to what you will cover in the assignment. also there is lots of unimportant information in regards to this assignment which is clouding your purpose of timeline, stages, genetics, past, present and future research. with this introduction paragraph, stating what topics you will cover and how these fit into using the frog as a model for embryology, hopefully it will flow better. all the best!

--[[User:Z3126328|Jin Lee]] 16:32, 26 September 2009 (EST) congulatulation Group5. The assignment looks good however, if you can make some additions it will be even better. Here is my suggestions: firstly the reference needs to be looked after. secondly some of sections are irrelevant(I found the 'anatomy of the frog' is irrelevant) and too much general information about the frog. May be better to focus on the assignment cirteria. For the history section, information is lacking(it's too brief) may be trying to add some more details about the each scietists...eg. in 1976, please mention which doctor you are reffering to. For the current research section, some more information needs. Overall, the assignment is visually well represented but may be concentrate on the main sections like timeline, stages, genetics, history and current research.

--[[User:Z3187802|Vishnnu Shanmugam]] 21:37, 26 September 2009 (EST)Great work frog group. The assignment you have put together is informative and well organized. One of the best features of the project is how clicking on the image takes you to another page with detailed and thorough explanations of the image. It is also good to see that you have added extra sections such as “abnormalities of the frog” and “the egg”. I note that too many groups are only interested in the headings specified in the marking criteria and have not done any extra work. The glossary is also a nice touch. Ways of improving the assignment:

- The background section introducing the frog needs to have information on why the frog model is useful. Include information on spawning, maintenance of specimens, genetic attributes and genetic similarities with humans.

- Although the addition of extra sections is good, it needs to be relevant to embryology. The anatomy of the frog section concentrates on the anatomy of the adult frog which is irrelevant for this project.

- The assignment should contain links to research laboratories and researchers as specified by the marking criteria. The external links do not do this.

- Remove the signature and time stamping at different sections of the assignment. The group project is collective effort, and the final presentation should not look like it has been split up. Do not worry about your contributions as these are logged and available for viewing under the “my contributions link”

- Some links in the text transfer you to Wikipedia pages on the frog....these should not be used as a source of information in academic projects.

- The assignment needs to be properly referenced as there are no references made in the actual text. see www.lc.unsw.edu.au/onlib/ref_apa.html for help with APA referencing

Overall a good project, some changes and additions are necessary to make it outstanding.

--[[User:Z3252340|Emily Wong]] 11:06, 27 September 2009 (EST) Firstly, Great work group 5. This project is very informative, well structured but a little unorganized. There is an extremely large amount of text presented. Perhaps a few more pictures or diagrams to negate some of the written work would be a way to improve the project. The work is well referenced with an extensive reference list. There is a lot of information on content that is not required. A way to improve your project would be to summarise a lot of this unnecessary information and maybe try and place it under one of the content headings. It appeared that a lot of this information was about stages or time points so maybe you could include this information in one of those sections.

--[[User:Z3217686|Thomas Dangerfield]] 14:25, 28 September 2009 (EST)Hey guys! Nice job! Plenty of information present, it just seems to jumble around a lot. Definitely needs an introduction, and possibly the first available section could be moved to after the anatomy of the frog. I don't mind the basic anatomy of the frog by the way, as it provides a little background to what the reader is going to end up with at the end of the development stage. Also the images could have a caption about what is actually happening in the image or what the images are trying to describe. There also seems to be a whole of a lot of information and plenty of images on the development and growth of the frog, but comparatively little on the genetics section. Chromosome maps can be very handy and comparisons with the human genome can help establish a picture of what you are trying to say. Just some organization and possible sifting of information would do the assignment nicely! Still, a very nice job on the frog guys!

--[[User:Z3185685|Sumaiya Rahman]] 17:16, 28 September 2009 (EST) Hey guys! Wow congrats on the assignment. I actually like the extra topics on the page. It makes it interesting and gives a lot of background knowledge to the reader. As mentioned, i am not sure why you have put in your signature stamps, this is not necessary. A lot of good images have been used but maybe instead of using figure 1, figure 2 etc. under the images; you could write what the image actually shows. I think this is what we were told to do? The links to the images in each stage are really good and help convey the information. The other thing that would help improve your page would be the addition of a glossary. Well done overall!

--[[User:Z3215682|Carly Mooney]] 11:56, 29 September 2009 (EST)
I think this was the assignment that looked the most professional. I liked the additional anatomy of the frog section, Few suggestions:
*a proper paragraphed introduction
*perhaps either in introduction of the history of the model needs a small explanation of why you use the frog as a model.
*remove the signatures, it is distracting and looks like it wasn't a group effort
*some sections were well referenced and others not, this needs to be unified.
*I think some of the sections with single images can afford to have those images enlarged slightly.
Overall this assignment looks the most unified of them all so congrats.

--[[User:Z3220040|Joanne Raffel]] 16:41, 29 September 2009 (EST) Well researched page. I would recommend including an introduction, which would make a better transition into the next section, also the growth and development, the egg and the anatomy section could have been condensed into one section. I thought there was too many main headings, I would recommend including subheadings, otherwise the information seems disjointed. I also got very confused reading through the page as I wasnt sure which heading was apart of another or whether it was something completely new. The history section was well formatted, however more information would have been appreciated as there didnt seem to be much of the actual history, more of a timeline of the frog. I thought the gametogenesis section was irrelevent. I also didnt need to know who wrote what section, this is a group assessment. Some of your headings could have been phrased more appropriately and clearer. The egg and fertilisation section would have been more impressive with subheadings rather than continuous main headings, whereby allowing the information to flow, also some of the information wasnt introduced in each section, it was just assumed. The maturation section would be better formatted in a table rather than a chunk of text. Cleavage, gastrulation, growth and modification, germ layer origin and structures derived from germ layer would be better as one section rather than multiple. The life cycle was extremly short and lacked information. The timeline was well formatted however I would have liked pictures. The staging section was organised clearly, however I would have liked to have seem part of the image rather than having to see it via the link. The abnormalities and genetics section would have been clearly as paragraphs with more information describing what is occuring rather than listing it, pictures would also be appreciated if possible. The current research section covered a number of topics however each section was very short. The glossary was appreciated however some of the words werent necessary (i.e. aquatic). Overall a very good page with some interesting images.

----

--[[User:S8600021|Mark Hill]] 01:50, 8 September 2009 (EST) Still coming along, you have a lot of interesting pieces of information and some fair images. But how do the images relate to the text and where is the linkage? It is always easier to paste a whole lot of text information without interpreting what it actually means. Some of the information is good, tough some text also looks to be sourced without referencing. Overall the page lacks an integrated feel and structure.

--[[User:S8600021|Mark Hill]] 08:45, 21 August 2009 (EST) This is a good start. It is important that the project page content/structure reflects what all members of the group have in mind. There should be a list of relevant references now on this discussion pages.

== Background Reading ==

--[[User:Z3255007|Sadaf Masood]] 21:44, 8 September 2009 (EST) This link is for you Gary
http://www.xenbase.org/xenbase/original/atlas/NF/NF1-10.html

--[[User:Z3126345|Gang Liu]] 15:18, 23 September 2009 (EST) hi could anyone tell me how to upload pictures on the main page. i'm trying to upload pictures from this link http://www.xenbase.org/xenbase/original/atlas/NF/NF1-10.html, into the last column of stages of frog embryo table. cheers!

Hey guys!!

I have only met one person in the group..and that was today in the lecture (3/08/09)

Still missing out on the third person here!

Lets decide on the animal guys before the lab!!!!

Cheers!

--[[User:Z3126345|Gang Liu]] 15:22, 16 August 2009 (EST)Hi all, I'm Gary and i've just enrolled into this subject mid-week last week. Will try to catch up with the group assignment and individual homework.

--[[User:Z3126345|Gang Liu]] 14:54, 19 August 2009 (EST)Hi group, since we are dividing the assessment. I would like to work on sections such as "The egg", "Fertilization", "Cleavage", "Gastrulation", and "Hand-drawing diagram". Thank you.

--[[User:Z3126345|Gang Liu]] 12:56, 20 August 2009 (EST)Hi all, Joe is working on the first six subheadings. And i'm happy to take whatever subheadings the rest of the group is not working on. Thank you.

--[[User:Z3126345|Gang Liu]] 14:07, 20 August 2009 (EST)Hi all, after this week's group dicussion in the lab, we split the tasks as the following:
*Joe is responsible for subheadings such as egg, fertilization, cleavage, gastrulation, differentiation and growth;
*Gary is responsible for subheadings such as anatomy of frog, timeline and stage(introduction), and abnormalities;
*Sando is responsible for subheadings such as reproduction(male and female)+random subheading;
*Sadaf is responsible for subheadings such as current research, genetics and glossary.

--[[User:Z3126345|Gang Liu]] 17:26, 23 August 2009 (EST)Hi all, should we mention ''Xenopus'', part of frog family? --[[User:Z3126345|Gang Liu]] 09:29, 27 August 2009 (EST)Please ignore this line

--[[User:Z3126345|Gang Liu]] 18:00, 26 August 2009 (EST)Joe, thank you for updating our group page. Will upload my contents as soon as possible.

Hey guys, i need the list of words for the glossary or do u want me to pick them out myself?
thanks!--[[User:Z3255007|Sadaf Masood]] 10:47, 27 August 2009 (EST)

--[[User:Z3126345|Gang Liu]] 11:24, 27 August 2009 (EST)Hi, sadaf, will upload my glossary by tomorrow. Thanks.

--[[User:Z3126345|Gang Liu]] 11:30, 27 August 2009 (EST)Hi group, i just realised there is no one doing history part. Is there anyone would like to take this part? Or else, i'll work on it. Let us know.

http://books.google.com.au/books?id=OeAf7ChZD8QC&printsec=frontcover&dq=frog+embryology&lr=#v=onepage&q=&f=false

sick website

http://www.youddl.com/

EGG:

http://www.youtube.com/watch?v=GO5YN_t1fqw
--[[User:Z3258567|Sando Rashed]] 18:17, 23 September 2009 (EST) as late as im posting this i havent had time this past week to upload my notes but im putting them up now

--[[User:Z3258567|Sando Rashed]] 18:18, 23 September 2009 (EST)Gastrulation of a frog embryology
An invagination of cells that is found in the area of the embryo where it occupies the middle of the gray crescent, this is the beginning of gastrulation.
This beginning is what creates the blastopore which in the future will become the anus, and a group of cells that would later on produce the notochord which will eventually become the backbone (also known as the speeman organizer). Stimulates the ectoderm to form neural tissue (rather than it forming skin), so it begins the staging of the neural folds, which eventually the tips of the folds will form the neural tube which will become the spinal chord and the brain.
During gastrulation three layers start forming, these layers are known as the ectoderm, endoderm and the mesoderm.
Layer Forms out of it

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Ectoderm which may form the Brain, skin, spinal chord

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Mesoderm which may form the Notochord, muscles, brain

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Endoderm which may form the Inner lining of lings, bladder, thymus forms here.

--[[User:Z3258567|Sando Rashed]] 22:24, 23 September 2009 (EST)Cleavage = the repeated division of a fertilised ovum
When the zygote nucleus forms the first cleavage forms, this nucleus undergoes a number of mitosis processes, a wrinkle forms down longitudinally passing the poles of the eggs where the sperm enters. This is how the egg is split up into two halves and this process is what forms the 2-cell stage.
The process of the second cleavage is the process that allows the 4-cell stage to occur, the wrinkle runs through the poles at right angles instead of running through it longitudinally.
The 8 stage cell is formed during the third cleavage it cuts across horizontally but it cuts through closer to the animal poles rather than the vegetal poles.
As cleavages continually occur a 16 and 32 cell embryo are formed, and as these cleavages continuously occur the cells closer to the animal poles divide more rapidly and in more numbers compared to the vegetal pole. Eventually with all these cells continuously forming the blastula forms and a blastoseal which is a fluid filled cavity forms within it (no growth of the embryo has formed).
--[[User:Z3258567|Sando Rashed]] 23:06, 23 September 2009 (EST)Anatomy of a Frog
----

The anatomy of a frog has many specialized features that are unique to the frog to help them live in their environment, they have long sticky tongues that help with them to grab food, they have specialized bones in the legs to help them jump.
When under water frogs are able to breathe through their skin, the oxygen is able to diffuse straight into the blood through the pores on the skin; they also have lungs that allow them to breathe on land.
In frogs they have 3 valves instead of the 4 valves in humans, they have one ventricle and two atria’s, the spiral valve does not allow blood with oxygen to mix with blood that has no oxygen.
Frogs are able to listen to sounds that have a low pitch through their skin as well as hearing sounds with a high pitch through their ears.

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The Egg

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The egg of a frog is approximately 1.6 million times larger than a normal frog cell. While all the embryological development is occurring through time it will eventually become a tadpole.
The egg can be divided into three different regions, the top part of the egg is known as the animal pole, the bottom half of the egg is known as the vegetal pole and a segment between the animal and vegetal pole is known as the gray crescent.--[[User:Z3258567|Sando Rashed]] 10:09, 24 September 2009 (EST)

Fertilization
----

This occurs once the sperm cell has inserted, following the insertion of the sperm cells meiosis II is completed, there is a 30 degree position change of the cytoplasm, gray crescent allows this change to be visible in some amphibians, the gray crescent is able what determines the expect ted outline of how the frog will form. The sperm cell joins with the nuclei of the egg which forms the diploid zygote nucleus. --[[User:Z3258567|Sando Rashed]] 10:09, 24 September 2009 (EST)

2009 Group Project 5

2009-10-14T22:50:21Z

Z3258567: /* External Links */

== The Embryology of Frogs ==

== The Frog ==

[[Image: Frog species .jpg|thumb|left|Image details: Wikipedia (2009) Frog species[http://en.wikipedia.org/wiki/Frog#Uses_in_agriculture_and_research].jpg]]

Frogs are scientifically identified by the structure of their long posterior limbs, a petite framework, webbed fingers and feet, budged eyes and the lack of a tail. The majority of frog species are extensively recognized as outstanding jumpers, due to their long, dominant legs, which are adaptations to progress jumping performance during activities. The Frog is one of the most frequently studied species in experimental embryology and most anatomical sciences. ''The Frog is a practically effective model for human embryological development given that the Frog:''

- Comprises of genes which can be effectively manipulated.

- Comprises of similar homogeny with humans species.

- Reproduces a large quantity of offspring in a short period of time.

- Are small species which can be simply sustained.

- Are not extremely luxurious and expensive.

== The History of the uses in agriculture and research ==

[[Image: Frog experiments .jpg|thumb|right|Image details: Scans of chemically cleared and dyed preserved deformed frogs and toads [http://www.sat.qc.ca/upload/residence/frog-04.jpg].jpg]]

There are numerous types of frog species that have been manipulated in many developmental experiments. The frog was traditionally used by countless of the early embryology investigators and presently there are several diverse molecular mechanisms regarding progression of the frog. Theses include:

'''1.''' Food source; frog legs are a delicacy and are eaten in European countries and in many parts of South American regions.

'''2.''' Frogs have the finest biochemical dissection of phenomena that take place in the egg and oocyte. Frogs are the evolutionarily closest to mammals, commonly used as a vertebrate model.

'''3.''' Frogs lay thousands of outsized eggs, from which cell extracts can be readily prepared that is capable of recapitulating most molecular phenomena in a test tube.

'''4.''' Frogs have been commonly used as a laboratory system for a very long period, and have an extensive history of producing crucial observations in countless fields of biology.

'''5.''' Frogs have a important historical connection to the study of epigenetics (John Gurdon-vertebrate cloning and reprogramming) which has been mostly performed on frog species.

'''6.''' Frogs also have very strong evidence of pattern formation and early development, as the embryos are large in size and experimentally manipulative.

'''7.''' Recent research into the biochemistry of chromatin and epigenetics has been performed with frog species and mammalian cultured cells.

'''8.''' The biggest weakness of the Frog model system is the difficulty of performing genetic experiments and analysis, as frogs are allotetraploid, meaning they take approximately a year to fully develop to sexual maturity, and the genome has not been completely sequenced. Nevertheless, biochemical manipulations of cell extracts, such as immunodepletions and application of heterologous DNAs and nuclei can avoid the need for genetic exploitation.

----

== Growth and development of the Frog ==

[[Image: Mature develop frog.jpg|thumb|Image details: Wikipedia (2009) Red Eyed Tree Frog Figure 1 Primary source:[http://en.wikipedia.org/wiki/File:Red-eyed_Tree_Frog_-_Litoria_chloris_edit1].jpg]]

* The frog is a well recognised species, abundant predominantly in ponds, swamps, though various species may also exist in damp or shady environments distant from moist habitats.

* Eggs of specific frogs are easily obtained and may be examined in from the beginning of fertilization onwards. The phases of embryonic development differs in various chordates, yet the typical phases are basically apparent in all frog species. The differences are associated principally to the amount of yolk particles present in an egg.

* The yolk particles offer nourishment of the developing embryo. The process of frog development will be discussed from the phases of gametogenesis to the adult stage.

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== The Egg ==
[[Image:Development of Poles in frog Fertilization.jpg|thumb|left|Development of Poles in Frog Fertilisation:J,Nassif 2009.jpg]]

- The embryology of a frog egg is a vast cell; its dimensions are approximately 1.4-1.6 million times larger than a typical aquatic species egg cell. Throughout the frog’s embryonic maturation period, the egg will be transformed into a tadpole encompassing millions of cells but still remains with its constant volume of genetic material, the vast prodction of cell have been illusttrated in the figure on the right revealing the production of eggs from female frogs. [http://en.wikipedia.org/wiki/Microhylidae]

- The early embryonic frog structure consists of three main segments the superior hemisphere known as the animal pole which is usually visible as a grey coloured area. The innermost layer appears to be between the outer two sections known as the gray crescent represented in black. Inferiorly, represents the vegetal pole typically lighter than the superior compartment illustrated in gold.

VIDEO RESOURCE: [http://www.youtube.com/watch?v=GO5YN_t1fqw&feature=related]

[[Image:Early Development of Frogs.jpg|thumb|left|Early Development of Frog:J,Nassif 2009.jpg]]

==History of frog embryology use ==

*'''1851''' - ''Henby Nelson''(MD): He identified a remarkable fact through the frog embryo. Henby observed the first cleavage of the yolk, in the egg of the frog. And cleaved structure corresponds in line of direction to the longitudinal axis of the body of the embryo of the frog species.

[[Image:Wilhelm Roux.jpg|thumb|right|Wilhelm Roux[http://images.google.com.au/imgres?imgurl=http://www.todayinsci.com/R/Roux_Wilhelm/RouxWilhelmThm.jpg&imgrefurl=http://www.todayinsci.com/6/6_09.htm&usg=__qRLTEMTHdZpAHxiNX12hWjcm9tA=&h=125&w=100&sz=4&hl=en&start=2&um=1&tbnid=LIKIwZTqCpk7MM:&tbnh=90&tbnw=72&prev=/images%3Fq%3DWilhelm%2BRoux%26gbv%3D2%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

*'''1888''' - ''Wilhelm Roux'': Wilhelm Roux attempted to solve the above observation by damaging one cell of a two-cell frog embryo with a hot needle. The cell stayed in place. However, it did not develop further. Its partner developed into a left or right half-embryo;

*'''1907''' - ''John Hopkins'' hospital: In order to identify the cellular source of neuronal fibres. Scientist placed small portions of frog embryo spinal cords in lymph on a microscope slide and was able to observe clear cut neuronal sprouting.

*'''1951''' - ''Robert Briggs'': Robert Briggs was able to clone a frog embryo by substituting the nucleus of an unfertilized frog egg cell with the nucleus of a frog embryo cell. This process is known as nuclear transplant, has formed the basis for all cloning.

*'''1952''' - ''Robert Briggs and T.J. King'': Robert Briggs and T.J. King used frog for test experiment. Because the size of the eggs in the frogs are enormous compared with those of mammals, which make them easier to manipulate.

*'''1976'''- Using the technique that had been successful in cloning frog embryos, the doctor transferred the nucleus of one cells into a donated egg cell. As an embryo began to develop, it was implanted into the uterus of a young woman.

*'''1997''' - ''Wilmut and Campbell'': Utilizing the cloning technique from frog embryo, Drs. Wilmut and Campbell tried the starvation technique on embryo cells to produce Megan and Morag, the world's first cloned sheep and, until now, the most famous sheep in history.

*'''2000''' - ''Tokyo University'': Scientists at Tokyo University have grown artificial eyeballs. Scientists formed them in tadpoles by using frog embryo cells.

*'''2001''' - ''Advanced Cell Technology'': Scientists from Advanced Cell Technology announced production of a human embryo clone. This is significant as its parthenogenesis has been artificially induced in frogs.

[[Image:John Gurdon .jpg|thumb|right|John Gurdon [http://images.google.com.au/imgres?imgurl=http://www.pnas.org/site/misc/images/gurdon.jpg&imgrefurl=http://www.pnas.org/site/misc/classics4.shtml&usg=__1p-GA1PdOYsxKL-cznMb3RHCm98=&h=526&w=400&sz=223&hl=en&start=1&um=1&tbnid=9k4lhuLssiWCAM:&tbnh=132&tbnw=100&prev=/images%3Fq%3DJohn%2BGurdon%26gbv%3D2%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

*'''2002''' - ''John Gurdon'': John Gurdon from Wellcome Cancer Research Institute in Cambridge experimented on cloned frog embryo.

== Gametogenesis ==

* The sexual reproduction occurs through the fusion of either mature reproductive cells or germ cells known as gametes, which include the sperm from the male frog and ova from female frog species so as to form a single cell, the fertilized zygote. The gametes are typically developed in parents of different sexes . [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

* Males gametes is a spermatozoon , the female frog gamete is an ovum. Each gamete is formed by a process, recognised as maturation or gametogenesis in gonads. The typical male frog gonads are testies in male, while the female gonads are ovaries. The synthesis of both gonads is associated with the process of fertilization. [http://en.wikipedia.org/wiki/Microhylidae]

* The zygote changes into a mature frog through the process of embryology and metamorphosis. Gametogenesis is a in progression which frog gametes are established from germ cells. Initial germ cells are called primordial germ cells, which can be recognised extremely early in the life of frog species.

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== The Egg & Fertilization ==

[[Image:Fertilized and Unfertilised Eggs.jpg|thumb|left|Fertilized and Unfertilized Eggs:J,Nassif 2009.jpg]]

[[Image:Egg Development.jpg|thumb|left|Egg Development:J,Nassif 2009.jpg]]

- This occurs once the sperm cell has inserted, following the insertion of the sperm cells meiosis II is completed, there is a 30 degree position change of the cytoplasm, gray crescent allows this change to be visible in some amphibians, the gray crescent is able what determines the expect ted outline of how the frog will form. The sperm cell joins with the nuclei of the egg which forms the diploid zygote nucleus. --Sando Rashed 10:09, 24 September 2009 (EST)

- The early phases in the development of the egg is visible, but must be studied in tadpoles throughout maturation. In embryonic tadpoles of about 10 millimetres in length, soon after the opening of the oral cavity, a pair of longitudinal ridge-like thickenings of peritoneum becomes apparent along the posterior surface of the body cavity situated near to the mesentery and along the inner boundaries of the kidneys. Genital ridges are established in all tadpoles of this age, sex is not distinct until a later period. The development of the egg is illustrated in the figure on the left revealing the structure of a developed egg and a mature of egg.

[[Image:Fertilisation life cyle.jpg|thumb|Fertilization of Life cycle:Derived from primary source:[http://en.wikipedia.org/wiki/Frog]]]

== Maturation of the Egg ==

- The eggs have currently accomplished their full size, and develop from the exterior of the ovaries like a small shot, but they still have to pass through the course of maturation before they are prepared to be fertilised. This progression of maturation relates to the nucleus almost completely.

- The nucleus component, containing the nuclear fluid that excludes through the nuclear membrane into the substance of the egg, a great segment of the nuclear reticulum vanishes and becomes degraded into separate globules known as nucleoli, but a extremely small division remains in the midpoint as a slender intricately thread recognised as the nuclear skets.
Relative to the egg getting discharged from the ovary, the follicles shatter allowing the eggs to fall into the abdominal cavity of the frog species, the egg then passes forwards, directly by the contraction of the muscular wall, somewhat by the movement of the cilia of the peritoneum, to the apex of the oviduct, which positioned at the anterior compartment of the body cavity opposite to the roots of the respiratory organs.

- The terminal part of the oviduct establishes a thin-walled pouch capable of great swelling, inside which the eggs gathers in large numbers. In conclusion, the eggs are migrated out through the cloaca into water which the albuminous investments of the eggs rapidly augment to form the gelatinous mass of the frogs spawn.

== Maturation phases ==

'''1. Nuclear skein''', moves from the midpoint of the egg to its outer surface, which it reaches opposite the midpoint of the black pole. The skein, subsequently an unevenly twisted thread, now presumes the specific arrangement of a nuclear spindle, for instance may be visible in the nucleus of an epithelial or additional cell instantly prior to division of the cell occurs.[http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

'''2. The first Polar Body,''' regarding the instance the egg is laid, but prior to its fertilistion, the egg develops a considerably flattened appearance at its upper or black pole, a definite sum of fluid being exuded among the egg and the vitelline membrane. The nuclear spindle currently separate into two identical segments, one of which remains with the egg, and the supplementary is extruded as the first polar body, a small ovoidal white globule, which is situated on the surface of the egg surrounding the exuded peri-vitellline fluid.

'''3. The Second Polar Body''', half of the nuclear spindle that stay behind then splits into two equivalent divisions, one of which remains inside the egg as the female pronucleus, whereas the other segment is extruded as the second polar body, a small white globule extremely related to the first polar body, and like this positioned in the perivitelline fluid on the superior portion of the egg.

'''4. Fertilisation of the egg''', includes the synthesis of the spermatozoon with to egg, specifically, synthesis of the nuclei of these two bodies. The spermatozoa, subsequent to being shed over the seed by the male, distribute vigorously by means of their extended tails, break through the gelatinous investment of the female eggs, bore their way through the vitelline membrane and so go through into the eggs themselves, which they penetrate relative to the superior or black hemispheres.
* Subsequently, an hour following the spermatozoon has entered; a progression may be visible projecting within from the exterior segement of the egg, with a liquid spot in the mid point. This liquid centre is the nucleus of the spermatozoon, and is said to be the male pronucleus, it break through beyond into the female egg, transporting the specialised pigment into it, so that it appears bounded by a pigmented capsule linked with the exterior of the egg by a pigmented stalk.

* By this instance, the second polar body has been established and extruded, and the female pronucleus is merely the only component of the primary egg nucleus still present. Both the male and female pronuceli, which are at initially distance separate to each other, merge and after having enlarged significantly in size then fuse mutually about two and half hours after fertilisation has originated to produce the segmentation nucleus.
* The segmentation nucleus is a huge sphere-shaped vesicle embedded in delicately granular protoplasm, and bounded by a distinct capsule of pigment, its arrangement by the synthesis of the male and female pronuclei completes the action of fertilisation. Specifically female pronucleus may be observe as an imperfect nucleus, and consequently result in the course of fertilisation. The nucleus of the spermatozoon or male pronucleus, replaces the component of the egg- nucleus which has been misplaced as the polar bodies.

'''5. Segmentation of the Egg''', the initial phase of growth consist in constant separation of the egg, whereby it becomes transformed from the unicellular state, which is everlasting only in the lowest species, to muliticelluar state charactertics of all higher species. To these early processes of growth the names segmentation is specified. Shorty subsequent to the competition of fertilisation and arrangement of the segmentation nucleus this later misplaces its sphere-shaped appearance and develops to be spindle-shaped, the yolk granules at the equivalent instance showing a tendency to develop into lines distributing outwards from the distal segment of the spindle.
* The nucleus now split into two halves, which shift away from one another, the yolk granules are likely to combined themselves around the two nuclei, and a slender vertical plate of delicately granular substance is left, dividing the egg.[http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

* Superiorly the eggs depression now becomes visible, initially as a small cavity and then develops as a groove, which almost immediately extends all round, and speedily deepening, splits the egg into two entirely separate halves along a plane equivalent with the vertical plane.

* Shorty after, the two nuclei soon separate again into two, and therefore a second cleft is created in the same state as before, its additionally in the vertical plane, however in a plane at 90 degrees to the initial one, and on its finishing point the egg comprises of four accurately similar segments, each containing a nucleus. The third cleft is horizontal in shape, but not equal, lying closer to the superior than the lower pole, it segregates each of the four cells into, an superior smaller and a inferior larger pole

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== Cleavage ==

[[Image: Frog Cleavage development.jpg|thumb|left|Cleavage Process details:[http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/F/FrogEmbryology.html].jpg]]

* The egg of the frog is scientifically identified as’ telolecithal’ meaning there is a outsized amount of yolk concentrated at a single pole, in contrast to the concentration of cytoplasm and the site of the nucleus. The cleavage phases are holoblastic, therefore the total and after the second cleavage they are asymmetrical .The initial cleavage stage appears about two and half to three hours after fertilization. It commences as a minor depression in close proximity to the centre of the animal hemisphere. It appears as if some interior force is pushing the surface the egg towards the centre. This small upturned fold steadily continues in the form of a channel until it surrounds the egg. This groove is shallow in the commencement, but develop into deeper eventually separating the fertilized egg into two halves recognised as the blastomeres. [The figure on the left symbolise the development and growth of the frog embryo during cleavage].

* Internally the separation is mitotic, consequently each daughter cell contains a nucleus resulting from the copulation nucleus of the fertilised egg. This cleavage is vertical, the two cells are indistinguishable in respect of cytoplasm, pigment and yolk. The subsequent cleavage appears about an hour after the first. The channel of this cleavage begins at the centre of the animal hemisphere, is at right angles to the first and is vertical. This divides the egg into four blastomeres. The fourth blastomere so produced are not qualitatively equal, since of these only two contain the material from the gray crescent. The cleavage begins about thirty minutes after the second is completed or four hours after fertilisation. the cleavage plane of the third furrow is horizontal and slightly above the equator. Thus the four upper cells are a little smaller than the four lower cells. The smaller blastomeres are called micromeres and the larger blastomeres are called macromeres. The fourth cleavages follow 20 minutes after the third and tend to be vertical. This is usually a double furrow.

* The cleavage rate is accelerated with each of the early divisions and since the blastomeres are of unequal size and have varying amounts of cytoplasm and yolk, synchronous cleavage is lost and there is an obvious overlapping of the division. The upper most cells divide more rapidly than the lowermost cells. From this point onwards perfect symmetry in cleavage and in blastomere is very rare, although the embryo developed perfectly. The fifth cleavage is also doubled, appearing first in the upper hemisphere and then in the lower.

* The cleavage thus far follows the rule that each cleavage plane comes in at right angles to the previous one. The subsequent divisions become so irregular that it is previous one. The subsequent division become so irregular that it is impossible to trace out any plan or procedure. The segmentation continues more rapidly in the pigmented regions, since at that place the protoplasm is most dense, whereas, yolk which is very abundant in the vegetal side delays cell division. The multicelluar embryo at this stage is called morula by some biologists.

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== Gastrulation ==

[[Image:FROG GASTRULATION .jpg|thumb|left|Frog Gastrulation Image details:[http://www.google.com.au/imgres?imgurl=http://bio1903.nicerweb.com/Locked/media/ch47/47_12FrogGastrulation.jpg&imgrefurl=http://bio1903.nicerweb.com/Locked/media/ch47/gastrulation-frog.html&h=540&w=480&sz=46&tbnid=N78sHjELreGGSM:&tbnh=132&tbnw=117&prev=/images%3Fq%3Dfrog%2B-%2Bgastrulation&hl=en&usg=__4VK9FYLft0W-4lBe6p5EtQAMiaI=&ei=qPy5SurtMJvE6wON8JmdAg&sa=X&oi=image_result&resnum=4&ct=image].jpg]]

''The phase of Blastulation is followed by the unique developmental progression of gastrulation. The process of frog gastrulation involves the following processes.''

'''1. Epiboly Phase'''

The pigmented cellular materials of blastula have the propensity to overgrow the yolk cells within the developing content. This course which is known as epiboly commences gradually in the final blastula and rapidly accelerates with advancing gastrulation development. The cellular matter within the animal pole reproduces and matures on all sides except in area surrounding the dorsal lip of the blastopore has been established.

'''2. Convergence'''

Scientists suggested that the unfolding was thought to result in spreading of the superficial cells over a substrate with suitable absorption properties. Consequently epiboly and convergence are an outcome to this spreading tendency, which is actually increased by a reduction in surface tension of the distributing cells.

'''3. Rotation'''

The epiboly phase is maintained until the region of the dorsal lip has migrated and is a to some extent greater than 90 degrees and the region of the white blastopore is reduced to small circular rings. This section will be positioned away from the developing vegetal pole. Laterally the complete developing gastrula has been rotated to a horizontal axis, allowing it to lie at right angles to the original median plane of the egg. Therefore, the course of rotation is such that the dorsal lip is practically pushed backwards in one direction as rapid or quicker than epiboly moves it forward in the other. The outcome will be that the blastopore produced at roughly the vegetal pole is posterior, and the dorsal and ventral lips are essentially dorsal and ventral. This in addition allows the eggs to form the antero-ventral side of the potential embryo whilst the area marked by the grey crescent is to develop the dorsal segment.

'''4. Invagination'''

Visible is a small fissure- like invagination which is apparent in the middle between the equator and the vegetal segment. The most superior or dorsal border of the cleft produce the dorsal lip of the blastopore. This imput move back and forth on the dorsal plane near the dorsal lip and migrates around the boundaries of the blastocoel in company with the extension of the lateral lips. This adapted invagination is maintained until the blastocoel cavity has been almost abolished; excluding the slender opening separating epiblasts from the hypoblast, the new segment formed is known as the archenteron cavity.

'''5. Involution'''

- Additional to previous course of action a distinct involution also occurs at the blastoporal borders. This is mainly dynamic at the median dorsal lip and gradually more less as it shifts across either side until it reaches the ventral lip where it constant.Throughout this progression, cells positioned beside the superior boundaries of the blastoporal lip migrate over the lip to the interior portion of the lip. These cells are remained within the embryo along the internal edge of the blastopore. This indicates the root of archenteron is composed of involuted cells and beyond this the external layer known as the ectoderm. The base and lateral sides are enclosed mainly of endodermal cellular material, which have been established from larger yolk cells, situated in the vegetal pole of the blastula.

- In the final phases of the gastrula development, the cells contributing to the floor of the archenteron, thin out significantly where they surround the blastocoel.
The hemispherical shaped dorsal lip of blastopore which become visible at the commencement of the gastruation stage carry on to augment, initially becoming semicircular, then transform into a horse shoe shaped and then finally forming into circular band. The band is the accomplished by the blastopore. Various yolk cells of vegetal pole present in the section are crowed into the blastoporal cavity where they form a gathering identified as a yolk plug. Blastopore rapidly reduces in size while the archenteron is still developing and becomes completely formed in the final stage; the yolk plug appears as only a small oval on the gastrula.

==Growth and Modification of Frog Species==

'''1. Changes in habits and habitats:'''

'''a)''' In frogs, metamorphosis is related with to the modifications and adaptations as a frog changes environmental habitats from an aquatic to a terrestrial mode. Metamorphosis has modified the adaption of frogs as this alteration it began during the aquatic adaptations in the surface of water to breathe air. Subsequently, it continues the terrestrial surroundings, therefore the frog species become abundant in vegetation area allowing the frog to transform in to amphibious species.

'''b)''' The transition during metamorphosis is linked with a change in food chain. The tadpoles being the embryonic origin of frogs are herbivorous, feeding on algae and green matter, which they collect by the adapted feature such as their teeth surrounding their mouths. Adult frogs, alternatively, are classified as carnivorous feeding on insects and worms. Occasionally, they also consume larger prey, for instance smaller frogs species and even little birds and rodents which they dominant and ingest.

[[Image:Development of frog from sperm to mature structure.jpg|thumb|left|Development of Frog from sperm to mature structure Image details:J,Nassif 2009.jpg]]

'''2. Changes in Morphology'''

These include the decrease or complete absence of specific organs or structures which are essential during development of early frog embryology, but not critical in the mature frog species. The significant alterations of this nature include the following developmental structures.

'''a)''' The long tail of the tadpole alongside the fin folds is absorbed again during metamorphosis and becomes absent at the final stage of the metamorphosis.

'''b) '''The developing gills are resorted, the gill clefts are congested and the branchial cavities start to become absent. The reabsorbtion of gills also takes place by autolysis.

'''c)''' The teeth of the perioral disc additionally the homey lining of the jaws are shed.

'''d)''' The lateral line sense organs within the skin of tadpoles vanish throughout metamorphosis.

'''e)''' The cloacal tube begins to condensed and reduced.

'''f)''' Various blood vessels, together with parts of the aortic arches, are reduced during mature development.

(The figure on the left represents the transformation from a tadpole to a developing structure.)[http://science.jrank.org/pages/2862/Frogs-Adult-morphology.html]

'''3. Progressive or constructive changes'''

This process comprises of the development of specific organs which mature into functional systems only during metamorphosis.

'''a)''' During development the limbs continue to augment in size and differentiation. The forelimbs, which in the tadpole mature under the opercular membrane, which then break through to the exterior. Simultaneously there is a increase in the length and strength of the hind limbs, joints develop in them and the toes become visible.

'''b)''' The middle ear becomes apparent in relation with the first pharyngeal pouch. The tympanic membrane matures. It is bounded by circular tympanic cartilage which allows the frog to retain air.

'''c)''' The visual organs bulge up on the dorsal surface of the head developing the nictitating membrane.

'''d)''' There is augmentation of the tongue and the formation of thevomerina teeth.

[[Image: Growth model.jpg|thumb|Growth Model Image details:J,Nassif2009:]]

'''4. Remodelling of some structures'''

Systematic organs which operate both in the early embryonic larva and the mature adult change their differentiation during metamorphosis so as to meet the requirements of the adult mode of life and due to the habitat adaptations. The figure on the right illustrates structures developing from specic germ cell layers.

'''a)''' The skin of the embryonic tadpole is lined with a double-layered epidermis. The number of layers of cells in the epidermis augments throughout metamorphosis. Superficial surface layers become cornified. Multicellular mucous and serous glands originate in the skin. The pigmentation of the skin continuously changes, new patterns and colour start to form.

'''b)''' There is a lengthening of the mouth gap as a result of rotation of the quadrate cartilage and the true jaws become functional.

'''c)''' The tongue rapidly progresses and becomes larger and more muscular.

'''d)''' The eyes become more specialised.

'''e)''' In early tadpoles, the GIT is extremely long and wound up into a spiral folds. The intestine become greatly lengthened in herbivorous species due to the vegetables food chain.[http://en.wikipedia.org/wiki/Frog]

'''5. Development of the reproductive system'''

(The figure below represents the reproductive and development cycle of a frog as it transform from egg to frog specie.)

In tadpoles, right after the mouth is being formed, two indentation like thickenings of peritoneum begin to appear near the body cavity (dorsal surface), which is nearest to the mesentery which is near the developing kidneys. These appear in all tadpoles.

These indentations appear here because of a change in the endothelial cells, everywhere else they are usually flat looking cells but they undergo a change and in this particular area become somewhat cuboidal/columnar.

Later on the indentations become more obvious due to the epithelial cells replicating numerously to form a thick layer. The posterior two thirds of the indentation for the female is the ovary and for the male it is the testis. The third that is left differentiates and becomes fat for the body.

[[Image: Mature frog life cyle.jpg|thumb|200px|left|Mature from life cycle Image details:Derived from primary source:http://www.scienceclarified.com/images/uesc_01_img0038.jpg]]

[[Image: Developing frog.jpg|thumb|Developing Frog Image details:
[[Image: Mature develop frog.jpg|thumb|Image details: Red eyed tree frog litoria chloris source:[http://en.wikipedia.org/wiki/File:Red-eyed_Tree_Frog_-_Litoria_chloris_edit1.jpg]].jpg]]

===Delamination===

Delamination indicates a mass separating a group of cellular matter from other cellular groups. It has been illustrated that the division of notochord, mesoderm and endoderm tissues from each other to form distinct cellular masses is completed by the progression of delamination, subsequent to these materials moving to the inside throughout gastrulation. During the developing gastrula, the germ layers are all recognized. These distinct segments of the embryo develop from these germ tissue layers.

===Polarity and Rotation===

Throughout fertilisation to the beginning of gastrulation, the frog’s egg continues in the original location in relation to its polarity. Subsequent to gastrulation its polarity begins to differentiate. This progression is linked with migration of materials within the gastrula and can be responsible for the alterations of the centre of gravity.

===Closing of Blastopore===

Subsequent to the formation of the gastrula, the blastopore is visible as a tiny round circular filled cavity containing the yolk plug. As it continues to reduce in dimension, it represented as a pear-shaped outline through the mutual approach of its lateral lips. Through it final progression these fuse entirely to produce a longitudinal groove, the streak which continue dorsally and ventrally in a small aperture. The inferior aperture closes, resulting in a depression called the anal pit. The superior region remains open for some period and begins to as the neural groove is laid down.

===Post Gastrulation or Organogenesis===

Throughout the duration of pre-gastrulation, all tissues for different organs vanish from the surface of blastula and migrate inside to take their final arrangement in the embryo structure where organs are developed from their potential regions. Consequently organogenesis transfers an embryo into free larva structure.

----

==Germ-layer origin of various body tissues==
[[Image: Development Models of Frog.jpg|thumb|right|Figure 13 Image details:Vertebrate Structure and Development.jpg]]

Ectoderm will give raise to structures such as skin, brain, spinal cord, neurons and sense receptors.
Mesoderm will give raise to structrues such as notochord, muscles, blood, bone and sex organs.
Endoderm will give raise to sturctures such as inner lining of gut, liver, pancreas, lungs and bladder, thyroid and parathyroid glands and thymus.

== Structures derived from Germ-layers of frog species ==

[[Image:Development of Frog Layers.jpg|thumb|left|Development of Frog Layers Primary source[http://www.bio.miami.edu/~cmallery/150/physiol/sf19x11b.jpg]Image details:J,Nassif 2009.jpg]]

[[Image:Development of frog layers.jpg|thumb|left|Development of Frog Layers Primary source [http://www.bio.miami.edu/~cmallery/150/physiol/sf19x11b.jpg]Image details:J,Nassif 2009.jpg]]

'''Ectoderm '''

''Establishes the epidermal segments and its derivatives, to the frog’s nervous system. The ectoderm also contributes to :''

1. The olfactory and auditory epithelium.

2. The retina and lens of the eye.

3. Sensory organs.

4. The epithelial lining of the oral cavity and the anus.

5. The pineal and pituitary body.

'''Mesoderm'''

''Mesoderm originates:''

1. Connective tissue.

2. Muscles, except the notochord.

3. Blood vessels.

4. Lymphatics.

5. The peritoneum and the urinary and reproductive system.

6. The dermis, parts of the eye excluding lens, cornea, and conjunctiva.

'''Endoderm'''

''From the endoderm arises:''

1. The epithelial lining to the gut and oesophagus, stomach, intestine, bile duct.

2. The hepatic cells of the liver, respiratory tract, larynx, trachea and lungs.

3. The lining of the urinary bladder, pancreas thyroid and thymus.

[The two figures reveal the development of structures deriving from the celluar components of the embryology of the frog].[Structures derived from Germ-layers of frog species ]

==Life cycle of a frog==

'''Fertilization-egg''':

The female lays eggs in the spring. A group of fertilized eggs is called spawn;

'''7-10 days''':

Fertilized egg feed on remaining yolk which is in its gut. Their gills, mouth and tail have poorly developed. Begin to swim and feed on algae;

'''10-30 days(4 weeks):'''

A layer of skin grows over gills. Teeth begin to appear. A coiled gut start to develop. This is aid in digestion;

'''30-60 days(6-9 weeks):'''

Legs being to grow and head is more distinct. Start to eat insects. Arms begin to grow;

'''60-80 days(12 weeks):'''

Resemble a frog. Still have remaining tail;

'''80-140 days(20 weeks):'''

Fully developed, spend most of time out of water. Majority of frog live between 4-15 years.

==Timeline of frog development==

Development of egg and embryo at temperature 18 degree celsius.

'''0 hours''' - fertilization of the egg

'''1 hours''' - formation of the gray crescent due to pigment migration

'''3.5 hours''' - early cleavage

'''4.5 hours''' - blastula stage(coeloblastula with eccentric blastocoel

'''26 hours''' - gastrulation

'''26 hours''' -'' early'' - crescent shaped dorsal lip

'''34 hours''' - ''middle''- semicircular blastoporal lip

'''42 hours''' - ''late'' - circular blastoporal lip

'''50 hours''' - neurulation

'''50 hours''' - ''early'' - medullary plate

'''62 hours''' -'' middle''- neural folds converging

'''67 hours''' - ''late'' - neural tube formed and ciliation of embryo

'''84 hours''' - tail bud stage(early organogeny)

'''96 hours''' - muscular response to tactile stimulation

'''118 hours''' - early heart beat, development of gill buds

'''140 hours''' - hatching and gill circulation

'''162 hours''' - mouth opens and cornea becomes transparent

'''192 hours''' - tail fin circulation established

'''216 hours''' - degeneration of external gills, formation of operculum, development of embryonic teeth

'''240 hours''' - opercular fold over brachial chamber except for spiracle and internal gills

'''255 hours''' - prolonged larval stage with refinement of organs

'''270 hours''' - development of hindlimbs, internal development of forelimbs in opercular cavity

'''275 hours''' - projection of forelimbs through operculum, left side first

'''280 hours''' - absorption of the tail and reduction in size of the gut

'''284 hours''' - metamorphosis complete, emergence from water as miniature, air breathing frog

==Stages of frog embryology==
--[[User:S8600021|Mark Hill]] 08:40, 9 October 2009 (EST) [[Talk:2009_Group_Project_5#Constructive_Criticism_of_Coordinator|see my comment on images]]

The rate of development of the egg and embryo will depend upon the temperature at which they are kept. The approximate schedule of development at 23 degree celsius is provided below.

{| border='1px'
|+ Table 1: Stages of frog development
!Stage !!Time since fertilisation (hours)!!Stage Characteristic !!Embryo characteristic !!Image of frog stage
|-
|1
|0.00-1.30
|fertilization of the egg, post fertilization
|animal hemisphere, gray crescent and vegetal hemisphere are present
|[[File:Stage01ventral.jpg|100px]]
|-
|2
|1.30-2.00
|splits into two cells
|appearance of first cleavage furrow
|[[File:Stage02ventral.jpg|100px]]
|-
|3
|2.00-2.15
|becomes four cells
|appearance of second cleavage furrow
|[[File:Stage03dorsolat.jpg|100px]]
|-
|4
|2.15-2.45
|becomes eight cells
|appearance of third cleavage furrow
|[[File:Stage04dorsolat.jpg|100px]]
|-
|5
|2.45-3.00
|becomes sixteen cells
|appearance of fourth cleavage furrow
|[[File:Stage05dorsal.jpg|100px]]
|-
|6
|3.00-3.30
|becomes thirty-two cells
|appearance of fifth cleavage furrow
|[[File:Stage06animal.jpg|100px]]
|-
|6.5
|3.30-4.00
|blastula stage
|Three dorsal folds become visible as a result of endoderm invagination. Pole cells no longer visible on surface
|[[File:Stage065dorsal.jpg|100px]]
|-
|7
|4.00-5.00
|Gastrulation stage
|two primary germ layers. epiblast and endoderm
|[[File:Stage07ventral.jpg|100px]]
|-
|8
|5.00-7.00
|neurulation
|medullary plate, neural folds and neural tube
|[[File:Stage08animal.jpg|100px]]
|-
|9
|7.00-9.00
|germ layer
|complete lip involution encircling yolk
|[[File:Stage09veg.jpg|100px]]
|-
|10
|9.00-11.00
|early gastrula
|two primary germ layers
|[[File:Stage10veg.jpg|100px]]
|-
|10.5
|11.00-11.45
|gastrula
|two germ layers
|[[File:Stage105vegb.jpg|100px]]
|-
|11
|11.45-12.30
|medulla plate
|Yolk sac protrudes dorsally, labium moves to midline on ventral side
|[[File:Stage11veg.jpg|100px]]
|-
|11.5
|12.30-13.15
|continuation of medulla plate
|start closing the plate
|[[File:Stage115veg.jpg|100px]]
|-
|12
|13.15-14.15
|early neurula
|thickened ectoderm give rise to CNS
|[[File:Stage12veg.jpg|100px]]
|-
|12.5
|14.15-14.45
|neural folds
|expansion of cavity
|[[File:Stage125postdors.jpg|100px]]
|-
|13
|14.45-16.15
|neural folds
|continue expanding cavity
|[[File:Stage13postdors.jpg|100px]]
|-
|14
|16.15-17.30
|neural folds
|continuation of cavity
|[[File:Stage14postdors.jpg|100px]]
|-
|15
|17.30-18.15
|tail bud stage
|early organogeny
|[[File:Stage15postdors.jpg|100px]]
|-
|16
|18.15-18.45
|tail bud stage
|posterior ventral view
|[[File:Stage16ant.jpg|100px]]
|-
|17
|18.45-19.45
|tail bud stage
|anterior view
|[[File:Stage17ant.jpg|100px]]
|-
|19
|20.45-21.45
|neural fold close complete
|dorsal view
|[[File:Stage19dorsal.jpg|100px]]
|-
|20
|21.45-22.30
|early tail bud
|anterior view
|[[File:Stage20dorsal.jpg|100px]]
|-
|21
|22.30-24.00
|termination of neural crest
|progress to next stage
|[[File:Stage21ant.jpg|100px]]
|-
|22
|24.00-24.45
|prolonged development
|elongation
|[[File:Stage22lat.jpg|100px]]
|-
|23
|24.45-26.15
|elongation of embryo
|later view
|[[File:Stage23lat.jpg|100px]]
|-
|24
|26.15-27.30
|continuation of elongation of embryo
|dorsal view
|[[File:Stage24latsmall.jpg|50px]]
|-
|25
|27.30-29.30
|organs development
|embryo elongates and develops dorsal thickening
|[[File:Stage25dorsal.jpg|50px]]
|-
|26
|29.30-31.15
|elongation
|dorsally forms neural and brain cavity
|[[File:Stage26lat.jpg|50px]]
|-
|27
|31.15-32.30
|elongation of embryo
|dorsal view
|[[File:Stage27lat.jpg|50px]]
|-
|28
|32.30-35.00
|further development
|lateral view
|[[File:Stage28lat.jpg|50px]]
|-
|29-30
|35.00-37.30
|tail bud
|growth
|[[File:Stage29-30lat.jpg|50px]]
|-
|31
|37.30-40.00
|prolonged development
|bud development
|[[File:Stage31lat.jpg|50px]]
|-
|32
|40.00-44.30
|early muscular development
|elongation
|[[File:Stage32lat.jpg|50px]]
|-
|33-34
|44.30-50.00
|muscular movement
|apparatus for locomotion
|[[File:Stage33-34lat.jpg|50px]]
|-
|35-36
|50.00-53.30
|muscular movement
|apparatus for locomotion
|[[File:Stage35-36lat.jpg|50px]]
|-
|37-38
|53.30-56.30
|heart beat
|develops apparatus
|[[File:Stage37-38lat.jpg|50px]]
|-
|39
|56.30-66.00
|mouth opens
|cornea transparent
|[[File:Stage39latsmall.jpg|50px]]
|-
|40
|66.00-76.00
|gill circulation
|hatching
|[[File:Stage40lat.jpg|50px]]
|-
|41
|76.00-80.00
|tail, fin circulation
|circulation
|[[File:Stage41lat.jpg|50px]]
|-
|42
|80.00-86.00
|internal gills, operculum
|opercular fold, teeth
|[[File:Stage42lat.jpg|50px]]
|-
|43
|86.00-98.00
|operculum complete
|operculum closed on right
|[[File:Stage43lat.jpg|50px]]
|-
|46
|98.00-106.00
|metamorphosis
|emergence from water as miniature, operculum complete|
|[[File:Stage46lat.jpg|50px]]
|-
|}

==Abnormalities of frog==

Abnormalities of frog could be caused by multiple factors. These include change in climate, predators, parasites, bacteria, fungi, viruses or pollution and contaminants such as pesticides, metals and fertilizer.[http://www.fws.gov/contaminants/documents/frogsrefup_septoct_2006.pdf]

The Abnormalities are further classified into different categories. These categories are:

===1. Infectious Diseases:===

'''Perkinsus Symptoms-''' caused by perkinsus-like protozoan organism. Symptoms include swollen viscera that leads to a bloated body and and infected swollen heart

'''Ichthyophonus symptoms-''' cause by parasitic genus, where symptoms include a swollen tail resorption site that matches the surrounding skin in color and translucency.

[[Image:Abnormalities of Frog species.jpg|thumb|left|Figure A Image details[waterwatchadelaide.net.au].jpg]]

===2. Surficial Abnormalities:===

Surficial abnormalities as the one that are visible on the surface of the skin. This includes abnormal pigmentation, , subcutaneous hemorrhaging, wounds due to trauma or from a predator
Edema is a fluid-filled swelling under skin whihc is also a surficial abnormality.

===3. Skeletal Abnormalities:===

This is further classified into three more categories:

'''a. Skeletal Malformations-'''

* Microcephaly (small head or blunt snout)
*Scoliosis (Curved spine in lateral direction)
*Shrunken Limb (Micromelia)
*Amelia (Completely missing limb with no stump)

'''b. Skeletal Abnormalities of Unclear Etiology-'''

This condition arises when a frog has ectromelia (missing limb), brachydactyly (missing digits) or other such condition with no visible trauma or external damage, then this will be classified as the Skeletal abnormality of unclear etiology.

'''c. Skeletal Injuries-'''

Any limb missing or broken due to trauma or other related reason which shows clear evidence of it is classified as skeletal injury

===4. Eye Abnormalities:===

Most common includes-

'''i. Anophthalmia:''' Skin covers the eye socket as there is no eye

'''ii. Abnormal Iris Coloration:''' Reduced pigment in either one eye or both resulting in two different colours of the iris at times

'''iii. Abnormal size or shape:''' Both eyes either deviating from each other or size of pupil or iris is different than the other eye

[http://www.fws.gov/contaminants/Amphibian/pdfs/AbnormalitySOP_woutpics_Jan08.pdf ]

==Genetics==

There are a wide variety of species that differ from each other when it comes to genetics and their functioning.

'''TAXONOMY:''' '''Phylum''' ''Chordata'' / '''Sub Phylum''' ''Vertebrata'' / '''Class''' ''Amphibia'' / '''Order''' ''Anura''

Their are more than two dozen different families of frogs, where suborders are:

'''1. ARCHAEBATRACHIA-''' most primitive frogs

'''2. MESOBATRACHIA-''' linked between the Archaebatrachia and Neobatrachia

'''3. NEOBATRACHIA-''' most modern frogs

{| border='4px'
|+ '''General Info:'''
! !!
|-
| '''Number of frogs' species'''
| 5280
|-
| '''Smallest frog genome size:'''
| 0.95pg, Ornate burrowing frog
|-
| '''Largest frog genome size:'''
| 13.40pg, Ornate horned frog
|-
| '''Mean of frogs' genome'''
| 4.68pg ± 0.13
|-
|}

[http://www.genomesize.com]

*Majority of frogs have only 22 to 26 chromosomes and polyploid is very common where they are almost bisexual.

*Polyploid Amphibians reduce their total cell number such that they acheive the same body size as diploids. One of the most unsual forms of polypoidy in amphibians is the water frog ''Rana esculenta'' from Europe and Western Asia.

* The species with larger genomes have more genes for e.g. the frog genus ''Xenopus'' includes 16 species, with genome sizes ranging from 3.5 x 10^9 bp to 1.6 x 10^10 bp. These differences have arisen by numerous events of polyploidization within the past 40 million years or so. The ancestral chromosome number for the genus seems to have been 18, but there are species with 36, 72 and 105 chromosomes [http://www.xenbase.org/common/]

{| border='4px'
|+ '''Difference within two families'''
! '''SPECIES''' !! ''X.LAEVIS'' !! ''X.TROPICALIS''
|-
| '''PLOIDY'''
| Allotetraploid
| Diploid
|-
| '''NO. OF CHROMOSOMES'''
| 36 chromosomes
| 20 chromosomes
|-
| '''GENOME SIZE'''
| 3.1 x 10^9 bp
| 1.7 x 10^9 bp
|-
| '''EGG SIZE'''
| 1-1.3 mm
| 0.7-0.8 mm
|-
| '''GENERATION TIME'''
| 1-2 years
| 4 months
|-
|}
[http://www.xenbase.org/common/]

===Genome Sequencing===

Since Frog has a huge family with many different species, only few main species that are used widely for the purposes of experiments have their genome sequenced.

''Xenopus tropicalis'' has one of the smallest genomes among amphibians and has the shortest generation time- four to six months and the only diploid genome among the 14 Xenopus species. This means it has no more than two copies of most genes, whereas the other species of Xenopus have four copies of most genes (pseudotetraploid). US Department of Energy's Joint Genome Institute (JGI) in Walnut Creek, California, initiated the X. tropicalis Genome Project, finding 1,700 million base pairs.
[http://www.genome.gov/Pages/Research/Sequencing/BACLibrary/xenopusTropicalis.pdf]

===Xenopus oocytes===

* The oocytes provide an important expression system for molecular biology.

* By injecting DNA or mRNA into the oocyte or developing embryo, scientists can study the protein products in a controlled system. This allows rapid functional expression of manipulated DNAs (or mRNA). This is particularly useful in electrophysiology, where the ease of recording from the oocyte makes expression of membrane channels attractive.

* One challenge of oocyte work is eliminating native proteins that might confound results, such as membrane channels native to the oocyte.

* Translation of proteins can be blocked or splicing of pre-mRNA can be modified by injection of Morpholino antisense oligos into the oocyte (for distribution throughout the embryo) or early embryo (for distribution only into daughter cells of the injected cell).
[http://www.staff.unibe.ch/sigel/xenopus.html]

===Xenopus Laevis===

* ''Xenopus Laevis'' is an important model organism in developmental biology. X. laevis is tetraploid and reaches sexual maturity in 1 to 2 years. What makes it important in developmental biology is its large and easily manipulable embryo.

* Extracts from the eggs of X. laevis frogs are also commonly used for biochemical studies of DNA replication and repair, as these extracts fully support DNA replication and other related processes in a cell-free environment which allows easier manipulation.

* The Human chorionic gonadotropin hormone (hCG) is present in the urine of the pregnant women in large quantities only. This hormone in the urine induces X.laevis oocyte production which formed the basis of first well-documented method of pregnancy testing X. laevis is also notable for its use as the first well-documented method of pregnancy testing when it was discovered. Today, commercially available HCG is injected into Xenopus males and females to induce mating behavior and breed these frogs in captivity at any time of the year.

===Gene cluster===

* The alpha and beta globin genes are closely linked in small cluster of frogs compared to human and chicken

* The similarity of architecture of two clusters found in X.laevis supports the tetraploid origin

* The two loci encoding the muscle specific creatine kinase isoenzymes and have large differences in developmental profile, therefore suggesting that duplicate loci that have not undergone silencing are not simply redundant copies but have acquired specialization.

* Contains twice number of genes for proteins i.e. haemoglobin and sarcomeric actin serum albumin compared with other species

----

==Current Embrology Research==

Currently, a number of fields have benefited from the development of frog embrology. These include cloning, verification of messenger RNA, and Cell cycle.

===Cloning===
[[Image:Robert Briggs.jpg|thumb|left|Figure 16 Image details:Robert Briggs.jpg]]

In 1952, Robert Briggs and Thomas J King cloned northern leopard frogs using a method of nuclear transfer. Briggs and King's experiment was similar to that envisioned - and piloted using salamanders - by Hans Spemann in his 1938 proposal for a 'fantastical experiment'. Later, John Gurdon extended this work and showed that nuclei from differentiated cells could support development, although less well than those from early embryos. [http://genome.wellcome.ac.uk/doc_WTD020799.html]

Lemaitre et a. (2005) from MRC Cancer Cell Unit, Cambridge, U.K. worked on experiments that demonstrated that importance of serial nuclear transplantation for the sucessful cloning of frogs. He demonstrated that exposure of somatic-cell nuclei (erythrocyte nuclei) and sperm nuclei to an extract of mitotic cell extract reorganizes the chromatin into shorter loops and allows replication at much shorter intervals along the DNA. This increases the efficiency of DNA replication in mammalian cell-free systems.

===Transgenesis techniques for functional genomics in Xenopus===

Transgenesis in Xenopus is made possible due to large embryos, a reliable fate map, ease of microinjection, ease of dissection/micromanipulation and existence of the neuroendocrine reflex of background adaptation as a model for activation/inact.

Recently, Hajime Ogino and Haruki Ochi from Nura Institute of Science and Technology in Japan focused on the genomic resources and principles of the transgenesis techniques in Xenopus, and discusses their applications to genome wide network analysis, with emphasis on the use of bioinformatics tools. This is will to understand the gene regulatory networks that control vertebrate development. [http://www.ingentaconnect.com/content/bsc/dgd/2009/00000051/00000004/art00001%3Bjsessionid=4ah96rms73gcu.alexandra]

Xenopus used to be a problem in earlier days when it came to transgenesis. Current methods involves isolated sperm nuclei from Xenopus testis that are microinjected into unfertilized eggs. The generated transgenic tadpoles contain 5-35 copies of the integrated plasmid that are expressed in all cells. If desired, expression of the transgene can be directed to the appropriate tissue and at the appropriate time by using specific promoters, mostly the Xenopus POMC gene promoter (isolated from a Xenopus genomic DNA library) to specifically direct expression of green fluorescent protein (GFP) at high levels to the intermediate pituitary cells, which can either be over expressed or inhibited.[http://molanphys.ruhosting.nl/transgenesis.htm]

[[File:Transgenesis.JPG]]

===Verification of messenger RNA===

While the existence and role of messenger RNA (mRNA) was known in bacteria, in the 1960s it was still debated whether it also existed in vertebrates. Taking haemoglobin mRNA from immature red blood cells and injecting it into a Xenopus oocyte, John Gurdon showed that the haemoglobin protein was indeed produced. Producing proteins in Xenopus oocytes has proved to be extremely useful in cell biology, in particular for the study of receptor proteins.[http://genome.wellcome.ac.uk/doc_WTD020799.html]

===Cell Cycle===

As they develop outside the mother, frog eggs are well stocked with the proteins needed to drive the development of the embryo. Studies of these processes has shed considerable light on the processes involved in cell division - termed the cell cycle. [http://genome.wellcome.ac.uk/doc_WTD020799.html]

===Limb development in Xenopus Laevis===

[[Image: Frog Limb development.jpg|thumb|right|From Limb Development Image details:Primary source:[http://images.google.com.au/imgres?imgurl=http://www.sciencedaily.com/images/2006/06/060616130718.jpg&imgrefurl=http://www.sciencedaily.com/releases/2006/06/060616130718.htm&usg=__xliPsPAvheUBME_kjv_q7auiFbo=&h=333&w=300&sz=11&hl=en&start=2&um=1&tbnid=y_ntJtmkRSK7WM:&tbnh=119&tbnw=107&prev=/images%3Fq%3DLimb%2Bdevelopment%2Bin%2BXenopus%2BLaevis%26ndsp%3D18%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

Donald D. Brown (2005),Department of Embryology, Carnegie Institution of Washington demonstrated factors related to limb development of Xenopus Laevis. Thyroid hormone (TH) is found to be required for limb development in this frog. Specific cell types in the growing limb were targeted for expression of a dominant negative form of the TH receptor by sperm-mediated transgenesis. Limb muscle development, the innervation of muscle from the spinal cord, and cartilage growth can be inhibited without affecting patterning of the limb or differentiation of other cell types. Remodeling of the skin occurs late in metamorphosis after the limb has formed. The coordination of these independent programs is affected in part by the control that TH exerts over DNA replication in all cell types of the limb. [http://www.pnas.org/content/102/35/12455.full]

----

== Glossary ==

[[Image: Frog species.jpg|thumb|left| Frog Species Image details:Primary source:www.olympus.co.jp/.../080925/large/p02L.jpg].jpg]]

*'''Amphibian:'''

''Relating to or characteristic of animals of the class amphibia.Amphibians are found in the taxonomic class of amphibia, amphibians are capable of both occupying and successfully living in both land and aquatic communities.amphibian''

*'''Augmentation:'''

''Enlargement/Increase in cellular size.''

*'''Autolysis:'''

''breakdown of a part or whole cell or tissue by self-produced enzymes''

*'''Blastomeres:'''

''The undifferentiated cells formed by cleavage of the fertilised ovum. This includes cells in the cleavage, morula, and blastula stages of the embryo''

*'''Carnivorous:'''
''
Flesh-eating; subsisting on animals as food.''

*'''Cleavage:'''

''he repeated division of a fertilised ovum ''

* '''Cleft:'''

''an opening, fissure, or V-shaped indentation made by or as if by splitting''

*'''Chordate:'''

''Members of a diverse phylum of animals that, as embryos, possess a (1) notochord; (2) a dorsal, hollow nerve cord, (3) pharyngeal gill slits; and (4) a post-anal tail''

''The act or state of splitting or dividing of a cell, particularly during the telophase of (animal) cell division.''

*'''Cytoplasm:'''

''The cytoplasm (of both eukaryotes and prokaryotes) is where the functions for cell expansion, growth, metabolism, and replication are carried out''

* '''Epiboly:'''
''The expansion of one cell sheet over other cells, as takes place during gastrulation''

*'''Fertilization:'''

''A process in sexual reproduction that involves the union of male (sperm) and female (ovum) gametes (each with a single, haploid set of chromosomes) to produce a diploid zygote.''

*'''Gamete:'''
''A reproductive cell (male (sperm) or female (egg)) that has only half the usual number of chromosomes''

*'''Gametogenesis:'''

''process leading to the production of gametes. The development and maturation of sex cells through meiosis.Another name for meiosis where a diploid cell is divided into two haploid cells with half the chromosome content of the diploid parent cell.''

*'''Herbivorous:'''

''eating plants; of or pertaining to the herbivora.''

*'''Holoblastic:'''

''The complete division of an isolecithal or microlecithal egg into blastomeres''

*'''Invagination:'''

''One of the methods by which the various germinal layers of the ovum are differentiated.''

*'''Isoenzymes:'''

''Isozymes (also known as isoenzymes) are enzymes that differ in amino acid sequence but catalyze the same chemical reaction.''

*'''Mesentery:'''

'' membranous fold attaching various organs to the body wall.''

*'''Metamorphosis:'''

''A change in the form and often habits of an animal after the embryonic stage during normal development.''

*'''Neuroendocrine:'''

''Neuroendocrine [IPA nʊəroʊˈɛndəkrɪn] cells are cells that release a hormone into the circulating blood in response to a neural stimulus.''

*'''Organogenesis:'''

''The part of embryonic development where the body's main organs develop.''

*'''Peritoneum:'''

''The smooth serous membrane which lines the cavity of the abdomen, or the whole body cavity when there is no diaphragm, and, turning back, surrounds the viscera, forming a closed, or nearly closed, sac.''

*'''Perivitelline space:'''

''The perivitelline space is the space between the zona pellucida and the plasma membrane (sometimes called the vitelline membrane) in a fertilized ovum.''

*'''Polyploidy:'''

''Cells with three or more sets of chromosomes.''

*'''Pronucleus:'''

''the nucleus of the ovum or sperm after fertilization but before they fuse to form the nucleus of the zygote ''

*'''Protoplasm:'''

''The fluid living content of the cell that consists of two major divisions, the cytoplasm and the nucleoplasm (cell nucleus). It is composed mainly of nucleic acids, proteins, lipids, carbohydrates, and inorganic salts''

*'''Segmentation:'''

''division of some metazoan bodies (such as annelida and Arthropoda) into repeated parts, segments. Segmentation can be homomeric (more or less the same) or heteromeric(different from each other).''

*'''Terrestrial:'''

''Of or on the ground, of the habitat of a plant, on land as opposed to in water, or on the ground as opposed to on another plant.''

*'''Transgenesis:'''

''Transgenesis is the process of introducing an exogenous gene - called a transgene - into a living organism so that the organism will exhibit a new property and transmit that property to its offspring.''

*'''Yolk:'''

''nutritive material of an ovum stored for the nutrition of an embryo''

*'''Zygote:'''

''The cell from which an organism develops, that results from the fertilization of the egg by the sperm.''

''Primary Resource "Biology- Online Dictionary''[http://www.biology-online.org/dictionary/Main_Page]

== References - Frog Embryology: ==

[[Image:Frog Research.jpg|thumb|left|Research being done on a Frog Image details:[http://images.google.com.au/imgres?imgurl=http://www.odt.co.nz/files/story/2008/09/university_of_otago_zoology_senior_lecturer_phil_b_3343259744.jpg&imgrefurl=http://www.odt.co.nz/on-campus/university-otago/21670/dunedin-frog-man-wins-zoo-award&usg=__JvJJU5QfOnIwY2bk4xo64UXuJRs=&h=600&w=404&sz=22&hl=en&start=14&um=1&tbnid=AbsP89yWcUiilM:&tbnh=135&tbnw=91&prev=/images%3Fq%3Dfrog%2Bresearch%26hl%3Den%26um%3D1].jpg]]

1. Savage, J. M. (2002). The Amphibians and Reptiles of Costa Rica. University of Chicago Press, Chicago [http://www.springerlink.com/content/vv015277w1746llw/]

2. Ford, L.S.; D.C. Cannatella (1993). "The major clades of frogs". Herpetological Monographs 7: 94–117 [http://digimorph.org/specimens/Xenopus_laevis/]

3. Tyler, M. J. (1994). Australian Frogs A Natural History. Reed Books [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.gracilenta.html]

4. Cogger, H.G.; R.G. Zweifel, and D. Kirschner (2004). Encyclopedia of Reptiles & Amphibians Second Edition. Fog City Press [http://en.wikipedia.org/wiki/Microhylidae]

5. Beltz, Ellin (2005). Frogs: Inside their Remarkable World. Firefly Books [http://unjobs.org/authors/ellin-beltz]

6. Tyler, M. J. (1994). Australian Frogs A Natural History. Reed Books [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

7. Moury JD, Hanken J (1995) Early cranial neural crest migration in the direct-developing frog, Eleutherodactylus coqui. Acta
Anatomica (Basel) 153, 243-253.

8.Raynaud A (1985) Development of limbs and embryonic limb reduction. In Biology of the Reptilia (ed. Gans C, Billett F), pp.
59-148. New York: John Wiley.[http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=9309]

9. Hanken J (1986) Developmental evidence for amphibian origins. In Evolutionary Biology (ed. Hecht MK, Wallace B, Prance GT), 20, pp. 389-417. New York: Plenum Press. [Hanken J (1986) Developmental evidence for amphibian origins. In Evolutionary Biology (ed. Hecht MK, Wallace B, Prance GT), 20, pp. 389-417. New York: Plenum Press.]

10. Elinson RP (1990) Direct development in frogs : wiping the recapitulationist slate clean. Seminars in Developmental Biology
1, 263-270.

11. Beebee, T. J. C. 1996. Ecology and Conservation of Amphibians. Chapman and Hall. London. [http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V5X-3SVHMKH-1X&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=1021245355&_rerunOrigin=google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=825868e10cd178d16a8a0e5ad14dc5ef]

12. Lehtinen, R. M. 2002. The use of screw pines (Pandanus spp.) by amphibians and reptiles in Madagascar. Herpetological Bulletin 2002:20–25.

13. Parris, K. M. and M. A. McCarthy. 1999. What influences the structure of frog assemblages at forest streams. Australian Journal of Ecology 24:495–502. CrossRef

14. Zug, G. R. 1993. Herpetology: An Introductory Biology of Amphibians and Reptiles. Academic Press. San Diego, CA.

15. Slack,J.M.W., Darlington,B.G., Heath,J.K. and Godsave,S.F. (1987)Mesoderm induction in early Xenopus embryos by heparin-binding growth factors. Nature, 326, 197-200.

16. Melton,D.A. (1990) Activins are expressed early in Xenopus embryogenesis and can induce axial mesoderm and anterior structures. Cell, 63, 485-493.

17. Harland,R.M. and Misher,L. (1988) Stability of RNA in developing Xenopus embryos and identification of a destabilizing sequence in TFIIIA RNA. Development, 102, 837-852.

18. Cunliffe,V. and Smith,J.C. (1992) Ectopic mesoderm formation in Xenopus embryos caused by widespread expression of a Brachyury homologue. Nature, 358, 427-430.

19. Kinoshita,K., Bessho,T. and Asashima,M. (1993) Competence prepattern in the animal hemisphere of the 8-cell-stage Xenopus embryo. Devel. Biol., 160, 276-284.

20. LaBonne,C., Burke,B. and Whitman,M. (1995) Role of MAP kinase in mesoderm induction and axial patterning in Xenopus development. Development, 121, 1475-1486.

21. Green,J.B.A., New,H.V. and Smith,J.C. (1992) Responses of embryonic Xenopus cells to activin and FGF are separated by multiple dose thresholds and correspond to distinct axes of the mesoderm. Cell, 71, 731-739.

22. Grainger R., Blumberg B., Harland R., Amemiya C., Importance of Xenopus Tropicalis to biomedical and biological research, Benaroya Research Institute, Virginia Mason Research Center [http://www.genome.gov/Pages/Research/Sequencing/BACLibrary/xenopusTropicalis.pdf ]

23. Gregory, T.R. (2005). Animal Genome Size Database. [http://www.genomesize.com]

24. U.S Fish and Wildlife Services, ABNORMALITY CLASSIFICATION SOP, [http://www.fws.gov/contaminants/Amphibian/pdfs/AbnormalitySOP_woutpics_Jan08.pdf ]

25. Donald D. Brown*, Liquan Cai*, Biswajit Das*, Nicholas Marsh-Armstrong‡, Alexander M. Schreiber*, and Rejeanne Juste*(2005), Thyroid hormone controls multiple independent programs required for limb development in Xenopus laevis metamorphosis [http://www.pnas.org/content/102/35/12455.full]

26. Ogino, Hajime; Ochi, Haruki, Resources and transgenesis techniques for functional genomics in Xenopus, Development Growth & Differentiation, Volume 51, Number 4, May 2009 , pp. 387-401(15) [http://www.ingentaconnect.com/content/bsc/dgd/2009/00000051/00000004/art00001%3Bjsessionid=4ah96rms73gcu.alexandra]

27. Giles Newton (2004) Why the frog? The Human Genome, [http://genome.wellcome.ac.uk/doc_WTD020799.html]

28. Xenbase, [http://www.xenbase.org/common/]

29. Donders Center for Neuroscience & Nijmegen Center for Molecular Life Sciences (NCMLS), Beyond the genome (Xenopus transgenesis for functional genomics),Faculty of Science, Radboud University [http://molanphys.ruhosting.nl/transgenesis.htm]

== External Links ==
[[Image:Frog links.jpg|thumb|left|Smart Frog Image details:[http://images.google.com.au/imgres?imgurl=http://2.bp.blogspot.com/_o93AaY0GzH4/SjY_ZYv0PII/AAAAAAAAAgk/skruNc2yN78/s400/computer%2Bfrog.jpg&imgrefurl=http://hellaheaven-ana.blogspot.com/2009/06/talking-frog-contemporary-fairy-tale.html&usg=__oxji1TGLV2Fi7xe0dnlmuYk8gDo=&h=288&w=288&sz=16&hl=en&start=2&um=1&tbnid=ywZd4zpdxC5plM:&tbnh=115&tbnw=115&prev=/images%3Fq%3Dfrog%2Bon%2Bcomputer%26hl%3Den%26um%3D1].jpg]]

1. Frog embryology [http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/F/FrogEmbryology.html Frog Embryology]

2. Frog cellular materials [http://www.xenbase.org/xenbase/original/cell/cell.html xenbase]

3. The zoology of frog species [http://worms.zoology.wisc.edu/frogs/mainmenu.html zoology frogs]

4. Frog cycle [http://www.bioethics.gov/images/sc_images/frog_dev.gif bioethics frog] Just a little cycle of FROG'S life cycle

5. Frog Embryology [http://embryology.med.unsw.edu.au/OtherEmb/Frog.htm UNSW Embryology]

6. Frog Research [http://apps.carleton.edu/campus/library/now/exhibits/wallcharts/frog/ carleton library exhibit]

{{Template:Projects09}}
[[Category:Frog]]

2009 Group Project 5

2009-10-14T22:49:57Z

Z3258567: /* References - Frog Embryology: */

== The Embryology of Frogs ==

== The Frog ==

[[Image: Frog species .jpg|thumb|left|Image details: Wikipedia (2009) Frog species[http://en.wikipedia.org/wiki/Frog#Uses_in_agriculture_and_research].jpg]]

Frogs are scientifically identified by the structure of their long posterior limbs, a petite framework, webbed fingers and feet, budged eyes and the lack of a tail. The majority of frog species are extensively recognized as outstanding jumpers, due to their long, dominant legs, which are adaptations to progress jumping performance during activities. The Frog is one of the most frequently studied species in experimental embryology and most anatomical sciences. ''The Frog is a practically effective model for human embryological development given that the Frog:''

- Comprises of genes which can be effectively manipulated.

- Comprises of similar homogeny with humans species.

- Reproduces a large quantity of offspring in a short period of time.

- Are small species which can be simply sustained.

- Are not extremely luxurious and expensive.

== The History of the uses in agriculture and research ==

[[Image: Frog experiments .jpg|thumb|right|Image details: Scans of chemically cleared and dyed preserved deformed frogs and toads [http://www.sat.qc.ca/upload/residence/frog-04.jpg].jpg]]

There are numerous types of frog species that have been manipulated in many developmental experiments. The frog was traditionally used by countless of the early embryology investigators and presently there are several diverse molecular mechanisms regarding progression of the frog. Theses include:

'''1.''' Food source; frog legs are a delicacy and are eaten in European countries and in many parts of South American regions.

'''2.''' Frogs have the finest biochemical dissection of phenomena that take place in the egg and oocyte. Frogs are the evolutionarily closest to mammals, commonly used as a vertebrate model.

'''3.''' Frogs lay thousands of outsized eggs, from which cell extracts can be readily prepared that is capable of recapitulating most molecular phenomena in a test tube.

'''4.''' Frogs have been commonly used as a laboratory system for a very long period, and have an extensive history of producing crucial observations in countless fields of biology.

'''5.''' Frogs have a important historical connection to the study of epigenetics (John Gurdon-vertebrate cloning and reprogramming) which has been mostly performed on frog species.

'''6.''' Frogs also have very strong evidence of pattern formation and early development, as the embryos are large in size and experimentally manipulative.

'''7.''' Recent research into the biochemistry of chromatin and epigenetics has been performed with frog species and mammalian cultured cells.

'''8.''' The biggest weakness of the Frog model system is the difficulty of performing genetic experiments and analysis, as frogs are allotetraploid, meaning they take approximately a year to fully develop to sexual maturity, and the genome has not been completely sequenced. Nevertheless, biochemical manipulations of cell extracts, such as immunodepletions and application of heterologous DNAs and nuclei can avoid the need for genetic exploitation.

----

== Growth and development of the Frog ==

[[Image: Mature develop frog.jpg|thumb|Image details: Wikipedia (2009) Red Eyed Tree Frog Figure 1 Primary source:[http://en.wikipedia.org/wiki/File:Red-eyed_Tree_Frog_-_Litoria_chloris_edit1].jpg]]

* The frog is a well recognised species, abundant predominantly in ponds, swamps, though various species may also exist in damp or shady environments distant from moist habitats.

* Eggs of specific frogs are easily obtained and may be examined in from the beginning of fertilization onwards. The phases of embryonic development differs in various chordates, yet the typical phases are basically apparent in all frog species. The differences are associated principally to the amount of yolk particles present in an egg.

* The yolk particles offer nourishment of the developing embryo. The process of frog development will be discussed from the phases of gametogenesis to the adult stage.

----

== The Egg ==
[[Image:Development of Poles in frog Fertilization.jpg|thumb|left|Development of Poles in Frog Fertilisation:J,Nassif 2009.jpg]]

- The embryology of a frog egg is a vast cell; its dimensions are approximately 1.4-1.6 million times larger than a typical aquatic species egg cell. Throughout the frog’s embryonic maturation period, the egg will be transformed into a tadpole encompassing millions of cells but still remains with its constant volume of genetic material, the vast prodction of cell have been illusttrated in the figure on the right revealing the production of eggs from female frogs. [http://en.wikipedia.org/wiki/Microhylidae]

- The early embryonic frog structure consists of three main segments the superior hemisphere known as the animal pole which is usually visible as a grey coloured area. The innermost layer appears to be between the outer two sections known as the gray crescent represented in black. Inferiorly, represents the vegetal pole typically lighter than the superior compartment illustrated in gold.

VIDEO RESOURCE: [http://www.youtube.com/watch?v=GO5YN_t1fqw&feature=related]

[[Image:Early Development of Frogs.jpg|thumb|left|Early Development of Frog:J,Nassif 2009.jpg]]

==History of frog embryology use ==

*'''1851''' - ''Henby Nelson''(MD): He identified a remarkable fact through the frog embryo. Henby observed the first cleavage of the yolk, in the egg of the frog. And cleaved structure corresponds in line of direction to the longitudinal axis of the body of the embryo of the frog species.

[[Image:Wilhelm Roux.jpg|thumb|right|Wilhelm Roux[http://images.google.com.au/imgres?imgurl=http://www.todayinsci.com/R/Roux_Wilhelm/RouxWilhelmThm.jpg&imgrefurl=http://www.todayinsci.com/6/6_09.htm&usg=__qRLTEMTHdZpAHxiNX12hWjcm9tA=&h=125&w=100&sz=4&hl=en&start=2&um=1&tbnid=LIKIwZTqCpk7MM:&tbnh=90&tbnw=72&prev=/images%3Fq%3DWilhelm%2BRoux%26gbv%3D2%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

*'''1888''' - ''Wilhelm Roux'': Wilhelm Roux attempted to solve the above observation by damaging one cell of a two-cell frog embryo with a hot needle. The cell stayed in place. However, it did not develop further. Its partner developed into a left or right half-embryo;

*'''1907''' - ''John Hopkins'' hospital: In order to identify the cellular source of neuronal fibres. Scientist placed small portions of frog embryo spinal cords in lymph on a microscope slide and was able to observe clear cut neuronal sprouting.

*'''1951''' - ''Robert Briggs'': Robert Briggs was able to clone a frog embryo by substituting the nucleus of an unfertilized frog egg cell with the nucleus of a frog embryo cell. This process is known as nuclear transplant, has formed the basis for all cloning.

*'''1952''' - ''Robert Briggs and T.J. King'': Robert Briggs and T.J. King used frog for test experiment. Because the size of the eggs in the frogs are enormous compared with those of mammals, which make them easier to manipulate.

*'''1976'''- Using the technique that had been successful in cloning frog embryos, the doctor transferred the nucleus of one cells into a donated egg cell. As an embryo began to develop, it was implanted into the uterus of a young woman.

*'''1997''' - ''Wilmut and Campbell'': Utilizing the cloning technique from frog embryo, Drs. Wilmut and Campbell tried the starvation technique on embryo cells to produce Megan and Morag, the world's first cloned sheep and, until now, the most famous sheep in history.

*'''2000''' - ''Tokyo University'': Scientists at Tokyo University have grown artificial eyeballs. Scientists formed them in tadpoles by using frog embryo cells.

*'''2001''' - ''Advanced Cell Technology'': Scientists from Advanced Cell Technology announced production of a human embryo clone. This is significant as its parthenogenesis has been artificially induced in frogs.

[[Image:John Gurdon .jpg|thumb|right|John Gurdon [http://images.google.com.au/imgres?imgurl=http://www.pnas.org/site/misc/images/gurdon.jpg&imgrefurl=http://www.pnas.org/site/misc/classics4.shtml&usg=__1p-GA1PdOYsxKL-cznMb3RHCm98=&h=526&w=400&sz=223&hl=en&start=1&um=1&tbnid=9k4lhuLssiWCAM:&tbnh=132&tbnw=100&prev=/images%3Fq%3DJohn%2BGurdon%26gbv%3D2%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

*'''2002''' - ''John Gurdon'': John Gurdon from Wellcome Cancer Research Institute in Cambridge experimented on cloned frog embryo.

== Gametogenesis ==

* The sexual reproduction occurs through the fusion of either mature reproductive cells or germ cells known as gametes, which include the sperm from the male frog and ova from female frog species so as to form a single cell, the fertilized zygote. The gametes are typically developed in parents of different sexes . [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

* Males gametes is a spermatozoon , the female frog gamete is an ovum. Each gamete is formed by a process, recognised as maturation or gametogenesis in gonads. The typical male frog gonads are testies in male, while the female gonads are ovaries. The synthesis of both gonads is associated with the process of fertilization. [http://en.wikipedia.org/wiki/Microhylidae]

* The zygote changes into a mature frog through the process of embryology and metamorphosis. Gametogenesis is a in progression which frog gametes are established from germ cells. Initial germ cells are called primordial germ cells, which can be recognised extremely early in the life of frog species.

----

== The Egg & Fertilization ==

[[Image:Fertilized and Unfertilised Eggs.jpg|thumb|left|Fertilized and Unfertilized Eggs:J,Nassif 2009.jpg]]

[[Image:Egg Development.jpg|thumb|left|Egg Development:J,Nassif 2009.jpg]]

- This occurs once the sperm cell has inserted, following the insertion of the sperm cells meiosis II is completed, there is a 30 degree position change of the cytoplasm, gray crescent allows this change to be visible in some amphibians, the gray crescent is able what determines the expect ted outline of how the frog will form. The sperm cell joins with the nuclei of the egg which forms the diploid zygote nucleus. --Sando Rashed 10:09, 24 September 2009 (EST)

- The early phases in the development of the egg is visible, but must be studied in tadpoles throughout maturation. In embryonic tadpoles of about 10 millimetres in length, soon after the opening of the oral cavity, a pair of longitudinal ridge-like thickenings of peritoneum becomes apparent along the posterior surface of the body cavity situated near to the mesentery and along the inner boundaries of the kidneys. Genital ridges are established in all tadpoles of this age, sex is not distinct until a later period. The development of the egg is illustrated in the figure on the left revealing the structure of a developed egg and a mature of egg.

[[Image:Fertilisation life cyle.jpg|thumb|Fertilization of Life cycle:Derived from primary source:[http://en.wikipedia.org/wiki/Frog]]]

== Maturation of the Egg ==

- The eggs have currently accomplished their full size, and develop from the exterior of the ovaries like a small shot, but they still have to pass through the course of maturation before they are prepared to be fertilised. This progression of maturation relates to the nucleus almost completely.

- The nucleus component, containing the nuclear fluid that excludes through the nuclear membrane into the substance of the egg, a great segment of the nuclear reticulum vanishes and becomes degraded into separate globules known as nucleoli, but a extremely small division remains in the midpoint as a slender intricately thread recognised as the nuclear skets.
Relative to the egg getting discharged from the ovary, the follicles shatter allowing the eggs to fall into the abdominal cavity of the frog species, the egg then passes forwards, directly by the contraction of the muscular wall, somewhat by the movement of the cilia of the peritoneum, to the apex of the oviduct, which positioned at the anterior compartment of the body cavity opposite to the roots of the respiratory organs.

- The terminal part of the oviduct establishes a thin-walled pouch capable of great swelling, inside which the eggs gathers in large numbers. In conclusion, the eggs are migrated out through the cloaca into water which the albuminous investments of the eggs rapidly augment to form the gelatinous mass of the frogs spawn.

== Maturation phases ==

'''1. Nuclear skein''', moves from the midpoint of the egg to its outer surface, which it reaches opposite the midpoint of the black pole. The skein, subsequently an unevenly twisted thread, now presumes the specific arrangement of a nuclear spindle, for instance may be visible in the nucleus of an epithelial or additional cell instantly prior to division of the cell occurs.[http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

'''2. The first Polar Body,''' regarding the instance the egg is laid, but prior to its fertilistion, the egg develops a considerably flattened appearance at its upper or black pole, a definite sum of fluid being exuded among the egg and the vitelline membrane. The nuclear spindle currently separate into two identical segments, one of which remains with the egg, and the supplementary is extruded as the first polar body, a small ovoidal white globule, which is situated on the surface of the egg surrounding the exuded peri-vitellline fluid.

'''3. The Second Polar Body''', half of the nuclear spindle that stay behind then splits into two equivalent divisions, one of which remains inside the egg as the female pronucleus, whereas the other segment is extruded as the second polar body, a small white globule extremely related to the first polar body, and like this positioned in the perivitelline fluid on the superior portion of the egg.

'''4. Fertilisation of the egg''', includes the synthesis of the spermatozoon with to egg, specifically, synthesis of the nuclei of these two bodies. The spermatozoa, subsequent to being shed over the seed by the male, distribute vigorously by means of their extended tails, break through the gelatinous investment of the female eggs, bore their way through the vitelline membrane and so go through into the eggs themselves, which they penetrate relative to the superior or black hemispheres.
* Subsequently, an hour following the spermatozoon has entered; a progression may be visible projecting within from the exterior segement of the egg, with a liquid spot in the mid point. This liquid centre is the nucleus of the spermatozoon, and is said to be the male pronucleus, it break through beyond into the female egg, transporting the specialised pigment into it, so that it appears bounded by a pigmented capsule linked with the exterior of the egg by a pigmented stalk.

* By this instance, the second polar body has been established and extruded, and the female pronucleus is merely the only component of the primary egg nucleus still present. Both the male and female pronuceli, which are at initially distance separate to each other, merge and after having enlarged significantly in size then fuse mutually about two and half hours after fertilisation has originated to produce the segmentation nucleus.
* The segmentation nucleus is a huge sphere-shaped vesicle embedded in delicately granular protoplasm, and bounded by a distinct capsule of pigment, its arrangement by the synthesis of the male and female pronuclei completes the action of fertilisation. Specifically female pronucleus may be observe as an imperfect nucleus, and consequently result in the course of fertilisation. The nucleus of the spermatozoon or male pronucleus, replaces the component of the egg- nucleus which has been misplaced as the polar bodies.

'''5. Segmentation of the Egg''', the initial phase of growth consist in constant separation of the egg, whereby it becomes transformed from the unicellular state, which is everlasting only in the lowest species, to muliticelluar state charactertics of all higher species. To these early processes of growth the names segmentation is specified. Shorty subsequent to the competition of fertilisation and arrangement of the segmentation nucleus this later misplaces its sphere-shaped appearance and develops to be spindle-shaped, the yolk granules at the equivalent instance showing a tendency to develop into lines distributing outwards from the distal segment of the spindle.
* The nucleus now split into two halves, which shift away from one another, the yolk granules are likely to combined themselves around the two nuclei, and a slender vertical plate of delicately granular substance is left, dividing the egg.[http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

* Superiorly the eggs depression now becomes visible, initially as a small cavity and then develops as a groove, which almost immediately extends all round, and speedily deepening, splits the egg into two entirely separate halves along a plane equivalent with the vertical plane.

* Shorty after, the two nuclei soon separate again into two, and therefore a second cleft is created in the same state as before, its additionally in the vertical plane, however in a plane at 90 degrees to the initial one, and on its finishing point the egg comprises of four accurately similar segments, each containing a nucleus. The third cleft is horizontal in shape, but not equal, lying closer to the superior than the lower pole, it segregates each of the four cells into, an superior smaller and a inferior larger pole

----

== Cleavage ==

[[Image: Frog Cleavage development.jpg|thumb|left|Cleavage Process details:[http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/F/FrogEmbryology.html].jpg]]

* The egg of the frog is scientifically identified as’ telolecithal’ meaning there is a outsized amount of yolk concentrated at a single pole, in contrast to the concentration of cytoplasm and the site of the nucleus. The cleavage phases are holoblastic, therefore the total and after the second cleavage they are asymmetrical .The initial cleavage stage appears about two and half to three hours after fertilization. It commences as a minor depression in close proximity to the centre of the animal hemisphere. It appears as if some interior force is pushing the surface the egg towards the centre. This small upturned fold steadily continues in the form of a channel until it surrounds the egg. This groove is shallow in the commencement, but develop into deeper eventually separating the fertilized egg into two halves recognised as the blastomeres. [The figure on the left symbolise the development and growth of the frog embryo during cleavage].

* Internally the separation is mitotic, consequently each daughter cell contains a nucleus resulting from the copulation nucleus of the fertilised egg. This cleavage is vertical, the two cells are indistinguishable in respect of cytoplasm, pigment and yolk. The subsequent cleavage appears about an hour after the first. The channel of this cleavage begins at the centre of the animal hemisphere, is at right angles to the first and is vertical. This divides the egg into four blastomeres. The fourth blastomere so produced are not qualitatively equal, since of these only two contain the material from the gray crescent. The cleavage begins about thirty minutes after the second is completed or four hours after fertilisation. the cleavage plane of the third furrow is horizontal and slightly above the equator. Thus the four upper cells are a little smaller than the four lower cells. The smaller blastomeres are called micromeres and the larger blastomeres are called macromeres. The fourth cleavages follow 20 minutes after the third and tend to be vertical. This is usually a double furrow.

* The cleavage rate is accelerated with each of the early divisions and since the blastomeres are of unequal size and have varying amounts of cytoplasm and yolk, synchronous cleavage is lost and there is an obvious overlapping of the division. The upper most cells divide more rapidly than the lowermost cells. From this point onwards perfect symmetry in cleavage and in blastomere is very rare, although the embryo developed perfectly. The fifth cleavage is also doubled, appearing first in the upper hemisphere and then in the lower.

* The cleavage thus far follows the rule that each cleavage plane comes in at right angles to the previous one. The subsequent divisions become so irregular that it is previous one. The subsequent division become so irregular that it is impossible to trace out any plan or procedure. The segmentation continues more rapidly in the pigmented regions, since at that place the protoplasm is most dense, whereas, yolk which is very abundant in the vegetal side delays cell division. The multicelluar embryo at this stage is called morula by some biologists.

----

== Gastrulation ==

[[Image:FROG GASTRULATION .jpg|thumb|left|Frog Gastrulation Image details:[http://www.google.com.au/imgres?imgurl=http://bio1903.nicerweb.com/Locked/media/ch47/47_12FrogGastrulation.jpg&imgrefurl=http://bio1903.nicerweb.com/Locked/media/ch47/gastrulation-frog.html&h=540&w=480&sz=46&tbnid=N78sHjELreGGSM:&tbnh=132&tbnw=117&prev=/images%3Fq%3Dfrog%2B-%2Bgastrulation&hl=en&usg=__4VK9FYLft0W-4lBe6p5EtQAMiaI=&ei=qPy5SurtMJvE6wON8JmdAg&sa=X&oi=image_result&resnum=4&ct=image].jpg]]

''The phase of Blastulation is followed by the unique developmental progression of gastrulation. The process of frog gastrulation involves the following processes.''

'''1. Epiboly Phase'''

The pigmented cellular materials of blastula have the propensity to overgrow the yolk cells within the developing content. This course which is known as epiboly commences gradually in the final blastula and rapidly accelerates with advancing gastrulation development. The cellular matter within the animal pole reproduces and matures on all sides except in area surrounding the dorsal lip of the blastopore has been established.

'''2. Convergence'''

Scientists suggested that the unfolding was thought to result in spreading of the superficial cells over a substrate with suitable absorption properties. Consequently epiboly and convergence are an outcome to this spreading tendency, which is actually increased by a reduction in surface tension of the distributing cells.

'''3. Rotation'''

The epiboly phase is maintained until the region of the dorsal lip has migrated and is a to some extent greater than 90 degrees and the region of the white blastopore is reduced to small circular rings. This section will be positioned away from the developing vegetal pole. Laterally the complete developing gastrula has been rotated to a horizontal axis, allowing it to lie at right angles to the original median plane of the egg. Therefore, the course of rotation is such that the dorsal lip is practically pushed backwards in one direction as rapid or quicker than epiboly moves it forward in the other. The outcome will be that the blastopore produced at roughly the vegetal pole is posterior, and the dorsal and ventral lips are essentially dorsal and ventral. This in addition allows the eggs to form the antero-ventral side of the potential embryo whilst the area marked by the grey crescent is to develop the dorsal segment.

'''4. Invagination'''

Visible is a small fissure- like invagination which is apparent in the middle between the equator and the vegetal segment. The most superior or dorsal border of the cleft produce the dorsal lip of the blastopore. This imput move back and forth on the dorsal plane near the dorsal lip and migrates around the boundaries of the blastocoel in company with the extension of the lateral lips. This adapted invagination is maintained until the blastocoel cavity has been almost abolished; excluding the slender opening separating epiblasts from the hypoblast, the new segment formed is known as the archenteron cavity.

'''5. Involution'''

- Additional to previous course of action a distinct involution also occurs at the blastoporal borders. This is mainly dynamic at the median dorsal lip and gradually more less as it shifts across either side until it reaches the ventral lip where it constant.Throughout this progression, cells positioned beside the superior boundaries of the blastoporal lip migrate over the lip to the interior portion of the lip. These cells are remained within the embryo along the internal edge of the blastopore. This indicates the root of archenteron is composed of involuted cells and beyond this the external layer known as the ectoderm. The base and lateral sides are enclosed mainly of endodermal cellular material, which have been established from larger yolk cells, situated in the vegetal pole of the blastula.

- In the final phases of the gastrula development, the cells contributing to the floor of the archenteron, thin out significantly where they surround the blastocoel.
The hemispherical shaped dorsal lip of blastopore which become visible at the commencement of the gastruation stage carry on to augment, initially becoming semicircular, then transform into a horse shoe shaped and then finally forming into circular band. The band is the accomplished by the blastopore. Various yolk cells of vegetal pole present in the section are crowed into the blastoporal cavity where they form a gathering identified as a yolk plug. Blastopore rapidly reduces in size while the archenteron is still developing and becomes completely formed in the final stage; the yolk plug appears as only a small oval on the gastrula.

==Growth and Modification of Frog Species==

'''1. Changes in habits and habitats:'''

'''a)''' In frogs, metamorphosis is related with to the modifications and adaptations as a frog changes environmental habitats from an aquatic to a terrestrial mode. Metamorphosis has modified the adaption of frogs as this alteration it began during the aquatic adaptations in the surface of water to breathe air. Subsequently, it continues the terrestrial surroundings, therefore the frog species become abundant in vegetation area allowing the frog to transform in to amphibious species.

'''b)''' The transition during metamorphosis is linked with a change in food chain. The tadpoles being the embryonic origin of frogs are herbivorous, feeding on algae and green matter, which they collect by the adapted feature such as their teeth surrounding their mouths. Adult frogs, alternatively, are classified as carnivorous feeding on insects and worms. Occasionally, they also consume larger prey, for instance smaller frogs species and even little birds and rodents which they dominant and ingest.

[[Image:Development of frog from sperm to mature structure.jpg|thumb|left|Development of Frog from sperm to mature structure Image details:J,Nassif 2009.jpg]]

'''2. Changes in Morphology'''

These include the decrease or complete absence of specific organs or structures which are essential during development of early frog embryology, but not critical in the mature frog species. The significant alterations of this nature include the following developmental structures.

'''a)''' The long tail of the tadpole alongside the fin folds is absorbed again during metamorphosis and becomes absent at the final stage of the metamorphosis.

'''b) '''The developing gills are resorted, the gill clefts are congested and the branchial cavities start to become absent. The reabsorbtion of gills also takes place by autolysis.

'''c)''' The teeth of the perioral disc additionally the homey lining of the jaws are shed.

'''d)''' The lateral line sense organs within the skin of tadpoles vanish throughout metamorphosis.

'''e)''' The cloacal tube begins to condensed and reduced.

'''f)''' Various blood vessels, together with parts of the aortic arches, are reduced during mature development.

(The figure on the left represents the transformation from a tadpole to a developing structure.)[http://science.jrank.org/pages/2862/Frogs-Adult-morphology.html]

'''3. Progressive or constructive changes'''

This process comprises of the development of specific organs which mature into functional systems only during metamorphosis.

'''a)''' During development the limbs continue to augment in size and differentiation. The forelimbs, which in the tadpole mature under the opercular membrane, which then break through to the exterior. Simultaneously there is a increase in the length and strength of the hind limbs, joints develop in them and the toes become visible.

'''b)''' The middle ear becomes apparent in relation with the first pharyngeal pouch. The tympanic membrane matures. It is bounded by circular tympanic cartilage which allows the frog to retain air.

'''c)''' The visual organs bulge up on the dorsal surface of the head developing the nictitating membrane.

'''d)''' There is augmentation of the tongue and the formation of thevomerina teeth.

[[Image: Growth model.jpg|thumb|Growth Model Image details:J,Nassif2009:]]

'''4. Remodelling of some structures'''

Systematic organs which operate both in the early embryonic larva and the mature adult change their differentiation during metamorphosis so as to meet the requirements of the adult mode of life and due to the habitat adaptations. The figure on the right illustrates structures developing from specic germ cell layers.

'''a)''' The skin of the embryonic tadpole is lined with a double-layered epidermis. The number of layers of cells in the epidermis augments throughout metamorphosis. Superficial surface layers become cornified. Multicellular mucous and serous glands originate in the skin. The pigmentation of the skin continuously changes, new patterns and colour start to form.

'''b)''' There is a lengthening of the mouth gap as a result of rotation of the quadrate cartilage and the true jaws become functional.

'''c)''' The tongue rapidly progresses and becomes larger and more muscular.

'''d)''' The eyes become more specialised.

'''e)''' In early tadpoles, the GIT is extremely long and wound up into a spiral folds. The intestine become greatly lengthened in herbivorous species due to the vegetables food chain.[http://en.wikipedia.org/wiki/Frog]

'''5. Development of the reproductive system'''

(The figure below represents the reproductive and development cycle of a frog as it transform from egg to frog specie.)

In tadpoles, right after the mouth is being formed, two indentation like thickenings of peritoneum begin to appear near the body cavity (dorsal surface), which is nearest to the mesentery which is near the developing kidneys. These appear in all tadpoles.

These indentations appear here because of a change in the endothelial cells, everywhere else they are usually flat looking cells but they undergo a change and in this particular area become somewhat cuboidal/columnar.

Later on the indentations become more obvious due to the epithelial cells replicating numerously to form a thick layer. The posterior two thirds of the indentation for the female is the ovary and for the male it is the testis. The third that is left differentiates and becomes fat for the body.

[[Image: Mature frog life cyle.jpg|thumb|200px|left|Mature from life cycle Image details:Derived from primary source:http://www.scienceclarified.com/images/uesc_01_img0038.jpg]]

[[Image: Developing frog.jpg|thumb|Developing Frog Image details:
[[Image: Mature develop frog.jpg|thumb|Image details: Red eyed tree frog litoria chloris source:[http://en.wikipedia.org/wiki/File:Red-eyed_Tree_Frog_-_Litoria_chloris_edit1.jpg]].jpg]]

===Delamination===

Delamination indicates a mass separating a group of cellular matter from other cellular groups. It has been illustrated that the division of notochord, mesoderm and endoderm tissues from each other to form distinct cellular masses is completed by the progression of delamination, subsequent to these materials moving to the inside throughout gastrulation. During the developing gastrula, the germ layers are all recognized. These distinct segments of the embryo develop from these germ tissue layers.

===Polarity and Rotation===

Throughout fertilisation to the beginning of gastrulation, the frog’s egg continues in the original location in relation to its polarity. Subsequent to gastrulation its polarity begins to differentiate. This progression is linked with migration of materials within the gastrula and can be responsible for the alterations of the centre of gravity.

===Closing of Blastopore===

Subsequent to the formation of the gastrula, the blastopore is visible as a tiny round circular filled cavity containing the yolk plug. As it continues to reduce in dimension, it represented as a pear-shaped outline through the mutual approach of its lateral lips. Through it final progression these fuse entirely to produce a longitudinal groove, the streak which continue dorsally and ventrally in a small aperture. The inferior aperture closes, resulting in a depression called the anal pit. The superior region remains open for some period and begins to as the neural groove is laid down.

===Post Gastrulation or Organogenesis===

Throughout the duration of pre-gastrulation, all tissues for different organs vanish from the surface of blastula and migrate inside to take their final arrangement in the embryo structure where organs are developed from their potential regions. Consequently organogenesis transfers an embryo into free larva structure.

----

==Germ-layer origin of various body tissues==
[[Image: Development Models of Frog.jpg|thumb|right|Figure 13 Image details:Vertebrate Structure and Development.jpg]]

Ectoderm will give raise to structures such as skin, brain, spinal cord, neurons and sense receptors.
Mesoderm will give raise to structrues such as notochord, muscles, blood, bone and sex organs.
Endoderm will give raise to sturctures such as inner lining of gut, liver, pancreas, lungs and bladder, thyroid and parathyroid glands and thymus.

== Structures derived from Germ-layers of frog species ==

[[Image:Development of Frog Layers.jpg|thumb|left|Development of Frog Layers Primary source[http://www.bio.miami.edu/~cmallery/150/physiol/sf19x11b.jpg]Image details:J,Nassif 2009.jpg]]

[[Image:Development of frog layers.jpg|thumb|left|Development of Frog Layers Primary source [http://www.bio.miami.edu/~cmallery/150/physiol/sf19x11b.jpg]Image details:J,Nassif 2009.jpg]]

'''Ectoderm '''

''Establishes the epidermal segments and its derivatives, to the frog’s nervous system. The ectoderm also contributes to :''

1. The olfactory and auditory epithelium.

2. The retina and lens of the eye.

3. Sensory organs.

4. The epithelial lining of the oral cavity and the anus.

5. The pineal and pituitary body.

'''Mesoderm'''

''Mesoderm originates:''

1. Connective tissue.

2. Muscles, except the notochord.

3. Blood vessels.

4. Lymphatics.

5. The peritoneum and the urinary and reproductive system.

6. The dermis, parts of the eye excluding lens, cornea, and conjunctiva.

'''Endoderm'''

''From the endoderm arises:''

1. The epithelial lining to the gut and oesophagus, stomach, intestine, bile duct.

2. The hepatic cells of the liver, respiratory tract, larynx, trachea and lungs.

3. The lining of the urinary bladder, pancreas thyroid and thymus.

[The two figures reveal the development of structures deriving from the celluar components of the embryology of the frog].[Structures derived from Germ-layers of frog species ]

==Life cycle of a frog==

'''Fertilization-egg''':

The female lays eggs in the spring. A group of fertilized eggs is called spawn;

'''7-10 days''':

Fertilized egg feed on remaining yolk which is in its gut. Their gills, mouth and tail have poorly developed. Begin to swim and feed on algae;

'''10-30 days(4 weeks):'''

A layer of skin grows over gills. Teeth begin to appear. A coiled gut start to develop. This is aid in digestion;

'''30-60 days(6-9 weeks):'''

Legs being to grow and head is more distinct. Start to eat insects. Arms begin to grow;

'''60-80 days(12 weeks):'''

Resemble a frog. Still have remaining tail;

'''80-140 days(20 weeks):'''

Fully developed, spend most of time out of water. Majority of frog live between 4-15 years.

==Timeline of frog development==

Development of egg and embryo at temperature 18 degree celsius.

'''0 hours''' - fertilization of the egg

'''1 hours''' - formation of the gray crescent due to pigment migration

'''3.5 hours''' - early cleavage

'''4.5 hours''' - blastula stage(coeloblastula with eccentric blastocoel

'''26 hours''' - gastrulation

'''26 hours''' -'' early'' - crescent shaped dorsal lip

'''34 hours''' - ''middle''- semicircular blastoporal lip

'''42 hours''' - ''late'' - circular blastoporal lip

'''50 hours''' - neurulation

'''50 hours''' - ''early'' - medullary plate

'''62 hours''' -'' middle''- neural folds converging

'''67 hours''' - ''late'' - neural tube formed and ciliation of embryo

'''84 hours''' - tail bud stage(early organogeny)

'''96 hours''' - muscular response to tactile stimulation

'''118 hours''' - early heart beat, development of gill buds

'''140 hours''' - hatching and gill circulation

'''162 hours''' - mouth opens and cornea becomes transparent

'''192 hours''' - tail fin circulation established

'''216 hours''' - degeneration of external gills, formation of operculum, development of embryonic teeth

'''240 hours''' - opercular fold over brachial chamber except for spiracle and internal gills

'''255 hours''' - prolonged larval stage with refinement of organs

'''270 hours''' - development of hindlimbs, internal development of forelimbs in opercular cavity

'''275 hours''' - projection of forelimbs through operculum, left side first

'''280 hours''' - absorption of the tail and reduction in size of the gut

'''284 hours''' - metamorphosis complete, emergence from water as miniature, air breathing frog

==Stages of frog embryology==
--[[User:S8600021|Mark Hill]] 08:40, 9 October 2009 (EST) [[Talk:2009_Group_Project_5#Constructive_Criticism_of_Coordinator|see my comment on images]]

The rate of development of the egg and embryo will depend upon the temperature at which they are kept. The approximate schedule of development at 23 degree celsius is provided below.

{| border='1px'
|+ Table 1: Stages of frog development
!Stage !!Time since fertilisation (hours)!!Stage Characteristic !!Embryo characteristic !!Image of frog stage
|-
|1
|0.00-1.30
|fertilization of the egg, post fertilization
|animal hemisphere, gray crescent and vegetal hemisphere are present
|[[File:Stage01ventral.jpg|100px]]
|-
|2
|1.30-2.00
|splits into two cells
|appearance of first cleavage furrow
|[[File:Stage02ventral.jpg|100px]]
|-
|3
|2.00-2.15
|becomes four cells
|appearance of second cleavage furrow
|[[File:Stage03dorsolat.jpg|100px]]
|-
|4
|2.15-2.45
|becomes eight cells
|appearance of third cleavage furrow
|[[File:Stage04dorsolat.jpg|100px]]
|-
|5
|2.45-3.00
|becomes sixteen cells
|appearance of fourth cleavage furrow
|[[File:Stage05dorsal.jpg|100px]]
|-
|6
|3.00-3.30
|becomes thirty-two cells
|appearance of fifth cleavage furrow
|[[File:Stage06animal.jpg|100px]]
|-
|6.5
|3.30-4.00
|blastula stage
|Three dorsal folds become visible as a result of endoderm invagination. Pole cells no longer visible on surface
|[[File:Stage065dorsal.jpg|100px]]
|-
|7
|4.00-5.00
|Gastrulation stage
|two primary germ layers. epiblast and endoderm
|[[File:Stage07ventral.jpg|100px]]
|-
|8
|5.00-7.00
|neurulation
|medullary plate, neural folds and neural tube
|[[File:Stage08animal.jpg|100px]]
|-
|9
|7.00-9.00
|germ layer
|complete lip involution encircling yolk
|[[File:Stage09veg.jpg|100px]]
|-
|10
|9.00-11.00
|early gastrula
|two primary germ layers
|[[File:Stage10veg.jpg|100px]]
|-
|10.5
|11.00-11.45
|gastrula
|two germ layers
|[[File:Stage105vegb.jpg|100px]]
|-
|11
|11.45-12.30
|medulla plate
|Yolk sac protrudes dorsally, labium moves to midline on ventral side
|[[File:Stage11veg.jpg|100px]]
|-
|11.5
|12.30-13.15
|continuation of medulla plate
|start closing the plate
|[[File:Stage115veg.jpg|100px]]
|-
|12
|13.15-14.15
|early neurula
|thickened ectoderm give rise to CNS
|[[File:Stage12veg.jpg|100px]]
|-
|12.5
|14.15-14.45
|neural folds
|expansion of cavity
|[[File:Stage125postdors.jpg|100px]]
|-
|13
|14.45-16.15
|neural folds
|continue expanding cavity
|[[File:Stage13postdors.jpg|100px]]
|-
|14
|16.15-17.30
|neural folds
|continuation of cavity
|[[File:Stage14postdors.jpg|100px]]
|-
|15
|17.30-18.15
|tail bud stage
|early organogeny
|[[File:Stage15postdors.jpg|100px]]
|-
|16
|18.15-18.45
|tail bud stage
|posterior ventral view
|[[File:Stage16ant.jpg|100px]]
|-
|17
|18.45-19.45
|tail bud stage
|anterior view
|[[File:Stage17ant.jpg|100px]]
|-
|19
|20.45-21.45
|neural fold close complete
|dorsal view
|[[File:Stage19dorsal.jpg|100px]]
|-
|20
|21.45-22.30
|early tail bud
|anterior view
|[[File:Stage20dorsal.jpg|100px]]
|-
|21
|22.30-24.00
|termination of neural crest
|progress to next stage
|[[File:Stage21ant.jpg|100px]]
|-
|22
|24.00-24.45
|prolonged development
|elongation
|[[File:Stage22lat.jpg|100px]]
|-
|23
|24.45-26.15
|elongation of embryo
|later view
|[[File:Stage23lat.jpg|100px]]
|-
|24
|26.15-27.30
|continuation of elongation of embryo
|dorsal view
|[[File:Stage24latsmall.jpg|50px]]
|-
|25
|27.30-29.30
|organs development
|embryo elongates and develops dorsal thickening
|[[File:Stage25dorsal.jpg|50px]]
|-
|26
|29.30-31.15
|elongation
|dorsally forms neural and brain cavity
|[[File:Stage26lat.jpg|50px]]
|-
|27
|31.15-32.30
|elongation of embryo
|dorsal view
|[[File:Stage27lat.jpg|50px]]
|-
|28
|32.30-35.00
|further development
|lateral view
|[[File:Stage28lat.jpg|50px]]
|-
|29-30
|35.00-37.30
|tail bud
|growth
|[[File:Stage29-30lat.jpg|50px]]
|-
|31
|37.30-40.00
|prolonged development
|bud development
|[[File:Stage31lat.jpg|50px]]
|-
|32
|40.00-44.30
|early muscular development
|elongation
|[[File:Stage32lat.jpg|50px]]
|-
|33-34
|44.30-50.00
|muscular movement
|apparatus for locomotion
|[[File:Stage33-34lat.jpg|50px]]
|-
|35-36
|50.00-53.30
|muscular movement
|apparatus for locomotion
|[[File:Stage35-36lat.jpg|50px]]
|-
|37-38
|53.30-56.30
|heart beat
|develops apparatus
|[[File:Stage37-38lat.jpg|50px]]
|-
|39
|56.30-66.00
|mouth opens
|cornea transparent
|[[File:Stage39latsmall.jpg|50px]]
|-
|40
|66.00-76.00
|gill circulation
|hatching
|[[File:Stage40lat.jpg|50px]]
|-
|41
|76.00-80.00
|tail, fin circulation
|circulation
|[[File:Stage41lat.jpg|50px]]
|-
|42
|80.00-86.00
|internal gills, operculum
|opercular fold, teeth
|[[File:Stage42lat.jpg|50px]]
|-
|43
|86.00-98.00
|operculum complete
|operculum closed on right
|[[File:Stage43lat.jpg|50px]]
|-
|46
|98.00-106.00
|metamorphosis
|emergence from water as miniature, operculum complete|
|[[File:Stage46lat.jpg|50px]]
|-
|}

==Abnormalities of frog==

Abnormalities of frog could be caused by multiple factors. These include change in climate, predators, parasites, bacteria, fungi, viruses or pollution and contaminants such as pesticides, metals and fertilizer.[http://www.fws.gov/contaminants/documents/frogsrefup_septoct_2006.pdf]

The Abnormalities are further classified into different categories. These categories are:

===1. Infectious Diseases:===

'''Perkinsus Symptoms-''' caused by perkinsus-like protozoan organism. Symptoms include swollen viscera that leads to a bloated body and and infected swollen heart

'''Ichthyophonus symptoms-''' cause by parasitic genus, where symptoms include a swollen tail resorption site that matches the surrounding skin in color and translucency.

[[Image:Abnormalities of Frog species.jpg|thumb|left|Figure A Image details[waterwatchadelaide.net.au].jpg]]

===2. Surficial Abnormalities:===

Surficial abnormalities as the one that are visible on the surface of the skin. This includes abnormal pigmentation, , subcutaneous hemorrhaging, wounds due to trauma or from a predator
Edema is a fluid-filled swelling under skin whihc is also a surficial abnormality.

===3. Skeletal Abnormalities:===

This is further classified into three more categories:

'''a. Skeletal Malformations-'''

* Microcephaly (small head or blunt snout)
*Scoliosis (Curved spine in lateral direction)
*Shrunken Limb (Micromelia)
*Amelia (Completely missing limb with no stump)

'''b. Skeletal Abnormalities of Unclear Etiology-'''

This condition arises when a frog has ectromelia (missing limb), brachydactyly (missing digits) or other such condition with no visible trauma or external damage, then this will be classified as the Skeletal abnormality of unclear etiology.

'''c. Skeletal Injuries-'''

Any limb missing or broken due to trauma or other related reason which shows clear evidence of it is classified as skeletal injury

===4. Eye Abnormalities:===

Most common includes-

'''i. Anophthalmia:''' Skin covers the eye socket as there is no eye

'''ii. Abnormal Iris Coloration:''' Reduced pigment in either one eye or both resulting in two different colours of the iris at times

'''iii. Abnormal size or shape:''' Both eyes either deviating from each other or size of pupil or iris is different than the other eye

[http://www.fws.gov/contaminants/Amphibian/pdfs/AbnormalitySOP_woutpics_Jan08.pdf ]

==Genetics==

There are a wide variety of species that differ from each other when it comes to genetics and their functioning.

'''TAXONOMY:''' '''Phylum''' ''Chordata'' / '''Sub Phylum''' ''Vertebrata'' / '''Class''' ''Amphibia'' / '''Order''' ''Anura''

Their are more than two dozen different families of frogs, where suborders are:

'''1. ARCHAEBATRACHIA-''' most primitive frogs

'''2. MESOBATRACHIA-''' linked between the Archaebatrachia and Neobatrachia

'''3. NEOBATRACHIA-''' most modern frogs

{| border='4px'
|+ '''General Info:'''
! !!
|-
| '''Number of frogs' species'''
| 5280
|-
| '''Smallest frog genome size:'''
| 0.95pg, Ornate burrowing frog
|-
| '''Largest frog genome size:'''
| 13.40pg, Ornate horned frog
|-
| '''Mean of frogs' genome'''
| 4.68pg ± 0.13
|-
|}

[http://www.genomesize.com]

*Majority of frogs have only 22 to 26 chromosomes and polyploid is very common where they are almost bisexual.

*Polyploid Amphibians reduce their total cell number such that they acheive the same body size as diploids. One of the most unsual forms of polypoidy in amphibians is the water frog ''Rana esculenta'' from Europe and Western Asia.

* The species with larger genomes have more genes for e.g. the frog genus ''Xenopus'' includes 16 species, with genome sizes ranging from 3.5 x 10^9 bp to 1.6 x 10^10 bp. These differences have arisen by numerous events of polyploidization within the past 40 million years or so. The ancestral chromosome number for the genus seems to have been 18, but there are species with 36, 72 and 105 chromosomes [http://www.xenbase.org/common/]

{| border='4px'
|+ '''Difference within two families'''
! '''SPECIES''' !! ''X.LAEVIS'' !! ''X.TROPICALIS''
|-
| '''PLOIDY'''
| Allotetraploid
| Diploid
|-
| '''NO. OF CHROMOSOMES'''
| 36 chromosomes
| 20 chromosomes
|-
| '''GENOME SIZE'''
| 3.1 x 10^9 bp
| 1.7 x 10^9 bp
|-
| '''EGG SIZE'''
| 1-1.3 mm
| 0.7-0.8 mm
|-
| '''GENERATION TIME'''
| 1-2 years
| 4 months
|-
|}
[http://www.xenbase.org/common/]

===Genome Sequencing===

Since Frog has a huge family with many different species, only few main species that are used widely for the purposes of experiments have their genome sequenced.

''Xenopus tropicalis'' has one of the smallest genomes among amphibians and has the shortest generation time- four to six months and the only diploid genome among the 14 Xenopus species. This means it has no more than two copies of most genes, whereas the other species of Xenopus have four copies of most genes (pseudotetraploid). US Department of Energy's Joint Genome Institute (JGI) in Walnut Creek, California, initiated the X. tropicalis Genome Project, finding 1,700 million base pairs.
[http://www.genome.gov/Pages/Research/Sequencing/BACLibrary/xenopusTropicalis.pdf]

===Xenopus oocytes===

* The oocytes provide an important expression system for molecular biology.

* By injecting DNA or mRNA into the oocyte or developing embryo, scientists can study the protein products in a controlled system. This allows rapid functional expression of manipulated DNAs (or mRNA). This is particularly useful in electrophysiology, where the ease of recording from the oocyte makes expression of membrane channels attractive.

* One challenge of oocyte work is eliminating native proteins that might confound results, such as membrane channels native to the oocyte.

* Translation of proteins can be blocked or splicing of pre-mRNA can be modified by injection of Morpholino antisense oligos into the oocyte (for distribution throughout the embryo) or early embryo (for distribution only into daughter cells of the injected cell).
[http://www.staff.unibe.ch/sigel/xenopus.html]

===Xenopus Laevis===

* ''Xenopus Laevis'' is an important model organism in developmental biology. X. laevis is tetraploid and reaches sexual maturity in 1 to 2 years. What makes it important in developmental biology is its large and easily manipulable embryo.

* Extracts from the eggs of X. laevis frogs are also commonly used for biochemical studies of DNA replication and repair, as these extracts fully support DNA replication and other related processes in a cell-free environment which allows easier manipulation.

* The Human chorionic gonadotropin hormone (hCG) is present in the urine of the pregnant women in large quantities only. This hormone in the urine induces X.laevis oocyte production which formed the basis of first well-documented method of pregnancy testing X. laevis is also notable for its use as the first well-documented method of pregnancy testing when it was discovered. Today, commercially available HCG is injected into Xenopus males and females to induce mating behavior and breed these frogs in captivity at any time of the year.

===Gene cluster===

* The alpha and beta globin genes are closely linked in small cluster of frogs compared to human and chicken

* The similarity of architecture of two clusters found in X.laevis supports the tetraploid origin

* The two loci encoding the muscle specific creatine kinase isoenzymes and have large differences in developmental profile, therefore suggesting that duplicate loci that have not undergone silencing are not simply redundant copies but have acquired specialization.

* Contains twice number of genes for proteins i.e. haemoglobin and sarcomeric actin serum albumin compared with other species

----

==Current Embrology Research==

Currently, a number of fields have benefited from the development of frog embrology. These include cloning, verification of messenger RNA, and Cell cycle.

===Cloning===
[[Image:Robert Briggs.jpg|thumb|left|Figure 16 Image details:Robert Briggs.jpg]]

In 1952, Robert Briggs and Thomas J King cloned northern leopard frogs using a method of nuclear transfer. Briggs and King's experiment was similar to that envisioned - and piloted using salamanders - by Hans Spemann in his 1938 proposal for a 'fantastical experiment'. Later, John Gurdon extended this work and showed that nuclei from differentiated cells could support development, although less well than those from early embryos. [http://genome.wellcome.ac.uk/doc_WTD020799.html]

Lemaitre et a. (2005) from MRC Cancer Cell Unit, Cambridge, U.K. worked on experiments that demonstrated that importance of serial nuclear transplantation for the sucessful cloning of frogs. He demonstrated that exposure of somatic-cell nuclei (erythrocyte nuclei) and sperm nuclei to an extract of mitotic cell extract reorganizes the chromatin into shorter loops and allows replication at much shorter intervals along the DNA. This increases the efficiency of DNA replication in mammalian cell-free systems.

===Transgenesis techniques for functional genomics in Xenopus===

Transgenesis in Xenopus is made possible due to large embryos, a reliable fate map, ease of microinjection, ease of dissection/micromanipulation and existence of the neuroendocrine reflex of background adaptation as a model for activation/inact.

Recently, Hajime Ogino and Haruki Ochi from Nura Institute of Science and Technology in Japan focused on the genomic resources and principles of the transgenesis techniques in Xenopus, and discusses their applications to genome wide network analysis, with emphasis on the use of bioinformatics tools. This is will to understand the gene regulatory networks that control vertebrate development. [http://www.ingentaconnect.com/content/bsc/dgd/2009/00000051/00000004/art00001%3Bjsessionid=4ah96rms73gcu.alexandra]

Xenopus used to be a problem in earlier days when it came to transgenesis. Current methods involves isolated sperm nuclei from Xenopus testis that are microinjected into unfertilized eggs. The generated transgenic tadpoles contain 5-35 copies of the integrated plasmid that are expressed in all cells. If desired, expression of the transgene can be directed to the appropriate tissue and at the appropriate time by using specific promoters, mostly the Xenopus POMC gene promoter (isolated from a Xenopus genomic DNA library) to specifically direct expression of green fluorescent protein (GFP) at high levels to the intermediate pituitary cells, which can either be over expressed or inhibited.[http://molanphys.ruhosting.nl/transgenesis.htm]

[[File:Transgenesis.JPG]]

===Verification of messenger RNA===

While the existence and role of messenger RNA (mRNA) was known in bacteria, in the 1960s it was still debated whether it also existed in vertebrates. Taking haemoglobin mRNA from immature red blood cells and injecting it into a Xenopus oocyte, John Gurdon showed that the haemoglobin protein was indeed produced. Producing proteins in Xenopus oocytes has proved to be extremely useful in cell biology, in particular for the study of receptor proteins.[http://genome.wellcome.ac.uk/doc_WTD020799.html]

===Cell Cycle===

As they develop outside the mother, frog eggs are well stocked with the proteins needed to drive the development of the embryo. Studies of these processes has shed considerable light on the processes involved in cell division - termed the cell cycle. [http://genome.wellcome.ac.uk/doc_WTD020799.html]

===Limb development in Xenopus Laevis===

[[Image: Frog Limb development.jpg|thumb|right|From Limb Development Image details:Primary source:[http://images.google.com.au/imgres?imgurl=http://www.sciencedaily.com/images/2006/06/060616130718.jpg&imgrefurl=http://www.sciencedaily.com/releases/2006/06/060616130718.htm&usg=__xliPsPAvheUBME_kjv_q7auiFbo=&h=333&w=300&sz=11&hl=en&start=2&um=1&tbnid=y_ntJtmkRSK7WM:&tbnh=119&tbnw=107&prev=/images%3Fq%3DLimb%2Bdevelopment%2Bin%2BXenopus%2BLaevis%26ndsp%3D18%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

Donald D. Brown (2005),Department of Embryology, Carnegie Institution of Washington demonstrated factors related to limb development of Xenopus Laevis. Thyroid hormone (TH) is found to be required for limb development in this frog. Specific cell types in the growing limb were targeted for expression of a dominant negative form of the TH receptor by sperm-mediated transgenesis. Limb muscle development, the innervation of muscle from the spinal cord, and cartilage growth can be inhibited without affecting patterning of the limb or differentiation of other cell types. Remodeling of the skin occurs late in metamorphosis after the limb has formed. The coordination of these independent programs is affected in part by the control that TH exerts over DNA replication in all cell types of the limb. [http://www.pnas.org/content/102/35/12455.full]

----

== Glossary ==

[[Image: Frog species.jpg|thumb|left| Frog Species Image details:Primary source:www.olympus.co.jp/.../080925/large/p02L.jpg].jpg]]

*'''Amphibian:'''

''Relating to or characteristic of animals of the class amphibia.Amphibians are found in the taxonomic class of amphibia, amphibians are capable of both occupying and successfully living in both land and aquatic communities.amphibian''

*'''Augmentation:'''

''Enlargement/Increase in cellular size.''

*'''Autolysis:'''

''breakdown of a part or whole cell or tissue by self-produced enzymes''

*'''Blastomeres:'''

''The undifferentiated cells formed by cleavage of the fertilised ovum. This includes cells in the cleavage, morula, and blastula stages of the embryo''

*'''Carnivorous:'''
''
Flesh-eating; subsisting on animals as food.''

*'''Cleavage:'''

''he repeated division of a fertilised ovum ''

* '''Cleft:'''

''an opening, fissure, or V-shaped indentation made by or as if by splitting''

*'''Chordate:'''

''Members of a diverse phylum of animals that, as embryos, possess a (1) notochord; (2) a dorsal, hollow nerve cord, (3) pharyngeal gill slits; and (4) a post-anal tail''

''The act or state of splitting or dividing of a cell, particularly during the telophase of (animal) cell division.''

*'''Cytoplasm:'''

''The cytoplasm (of both eukaryotes and prokaryotes) is where the functions for cell expansion, growth, metabolism, and replication are carried out''

* '''Epiboly:'''
''The expansion of one cell sheet over other cells, as takes place during gastrulation''

*'''Fertilization:'''

''A process in sexual reproduction that involves the union of male (sperm) and female (ovum) gametes (each with a single, haploid set of chromosomes) to produce a diploid zygote.''

*'''Gamete:'''
''A reproductive cell (male (sperm) or female (egg)) that has only half the usual number of chromosomes''

*'''Gametogenesis:'''

''process leading to the production of gametes. The development and maturation of sex cells through meiosis.Another name for meiosis where a diploid cell is divided into two haploid cells with half the chromosome content of the diploid parent cell.''

*'''Herbivorous:'''

''eating plants; of or pertaining to the herbivora.''

*'''Holoblastic:'''

''The complete division of an isolecithal or microlecithal egg into blastomeres''

*'''Invagination:'''

''One of the methods by which the various germinal layers of the ovum are differentiated.''

*'''Isoenzymes:'''

''Isozymes (also known as isoenzymes) are enzymes that differ in amino acid sequence but catalyze the same chemical reaction.''

*'''Mesentery:'''

'' membranous fold attaching various organs to the body wall.''

*'''Metamorphosis:'''

''A change in the form and often habits of an animal after the embryonic stage during normal development.''

*'''Neuroendocrine:'''

''Neuroendocrine [IPA nʊəroʊˈɛndəkrɪn] cells are cells that release a hormone into the circulating blood in response to a neural stimulus.''

*'''Organogenesis:'''

''The part of embryonic development where the body's main organs develop.''

*'''Peritoneum:'''

''The smooth serous membrane which lines the cavity of the abdomen, or the whole body cavity when there is no diaphragm, and, turning back, surrounds the viscera, forming a closed, or nearly closed, sac.''

*'''Perivitelline space:'''

''The perivitelline space is the space between the zona pellucida and the plasma membrane (sometimes called the vitelline membrane) in a fertilized ovum.''

*'''Polyploidy:'''

''Cells with three or more sets of chromosomes.''

*'''Pronucleus:'''

''the nucleus of the ovum or sperm after fertilization but before they fuse to form the nucleus of the zygote ''

*'''Protoplasm:'''

''The fluid living content of the cell that consists of two major divisions, the cytoplasm and the nucleoplasm (cell nucleus). It is composed mainly of nucleic acids, proteins, lipids, carbohydrates, and inorganic salts''

*'''Segmentation:'''

''division of some metazoan bodies (such as annelida and Arthropoda) into repeated parts, segments. Segmentation can be homomeric (more or less the same) or heteromeric(different from each other).''

*'''Terrestrial:'''

''Of or on the ground, of the habitat of a plant, on land as opposed to in water, or on the ground as opposed to on another plant.''

*'''Transgenesis:'''

''Transgenesis is the process of introducing an exogenous gene - called a transgene - into a living organism so that the organism will exhibit a new property and transmit that property to its offspring.''

*'''Yolk:'''

''nutritive material of an ovum stored for the nutrition of an embryo''

*'''Zygote:'''

''The cell from which an organism develops, that results from the fertilization of the egg by the sperm.''

''Primary Resource "Biology- Online Dictionary''[http://www.biology-online.org/dictionary/Main_Page]

== References - Frog Embryology: ==

[[Image:Frog Research.jpg|thumb|left|Research being done on a Frog Image details:[http://images.google.com.au/imgres?imgurl=http://www.odt.co.nz/files/story/2008/09/university_of_otago_zoology_senior_lecturer_phil_b_3343259744.jpg&imgrefurl=http://www.odt.co.nz/on-campus/university-otago/21670/dunedin-frog-man-wins-zoo-award&usg=__JvJJU5QfOnIwY2bk4xo64UXuJRs=&h=600&w=404&sz=22&hl=en&start=14&um=1&tbnid=AbsP89yWcUiilM:&tbnh=135&tbnw=91&prev=/images%3Fq%3Dfrog%2Bresearch%26hl%3Den%26um%3D1].jpg]]

1. Savage, J. M. (2002). The Amphibians and Reptiles of Costa Rica. University of Chicago Press, Chicago [http://www.springerlink.com/content/vv015277w1746llw/]

2. Ford, L.S.; D.C. Cannatella (1993). "The major clades of frogs". Herpetological Monographs 7: 94–117 [http://digimorph.org/specimens/Xenopus_laevis/]

3. Tyler, M. J. (1994). Australian Frogs A Natural History. Reed Books [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.gracilenta.html]

4. Cogger, H.G.; R.G. Zweifel, and D. Kirschner (2004). Encyclopedia of Reptiles & Amphibians Second Edition. Fog City Press [http://en.wikipedia.org/wiki/Microhylidae]

5. Beltz, Ellin (2005). Frogs: Inside their Remarkable World. Firefly Books [http://unjobs.org/authors/ellin-beltz]

6. Tyler, M. J. (1994). Australian Frogs A Natural History. Reed Books [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

7. Moury JD, Hanken J (1995) Early cranial neural crest migration in the direct-developing frog, Eleutherodactylus coqui. Acta
Anatomica (Basel) 153, 243-253.

8.Raynaud A (1985) Development of limbs and embryonic limb reduction. In Biology of the Reptilia (ed. Gans C, Billett F), pp.
59-148. New York: John Wiley.[http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=9309]

9. Hanken J (1986) Developmental evidence for amphibian origins. In Evolutionary Biology (ed. Hecht MK, Wallace B, Prance GT), 20, pp. 389-417. New York: Plenum Press. [Hanken J (1986) Developmental evidence for amphibian origins. In Evolutionary Biology (ed. Hecht MK, Wallace B, Prance GT), 20, pp. 389-417. New York: Plenum Press.]

10. Elinson RP (1990) Direct development in frogs : wiping the recapitulationist slate clean. Seminars in Developmental Biology
1, 263-270.

11. Beebee, T. J. C. 1996. Ecology and Conservation of Amphibians. Chapman and Hall. London. [http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V5X-3SVHMKH-1X&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=1021245355&_rerunOrigin=google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=825868e10cd178d16a8a0e5ad14dc5ef]

12. Lehtinen, R. M. 2002. The use of screw pines (Pandanus spp.) by amphibians and reptiles in Madagascar. Herpetological Bulletin 2002:20–25.

13. Parris, K. M. and M. A. McCarthy. 1999. What influences the structure of frog assemblages at forest streams. Australian Journal of Ecology 24:495–502. CrossRef

14. Zug, G. R. 1993. Herpetology: An Introductory Biology of Amphibians and Reptiles. Academic Press. San Diego, CA.

15. Slack,J.M.W., Darlington,B.G., Heath,J.K. and Godsave,S.F. (1987)Mesoderm induction in early Xenopus embryos by heparin-binding growth factors. Nature, 326, 197-200.

16. Melton,D.A. (1990) Activins are expressed early in Xenopus embryogenesis and can induce axial mesoderm and anterior structures. Cell, 63, 485-493.

17. Harland,R.M. and Misher,L. (1988) Stability of RNA in developing Xenopus embryos and identification of a destabilizing sequence in TFIIIA RNA. Development, 102, 837-852.

18. Cunliffe,V. and Smith,J.C. (1992) Ectopic mesoderm formation in Xenopus embryos caused by widespread expression of a Brachyury homologue. Nature, 358, 427-430.

19. Kinoshita,K., Bessho,T. and Asashima,M. (1993) Competence prepattern in the animal hemisphere of the 8-cell-stage Xenopus embryo. Devel. Biol., 160, 276-284.

20. LaBonne,C., Burke,B. and Whitman,M. (1995) Role of MAP kinase in mesoderm induction and axial patterning in Xenopus development. Development, 121, 1475-1486.

21. Green,J.B.A., New,H.V. and Smith,J.C. (1992) Responses of embryonic Xenopus cells to activin and FGF are separated by multiple dose thresholds and correspond to distinct axes of the mesoderm. Cell, 71, 731-739.

22. Grainger R., Blumberg B., Harland R., Amemiya C., Importance of Xenopus Tropicalis to biomedical and biological research, Benaroya Research Institute, Virginia Mason Research Center [http://www.genome.gov/Pages/Research/Sequencing/BACLibrary/xenopusTropicalis.pdf ]

23. Gregory, T.R. (2005). Animal Genome Size Database. [http://www.genomesize.com]

24. U.S Fish and Wildlife Services, ABNORMALITY CLASSIFICATION SOP, [http://www.fws.gov/contaminants/Amphibian/pdfs/AbnormalitySOP_woutpics_Jan08.pdf ]

25. Donald D. Brown*, Liquan Cai*, Biswajit Das*, Nicholas Marsh-Armstrong‡, Alexander M. Schreiber*, and Rejeanne Juste*(2005), Thyroid hormone controls multiple independent programs required for limb development in Xenopus laevis metamorphosis [http://www.pnas.org/content/102/35/12455.full]

26. Ogino, Hajime; Ochi, Haruki, Resources and transgenesis techniques for functional genomics in Xenopus, Development Growth & Differentiation, Volume 51, Number 4, May 2009 , pp. 387-401(15) [http://www.ingentaconnect.com/content/bsc/dgd/2009/00000051/00000004/art00001%3Bjsessionid=4ah96rms73gcu.alexandra]

27. Giles Newton (2004) Why the frog? The Human Genome, [http://genome.wellcome.ac.uk/doc_WTD020799.html]

28. Xenbase, [http://www.xenbase.org/common/]

29. Donders Center for Neuroscience & Nijmegen Center for Molecular Life Sciences (NCMLS), Beyond the genome (Xenopus transgenesis for functional genomics),Faculty of Science, Radboud University [http://molanphys.ruhosting.nl/transgenesis.htm]

== External Links ==
[[Image:Frog links.jpg|thumb|left|Image details:[http://images.google.com.au/imgres?imgurl=http://2.bp.blogspot.com/_o93AaY0GzH4/SjY_ZYv0PII/AAAAAAAAAgk/skruNc2yN78/s400/computer%2Bfrog.jpg&imgrefurl=http://hellaheaven-ana.blogspot.com/2009/06/talking-frog-contemporary-fairy-tale.html&usg=__oxji1TGLV2Fi7xe0dnlmuYk8gDo=&h=288&w=288&sz=16&hl=en&start=2&um=1&tbnid=ywZd4zpdxC5plM:&tbnh=115&tbnw=115&prev=/images%3Fq%3Dfrog%2Bon%2Bcomputer%26hl%3Den%26um%3D1].jpg]]

1. Frog embryology [http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/F/FrogEmbryology.html Frog Embryology]

2. Frog cellular materials [http://www.xenbase.org/xenbase/original/cell/cell.html xenbase]

3. The zoology of frog species [http://worms.zoology.wisc.edu/frogs/mainmenu.html zoology frogs]

4. Frog cycle [http://www.bioethics.gov/images/sc_images/frog_dev.gif bioethics frog] Just a little cycle of FROG'S life cycle

5. Frog Embryology [http://embryology.med.unsw.edu.au/OtherEmb/Frog.htm UNSW Embryology]

6. Frog Research [http://apps.carleton.edu/campus/library/now/exhibits/wallcharts/frog/ carleton library exhibit]

{{Template:Projects09}}
[[Category:Frog]]

2009 Group Project 5

2009-10-14T22:48:17Z

Z3258567: /* Glossary */

== The Embryology of Frogs ==

== The Frog ==

[[Image: Frog species .jpg|thumb|left|Image details: Wikipedia (2009) Frog species[http://en.wikipedia.org/wiki/Frog#Uses_in_agriculture_and_research].jpg]]

Frogs are scientifically identified by the structure of their long posterior limbs, a petite framework, webbed fingers and feet, budged eyes and the lack of a tail. The majority of frog species are extensively recognized as outstanding jumpers, due to their long, dominant legs, which are adaptations to progress jumping performance during activities. The Frog is one of the most frequently studied species in experimental embryology and most anatomical sciences. ''The Frog is a practically effective model for human embryological development given that the Frog:''

- Comprises of genes which can be effectively manipulated.

- Comprises of similar homogeny with humans species.

- Reproduces a large quantity of offspring in a short period of time.

- Are small species which can be simply sustained.

- Are not extremely luxurious and expensive.

== The History of the uses in agriculture and research ==

[[Image: Frog experiments .jpg|thumb|right|Image details: Scans of chemically cleared and dyed preserved deformed frogs and toads [http://www.sat.qc.ca/upload/residence/frog-04.jpg].jpg]]

There are numerous types of frog species that have been manipulated in many developmental experiments. The frog was traditionally used by countless of the early embryology investigators and presently there are several diverse molecular mechanisms regarding progression of the frog. Theses include:

'''1.''' Food source; frog legs are a delicacy and are eaten in European countries and in many parts of South American regions.

'''2.''' Frogs have the finest biochemical dissection of phenomena that take place in the egg and oocyte. Frogs are the evolutionarily closest to mammals, commonly used as a vertebrate model.

'''3.''' Frogs lay thousands of outsized eggs, from which cell extracts can be readily prepared that is capable of recapitulating most molecular phenomena in a test tube.

'''4.''' Frogs have been commonly used as a laboratory system for a very long period, and have an extensive history of producing crucial observations in countless fields of biology.

'''5.''' Frogs have a important historical connection to the study of epigenetics (John Gurdon-vertebrate cloning and reprogramming) which has been mostly performed on frog species.

'''6.''' Frogs also have very strong evidence of pattern formation and early development, as the embryos are large in size and experimentally manipulative.

'''7.''' Recent research into the biochemistry of chromatin and epigenetics has been performed with frog species and mammalian cultured cells.

'''8.''' The biggest weakness of the Frog model system is the difficulty of performing genetic experiments and analysis, as frogs are allotetraploid, meaning they take approximately a year to fully develop to sexual maturity, and the genome has not been completely sequenced. Nevertheless, biochemical manipulations of cell extracts, such as immunodepletions and application of heterologous DNAs and nuclei can avoid the need for genetic exploitation.

----

== Growth and development of the Frog ==

[[Image: Mature develop frog.jpg|thumb|Image details: Wikipedia (2009) Red Eyed Tree Frog Figure 1 Primary source:[http://en.wikipedia.org/wiki/File:Red-eyed_Tree_Frog_-_Litoria_chloris_edit1].jpg]]

* The frog is a well recognised species, abundant predominantly in ponds, swamps, though various species may also exist in damp or shady environments distant from moist habitats.

* Eggs of specific frogs are easily obtained and may be examined in from the beginning of fertilization onwards. The phases of embryonic development differs in various chordates, yet the typical phases are basically apparent in all frog species. The differences are associated principally to the amount of yolk particles present in an egg.

* The yolk particles offer nourishment of the developing embryo. The process of frog development will be discussed from the phases of gametogenesis to the adult stage.

----

== The Egg ==
[[Image:Development of Poles in frog Fertilization.jpg|thumb|left|Development of Poles in Frog Fertilisation:J,Nassif 2009.jpg]]

- The embryology of a frog egg is a vast cell; its dimensions are approximately 1.4-1.6 million times larger than a typical aquatic species egg cell. Throughout the frog’s embryonic maturation period, the egg will be transformed into a tadpole encompassing millions of cells but still remains with its constant volume of genetic material, the vast prodction of cell have been illusttrated in the figure on the right revealing the production of eggs from female frogs. [http://en.wikipedia.org/wiki/Microhylidae]

- The early embryonic frog structure consists of three main segments the superior hemisphere known as the animal pole which is usually visible as a grey coloured area. The innermost layer appears to be between the outer two sections known as the gray crescent represented in black. Inferiorly, represents the vegetal pole typically lighter than the superior compartment illustrated in gold.

VIDEO RESOURCE: [http://www.youtube.com/watch?v=GO5YN_t1fqw&feature=related]

[[Image:Early Development of Frogs.jpg|thumb|left|Early Development of Frog:J,Nassif 2009.jpg]]

==History of frog embryology use ==

*'''1851''' - ''Henby Nelson''(MD): He identified a remarkable fact through the frog embryo. Henby observed the first cleavage of the yolk, in the egg of the frog. And cleaved structure corresponds in line of direction to the longitudinal axis of the body of the embryo of the frog species.

[[Image:Wilhelm Roux.jpg|thumb|right|Wilhelm Roux[http://images.google.com.au/imgres?imgurl=http://www.todayinsci.com/R/Roux_Wilhelm/RouxWilhelmThm.jpg&imgrefurl=http://www.todayinsci.com/6/6_09.htm&usg=__qRLTEMTHdZpAHxiNX12hWjcm9tA=&h=125&w=100&sz=4&hl=en&start=2&um=1&tbnid=LIKIwZTqCpk7MM:&tbnh=90&tbnw=72&prev=/images%3Fq%3DWilhelm%2BRoux%26gbv%3D2%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

*'''1888''' - ''Wilhelm Roux'': Wilhelm Roux attempted to solve the above observation by damaging one cell of a two-cell frog embryo with a hot needle. The cell stayed in place. However, it did not develop further. Its partner developed into a left or right half-embryo;

*'''1907''' - ''John Hopkins'' hospital: In order to identify the cellular source of neuronal fibres. Scientist placed small portions of frog embryo spinal cords in lymph on a microscope slide and was able to observe clear cut neuronal sprouting.

*'''1951''' - ''Robert Briggs'': Robert Briggs was able to clone a frog embryo by substituting the nucleus of an unfertilized frog egg cell with the nucleus of a frog embryo cell. This process is known as nuclear transplant, has formed the basis for all cloning.

*'''1952''' - ''Robert Briggs and T.J. King'': Robert Briggs and T.J. King used frog for test experiment. Because the size of the eggs in the frogs are enormous compared with those of mammals, which make them easier to manipulate.

*'''1976'''- Using the technique that had been successful in cloning frog embryos, the doctor transferred the nucleus of one cells into a donated egg cell. As an embryo began to develop, it was implanted into the uterus of a young woman.

*'''1997''' - ''Wilmut and Campbell'': Utilizing the cloning technique from frog embryo, Drs. Wilmut and Campbell tried the starvation technique on embryo cells to produce Megan and Morag, the world's first cloned sheep and, until now, the most famous sheep in history.

*'''2000''' - ''Tokyo University'': Scientists at Tokyo University have grown artificial eyeballs. Scientists formed them in tadpoles by using frog embryo cells.

*'''2001''' - ''Advanced Cell Technology'': Scientists from Advanced Cell Technology announced production of a human embryo clone. This is significant as its parthenogenesis has been artificially induced in frogs.

[[Image:John Gurdon .jpg|thumb|right|John Gurdon [http://images.google.com.au/imgres?imgurl=http://www.pnas.org/site/misc/images/gurdon.jpg&imgrefurl=http://www.pnas.org/site/misc/classics4.shtml&usg=__1p-GA1PdOYsxKL-cznMb3RHCm98=&h=526&w=400&sz=223&hl=en&start=1&um=1&tbnid=9k4lhuLssiWCAM:&tbnh=132&tbnw=100&prev=/images%3Fq%3DJohn%2BGurdon%26gbv%3D2%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

*'''2002''' - ''John Gurdon'': John Gurdon from Wellcome Cancer Research Institute in Cambridge experimented on cloned frog embryo.

== Gametogenesis ==

* The sexual reproduction occurs through the fusion of either mature reproductive cells or germ cells known as gametes, which include the sperm from the male frog and ova from female frog species so as to form a single cell, the fertilized zygote. The gametes are typically developed in parents of different sexes . [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

* Males gametes is a spermatozoon , the female frog gamete is an ovum. Each gamete is formed by a process, recognised as maturation or gametogenesis in gonads. The typical male frog gonads are testies in male, while the female gonads are ovaries. The synthesis of both gonads is associated with the process of fertilization. [http://en.wikipedia.org/wiki/Microhylidae]

* The zygote changes into a mature frog through the process of embryology and metamorphosis. Gametogenesis is a in progression which frog gametes are established from germ cells. Initial germ cells are called primordial germ cells, which can be recognised extremely early in the life of frog species.

----

== The Egg & Fertilization ==

[[Image:Fertilized and Unfertilised Eggs.jpg|thumb|left|Fertilized and Unfertilized Eggs:J,Nassif 2009.jpg]]

[[Image:Egg Development.jpg|thumb|left|Egg Development:J,Nassif 2009.jpg]]

- This occurs once the sperm cell has inserted, following the insertion of the sperm cells meiosis II is completed, there is a 30 degree position change of the cytoplasm, gray crescent allows this change to be visible in some amphibians, the gray crescent is able what determines the expect ted outline of how the frog will form. The sperm cell joins with the nuclei of the egg which forms the diploid zygote nucleus. --Sando Rashed 10:09, 24 September 2009 (EST)

- The early phases in the development of the egg is visible, but must be studied in tadpoles throughout maturation. In embryonic tadpoles of about 10 millimetres in length, soon after the opening of the oral cavity, a pair of longitudinal ridge-like thickenings of peritoneum becomes apparent along the posterior surface of the body cavity situated near to the mesentery and along the inner boundaries of the kidneys. Genital ridges are established in all tadpoles of this age, sex is not distinct until a later period. The development of the egg is illustrated in the figure on the left revealing the structure of a developed egg and a mature of egg.

[[Image:Fertilisation life cyle.jpg|thumb|Fertilization of Life cycle:Derived from primary source:[http://en.wikipedia.org/wiki/Frog]]]

== Maturation of the Egg ==

- The eggs have currently accomplished their full size, and develop from the exterior of the ovaries like a small shot, but they still have to pass through the course of maturation before they are prepared to be fertilised. This progression of maturation relates to the nucleus almost completely.

- The nucleus component, containing the nuclear fluid that excludes through the nuclear membrane into the substance of the egg, a great segment of the nuclear reticulum vanishes and becomes degraded into separate globules known as nucleoli, but a extremely small division remains in the midpoint as a slender intricately thread recognised as the nuclear skets.
Relative to the egg getting discharged from the ovary, the follicles shatter allowing the eggs to fall into the abdominal cavity of the frog species, the egg then passes forwards, directly by the contraction of the muscular wall, somewhat by the movement of the cilia of the peritoneum, to the apex of the oviduct, which positioned at the anterior compartment of the body cavity opposite to the roots of the respiratory organs.

- The terminal part of the oviduct establishes a thin-walled pouch capable of great swelling, inside which the eggs gathers in large numbers. In conclusion, the eggs are migrated out through the cloaca into water which the albuminous investments of the eggs rapidly augment to form the gelatinous mass of the frogs spawn.

== Maturation phases ==

'''1. Nuclear skein''', moves from the midpoint of the egg to its outer surface, which it reaches opposite the midpoint of the black pole. The skein, subsequently an unevenly twisted thread, now presumes the specific arrangement of a nuclear spindle, for instance may be visible in the nucleus of an epithelial or additional cell instantly prior to division of the cell occurs.[http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

'''2. The first Polar Body,''' regarding the instance the egg is laid, but prior to its fertilistion, the egg develops a considerably flattened appearance at its upper or black pole, a definite sum of fluid being exuded among the egg and the vitelline membrane. The nuclear spindle currently separate into two identical segments, one of which remains with the egg, and the supplementary is extruded as the first polar body, a small ovoidal white globule, which is situated on the surface of the egg surrounding the exuded peri-vitellline fluid.

'''3. The Second Polar Body''', half of the nuclear spindle that stay behind then splits into two equivalent divisions, one of which remains inside the egg as the female pronucleus, whereas the other segment is extruded as the second polar body, a small white globule extremely related to the first polar body, and like this positioned in the perivitelline fluid on the superior portion of the egg.

'''4. Fertilisation of the egg''', includes the synthesis of the spermatozoon with to egg, specifically, synthesis of the nuclei of these two bodies. The spermatozoa, subsequent to being shed over the seed by the male, distribute vigorously by means of their extended tails, break through the gelatinous investment of the female eggs, bore their way through the vitelline membrane and so go through into the eggs themselves, which they penetrate relative to the superior or black hemispheres.
* Subsequently, an hour following the spermatozoon has entered; a progression may be visible projecting within from the exterior segement of the egg, with a liquid spot in the mid point. This liquid centre is the nucleus of the spermatozoon, and is said to be the male pronucleus, it break through beyond into the female egg, transporting the specialised pigment into it, so that it appears bounded by a pigmented capsule linked with the exterior of the egg by a pigmented stalk.

* By this instance, the second polar body has been established and extruded, and the female pronucleus is merely the only component of the primary egg nucleus still present. Both the male and female pronuceli, which are at initially distance separate to each other, merge and after having enlarged significantly in size then fuse mutually about two and half hours after fertilisation has originated to produce the segmentation nucleus.
* The segmentation nucleus is a huge sphere-shaped vesicle embedded in delicately granular protoplasm, and bounded by a distinct capsule of pigment, its arrangement by the synthesis of the male and female pronuclei completes the action of fertilisation. Specifically female pronucleus may be observe as an imperfect nucleus, and consequently result in the course of fertilisation. The nucleus of the spermatozoon or male pronucleus, replaces the component of the egg- nucleus which has been misplaced as the polar bodies.

'''5. Segmentation of the Egg''', the initial phase of growth consist in constant separation of the egg, whereby it becomes transformed from the unicellular state, which is everlasting only in the lowest species, to muliticelluar state charactertics of all higher species. To these early processes of growth the names segmentation is specified. Shorty subsequent to the competition of fertilisation and arrangement of the segmentation nucleus this later misplaces its sphere-shaped appearance and develops to be spindle-shaped, the yolk granules at the equivalent instance showing a tendency to develop into lines distributing outwards from the distal segment of the spindle.
* The nucleus now split into two halves, which shift away from one another, the yolk granules are likely to combined themselves around the two nuclei, and a slender vertical plate of delicately granular substance is left, dividing the egg.[http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

* Superiorly the eggs depression now becomes visible, initially as a small cavity and then develops as a groove, which almost immediately extends all round, and speedily deepening, splits the egg into two entirely separate halves along a plane equivalent with the vertical plane.

* Shorty after, the two nuclei soon separate again into two, and therefore a second cleft is created in the same state as before, its additionally in the vertical plane, however in a plane at 90 degrees to the initial one, and on its finishing point the egg comprises of four accurately similar segments, each containing a nucleus. The third cleft is horizontal in shape, but not equal, lying closer to the superior than the lower pole, it segregates each of the four cells into, an superior smaller and a inferior larger pole

----

== Cleavage ==

[[Image: Frog Cleavage development.jpg|thumb|left|Cleavage Process details:[http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/F/FrogEmbryology.html].jpg]]

* The egg of the frog is scientifically identified as’ telolecithal’ meaning there is a outsized amount of yolk concentrated at a single pole, in contrast to the concentration of cytoplasm and the site of the nucleus. The cleavage phases are holoblastic, therefore the total and after the second cleavage they are asymmetrical .The initial cleavage stage appears about two and half to three hours after fertilization. It commences as a minor depression in close proximity to the centre of the animal hemisphere. It appears as if some interior force is pushing the surface the egg towards the centre. This small upturned fold steadily continues in the form of a channel until it surrounds the egg. This groove is shallow in the commencement, but develop into deeper eventually separating the fertilized egg into two halves recognised as the blastomeres. [The figure on the left symbolise the development and growth of the frog embryo during cleavage].

* Internally the separation is mitotic, consequently each daughter cell contains a nucleus resulting from the copulation nucleus of the fertilised egg. This cleavage is vertical, the two cells are indistinguishable in respect of cytoplasm, pigment and yolk. The subsequent cleavage appears about an hour after the first. The channel of this cleavage begins at the centre of the animal hemisphere, is at right angles to the first and is vertical. This divides the egg into four blastomeres. The fourth blastomere so produced are not qualitatively equal, since of these only two contain the material from the gray crescent. The cleavage begins about thirty minutes after the second is completed or four hours after fertilisation. the cleavage plane of the third furrow is horizontal and slightly above the equator. Thus the four upper cells are a little smaller than the four lower cells. The smaller blastomeres are called micromeres and the larger blastomeres are called macromeres. The fourth cleavages follow 20 minutes after the third and tend to be vertical. This is usually a double furrow.

* The cleavage rate is accelerated with each of the early divisions and since the blastomeres are of unequal size and have varying amounts of cytoplasm and yolk, synchronous cleavage is lost and there is an obvious overlapping of the division. The upper most cells divide more rapidly than the lowermost cells. From this point onwards perfect symmetry in cleavage and in blastomere is very rare, although the embryo developed perfectly. The fifth cleavage is also doubled, appearing first in the upper hemisphere and then in the lower.

* The cleavage thus far follows the rule that each cleavage plane comes in at right angles to the previous one. The subsequent divisions become so irregular that it is previous one. The subsequent division become so irregular that it is impossible to trace out any plan or procedure. The segmentation continues more rapidly in the pigmented regions, since at that place the protoplasm is most dense, whereas, yolk which is very abundant in the vegetal side delays cell division. The multicelluar embryo at this stage is called morula by some biologists.

----

== Gastrulation ==

[[Image:FROG GASTRULATION .jpg|thumb|left|Frog Gastrulation Image details:[http://www.google.com.au/imgres?imgurl=http://bio1903.nicerweb.com/Locked/media/ch47/47_12FrogGastrulation.jpg&imgrefurl=http://bio1903.nicerweb.com/Locked/media/ch47/gastrulation-frog.html&h=540&w=480&sz=46&tbnid=N78sHjELreGGSM:&tbnh=132&tbnw=117&prev=/images%3Fq%3Dfrog%2B-%2Bgastrulation&hl=en&usg=__4VK9FYLft0W-4lBe6p5EtQAMiaI=&ei=qPy5SurtMJvE6wON8JmdAg&sa=X&oi=image_result&resnum=4&ct=image].jpg]]

''The phase of Blastulation is followed by the unique developmental progression of gastrulation. The process of frog gastrulation involves the following processes.''

'''1. Epiboly Phase'''

The pigmented cellular materials of blastula have the propensity to overgrow the yolk cells within the developing content. This course which is known as epiboly commences gradually in the final blastula and rapidly accelerates with advancing gastrulation development. The cellular matter within the animal pole reproduces and matures on all sides except in area surrounding the dorsal lip of the blastopore has been established.

'''2. Convergence'''

Scientists suggested that the unfolding was thought to result in spreading of the superficial cells over a substrate with suitable absorption properties. Consequently epiboly and convergence are an outcome to this spreading tendency, which is actually increased by a reduction in surface tension of the distributing cells.

'''3. Rotation'''

The epiboly phase is maintained until the region of the dorsal lip has migrated and is a to some extent greater than 90 degrees and the region of the white blastopore is reduced to small circular rings. This section will be positioned away from the developing vegetal pole. Laterally the complete developing gastrula has been rotated to a horizontal axis, allowing it to lie at right angles to the original median plane of the egg. Therefore, the course of rotation is such that the dorsal lip is practically pushed backwards in one direction as rapid or quicker than epiboly moves it forward in the other. The outcome will be that the blastopore produced at roughly the vegetal pole is posterior, and the dorsal and ventral lips are essentially dorsal and ventral. This in addition allows the eggs to form the antero-ventral side of the potential embryo whilst the area marked by the grey crescent is to develop the dorsal segment.

'''4. Invagination'''

Visible is a small fissure- like invagination which is apparent in the middle between the equator and the vegetal segment. The most superior or dorsal border of the cleft produce the dorsal lip of the blastopore. This imput move back and forth on the dorsal plane near the dorsal lip and migrates around the boundaries of the blastocoel in company with the extension of the lateral lips. This adapted invagination is maintained until the blastocoel cavity has been almost abolished; excluding the slender opening separating epiblasts from the hypoblast, the new segment formed is known as the archenteron cavity.

'''5. Involution'''

- Additional to previous course of action a distinct involution also occurs at the blastoporal borders. This is mainly dynamic at the median dorsal lip and gradually more less as it shifts across either side until it reaches the ventral lip where it constant.Throughout this progression, cells positioned beside the superior boundaries of the blastoporal lip migrate over the lip to the interior portion of the lip. These cells are remained within the embryo along the internal edge of the blastopore. This indicates the root of archenteron is composed of involuted cells and beyond this the external layer known as the ectoderm. The base and lateral sides are enclosed mainly of endodermal cellular material, which have been established from larger yolk cells, situated in the vegetal pole of the blastula.

- In the final phases of the gastrula development, the cells contributing to the floor of the archenteron, thin out significantly where they surround the blastocoel.
The hemispherical shaped dorsal lip of blastopore which become visible at the commencement of the gastruation stage carry on to augment, initially becoming semicircular, then transform into a horse shoe shaped and then finally forming into circular band. The band is the accomplished by the blastopore. Various yolk cells of vegetal pole present in the section are crowed into the blastoporal cavity where they form a gathering identified as a yolk plug. Blastopore rapidly reduces in size while the archenteron is still developing and becomes completely formed in the final stage; the yolk plug appears as only a small oval on the gastrula.

==Growth and Modification of Frog Species==

'''1. Changes in habits and habitats:'''

'''a)''' In frogs, metamorphosis is related with to the modifications and adaptations as a frog changes environmental habitats from an aquatic to a terrestrial mode. Metamorphosis has modified the adaption of frogs as this alteration it began during the aquatic adaptations in the surface of water to breathe air. Subsequently, it continues the terrestrial surroundings, therefore the frog species become abundant in vegetation area allowing the frog to transform in to amphibious species.

'''b)''' The transition during metamorphosis is linked with a change in food chain. The tadpoles being the embryonic origin of frogs are herbivorous, feeding on algae and green matter, which they collect by the adapted feature such as their teeth surrounding their mouths. Adult frogs, alternatively, are classified as carnivorous feeding on insects and worms. Occasionally, they also consume larger prey, for instance smaller frogs species and even little birds and rodents which they dominant and ingest.

[[Image:Development of frog from sperm to mature structure.jpg|thumb|left|Development of Frog from sperm to mature structure Image details:J,Nassif 2009.jpg]]

'''2. Changes in Morphology'''

These include the decrease or complete absence of specific organs or structures which are essential during development of early frog embryology, but not critical in the mature frog species. The significant alterations of this nature include the following developmental structures.

'''a)''' The long tail of the tadpole alongside the fin folds is absorbed again during metamorphosis and becomes absent at the final stage of the metamorphosis.

'''b) '''The developing gills are resorted, the gill clefts are congested and the branchial cavities start to become absent. The reabsorbtion of gills also takes place by autolysis.

'''c)''' The teeth of the perioral disc additionally the homey lining of the jaws are shed.

'''d)''' The lateral line sense organs within the skin of tadpoles vanish throughout metamorphosis.

'''e)''' The cloacal tube begins to condensed and reduced.

'''f)''' Various blood vessels, together with parts of the aortic arches, are reduced during mature development.

(The figure on the left represents the transformation from a tadpole to a developing structure.)[http://science.jrank.org/pages/2862/Frogs-Adult-morphology.html]

'''3. Progressive or constructive changes'''

This process comprises of the development of specific organs which mature into functional systems only during metamorphosis.

'''a)''' During development the limbs continue to augment in size and differentiation. The forelimbs, which in the tadpole mature under the opercular membrane, which then break through to the exterior. Simultaneously there is a increase in the length and strength of the hind limbs, joints develop in them and the toes become visible.

'''b)''' The middle ear becomes apparent in relation with the first pharyngeal pouch. The tympanic membrane matures. It is bounded by circular tympanic cartilage which allows the frog to retain air.

'''c)''' The visual organs bulge up on the dorsal surface of the head developing the nictitating membrane.

'''d)''' There is augmentation of the tongue and the formation of thevomerina teeth.

[[Image: Growth model.jpg|thumb|Growth Model Image details:J,Nassif2009:]]

'''4. Remodelling of some structures'''

Systematic organs which operate both in the early embryonic larva and the mature adult change their differentiation during metamorphosis so as to meet the requirements of the adult mode of life and due to the habitat adaptations. The figure on the right illustrates structures developing from specic germ cell layers.

'''a)''' The skin of the embryonic tadpole is lined with a double-layered epidermis. The number of layers of cells in the epidermis augments throughout metamorphosis. Superficial surface layers become cornified. Multicellular mucous and serous glands originate in the skin. The pigmentation of the skin continuously changes, new patterns and colour start to form.

'''b)''' There is a lengthening of the mouth gap as a result of rotation of the quadrate cartilage and the true jaws become functional.

'''c)''' The tongue rapidly progresses and becomes larger and more muscular.

'''d)''' The eyes become more specialised.

'''e)''' In early tadpoles, the GIT is extremely long and wound up into a spiral folds. The intestine become greatly lengthened in herbivorous species due to the vegetables food chain.[http://en.wikipedia.org/wiki/Frog]

'''5. Development of the reproductive system'''

(The figure below represents the reproductive and development cycle of a frog as it transform from egg to frog specie.)

In tadpoles, right after the mouth is being formed, two indentation like thickenings of peritoneum begin to appear near the body cavity (dorsal surface), which is nearest to the mesentery which is near the developing kidneys. These appear in all tadpoles.

These indentations appear here because of a change in the endothelial cells, everywhere else they are usually flat looking cells but they undergo a change and in this particular area become somewhat cuboidal/columnar.

Later on the indentations become more obvious due to the epithelial cells replicating numerously to form a thick layer. The posterior two thirds of the indentation for the female is the ovary and for the male it is the testis. The third that is left differentiates and becomes fat for the body.

[[Image: Mature frog life cyle.jpg|thumb|200px|left|Mature from life cycle Image details:Derived from primary source:http://www.scienceclarified.com/images/uesc_01_img0038.jpg]]

[[Image: Developing frog.jpg|thumb|Developing Frog Image details:
[[Image: Mature develop frog.jpg|thumb|Image details: Red eyed tree frog litoria chloris source:[http://en.wikipedia.org/wiki/File:Red-eyed_Tree_Frog_-_Litoria_chloris_edit1.jpg]].jpg]]

===Delamination===

Delamination indicates a mass separating a group of cellular matter from other cellular groups. It has been illustrated that the division of notochord, mesoderm and endoderm tissues from each other to form distinct cellular masses is completed by the progression of delamination, subsequent to these materials moving to the inside throughout gastrulation. During the developing gastrula, the germ layers are all recognized. These distinct segments of the embryo develop from these germ tissue layers.

===Polarity and Rotation===

Throughout fertilisation to the beginning of gastrulation, the frog’s egg continues in the original location in relation to its polarity. Subsequent to gastrulation its polarity begins to differentiate. This progression is linked with migration of materials within the gastrula and can be responsible for the alterations of the centre of gravity.

===Closing of Blastopore===

Subsequent to the formation of the gastrula, the blastopore is visible as a tiny round circular filled cavity containing the yolk plug. As it continues to reduce in dimension, it represented as a pear-shaped outline through the mutual approach of its lateral lips. Through it final progression these fuse entirely to produce a longitudinal groove, the streak which continue dorsally and ventrally in a small aperture. The inferior aperture closes, resulting in a depression called the anal pit. The superior region remains open for some period and begins to as the neural groove is laid down.

===Post Gastrulation or Organogenesis===

Throughout the duration of pre-gastrulation, all tissues for different organs vanish from the surface of blastula and migrate inside to take their final arrangement in the embryo structure where organs are developed from their potential regions. Consequently organogenesis transfers an embryo into free larva structure.

----

==Germ-layer origin of various body tissues==
[[Image: Development Models of Frog.jpg|thumb|right|Figure 13 Image details:Vertebrate Structure and Development.jpg]]

Ectoderm will give raise to structures such as skin, brain, spinal cord, neurons and sense receptors.
Mesoderm will give raise to structrues such as notochord, muscles, blood, bone and sex organs.
Endoderm will give raise to sturctures such as inner lining of gut, liver, pancreas, lungs and bladder, thyroid and parathyroid glands and thymus.

== Structures derived from Germ-layers of frog species ==

[[Image:Development of Frog Layers.jpg|thumb|left|Development of Frog Layers Primary source[http://www.bio.miami.edu/~cmallery/150/physiol/sf19x11b.jpg]Image details:J,Nassif 2009.jpg]]

[[Image:Development of frog layers.jpg|thumb|left|Development of Frog Layers Primary source [http://www.bio.miami.edu/~cmallery/150/physiol/sf19x11b.jpg]Image details:J,Nassif 2009.jpg]]

'''Ectoderm '''

''Establishes the epidermal segments and its derivatives, to the frog’s nervous system. The ectoderm also contributes to :''

1. The olfactory and auditory epithelium.

2. The retina and lens of the eye.

3. Sensory organs.

4. The epithelial lining of the oral cavity and the anus.

5. The pineal and pituitary body.

'''Mesoderm'''

''Mesoderm originates:''

1. Connective tissue.

2. Muscles, except the notochord.

3. Blood vessels.

4. Lymphatics.

5. The peritoneum and the urinary and reproductive system.

6. The dermis, parts of the eye excluding lens, cornea, and conjunctiva.

'''Endoderm'''

''From the endoderm arises:''

1. The epithelial lining to the gut and oesophagus, stomach, intestine, bile duct.

2. The hepatic cells of the liver, respiratory tract, larynx, trachea and lungs.

3. The lining of the urinary bladder, pancreas thyroid and thymus.

[The two figures reveal the development of structures deriving from the celluar components of the embryology of the frog].[Structures derived from Germ-layers of frog species ]

==Life cycle of a frog==

'''Fertilization-egg''':

The female lays eggs in the spring. A group of fertilized eggs is called spawn;

'''7-10 days''':

Fertilized egg feed on remaining yolk which is in its gut. Their gills, mouth and tail have poorly developed. Begin to swim and feed on algae;

'''10-30 days(4 weeks):'''

A layer of skin grows over gills. Teeth begin to appear. A coiled gut start to develop. This is aid in digestion;

'''30-60 days(6-9 weeks):'''

Legs being to grow and head is more distinct. Start to eat insects. Arms begin to grow;

'''60-80 days(12 weeks):'''

Resemble a frog. Still have remaining tail;

'''80-140 days(20 weeks):'''

Fully developed, spend most of time out of water. Majority of frog live between 4-15 years.

==Timeline of frog development==

Development of egg and embryo at temperature 18 degree celsius.

'''0 hours''' - fertilization of the egg

'''1 hours''' - formation of the gray crescent due to pigment migration

'''3.5 hours''' - early cleavage

'''4.5 hours''' - blastula stage(coeloblastula with eccentric blastocoel

'''26 hours''' - gastrulation

'''26 hours''' -'' early'' - crescent shaped dorsal lip

'''34 hours''' - ''middle''- semicircular blastoporal lip

'''42 hours''' - ''late'' - circular blastoporal lip

'''50 hours''' - neurulation

'''50 hours''' - ''early'' - medullary plate

'''62 hours''' -'' middle''- neural folds converging

'''67 hours''' - ''late'' - neural tube formed and ciliation of embryo

'''84 hours''' - tail bud stage(early organogeny)

'''96 hours''' - muscular response to tactile stimulation

'''118 hours''' - early heart beat, development of gill buds

'''140 hours''' - hatching and gill circulation

'''162 hours''' - mouth opens and cornea becomes transparent

'''192 hours''' - tail fin circulation established

'''216 hours''' - degeneration of external gills, formation of operculum, development of embryonic teeth

'''240 hours''' - opercular fold over brachial chamber except for spiracle and internal gills

'''255 hours''' - prolonged larval stage with refinement of organs

'''270 hours''' - development of hindlimbs, internal development of forelimbs in opercular cavity

'''275 hours''' - projection of forelimbs through operculum, left side first

'''280 hours''' - absorption of the tail and reduction in size of the gut

'''284 hours''' - metamorphosis complete, emergence from water as miniature, air breathing frog

==Stages of frog embryology==
--[[User:S8600021|Mark Hill]] 08:40, 9 October 2009 (EST) [[Talk:2009_Group_Project_5#Constructive_Criticism_of_Coordinator|see my comment on images]]

The rate of development of the egg and embryo will depend upon the temperature at which they are kept. The approximate schedule of development at 23 degree celsius is provided below.

{| border='1px'
|+ Table 1: Stages of frog development
!Stage !!Time since fertilisation (hours)!!Stage Characteristic !!Embryo characteristic !!Image of frog stage
|-
|1
|0.00-1.30
|fertilization of the egg, post fertilization
|animal hemisphere, gray crescent and vegetal hemisphere are present
|[[File:Stage01ventral.jpg|100px]]
|-
|2
|1.30-2.00
|splits into two cells
|appearance of first cleavage furrow
|[[File:Stage02ventral.jpg|100px]]
|-
|3
|2.00-2.15
|becomes four cells
|appearance of second cleavage furrow
|[[File:Stage03dorsolat.jpg|100px]]
|-
|4
|2.15-2.45
|becomes eight cells
|appearance of third cleavage furrow
|[[File:Stage04dorsolat.jpg|100px]]
|-
|5
|2.45-3.00
|becomes sixteen cells
|appearance of fourth cleavage furrow
|[[File:Stage05dorsal.jpg|100px]]
|-
|6
|3.00-3.30
|becomes thirty-two cells
|appearance of fifth cleavage furrow
|[[File:Stage06animal.jpg|100px]]
|-
|6.5
|3.30-4.00
|blastula stage
|Three dorsal folds become visible as a result of endoderm invagination. Pole cells no longer visible on surface
|[[File:Stage065dorsal.jpg|100px]]
|-
|7
|4.00-5.00
|Gastrulation stage
|two primary germ layers. epiblast and endoderm
|[[File:Stage07ventral.jpg|100px]]
|-
|8
|5.00-7.00
|neurulation
|medullary plate, neural folds and neural tube
|[[File:Stage08animal.jpg|100px]]
|-
|9
|7.00-9.00
|germ layer
|complete lip involution encircling yolk
|[[File:Stage09veg.jpg|100px]]
|-
|10
|9.00-11.00
|early gastrula
|two primary germ layers
|[[File:Stage10veg.jpg|100px]]
|-
|10.5
|11.00-11.45
|gastrula
|two germ layers
|[[File:Stage105vegb.jpg|100px]]
|-
|11
|11.45-12.30
|medulla plate
|Yolk sac protrudes dorsally, labium moves to midline on ventral side
|[[File:Stage11veg.jpg|100px]]
|-
|11.5
|12.30-13.15
|continuation of medulla plate
|start closing the plate
|[[File:Stage115veg.jpg|100px]]
|-
|12
|13.15-14.15
|early neurula
|thickened ectoderm give rise to CNS
|[[File:Stage12veg.jpg|100px]]
|-
|12.5
|14.15-14.45
|neural folds
|expansion of cavity
|[[File:Stage125postdors.jpg|100px]]
|-
|13
|14.45-16.15
|neural folds
|continue expanding cavity
|[[File:Stage13postdors.jpg|100px]]
|-
|14
|16.15-17.30
|neural folds
|continuation of cavity
|[[File:Stage14postdors.jpg|100px]]
|-
|15
|17.30-18.15
|tail bud stage
|early organogeny
|[[File:Stage15postdors.jpg|100px]]
|-
|16
|18.15-18.45
|tail bud stage
|posterior ventral view
|[[File:Stage16ant.jpg|100px]]
|-
|17
|18.45-19.45
|tail bud stage
|anterior view
|[[File:Stage17ant.jpg|100px]]
|-
|19
|20.45-21.45
|neural fold close complete
|dorsal view
|[[File:Stage19dorsal.jpg|100px]]
|-
|20
|21.45-22.30
|early tail bud
|anterior view
|[[File:Stage20dorsal.jpg|100px]]
|-
|21
|22.30-24.00
|termination of neural crest
|progress to next stage
|[[File:Stage21ant.jpg|100px]]
|-
|22
|24.00-24.45
|prolonged development
|elongation
|[[File:Stage22lat.jpg|100px]]
|-
|23
|24.45-26.15
|elongation of embryo
|later view
|[[File:Stage23lat.jpg|100px]]
|-
|24
|26.15-27.30
|continuation of elongation of embryo
|dorsal view
|[[File:Stage24latsmall.jpg|50px]]
|-
|25
|27.30-29.30
|organs development
|embryo elongates and develops dorsal thickening
|[[File:Stage25dorsal.jpg|50px]]
|-
|26
|29.30-31.15
|elongation
|dorsally forms neural and brain cavity
|[[File:Stage26lat.jpg|50px]]
|-
|27
|31.15-32.30
|elongation of embryo
|dorsal view
|[[File:Stage27lat.jpg|50px]]
|-
|28
|32.30-35.00
|further development
|lateral view
|[[File:Stage28lat.jpg|50px]]
|-
|29-30
|35.00-37.30
|tail bud
|growth
|[[File:Stage29-30lat.jpg|50px]]
|-
|31
|37.30-40.00
|prolonged development
|bud development
|[[File:Stage31lat.jpg|50px]]
|-
|32
|40.00-44.30
|early muscular development
|elongation
|[[File:Stage32lat.jpg|50px]]
|-
|33-34
|44.30-50.00
|muscular movement
|apparatus for locomotion
|[[File:Stage33-34lat.jpg|50px]]
|-
|35-36
|50.00-53.30
|muscular movement
|apparatus for locomotion
|[[File:Stage35-36lat.jpg|50px]]
|-
|37-38
|53.30-56.30
|heart beat
|develops apparatus
|[[File:Stage37-38lat.jpg|50px]]
|-
|39
|56.30-66.00
|mouth opens
|cornea transparent
|[[File:Stage39latsmall.jpg|50px]]
|-
|40
|66.00-76.00
|gill circulation
|hatching
|[[File:Stage40lat.jpg|50px]]
|-
|41
|76.00-80.00
|tail, fin circulation
|circulation
|[[File:Stage41lat.jpg|50px]]
|-
|42
|80.00-86.00
|internal gills, operculum
|opercular fold, teeth
|[[File:Stage42lat.jpg|50px]]
|-
|43
|86.00-98.00
|operculum complete
|operculum closed on right
|[[File:Stage43lat.jpg|50px]]
|-
|46
|98.00-106.00
|metamorphosis
|emergence from water as miniature, operculum complete|
|[[File:Stage46lat.jpg|50px]]
|-
|}

==Abnormalities of frog==

Abnormalities of frog could be caused by multiple factors. These include change in climate, predators, parasites, bacteria, fungi, viruses or pollution and contaminants such as pesticides, metals and fertilizer.[http://www.fws.gov/contaminants/documents/frogsrefup_septoct_2006.pdf]

The Abnormalities are further classified into different categories. These categories are:

===1. Infectious Diseases:===

'''Perkinsus Symptoms-''' caused by perkinsus-like protozoan organism. Symptoms include swollen viscera that leads to a bloated body and and infected swollen heart

'''Ichthyophonus symptoms-''' cause by parasitic genus, where symptoms include a swollen tail resorption site that matches the surrounding skin in color and translucency.

[[Image:Abnormalities of Frog species.jpg|thumb|left|Figure A Image details[waterwatchadelaide.net.au].jpg]]

===2. Surficial Abnormalities:===

Surficial abnormalities as the one that are visible on the surface of the skin. This includes abnormal pigmentation, , subcutaneous hemorrhaging, wounds due to trauma or from a predator
Edema is a fluid-filled swelling under skin whihc is also a surficial abnormality.

===3. Skeletal Abnormalities:===

This is further classified into three more categories:

'''a. Skeletal Malformations-'''

* Microcephaly (small head or blunt snout)
*Scoliosis (Curved spine in lateral direction)
*Shrunken Limb (Micromelia)
*Amelia (Completely missing limb with no stump)

'''b. Skeletal Abnormalities of Unclear Etiology-'''

This condition arises when a frog has ectromelia (missing limb), brachydactyly (missing digits) or other such condition with no visible trauma or external damage, then this will be classified as the Skeletal abnormality of unclear etiology.

'''c. Skeletal Injuries-'''

Any limb missing or broken due to trauma or other related reason which shows clear evidence of it is classified as skeletal injury

===4. Eye Abnormalities:===

Most common includes-

'''i. Anophthalmia:''' Skin covers the eye socket as there is no eye

'''ii. Abnormal Iris Coloration:''' Reduced pigment in either one eye or both resulting in two different colours of the iris at times

'''iii. Abnormal size or shape:''' Both eyes either deviating from each other or size of pupil or iris is different than the other eye

[http://www.fws.gov/contaminants/Amphibian/pdfs/AbnormalitySOP_woutpics_Jan08.pdf ]

==Genetics==

There are a wide variety of species that differ from each other when it comes to genetics and their functioning.

'''TAXONOMY:''' '''Phylum''' ''Chordata'' / '''Sub Phylum''' ''Vertebrata'' / '''Class''' ''Amphibia'' / '''Order''' ''Anura''

Their are more than two dozen different families of frogs, where suborders are:

'''1. ARCHAEBATRACHIA-''' most primitive frogs

'''2. MESOBATRACHIA-''' linked between the Archaebatrachia and Neobatrachia

'''3. NEOBATRACHIA-''' most modern frogs

{| border='4px'
|+ '''General Info:'''
! !!
|-
| '''Number of frogs' species'''
| 5280
|-
| '''Smallest frog genome size:'''
| 0.95pg, Ornate burrowing frog
|-
| '''Largest frog genome size:'''
| 13.40pg, Ornate horned frog
|-
| '''Mean of frogs' genome'''
| 4.68pg ± 0.13
|-
|}

[http://www.genomesize.com]

*Majority of frogs have only 22 to 26 chromosomes and polyploid is very common where they are almost bisexual.

*Polyploid Amphibians reduce their total cell number such that they acheive the same body size as diploids. One of the most unsual forms of polypoidy in amphibians is the water frog ''Rana esculenta'' from Europe and Western Asia.

* The species with larger genomes have more genes for e.g. the frog genus ''Xenopus'' includes 16 species, with genome sizes ranging from 3.5 x 10^9 bp to 1.6 x 10^10 bp. These differences have arisen by numerous events of polyploidization within the past 40 million years or so. The ancestral chromosome number for the genus seems to have been 18, but there are species with 36, 72 and 105 chromosomes [http://www.xenbase.org/common/]

{| border='4px'
|+ '''Difference within two families'''
! '''SPECIES''' !! ''X.LAEVIS'' !! ''X.TROPICALIS''
|-
| '''PLOIDY'''
| Allotetraploid
| Diploid
|-
| '''NO. OF CHROMOSOMES'''
| 36 chromosomes
| 20 chromosomes
|-
| '''GENOME SIZE'''
| 3.1 x 10^9 bp
| 1.7 x 10^9 bp
|-
| '''EGG SIZE'''
| 1-1.3 mm
| 0.7-0.8 mm
|-
| '''GENERATION TIME'''
| 1-2 years
| 4 months
|-
|}
[http://www.xenbase.org/common/]

===Genome Sequencing===

Since Frog has a huge family with many different species, only few main species that are used widely for the purposes of experiments have their genome sequenced.

''Xenopus tropicalis'' has one of the smallest genomes among amphibians and has the shortest generation time- four to six months and the only diploid genome among the 14 Xenopus species. This means it has no more than two copies of most genes, whereas the other species of Xenopus have four copies of most genes (pseudotetraploid). US Department of Energy's Joint Genome Institute (JGI) in Walnut Creek, California, initiated the X. tropicalis Genome Project, finding 1,700 million base pairs.
[http://www.genome.gov/Pages/Research/Sequencing/BACLibrary/xenopusTropicalis.pdf]

===Xenopus oocytes===

* The oocytes provide an important expression system for molecular biology.

* By injecting DNA or mRNA into the oocyte or developing embryo, scientists can study the protein products in a controlled system. This allows rapid functional expression of manipulated DNAs (or mRNA). This is particularly useful in electrophysiology, where the ease of recording from the oocyte makes expression of membrane channels attractive.

* One challenge of oocyte work is eliminating native proteins that might confound results, such as membrane channels native to the oocyte.

* Translation of proteins can be blocked or splicing of pre-mRNA can be modified by injection of Morpholino antisense oligos into the oocyte (for distribution throughout the embryo) or early embryo (for distribution only into daughter cells of the injected cell).
[http://www.staff.unibe.ch/sigel/xenopus.html]

===Xenopus Laevis===

* ''Xenopus Laevis'' is an important model organism in developmental biology. X. laevis is tetraploid and reaches sexual maturity in 1 to 2 years. What makes it important in developmental biology is its large and easily manipulable embryo.

* Extracts from the eggs of X. laevis frogs are also commonly used for biochemical studies of DNA replication and repair, as these extracts fully support DNA replication and other related processes in a cell-free environment which allows easier manipulation.

* The Human chorionic gonadotropin hormone (hCG) is present in the urine of the pregnant women in large quantities only. This hormone in the urine induces X.laevis oocyte production which formed the basis of first well-documented method of pregnancy testing X. laevis is also notable for its use as the first well-documented method of pregnancy testing when it was discovered. Today, commercially available HCG is injected into Xenopus males and females to induce mating behavior and breed these frogs in captivity at any time of the year.

===Gene cluster===

* The alpha and beta globin genes are closely linked in small cluster of frogs compared to human and chicken

* The similarity of architecture of two clusters found in X.laevis supports the tetraploid origin

* The two loci encoding the muscle specific creatine kinase isoenzymes and have large differences in developmental profile, therefore suggesting that duplicate loci that have not undergone silencing are not simply redundant copies but have acquired specialization.

* Contains twice number of genes for proteins i.e. haemoglobin and sarcomeric actin serum albumin compared with other species

----

==Current Embrology Research==

Currently, a number of fields have benefited from the development of frog embrology. These include cloning, verification of messenger RNA, and Cell cycle.

===Cloning===
[[Image:Robert Briggs.jpg|thumb|left|Figure 16 Image details:Robert Briggs.jpg]]

In 1952, Robert Briggs and Thomas J King cloned northern leopard frogs using a method of nuclear transfer. Briggs and King's experiment was similar to that envisioned - and piloted using salamanders - by Hans Spemann in his 1938 proposal for a 'fantastical experiment'. Later, John Gurdon extended this work and showed that nuclei from differentiated cells could support development, although less well than those from early embryos. [http://genome.wellcome.ac.uk/doc_WTD020799.html]

Lemaitre et a. (2005) from MRC Cancer Cell Unit, Cambridge, U.K. worked on experiments that demonstrated that importance of serial nuclear transplantation for the sucessful cloning of frogs. He demonstrated that exposure of somatic-cell nuclei (erythrocyte nuclei) and sperm nuclei to an extract of mitotic cell extract reorganizes the chromatin into shorter loops and allows replication at much shorter intervals along the DNA. This increases the efficiency of DNA replication in mammalian cell-free systems.

===Transgenesis techniques for functional genomics in Xenopus===

Transgenesis in Xenopus is made possible due to large embryos, a reliable fate map, ease of microinjection, ease of dissection/micromanipulation and existence of the neuroendocrine reflex of background adaptation as a model for activation/inact.

Recently, Hajime Ogino and Haruki Ochi from Nura Institute of Science and Technology in Japan focused on the genomic resources and principles of the transgenesis techniques in Xenopus, and discusses their applications to genome wide network analysis, with emphasis on the use of bioinformatics tools. This is will to understand the gene regulatory networks that control vertebrate development. [http://www.ingentaconnect.com/content/bsc/dgd/2009/00000051/00000004/art00001%3Bjsessionid=4ah96rms73gcu.alexandra]

Xenopus used to be a problem in earlier days when it came to transgenesis. Current methods involves isolated sperm nuclei from Xenopus testis that are microinjected into unfertilized eggs. The generated transgenic tadpoles contain 5-35 copies of the integrated plasmid that are expressed in all cells. If desired, expression of the transgene can be directed to the appropriate tissue and at the appropriate time by using specific promoters, mostly the Xenopus POMC gene promoter (isolated from a Xenopus genomic DNA library) to specifically direct expression of green fluorescent protein (GFP) at high levels to the intermediate pituitary cells, which can either be over expressed or inhibited.[http://molanphys.ruhosting.nl/transgenesis.htm]

[[File:Transgenesis.JPG]]

===Verification of messenger RNA===

While the existence and role of messenger RNA (mRNA) was known in bacteria, in the 1960s it was still debated whether it also existed in vertebrates. Taking haemoglobin mRNA from immature red blood cells and injecting it into a Xenopus oocyte, John Gurdon showed that the haemoglobin protein was indeed produced. Producing proteins in Xenopus oocytes has proved to be extremely useful in cell biology, in particular for the study of receptor proteins.[http://genome.wellcome.ac.uk/doc_WTD020799.html]

===Cell Cycle===

As they develop outside the mother, frog eggs are well stocked with the proteins needed to drive the development of the embryo. Studies of these processes has shed considerable light on the processes involved in cell division - termed the cell cycle. [http://genome.wellcome.ac.uk/doc_WTD020799.html]

===Limb development in Xenopus Laevis===

[[Image: Frog Limb development.jpg|thumb|right|From Limb Development Image details:Primary source:[http://images.google.com.au/imgres?imgurl=http://www.sciencedaily.com/images/2006/06/060616130718.jpg&imgrefurl=http://www.sciencedaily.com/releases/2006/06/060616130718.htm&usg=__xliPsPAvheUBME_kjv_q7auiFbo=&h=333&w=300&sz=11&hl=en&start=2&um=1&tbnid=y_ntJtmkRSK7WM:&tbnh=119&tbnw=107&prev=/images%3Fq%3DLimb%2Bdevelopment%2Bin%2BXenopus%2BLaevis%26ndsp%3D18%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

Donald D. Brown (2005),Department of Embryology, Carnegie Institution of Washington demonstrated factors related to limb development of Xenopus Laevis. Thyroid hormone (TH) is found to be required for limb development in this frog. Specific cell types in the growing limb were targeted for expression of a dominant negative form of the TH receptor by sperm-mediated transgenesis. Limb muscle development, the innervation of muscle from the spinal cord, and cartilage growth can be inhibited without affecting patterning of the limb or differentiation of other cell types. Remodeling of the skin occurs late in metamorphosis after the limb has formed. The coordination of these independent programs is affected in part by the control that TH exerts over DNA replication in all cell types of the limb. [http://www.pnas.org/content/102/35/12455.full]

----

== Glossary ==

[[Image: Frog species.jpg|thumb|left| Frog Species Image details:Primary source:www.olympus.co.jp/.../080925/large/p02L.jpg].jpg]]

*'''Amphibian:'''

''Relating to or characteristic of animals of the class amphibia.Amphibians are found in the taxonomic class of amphibia, amphibians are capable of both occupying and successfully living in both land and aquatic communities.amphibian''

*'''Augmentation:'''

''Enlargement/Increase in cellular size.''

*'''Autolysis:'''

''breakdown of a part or whole cell or tissue by self-produced enzymes''

*'''Blastomeres:'''

''The undifferentiated cells formed by cleavage of the fertilised ovum. This includes cells in the cleavage, morula, and blastula stages of the embryo''

*'''Carnivorous:'''
''
Flesh-eating; subsisting on animals as food.''

*'''Cleavage:'''

''he repeated division of a fertilised ovum ''

* '''Cleft:'''

''an opening, fissure, or V-shaped indentation made by or as if by splitting''

*'''Chordate:'''

''Members of a diverse phylum of animals that, as embryos, possess a (1) notochord; (2) a dorsal, hollow nerve cord, (3) pharyngeal gill slits; and (4) a post-anal tail''

''The act or state of splitting or dividing of a cell, particularly during the telophase of (animal) cell division.''

*'''Cytoplasm:'''

''The cytoplasm (of both eukaryotes and prokaryotes) is where the functions for cell expansion, growth, metabolism, and replication are carried out''

* '''Epiboly:'''
''The expansion of one cell sheet over other cells, as takes place during gastrulation''

*'''Fertilization:'''

''A process in sexual reproduction that involves the union of male (sperm) and female (ovum) gametes (each with a single, haploid set of chromosomes) to produce a diploid zygote.''

*'''Gamete:'''
''A reproductive cell (male (sperm) or female (egg)) that has only half the usual number of chromosomes''

*'''Gametogenesis:'''

''process leading to the production of gametes. The development and maturation of sex cells through meiosis.Another name for meiosis where a diploid cell is divided into two haploid cells with half the chromosome content of the diploid parent cell.''

*'''Herbivorous:'''

''eating plants; of or pertaining to the herbivora.''

*'''Holoblastic:'''

''The complete division of an isolecithal or microlecithal egg into blastomeres''

*'''Invagination:'''

''One of the methods by which the various germinal layers of the ovum are differentiated.''

*'''Isoenzymes:'''

''Isozymes (also known as isoenzymes) are enzymes that differ in amino acid sequence but catalyze the same chemical reaction.''

*'''Mesentery:'''

'' membranous fold attaching various organs to the body wall.''

*'''Metamorphosis:'''

''A change in the form and often habits of an animal after the embryonic stage during normal development.''

*'''Neuroendocrine:'''

''Neuroendocrine [IPA nʊəroʊˈɛndəkrɪn] cells are cells that release a hormone into the circulating blood in response to a neural stimulus.''

*'''Organogenesis:'''

''The part of embryonic development where the body's main organs develop.''

*'''Peritoneum:'''

''The smooth serous membrane which lines the cavity of the abdomen, or the whole body cavity when there is no diaphragm, and, turning back, surrounds the viscera, forming a closed, or nearly closed, sac.''

*'''Perivitelline space:'''

''The perivitelline space is the space between the zona pellucida and the plasma membrane (sometimes called the vitelline membrane) in a fertilized ovum.''

*'''Polyploidy:'''

''Cells with three or more sets of chromosomes.''

*'''Pronucleus:'''

''the nucleus of the ovum or sperm after fertilization but before they fuse to form the nucleus of the zygote ''

*'''Protoplasm:'''

''The fluid living content of the cell that consists of two major divisions, the cytoplasm and the nucleoplasm (cell nucleus). It is composed mainly of nucleic acids, proteins, lipids, carbohydrates, and inorganic salts''

*'''Segmentation:'''

''division of some metazoan bodies (such as annelida and Arthropoda) into repeated parts, segments. Segmentation can be homomeric (more or less the same) or heteromeric(different from each other).''

*'''Terrestrial:'''

''Of or on the ground, of the habitat of a plant, on land as opposed to in water, or on the ground as opposed to on another plant.''

*'''Transgenesis:'''

''Transgenesis is the process of introducing an exogenous gene - called a transgene - into a living organism so that the organism will exhibit a new property and transmit that property to its offspring.''

*'''Yolk:'''

''nutritive material of an ovum stored for the nutrition of an embryo''

*'''Zygote:'''

''The cell from which an organism develops, that results from the fertilization of the egg by the sperm.''

''Primary Resource "Biology- Online Dictionary''[http://www.biology-online.org/dictionary/Main_Page]

== References - Frog Embryology: ==

[[Image:Frog Research.jpg|thumb|left|Image details:[http://images.google.com.au/imgres?imgurl=http://www.odt.co.nz/files/story/2008/09/university_of_otago_zoology_senior_lecturer_phil_b_3343259744.jpg&imgrefurl=http://www.odt.co.nz/on-campus/university-otago/21670/dunedin-frog-man-wins-zoo-award&usg=__JvJJU5QfOnIwY2bk4xo64UXuJRs=&h=600&w=404&sz=22&hl=en&start=14&um=1&tbnid=AbsP89yWcUiilM:&tbnh=135&tbnw=91&prev=/images%3Fq%3Dfrog%2Bresearch%26hl%3Den%26um%3D1].jpg]]

1. Savage, J. M. (2002). The Amphibians and Reptiles of Costa Rica. University of Chicago Press, Chicago [http://www.springerlink.com/content/vv015277w1746llw/]

2. Ford, L.S.; D.C. Cannatella (1993). "The major clades of frogs". Herpetological Monographs 7: 94–117 [http://digimorph.org/specimens/Xenopus_laevis/]

3. Tyler, M. J. (1994). Australian Frogs A Natural History. Reed Books [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.gracilenta.html]

4. Cogger, H.G.; R.G. Zweifel, and D. Kirschner (2004). Encyclopedia of Reptiles & Amphibians Second Edition. Fog City Press [http://en.wikipedia.org/wiki/Microhylidae]

5. Beltz, Ellin (2005). Frogs: Inside their Remarkable World. Firefly Books [http://unjobs.org/authors/ellin-beltz]

6. Tyler, M. J. (1994). Australian Frogs A Natural History. Reed Books [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

7. Moury JD, Hanken J (1995) Early cranial neural crest migration in the direct-developing frog, Eleutherodactylus coqui. Acta
Anatomica (Basel) 153, 243-253.

8.Raynaud A (1985) Development of limbs and embryonic limb reduction. In Biology of the Reptilia (ed. Gans C, Billett F), pp.
59-148. New York: John Wiley.[http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=9309]

9. Hanken J (1986) Developmental evidence for amphibian origins. In Evolutionary Biology (ed. Hecht MK, Wallace B, Prance GT), 20, pp. 389-417. New York: Plenum Press. [Hanken J (1986) Developmental evidence for amphibian origins. In Evolutionary Biology (ed. Hecht MK, Wallace B, Prance GT), 20, pp. 389-417. New York: Plenum Press.]

10. Elinson RP (1990) Direct development in frogs : wiping the recapitulationist slate clean. Seminars in Developmental Biology
1, 263-270.

11. Beebee, T. J. C. 1996. Ecology and Conservation of Amphibians. Chapman and Hall. London. [http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V5X-3SVHMKH-1X&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=1021245355&_rerunOrigin=google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=825868e10cd178d16a8a0e5ad14dc5ef]

12. Lehtinen, R. M. 2002. The use of screw pines (Pandanus spp.) by amphibians and reptiles in Madagascar. Herpetological Bulletin 2002:20–25.

13. Parris, K. M. and M. A. McCarthy. 1999. What influences the structure of frog assemblages at forest streams. Australian Journal of Ecology 24:495–502. CrossRef

14. Zug, G. R. 1993. Herpetology: An Introductory Biology of Amphibians and Reptiles. Academic Press. San Diego, CA.

15. Slack,J.M.W., Darlington,B.G., Heath,J.K. and Godsave,S.F. (1987)Mesoderm induction in early Xenopus embryos by heparin-binding growth factors. Nature, 326, 197-200.

16. Melton,D.A. (1990) Activins are expressed early in Xenopus embryogenesis and can induce axial mesoderm and anterior structures. Cell, 63, 485-493.

17. Harland,R.M. and Misher,L. (1988) Stability of RNA in developing Xenopus embryos and identification of a destabilizing sequence in TFIIIA RNA. Development, 102, 837-852.

18. Cunliffe,V. and Smith,J.C. (1992) Ectopic mesoderm formation in Xenopus embryos caused by widespread expression of a Brachyury homologue. Nature, 358, 427-430.

19. Kinoshita,K., Bessho,T. and Asashima,M. (1993) Competence prepattern in the animal hemisphere of the 8-cell-stage Xenopus embryo. Devel. Biol., 160, 276-284.

20. LaBonne,C., Burke,B. and Whitman,M. (1995) Role of MAP kinase in mesoderm induction and axial patterning in Xenopus development. Development, 121, 1475-1486.

21. Green,J.B.A., New,H.V. and Smith,J.C. (1992) Responses of embryonic Xenopus cells to activin and FGF are separated by multiple dose thresholds and correspond to distinct axes of the mesoderm. Cell, 71, 731-739.

22. Grainger R., Blumberg B., Harland R., Amemiya C., Importance of Xenopus Tropicalis to biomedical and biological research, Benaroya Research Institute, Virginia Mason Research Center [http://www.genome.gov/Pages/Research/Sequencing/BACLibrary/xenopusTropicalis.pdf ]

23. Gregory, T.R. (2005). Animal Genome Size Database. [http://www.genomesize.com]

24. U.S Fish and Wildlife Services, ABNORMALITY CLASSIFICATION SOP, [http://www.fws.gov/contaminants/Amphibian/pdfs/AbnormalitySOP_woutpics_Jan08.pdf ]

25. Donald D. Brown*, Liquan Cai*, Biswajit Das*, Nicholas Marsh-Armstrong‡, Alexander M. Schreiber*, and Rejeanne Juste*(2005), Thyroid hormone controls multiple independent programs required for limb development in Xenopus laevis metamorphosis [http://www.pnas.org/content/102/35/12455.full]

26. Ogino, Hajime; Ochi, Haruki, Resources and transgenesis techniques for functional genomics in Xenopus, Development Growth & Differentiation, Volume 51, Number 4, May 2009 , pp. 387-401(15) [http://www.ingentaconnect.com/content/bsc/dgd/2009/00000051/00000004/art00001%3Bjsessionid=4ah96rms73gcu.alexandra]

27. Giles Newton (2004) Why the frog? The Human Genome, [http://genome.wellcome.ac.uk/doc_WTD020799.html]

28. Xenbase, [http://www.xenbase.org/common/]

29. Donders Center for Neuroscience & Nijmegen Center for Molecular Life Sciences (NCMLS), Beyond the genome (Xenopus transgenesis for functional genomics),Faculty of Science, Radboud University [http://molanphys.ruhosting.nl/transgenesis.htm]

== External Links ==
[[Image:Frog links.jpg|thumb|left|Image details:[http://images.google.com.au/imgres?imgurl=http://2.bp.blogspot.com/_o93AaY0GzH4/SjY_ZYv0PII/AAAAAAAAAgk/skruNc2yN78/s400/computer%2Bfrog.jpg&imgrefurl=http://hellaheaven-ana.blogspot.com/2009/06/talking-frog-contemporary-fairy-tale.html&usg=__oxji1TGLV2Fi7xe0dnlmuYk8gDo=&h=288&w=288&sz=16&hl=en&start=2&um=1&tbnid=ywZd4zpdxC5plM:&tbnh=115&tbnw=115&prev=/images%3Fq%3Dfrog%2Bon%2Bcomputer%26hl%3Den%26um%3D1].jpg]]

1. Frog embryology [http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/F/FrogEmbryology.html Frog Embryology]

2. Frog cellular materials [http://www.xenbase.org/xenbase/original/cell/cell.html xenbase]

3. The zoology of frog species [http://worms.zoology.wisc.edu/frogs/mainmenu.html zoology frogs]

4. Frog cycle [http://www.bioethics.gov/images/sc_images/frog_dev.gif bioethics frog] Just a little cycle of FROG'S life cycle

5. Frog Embryology [http://embryology.med.unsw.edu.au/OtherEmb/Frog.htm UNSW Embryology]

6. Frog Research [http://apps.carleton.edu/campus/library/now/exhibits/wallcharts/frog/ carleton library exhibit]

{{Template:Projects09}}
[[Category:Frog]]

2009 Group Project 5

2009-10-14T22:47:09Z

Z3258567: /* Limb development in Xenopus Laevis */

== The Embryology of Frogs ==

== The Frog ==

[[Image: Frog species .jpg|thumb|left|Image details: Wikipedia (2009) Frog species[http://en.wikipedia.org/wiki/Frog#Uses_in_agriculture_and_research].jpg]]

Frogs are scientifically identified by the structure of their long posterior limbs, a petite framework, webbed fingers and feet, budged eyes and the lack of a tail. The majority of frog species are extensively recognized as outstanding jumpers, due to their long, dominant legs, which are adaptations to progress jumping performance during activities. The Frog is one of the most frequently studied species in experimental embryology and most anatomical sciences. ''The Frog is a practically effective model for human embryological development given that the Frog:''

- Comprises of genes which can be effectively manipulated.

- Comprises of similar homogeny with humans species.

- Reproduces a large quantity of offspring in a short period of time.

- Are small species which can be simply sustained.

- Are not extremely luxurious and expensive.

== The History of the uses in agriculture and research ==

[[Image: Frog experiments .jpg|thumb|right|Image details: Scans of chemically cleared and dyed preserved deformed frogs and toads [http://www.sat.qc.ca/upload/residence/frog-04.jpg].jpg]]

There are numerous types of frog species that have been manipulated in many developmental experiments. The frog was traditionally used by countless of the early embryology investigators and presently there are several diverse molecular mechanisms regarding progression of the frog. Theses include:

'''1.''' Food source; frog legs are a delicacy and are eaten in European countries and in many parts of South American regions.

'''2.''' Frogs have the finest biochemical dissection of phenomena that take place in the egg and oocyte. Frogs are the evolutionarily closest to mammals, commonly used as a vertebrate model.

'''3.''' Frogs lay thousands of outsized eggs, from which cell extracts can be readily prepared that is capable of recapitulating most molecular phenomena in a test tube.

'''4.''' Frogs have been commonly used as a laboratory system for a very long period, and have an extensive history of producing crucial observations in countless fields of biology.

'''5.''' Frogs have a important historical connection to the study of epigenetics (John Gurdon-vertebrate cloning and reprogramming) which has been mostly performed on frog species.

'''6.''' Frogs also have very strong evidence of pattern formation and early development, as the embryos are large in size and experimentally manipulative.

'''7.''' Recent research into the biochemistry of chromatin and epigenetics has been performed with frog species and mammalian cultured cells.

'''8.''' The biggest weakness of the Frog model system is the difficulty of performing genetic experiments and analysis, as frogs are allotetraploid, meaning they take approximately a year to fully develop to sexual maturity, and the genome has not been completely sequenced. Nevertheless, biochemical manipulations of cell extracts, such as immunodepletions and application of heterologous DNAs and nuclei can avoid the need for genetic exploitation.

----

== Growth and development of the Frog ==

[[Image: Mature develop frog.jpg|thumb|Image details: Wikipedia (2009) Red Eyed Tree Frog Figure 1 Primary source:[http://en.wikipedia.org/wiki/File:Red-eyed_Tree_Frog_-_Litoria_chloris_edit1].jpg]]

* The frog is a well recognised species, abundant predominantly in ponds, swamps, though various species may also exist in damp or shady environments distant from moist habitats.

* Eggs of specific frogs are easily obtained and may be examined in from the beginning of fertilization onwards. The phases of embryonic development differs in various chordates, yet the typical phases are basically apparent in all frog species. The differences are associated principally to the amount of yolk particles present in an egg.

* The yolk particles offer nourishment of the developing embryo. The process of frog development will be discussed from the phases of gametogenesis to the adult stage.

----

== The Egg ==
[[Image:Development of Poles in frog Fertilization.jpg|thumb|left|Development of Poles in Frog Fertilisation:J,Nassif 2009.jpg]]

- The embryology of a frog egg is a vast cell; its dimensions are approximately 1.4-1.6 million times larger than a typical aquatic species egg cell. Throughout the frog’s embryonic maturation period, the egg will be transformed into a tadpole encompassing millions of cells but still remains with its constant volume of genetic material, the vast prodction of cell have been illusttrated in the figure on the right revealing the production of eggs from female frogs. [http://en.wikipedia.org/wiki/Microhylidae]

- The early embryonic frog structure consists of three main segments the superior hemisphere known as the animal pole which is usually visible as a grey coloured area. The innermost layer appears to be between the outer two sections known as the gray crescent represented in black. Inferiorly, represents the vegetal pole typically lighter than the superior compartment illustrated in gold.

VIDEO RESOURCE: [http://www.youtube.com/watch?v=GO5YN_t1fqw&feature=related]

[[Image:Early Development of Frogs.jpg|thumb|left|Early Development of Frog:J,Nassif 2009.jpg]]

==History of frog embryology use ==

*'''1851''' - ''Henby Nelson''(MD): He identified a remarkable fact through the frog embryo. Henby observed the first cleavage of the yolk, in the egg of the frog. And cleaved structure corresponds in line of direction to the longitudinal axis of the body of the embryo of the frog species.

[[Image:Wilhelm Roux.jpg|thumb|right|Wilhelm Roux[http://images.google.com.au/imgres?imgurl=http://www.todayinsci.com/R/Roux_Wilhelm/RouxWilhelmThm.jpg&imgrefurl=http://www.todayinsci.com/6/6_09.htm&usg=__qRLTEMTHdZpAHxiNX12hWjcm9tA=&h=125&w=100&sz=4&hl=en&start=2&um=1&tbnid=LIKIwZTqCpk7MM:&tbnh=90&tbnw=72&prev=/images%3Fq%3DWilhelm%2BRoux%26gbv%3D2%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

*'''1888''' - ''Wilhelm Roux'': Wilhelm Roux attempted to solve the above observation by damaging one cell of a two-cell frog embryo with a hot needle. The cell stayed in place. However, it did not develop further. Its partner developed into a left or right half-embryo;

*'''1907''' - ''John Hopkins'' hospital: In order to identify the cellular source of neuronal fibres. Scientist placed small portions of frog embryo spinal cords in lymph on a microscope slide and was able to observe clear cut neuronal sprouting.

*'''1951''' - ''Robert Briggs'': Robert Briggs was able to clone a frog embryo by substituting the nucleus of an unfertilized frog egg cell with the nucleus of a frog embryo cell. This process is known as nuclear transplant, has formed the basis for all cloning.

*'''1952''' - ''Robert Briggs and T.J. King'': Robert Briggs and T.J. King used frog for test experiment. Because the size of the eggs in the frogs are enormous compared with those of mammals, which make them easier to manipulate.

*'''1976'''- Using the technique that had been successful in cloning frog embryos, the doctor transferred the nucleus of one cells into a donated egg cell. As an embryo began to develop, it was implanted into the uterus of a young woman.

*'''1997''' - ''Wilmut and Campbell'': Utilizing the cloning technique from frog embryo, Drs. Wilmut and Campbell tried the starvation technique on embryo cells to produce Megan and Morag, the world's first cloned sheep and, until now, the most famous sheep in history.

*'''2000''' - ''Tokyo University'': Scientists at Tokyo University have grown artificial eyeballs. Scientists formed them in tadpoles by using frog embryo cells.

*'''2001''' - ''Advanced Cell Technology'': Scientists from Advanced Cell Technology announced production of a human embryo clone. This is significant as its parthenogenesis has been artificially induced in frogs.

[[Image:John Gurdon .jpg|thumb|right|John Gurdon [http://images.google.com.au/imgres?imgurl=http://www.pnas.org/site/misc/images/gurdon.jpg&imgrefurl=http://www.pnas.org/site/misc/classics4.shtml&usg=__1p-GA1PdOYsxKL-cznMb3RHCm98=&h=526&w=400&sz=223&hl=en&start=1&um=1&tbnid=9k4lhuLssiWCAM:&tbnh=132&tbnw=100&prev=/images%3Fq%3DJohn%2BGurdon%26gbv%3D2%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

*'''2002''' - ''John Gurdon'': John Gurdon from Wellcome Cancer Research Institute in Cambridge experimented on cloned frog embryo.

== Gametogenesis ==

* The sexual reproduction occurs through the fusion of either mature reproductive cells or germ cells known as gametes, which include the sperm from the male frog and ova from female frog species so as to form a single cell, the fertilized zygote. The gametes are typically developed in parents of different sexes . [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

* Males gametes is a spermatozoon , the female frog gamete is an ovum. Each gamete is formed by a process, recognised as maturation or gametogenesis in gonads. The typical male frog gonads are testies in male, while the female gonads are ovaries. The synthesis of both gonads is associated with the process of fertilization. [http://en.wikipedia.org/wiki/Microhylidae]

* The zygote changes into a mature frog through the process of embryology and metamorphosis. Gametogenesis is a in progression which frog gametes are established from germ cells. Initial germ cells are called primordial germ cells, which can be recognised extremely early in the life of frog species.

----

== The Egg & Fertilization ==

[[Image:Fertilized and Unfertilised Eggs.jpg|thumb|left|Fertilized and Unfertilized Eggs:J,Nassif 2009.jpg]]

[[Image:Egg Development.jpg|thumb|left|Egg Development:J,Nassif 2009.jpg]]

- This occurs once the sperm cell has inserted, following the insertion of the sperm cells meiosis II is completed, there is a 30 degree position change of the cytoplasm, gray crescent allows this change to be visible in some amphibians, the gray crescent is able what determines the expect ted outline of how the frog will form. The sperm cell joins with the nuclei of the egg which forms the diploid zygote nucleus. --Sando Rashed 10:09, 24 September 2009 (EST)

- The early phases in the development of the egg is visible, but must be studied in tadpoles throughout maturation. In embryonic tadpoles of about 10 millimetres in length, soon after the opening of the oral cavity, a pair of longitudinal ridge-like thickenings of peritoneum becomes apparent along the posterior surface of the body cavity situated near to the mesentery and along the inner boundaries of the kidneys. Genital ridges are established in all tadpoles of this age, sex is not distinct until a later period. The development of the egg is illustrated in the figure on the left revealing the structure of a developed egg and a mature of egg.

[[Image:Fertilisation life cyle.jpg|thumb|Fertilization of Life cycle:Derived from primary source:[http://en.wikipedia.org/wiki/Frog]]]

== Maturation of the Egg ==

- The eggs have currently accomplished their full size, and develop from the exterior of the ovaries like a small shot, but they still have to pass through the course of maturation before they are prepared to be fertilised. This progression of maturation relates to the nucleus almost completely.

- The nucleus component, containing the nuclear fluid that excludes through the nuclear membrane into the substance of the egg, a great segment of the nuclear reticulum vanishes and becomes degraded into separate globules known as nucleoli, but a extremely small division remains in the midpoint as a slender intricately thread recognised as the nuclear skets.
Relative to the egg getting discharged from the ovary, the follicles shatter allowing the eggs to fall into the abdominal cavity of the frog species, the egg then passes forwards, directly by the contraction of the muscular wall, somewhat by the movement of the cilia of the peritoneum, to the apex of the oviduct, which positioned at the anterior compartment of the body cavity opposite to the roots of the respiratory organs.

- The terminal part of the oviduct establishes a thin-walled pouch capable of great swelling, inside which the eggs gathers in large numbers. In conclusion, the eggs are migrated out through the cloaca into water which the albuminous investments of the eggs rapidly augment to form the gelatinous mass of the frogs spawn.

== Maturation phases ==

'''1. Nuclear skein''', moves from the midpoint of the egg to its outer surface, which it reaches opposite the midpoint of the black pole. The skein, subsequently an unevenly twisted thread, now presumes the specific arrangement of a nuclear spindle, for instance may be visible in the nucleus of an epithelial or additional cell instantly prior to division of the cell occurs.[http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

'''2. The first Polar Body,''' regarding the instance the egg is laid, but prior to its fertilistion, the egg develops a considerably flattened appearance at its upper or black pole, a definite sum of fluid being exuded among the egg and the vitelline membrane. The nuclear spindle currently separate into two identical segments, one of which remains with the egg, and the supplementary is extruded as the first polar body, a small ovoidal white globule, which is situated on the surface of the egg surrounding the exuded peri-vitellline fluid.

'''3. The Second Polar Body''', half of the nuclear spindle that stay behind then splits into two equivalent divisions, one of which remains inside the egg as the female pronucleus, whereas the other segment is extruded as the second polar body, a small white globule extremely related to the first polar body, and like this positioned in the perivitelline fluid on the superior portion of the egg.

'''4. Fertilisation of the egg''', includes the synthesis of the spermatozoon with to egg, specifically, synthesis of the nuclei of these two bodies. The spermatozoa, subsequent to being shed over the seed by the male, distribute vigorously by means of their extended tails, break through the gelatinous investment of the female eggs, bore their way through the vitelline membrane and so go through into the eggs themselves, which they penetrate relative to the superior or black hemispheres.
* Subsequently, an hour following the spermatozoon has entered; a progression may be visible projecting within from the exterior segement of the egg, with a liquid spot in the mid point. This liquid centre is the nucleus of the spermatozoon, and is said to be the male pronucleus, it break through beyond into the female egg, transporting the specialised pigment into it, so that it appears bounded by a pigmented capsule linked with the exterior of the egg by a pigmented stalk.

* By this instance, the second polar body has been established and extruded, and the female pronucleus is merely the only component of the primary egg nucleus still present. Both the male and female pronuceli, which are at initially distance separate to each other, merge and after having enlarged significantly in size then fuse mutually about two and half hours after fertilisation has originated to produce the segmentation nucleus.
* The segmentation nucleus is a huge sphere-shaped vesicle embedded in delicately granular protoplasm, and bounded by a distinct capsule of pigment, its arrangement by the synthesis of the male and female pronuclei completes the action of fertilisation. Specifically female pronucleus may be observe as an imperfect nucleus, and consequently result in the course of fertilisation. The nucleus of the spermatozoon or male pronucleus, replaces the component of the egg- nucleus which has been misplaced as the polar bodies.

'''5. Segmentation of the Egg''', the initial phase of growth consist in constant separation of the egg, whereby it becomes transformed from the unicellular state, which is everlasting only in the lowest species, to muliticelluar state charactertics of all higher species. To these early processes of growth the names segmentation is specified. Shorty subsequent to the competition of fertilisation and arrangement of the segmentation nucleus this later misplaces its sphere-shaped appearance and develops to be spindle-shaped, the yolk granules at the equivalent instance showing a tendency to develop into lines distributing outwards from the distal segment of the spindle.
* The nucleus now split into two halves, which shift away from one another, the yolk granules are likely to combined themselves around the two nuclei, and a slender vertical plate of delicately granular substance is left, dividing the egg.[http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

* Superiorly the eggs depression now becomes visible, initially as a small cavity and then develops as a groove, which almost immediately extends all round, and speedily deepening, splits the egg into two entirely separate halves along a plane equivalent with the vertical plane.

* Shorty after, the two nuclei soon separate again into two, and therefore a second cleft is created in the same state as before, its additionally in the vertical plane, however in a plane at 90 degrees to the initial one, and on its finishing point the egg comprises of four accurately similar segments, each containing a nucleus. The third cleft is horizontal in shape, but not equal, lying closer to the superior than the lower pole, it segregates each of the four cells into, an superior smaller and a inferior larger pole

----

== Cleavage ==

[[Image: Frog Cleavage development.jpg|thumb|left|Cleavage Process details:[http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/F/FrogEmbryology.html].jpg]]

* The egg of the frog is scientifically identified as’ telolecithal’ meaning there is a outsized amount of yolk concentrated at a single pole, in contrast to the concentration of cytoplasm and the site of the nucleus. The cleavage phases are holoblastic, therefore the total and after the second cleavage they are asymmetrical .The initial cleavage stage appears about two and half to three hours after fertilization. It commences as a minor depression in close proximity to the centre of the animal hemisphere. It appears as if some interior force is pushing the surface the egg towards the centre. This small upturned fold steadily continues in the form of a channel until it surrounds the egg. This groove is shallow in the commencement, but develop into deeper eventually separating the fertilized egg into two halves recognised as the blastomeres. [The figure on the left symbolise the development and growth of the frog embryo during cleavage].

* Internally the separation is mitotic, consequently each daughter cell contains a nucleus resulting from the copulation nucleus of the fertilised egg. This cleavage is vertical, the two cells are indistinguishable in respect of cytoplasm, pigment and yolk. The subsequent cleavage appears about an hour after the first. The channel of this cleavage begins at the centre of the animal hemisphere, is at right angles to the first and is vertical. This divides the egg into four blastomeres. The fourth blastomere so produced are not qualitatively equal, since of these only two contain the material from the gray crescent. The cleavage begins about thirty minutes after the second is completed or four hours after fertilisation. the cleavage plane of the third furrow is horizontal and slightly above the equator. Thus the four upper cells are a little smaller than the four lower cells. The smaller blastomeres are called micromeres and the larger blastomeres are called macromeres. The fourth cleavages follow 20 minutes after the third and tend to be vertical. This is usually a double furrow.

* The cleavage rate is accelerated with each of the early divisions and since the blastomeres are of unequal size and have varying amounts of cytoplasm and yolk, synchronous cleavage is lost and there is an obvious overlapping of the division. The upper most cells divide more rapidly than the lowermost cells. From this point onwards perfect symmetry in cleavage and in blastomere is very rare, although the embryo developed perfectly. The fifth cleavage is also doubled, appearing first in the upper hemisphere and then in the lower.

* The cleavage thus far follows the rule that each cleavage plane comes in at right angles to the previous one. The subsequent divisions become so irregular that it is previous one. The subsequent division become so irregular that it is impossible to trace out any plan or procedure. The segmentation continues more rapidly in the pigmented regions, since at that place the protoplasm is most dense, whereas, yolk which is very abundant in the vegetal side delays cell division. The multicelluar embryo at this stage is called morula by some biologists.

----

== Gastrulation ==

[[Image:FROG GASTRULATION .jpg|thumb|left|Frog Gastrulation Image details:[http://www.google.com.au/imgres?imgurl=http://bio1903.nicerweb.com/Locked/media/ch47/47_12FrogGastrulation.jpg&imgrefurl=http://bio1903.nicerweb.com/Locked/media/ch47/gastrulation-frog.html&h=540&w=480&sz=46&tbnid=N78sHjELreGGSM:&tbnh=132&tbnw=117&prev=/images%3Fq%3Dfrog%2B-%2Bgastrulation&hl=en&usg=__4VK9FYLft0W-4lBe6p5EtQAMiaI=&ei=qPy5SurtMJvE6wON8JmdAg&sa=X&oi=image_result&resnum=4&ct=image].jpg]]

''The phase of Blastulation is followed by the unique developmental progression of gastrulation. The process of frog gastrulation involves the following processes.''

'''1. Epiboly Phase'''

The pigmented cellular materials of blastula have the propensity to overgrow the yolk cells within the developing content. This course which is known as epiboly commences gradually in the final blastula and rapidly accelerates with advancing gastrulation development. The cellular matter within the animal pole reproduces and matures on all sides except in area surrounding the dorsal lip of the blastopore has been established.

'''2. Convergence'''

Scientists suggested that the unfolding was thought to result in spreading of the superficial cells over a substrate with suitable absorption properties. Consequently epiboly and convergence are an outcome to this spreading tendency, which is actually increased by a reduction in surface tension of the distributing cells.

'''3. Rotation'''

The epiboly phase is maintained until the region of the dorsal lip has migrated and is a to some extent greater than 90 degrees and the region of the white blastopore is reduced to small circular rings. This section will be positioned away from the developing vegetal pole. Laterally the complete developing gastrula has been rotated to a horizontal axis, allowing it to lie at right angles to the original median plane of the egg. Therefore, the course of rotation is such that the dorsal lip is practically pushed backwards in one direction as rapid or quicker than epiboly moves it forward in the other. The outcome will be that the blastopore produced at roughly the vegetal pole is posterior, and the dorsal and ventral lips are essentially dorsal and ventral. This in addition allows the eggs to form the antero-ventral side of the potential embryo whilst the area marked by the grey crescent is to develop the dorsal segment.

'''4. Invagination'''

Visible is a small fissure- like invagination which is apparent in the middle between the equator and the vegetal segment. The most superior or dorsal border of the cleft produce the dorsal lip of the blastopore. This imput move back and forth on the dorsal plane near the dorsal lip and migrates around the boundaries of the blastocoel in company with the extension of the lateral lips. This adapted invagination is maintained until the blastocoel cavity has been almost abolished; excluding the slender opening separating epiblasts from the hypoblast, the new segment formed is known as the archenteron cavity.

'''5. Involution'''

- Additional to previous course of action a distinct involution also occurs at the blastoporal borders. This is mainly dynamic at the median dorsal lip and gradually more less as it shifts across either side until it reaches the ventral lip where it constant.Throughout this progression, cells positioned beside the superior boundaries of the blastoporal lip migrate over the lip to the interior portion of the lip. These cells are remained within the embryo along the internal edge of the blastopore. This indicates the root of archenteron is composed of involuted cells and beyond this the external layer known as the ectoderm. The base and lateral sides are enclosed mainly of endodermal cellular material, which have been established from larger yolk cells, situated in the vegetal pole of the blastula.

- In the final phases of the gastrula development, the cells contributing to the floor of the archenteron, thin out significantly where they surround the blastocoel.
The hemispherical shaped dorsal lip of blastopore which become visible at the commencement of the gastruation stage carry on to augment, initially becoming semicircular, then transform into a horse shoe shaped and then finally forming into circular band. The band is the accomplished by the blastopore. Various yolk cells of vegetal pole present in the section are crowed into the blastoporal cavity where they form a gathering identified as a yolk plug. Blastopore rapidly reduces in size while the archenteron is still developing and becomes completely formed in the final stage; the yolk plug appears as only a small oval on the gastrula.

==Growth and Modification of Frog Species==

'''1. Changes in habits and habitats:'''

'''a)''' In frogs, metamorphosis is related with to the modifications and adaptations as a frog changes environmental habitats from an aquatic to a terrestrial mode. Metamorphosis has modified the adaption of frogs as this alteration it began during the aquatic adaptations in the surface of water to breathe air. Subsequently, it continues the terrestrial surroundings, therefore the frog species become abundant in vegetation area allowing the frog to transform in to amphibious species.

'''b)''' The transition during metamorphosis is linked with a change in food chain. The tadpoles being the embryonic origin of frogs are herbivorous, feeding on algae and green matter, which they collect by the adapted feature such as their teeth surrounding their mouths. Adult frogs, alternatively, are classified as carnivorous feeding on insects and worms. Occasionally, they also consume larger prey, for instance smaller frogs species and even little birds and rodents which they dominant and ingest.

[[Image:Development of frog from sperm to mature structure.jpg|thumb|left|Development of Frog from sperm to mature structure Image details:J,Nassif 2009.jpg]]

'''2. Changes in Morphology'''

These include the decrease or complete absence of specific organs or structures which are essential during development of early frog embryology, but not critical in the mature frog species. The significant alterations of this nature include the following developmental structures.

'''a)''' The long tail of the tadpole alongside the fin folds is absorbed again during metamorphosis and becomes absent at the final stage of the metamorphosis.

'''b) '''The developing gills are resorted, the gill clefts are congested and the branchial cavities start to become absent. The reabsorbtion of gills also takes place by autolysis.

'''c)''' The teeth of the perioral disc additionally the homey lining of the jaws are shed.

'''d)''' The lateral line sense organs within the skin of tadpoles vanish throughout metamorphosis.

'''e)''' The cloacal tube begins to condensed and reduced.

'''f)''' Various blood vessels, together with parts of the aortic arches, are reduced during mature development.

(The figure on the left represents the transformation from a tadpole to a developing structure.)[http://science.jrank.org/pages/2862/Frogs-Adult-morphology.html]

'''3. Progressive or constructive changes'''

This process comprises of the development of specific organs which mature into functional systems only during metamorphosis.

'''a)''' During development the limbs continue to augment in size and differentiation. The forelimbs, which in the tadpole mature under the opercular membrane, which then break through to the exterior. Simultaneously there is a increase in the length and strength of the hind limbs, joints develop in them and the toes become visible.

'''b)''' The middle ear becomes apparent in relation with the first pharyngeal pouch. The tympanic membrane matures. It is bounded by circular tympanic cartilage which allows the frog to retain air.

'''c)''' The visual organs bulge up on the dorsal surface of the head developing the nictitating membrane.

'''d)''' There is augmentation of the tongue and the formation of thevomerina teeth.

[[Image: Growth model.jpg|thumb|Growth Model Image details:J,Nassif2009:]]

'''4. Remodelling of some structures'''

Systematic organs which operate both in the early embryonic larva and the mature adult change their differentiation during metamorphosis so as to meet the requirements of the adult mode of life and due to the habitat adaptations. The figure on the right illustrates structures developing from specic germ cell layers.

'''a)''' The skin of the embryonic tadpole is lined with a double-layered epidermis. The number of layers of cells in the epidermis augments throughout metamorphosis. Superficial surface layers become cornified. Multicellular mucous and serous glands originate in the skin. The pigmentation of the skin continuously changes, new patterns and colour start to form.

'''b)''' There is a lengthening of the mouth gap as a result of rotation of the quadrate cartilage and the true jaws become functional.

'''c)''' The tongue rapidly progresses and becomes larger and more muscular.

'''d)''' The eyes become more specialised.

'''e)''' In early tadpoles, the GIT is extremely long and wound up into a spiral folds. The intestine become greatly lengthened in herbivorous species due to the vegetables food chain.[http://en.wikipedia.org/wiki/Frog]

'''5. Development of the reproductive system'''

(The figure below represents the reproductive and development cycle of a frog as it transform from egg to frog specie.)

In tadpoles, right after the mouth is being formed, two indentation like thickenings of peritoneum begin to appear near the body cavity (dorsal surface), which is nearest to the mesentery which is near the developing kidneys. These appear in all tadpoles.

These indentations appear here because of a change in the endothelial cells, everywhere else they are usually flat looking cells but they undergo a change and in this particular area become somewhat cuboidal/columnar.

Later on the indentations become more obvious due to the epithelial cells replicating numerously to form a thick layer. The posterior two thirds of the indentation for the female is the ovary and for the male it is the testis. The third that is left differentiates and becomes fat for the body.

[[Image: Mature frog life cyle.jpg|thumb|200px|left|Mature from life cycle Image details:Derived from primary source:http://www.scienceclarified.com/images/uesc_01_img0038.jpg]]

[[Image: Developing frog.jpg|thumb|Developing Frog Image details:
[[Image: Mature develop frog.jpg|thumb|Image details: Red eyed tree frog litoria chloris source:[http://en.wikipedia.org/wiki/File:Red-eyed_Tree_Frog_-_Litoria_chloris_edit1.jpg]].jpg]]

===Delamination===

Delamination indicates a mass separating a group of cellular matter from other cellular groups. It has been illustrated that the division of notochord, mesoderm and endoderm tissues from each other to form distinct cellular masses is completed by the progression of delamination, subsequent to these materials moving to the inside throughout gastrulation. During the developing gastrula, the germ layers are all recognized. These distinct segments of the embryo develop from these germ tissue layers.

===Polarity and Rotation===

Throughout fertilisation to the beginning of gastrulation, the frog’s egg continues in the original location in relation to its polarity. Subsequent to gastrulation its polarity begins to differentiate. This progression is linked with migration of materials within the gastrula and can be responsible for the alterations of the centre of gravity.

===Closing of Blastopore===

Subsequent to the formation of the gastrula, the blastopore is visible as a tiny round circular filled cavity containing the yolk plug. As it continues to reduce in dimension, it represented as a pear-shaped outline through the mutual approach of its lateral lips. Through it final progression these fuse entirely to produce a longitudinal groove, the streak which continue dorsally and ventrally in a small aperture. The inferior aperture closes, resulting in a depression called the anal pit. The superior region remains open for some period and begins to as the neural groove is laid down.

===Post Gastrulation or Organogenesis===

Throughout the duration of pre-gastrulation, all tissues for different organs vanish from the surface of blastula and migrate inside to take their final arrangement in the embryo structure where organs are developed from their potential regions. Consequently organogenesis transfers an embryo into free larva structure.

----

==Germ-layer origin of various body tissues==
[[Image: Development Models of Frog.jpg|thumb|right|Figure 13 Image details:Vertebrate Structure and Development.jpg]]

Ectoderm will give raise to structures such as skin, brain, spinal cord, neurons and sense receptors.
Mesoderm will give raise to structrues such as notochord, muscles, blood, bone and sex organs.
Endoderm will give raise to sturctures such as inner lining of gut, liver, pancreas, lungs and bladder, thyroid and parathyroid glands and thymus.

== Structures derived from Germ-layers of frog species ==

[[Image:Development of Frog Layers.jpg|thumb|left|Development of Frog Layers Primary source[http://www.bio.miami.edu/~cmallery/150/physiol/sf19x11b.jpg]Image details:J,Nassif 2009.jpg]]

[[Image:Development of frog layers.jpg|thumb|left|Development of Frog Layers Primary source [http://www.bio.miami.edu/~cmallery/150/physiol/sf19x11b.jpg]Image details:J,Nassif 2009.jpg]]

'''Ectoderm '''

''Establishes the epidermal segments and its derivatives, to the frog’s nervous system. The ectoderm also contributes to :''

1. The olfactory and auditory epithelium.

2. The retina and lens of the eye.

3. Sensory organs.

4. The epithelial lining of the oral cavity and the anus.

5. The pineal and pituitary body.

'''Mesoderm'''

''Mesoderm originates:''

1. Connective tissue.

2. Muscles, except the notochord.

3. Blood vessels.

4. Lymphatics.

5. The peritoneum and the urinary and reproductive system.

6. The dermis, parts of the eye excluding lens, cornea, and conjunctiva.

'''Endoderm'''

''From the endoderm arises:''

1. The epithelial lining to the gut and oesophagus, stomach, intestine, bile duct.

2. The hepatic cells of the liver, respiratory tract, larynx, trachea and lungs.

3. The lining of the urinary bladder, pancreas thyroid and thymus.

[The two figures reveal the development of structures deriving from the celluar components of the embryology of the frog].[Structures derived from Germ-layers of frog species ]

==Life cycle of a frog==

'''Fertilization-egg''':

The female lays eggs in the spring. A group of fertilized eggs is called spawn;

'''7-10 days''':

Fertilized egg feed on remaining yolk which is in its gut. Their gills, mouth and tail have poorly developed. Begin to swim and feed on algae;

'''10-30 days(4 weeks):'''

A layer of skin grows over gills. Teeth begin to appear. A coiled gut start to develop. This is aid in digestion;

'''30-60 days(6-9 weeks):'''

Legs being to grow and head is more distinct. Start to eat insects. Arms begin to grow;

'''60-80 days(12 weeks):'''

Resemble a frog. Still have remaining tail;

'''80-140 days(20 weeks):'''

Fully developed, spend most of time out of water. Majority of frog live between 4-15 years.

==Timeline of frog development==

Development of egg and embryo at temperature 18 degree celsius.

'''0 hours''' - fertilization of the egg

'''1 hours''' - formation of the gray crescent due to pigment migration

'''3.5 hours''' - early cleavage

'''4.5 hours''' - blastula stage(coeloblastula with eccentric blastocoel

'''26 hours''' - gastrulation

'''26 hours''' -'' early'' - crescent shaped dorsal lip

'''34 hours''' - ''middle''- semicircular blastoporal lip

'''42 hours''' - ''late'' - circular blastoporal lip

'''50 hours''' - neurulation

'''50 hours''' - ''early'' - medullary plate

'''62 hours''' -'' middle''- neural folds converging

'''67 hours''' - ''late'' - neural tube formed and ciliation of embryo

'''84 hours''' - tail bud stage(early organogeny)

'''96 hours''' - muscular response to tactile stimulation

'''118 hours''' - early heart beat, development of gill buds

'''140 hours''' - hatching and gill circulation

'''162 hours''' - mouth opens and cornea becomes transparent

'''192 hours''' - tail fin circulation established

'''216 hours''' - degeneration of external gills, formation of operculum, development of embryonic teeth

'''240 hours''' - opercular fold over brachial chamber except for spiracle and internal gills

'''255 hours''' - prolonged larval stage with refinement of organs

'''270 hours''' - development of hindlimbs, internal development of forelimbs in opercular cavity

'''275 hours''' - projection of forelimbs through operculum, left side first

'''280 hours''' - absorption of the tail and reduction in size of the gut

'''284 hours''' - metamorphosis complete, emergence from water as miniature, air breathing frog

==Stages of frog embryology==
--[[User:S8600021|Mark Hill]] 08:40, 9 October 2009 (EST) [[Talk:2009_Group_Project_5#Constructive_Criticism_of_Coordinator|see my comment on images]]

The rate of development of the egg and embryo will depend upon the temperature at which they are kept. The approximate schedule of development at 23 degree celsius is provided below.

{| border='1px'
|+ Table 1: Stages of frog development
!Stage !!Time since fertilisation (hours)!!Stage Characteristic !!Embryo characteristic !!Image of frog stage
|-
|1
|0.00-1.30
|fertilization of the egg, post fertilization
|animal hemisphere, gray crescent and vegetal hemisphere are present
|[[File:Stage01ventral.jpg|100px]]
|-
|2
|1.30-2.00
|splits into two cells
|appearance of first cleavage furrow
|[[File:Stage02ventral.jpg|100px]]
|-
|3
|2.00-2.15
|becomes four cells
|appearance of second cleavage furrow
|[[File:Stage03dorsolat.jpg|100px]]
|-
|4
|2.15-2.45
|becomes eight cells
|appearance of third cleavage furrow
|[[File:Stage04dorsolat.jpg|100px]]
|-
|5
|2.45-3.00
|becomes sixteen cells
|appearance of fourth cleavage furrow
|[[File:Stage05dorsal.jpg|100px]]
|-
|6
|3.00-3.30
|becomes thirty-two cells
|appearance of fifth cleavage furrow
|[[File:Stage06animal.jpg|100px]]
|-
|6.5
|3.30-4.00
|blastula stage
|Three dorsal folds become visible as a result of endoderm invagination. Pole cells no longer visible on surface
|[[File:Stage065dorsal.jpg|100px]]
|-
|7
|4.00-5.00
|Gastrulation stage
|two primary germ layers. epiblast and endoderm
|[[File:Stage07ventral.jpg|100px]]
|-
|8
|5.00-7.00
|neurulation
|medullary plate, neural folds and neural tube
|[[File:Stage08animal.jpg|100px]]
|-
|9
|7.00-9.00
|germ layer
|complete lip involution encircling yolk
|[[File:Stage09veg.jpg|100px]]
|-
|10
|9.00-11.00
|early gastrula
|two primary germ layers
|[[File:Stage10veg.jpg|100px]]
|-
|10.5
|11.00-11.45
|gastrula
|two germ layers
|[[File:Stage105vegb.jpg|100px]]
|-
|11
|11.45-12.30
|medulla plate
|Yolk sac protrudes dorsally, labium moves to midline on ventral side
|[[File:Stage11veg.jpg|100px]]
|-
|11.5
|12.30-13.15
|continuation of medulla plate
|start closing the plate
|[[File:Stage115veg.jpg|100px]]
|-
|12
|13.15-14.15
|early neurula
|thickened ectoderm give rise to CNS
|[[File:Stage12veg.jpg|100px]]
|-
|12.5
|14.15-14.45
|neural folds
|expansion of cavity
|[[File:Stage125postdors.jpg|100px]]
|-
|13
|14.45-16.15
|neural folds
|continue expanding cavity
|[[File:Stage13postdors.jpg|100px]]
|-
|14
|16.15-17.30
|neural folds
|continuation of cavity
|[[File:Stage14postdors.jpg|100px]]
|-
|15
|17.30-18.15
|tail bud stage
|early organogeny
|[[File:Stage15postdors.jpg|100px]]
|-
|16
|18.15-18.45
|tail bud stage
|posterior ventral view
|[[File:Stage16ant.jpg|100px]]
|-
|17
|18.45-19.45
|tail bud stage
|anterior view
|[[File:Stage17ant.jpg|100px]]
|-
|19
|20.45-21.45
|neural fold close complete
|dorsal view
|[[File:Stage19dorsal.jpg|100px]]
|-
|20
|21.45-22.30
|early tail bud
|anterior view
|[[File:Stage20dorsal.jpg|100px]]
|-
|21
|22.30-24.00
|termination of neural crest
|progress to next stage
|[[File:Stage21ant.jpg|100px]]
|-
|22
|24.00-24.45
|prolonged development
|elongation
|[[File:Stage22lat.jpg|100px]]
|-
|23
|24.45-26.15
|elongation of embryo
|later view
|[[File:Stage23lat.jpg|100px]]
|-
|24
|26.15-27.30
|continuation of elongation of embryo
|dorsal view
|[[File:Stage24latsmall.jpg|50px]]
|-
|25
|27.30-29.30
|organs development
|embryo elongates and develops dorsal thickening
|[[File:Stage25dorsal.jpg|50px]]
|-
|26
|29.30-31.15
|elongation
|dorsally forms neural and brain cavity
|[[File:Stage26lat.jpg|50px]]
|-
|27
|31.15-32.30
|elongation of embryo
|dorsal view
|[[File:Stage27lat.jpg|50px]]
|-
|28
|32.30-35.00
|further development
|lateral view
|[[File:Stage28lat.jpg|50px]]
|-
|29-30
|35.00-37.30
|tail bud
|growth
|[[File:Stage29-30lat.jpg|50px]]
|-
|31
|37.30-40.00
|prolonged development
|bud development
|[[File:Stage31lat.jpg|50px]]
|-
|32
|40.00-44.30
|early muscular development
|elongation
|[[File:Stage32lat.jpg|50px]]
|-
|33-34
|44.30-50.00
|muscular movement
|apparatus for locomotion
|[[File:Stage33-34lat.jpg|50px]]
|-
|35-36
|50.00-53.30
|muscular movement
|apparatus for locomotion
|[[File:Stage35-36lat.jpg|50px]]
|-
|37-38
|53.30-56.30
|heart beat
|develops apparatus
|[[File:Stage37-38lat.jpg|50px]]
|-
|39
|56.30-66.00
|mouth opens
|cornea transparent
|[[File:Stage39latsmall.jpg|50px]]
|-
|40
|66.00-76.00
|gill circulation
|hatching
|[[File:Stage40lat.jpg|50px]]
|-
|41
|76.00-80.00
|tail, fin circulation
|circulation
|[[File:Stage41lat.jpg|50px]]
|-
|42
|80.00-86.00
|internal gills, operculum
|opercular fold, teeth
|[[File:Stage42lat.jpg|50px]]
|-
|43
|86.00-98.00
|operculum complete
|operculum closed on right
|[[File:Stage43lat.jpg|50px]]
|-
|46
|98.00-106.00
|metamorphosis
|emergence from water as miniature, operculum complete|
|[[File:Stage46lat.jpg|50px]]
|-
|}

==Abnormalities of frog==

Abnormalities of frog could be caused by multiple factors. These include change in climate, predators, parasites, bacteria, fungi, viruses or pollution and contaminants such as pesticides, metals and fertilizer.[http://www.fws.gov/contaminants/documents/frogsrefup_septoct_2006.pdf]

The Abnormalities are further classified into different categories. These categories are:

===1. Infectious Diseases:===

'''Perkinsus Symptoms-''' caused by perkinsus-like protozoan organism. Symptoms include swollen viscera that leads to a bloated body and and infected swollen heart

'''Ichthyophonus symptoms-''' cause by parasitic genus, where symptoms include a swollen tail resorption site that matches the surrounding skin in color and translucency.

[[Image:Abnormalities of Frog species.jpg|thumb|left|Figure A Image details[waterwatchadelaide.net.au].jpg]]

===2. Surficial Abnormalities:===

Surficial abnormalities as the one that are visible on the surface of the skin. This includes abnormal pigmentation, , subcutaneous hemorrhaging, wounds due to trauma or from a predator
Edema is a fluid-filled swelling under skin whihc is also a surficial abnormality.

===3. Skeletal Abnormalities:===

This is further classified into three more categories:

'''a. Skeletal Malformations-'''

* Microcephaly (small head or blunt snout)
*Scoliosis (Curved spine in lateral direction)
*Shrunken Limb (Micromelia)
*Amelia (Completely missing limb with no stump)

'''b. Skeletal Abnormalities of Unclear Etiology-'''

This condition arises when a frog has ectromelia (missing limb), brachydactyly (missing digits) or other such condition with no visible trauma or external damage, then this will be classified as the Skeletal abnormality of unclear etiology.

'''c. Skeletal Injuries-'''

Any limb missing or broken due to trauma or other related reason which shows clear evidence of it is classified as skeletal injury

===4. Eye Abnormalities:===

Most common includes-

'''i. Anophthalmia:''' Skin covers the eye socket as there is no eye

'''ii. Abnormal Iris Coloration:''' Reduced pigment in either one eye or both resulting in two different colours of the iris at times

'''iii. Abnormal size or shape:''' Both eyes either deviating from each other or size of pupil or iris is different than the other eye

[http://www.fws.gov/contaminants/Amphibian/pdfs/AbnormalitySOP_woutpics_Jan08.pdf ]

==Genetics==

There are a wide variety of species that differ from each other when it comes to genetics and their functioning.

'''TAXONOMY:''' '''Phylum''' ''Chordata'' / '''Sub Phylum''' ''Vertebrata'' / '''Class''' ''Amphibia'' / '''Order''' ''Anura''

Their are more than two dozen different families of frogs, where suborders are:

'''1. ARCHAEBATRACHIA-''' most primitive frogs

'''2. MESOBATRACHIA-''' linked between the Archaebatrachia and Neobatrachia

'''3. NEOBATRACHIA-''' most modern frogs

{| border='4px'
|+ '''General Info:'''
! !!
|-
| '''Number of frogs' species'''
| 5280
|-
| '''Smallest frog genome size:'''
| 0.95pg, Ornate burrowing frog
|-
| '''Largest frog genome size:'''
| 13.40pg, Ornate horned frog
|-
| '''Mean of frogs' genome'''
| 4.68pg ± 0.13
|-
|}

[http://www.genomesize.com]

*Majority of frogs have only 22 to 26 chromosomes and polyploid is very common where they are almost bisexual.

*Polyploid Amphibians reduce their total cell number such that they acheive the same body size as diploids. One of the most unsual forms of polypoidy in amphibians is the water frog ''Rana esculenta'' from Europe and Western Asia.

* The species with larger genomes have more genes for e.g. the frog genus ''Xenopus'' includes 16 species, with genome sizes ranging from 3.5 x 10^9 bp to 1.6 x 10^10 bp. These differences have arisen by numerous events of polyploidization within the past 40 million years or so. The ancestral chromosome number for the genus seems to have been 18, but there are species with 36, 72 and 105 chromosomes [http://www.xenbase.org/common/]

{| border='4px'
|+ '''Difference within two families'''
! '''SPECIES''' !! ''X.LAEVIS'' !! ''X.TROPICALIS''
|-
| '''PLOIDY'''
| Allotetraploid
| Diploid
|-
| '''NO. OF CHROMOSOMES'''
| 36 chromosomes
| 20 chromosomes
|-
| '''GENOME SIZE'''
| 3.1 x 10^9 bp
| 1.7 x 10^9 bp
|-
| '''EGG SIZE'''
| 1-1.3 mm
| 0.7-0.8 mm
|-
| '''GENERATION TIME'''
| 1-2 years
| 4 months
|-
|}
[http://www.xenbase.org/common/]

===Genome Sequencing===

Since Frog has a huge family with many different species, only few main species that are used widely for the purposes of experiments have their genome sequenced.

''Xenopus tropicalis'' has one of the smallest genomes among amphibians and has the shortest generation time- four to six months and the only diploid genome among the 14 Xenopus species. This means it has no more than two copies of most genes, whereas the other species of Xenopus have four copies of most genes (pseudotetraploid). US Department of Energy's Joint Genome Institute (JGI) in Walnut Creek, California, initiated the X. tropicalis Genome Project, finding 1,700 million base pairs.
[http://www.genome.gov/Pages/Research/Sequencing/BACLibrary/xenopusTropicalis.pdf]

===Xenopus oocytes===

* The oocytes provide an important expression system for molecular biology.

* By injecting DNA or mRNA into the oocyte or developing embryo, scientists can study the protein products in a controlled system. This allows rapid functional expression of manipulated DNAs (or mRNA). This is particularly useful in electrophysiology, where the ease of recording from the oocyte makes expression of membrane channels attractive.

* One challenge of oocyte work is eliminating native proteins that might confound results, such as membrane channels native to the oocyte.

* Translation of proteins can be blocked or splicing of pre-mRNA can be modified by injection of Morpholino antisense oligos into the oocyte (for distribution throughout the embryo) or early embryo (for distribution only into daughter cells of the injected cell).
[http://www.staff.unibe.ch/sigel/xenopus.html]

===Xenopus Laevis===

* ''Xenopus Laevis'' is an important model organism in developmental biology. X. laevis is tetraploid and reaches sexual maturity in 1 to 2 years. What makes it important in developmental biology is its large and easily manipulable embryo.

* Extracts from the eggs of X. laevis frogs are also commonly used for biochemical studies of DNA replication and repair, as these extracts fully support DNA replication and other related processes in a cell-free environment which allows easier manipulation.

* The Human chorionic gonadotropin hormone (hCG) is present in the urine of the pregnant women in large quantities only. This hormone in the urine induces X.laevis oocyte production which formed the basis of first well-documented method of pregnancy testing X. laevis is also notable for its use as the first well-documented method of pregnancy testing when it was discovered. Today, commercially available HCG is injected into Xenopus males and females to induce mating behavior and breed these frogs in captivity at any time of the year.

===Gene cluster===

* The alpha and beta globin genes are closely linked in small cluster of frogs compared to human and chicken

* The similarity of architecture of two clusters found in X.laevis supports the tetraploid origin

* The two loci encoding the muscle specific creatine kinase isoenzymes and have large differences in developmental profile, therefore suggesting that duplicate loci that have not undergone silencing are not simply redundant copies but have acquired specialization.

* Contains twice number of genes for proteins i.e. haemoglobin and sarcomeric actin serum albumin compared with other species

----

==Current Embrology Research==

Currently, a number of fields have benefited from the development of frog embrology. These include cloning, verification of messenger RNA, and Cell cycle.

===Cloning===
[[Image:Robert Briggs.jpg|thumb|left|Figure 16 Image details:Robert Briggs.jpg]]

In 1952, Robert Briggs and Thomas J King cloned northern leopard frogs using a method of nuclear transfer. Briggs and King's experiment was similar to that envisioned - and piloted using salamanders - by Hans Spemann in his 1938 proposal for a 'fantastical experiment'. Later, John Gurdon extended this work and showed that nuclei from differentiated cells could support development, although less well than those from early embryos. [http://genome.wellcome.ac.uk/doc_WTD020799.html]

Lemaitre et a. (2005) from MRC Cancer Cell Unit, Cambridge, U.K. worked on experiments that demonstrated that importance of serial nuclear transplantation for the sucessful cloning of frogs. He demonstrated that exposure of somatic-cell nuclei (erythrocyte nuclei) and sperm nuclei to an extract of mitotic cell extract reorganizes the chromatin into shorter loops and allows replication at much shorter intervals along the DNA. This increases the efficiency of DNA replication in mammalian cell-free systems.

===Transgenesis techniques for functional genomics in Xenopus===

Transgenesis in Xenopus is made possible due to large embryos, a reliable fate map, ease of microinjection, ease of dissection/micromanipulation and existence of the neuroendocrine reflex of background adaptation as a model for activation/inact.

Recently, Hajime Ogino and Haruki Ochi from Nura Institute of Science and Technology in Japan focused on the genomic resources and principles of the transgenesis techniques in Xenopus, and discusses their applications to genome wide network analysis, with emphasis on the use of bioinformatics tools. This is will to understand the gene regulatory networks that control vertebrate development. [http://www.ingentaconnect.com/content/bsc/dgd/2009/00000051/00000004/art00001%3Bjsessionid=4ah96rms73gcu.alexandra]

Xenopus used to be a problem in earlier days when it came to transgenesis. Current methods involves isolated sperm nuclei from Xenopus testis that are microinjected into unfertilized eggs. The generated transgenic tadpoles contain 5-35 copies of the integrated plasmid that are expressed in all cells. If desired, expression of the transgene can be directed to the appropriate tissue and at the appropriate time by using specific promoters, mostly the Xenopus POMC gene promoter (isolated from a Xenopus genomic DNA library) to specifically direct expression of green fluorescent protein (GFP) at high levels to the intermediate pituitary cells, which can either be over expressed or inhibited.[http://molanphys.ruhosting.nl/transgenesis.htm]

[[File:Transgenesis.JPG]]

===Verification of messenger RNA===

While the existence and role of messenger RNA (mRNA) was known in bacteria, in the 1960s it was still debated whether it also existed in vertebrates. Taking haemoglobin mRNA from immature red blood cells and injecting it into a Xenopus oocyte, John Gurdon showed that the haemoglobin protein was indeed produced. Producing proteins in Xenopus oocytes has proved to be extremely useful in cell biology, in particular for the study of receptor proteins.[http://genome.wellcome.ac.uk/doc_WTD020799.html]

===Cell Cycle===

As they develop outside the mother, frog eggs are well stocked with the proteins needed to drive the development of the embryo. Studies of these processes has shed considerable light on the processes involved in cell division - termed the cell cycle. [http://genome.wellcome.ac.uk/doc_WTD020799.html]

===Limb development in Xenopus Laevis===

[[Image: Frog Limb development.jpg|thumb|right|From Limb Development Image details:Primary source:[http://images.google.com.au/imgres?imgurl=http://www.sciencedaily.com/images/2006/06/060616130718.jpg&imgrefurl=http://www.sciencedaily.com/releases/2006/06/060616130718.htm&usg=__xliPsPAvheUBME_kjv_q7auiFbo=&h=333&w=300&sz=11&hl=en&start=2&um=1&tbnid=y_ntJtmkRSK7WM:&tbnh=119&tbnw=107&prev=/images%3Fq%3DLimb%2Bdevelopment%2Bin%2BXenopus%2BLaevis%26ndsp%3D18%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

Donald D. Brown (2005),Department of Embryology, Carnegie Institution of Washington demonstrated factors related to limb development of Xenopus Laevis. Thyroid hormone (TH) is found to be required for limb development in this frog. Specific cell types in the growing limb were targeted for expression of a dominant negative form of the TH receptor by sperm-mediated transgenesis. Limb muscle development, the innervation of muscle from the spinal cord, and cartilage growth can be inhibited without affecting patterning of the limb or differentiation of other cell types. Remodeling of the skin occurs late in metamorphosis after the limb has formed. The coordination of these independent programs is affected in part by the control that TH exerts over DNA replication in all cell types of the limb. [http://www.pnas.org/content/102/35/12455.full]

----

== Glossary ==

[[Image: Frog species.jpg|thumb|left|Image details:Primary source:www.olympus.co.jp/.../080925/large/p02L.jpg].jpg]]

*'''Amphibian:'''

''Relating to or characteristic of animals of the class amphibia.Amphibians are found in the taxonomic class of amphibia, amphibians are capable of both occupying and successfully living in both land and aquatic communities.amphibian''

*'''Augmentation:'''

''Enlargement/Increase in cellular size.''

*'''Autolysis:'''

''breakdown of a part or whole cell or tissue by self-produced enzymes''

*'''Blastomeres:'''

''The undifferentiated cells formed by cleavage of the fertilised ovum. This includes cells in the cleavage, morula, and blastula stages of the embryo''

*'''Carnivorous:'''
''
Flesh-eating; subsisting on animals as food.''

*'''Cleavage:'''

''he repeated division of a fertilised ovum ''

* '''Cleft:'''

''an opening, fissure, or V-shaped indentation made by or as if by splitting''

*'''Chordate:'''

''Members of a diverse phylum of animals that, as embryos, possess a (1) notochord; (2) a dorsal, hollow nerve cord, (3) pharyngeal gill slits; and (4) a post-anal tail''

''The act or state of splitting or dividing of a cell, particularly during the telophase of (animal) cell division.''

*'''Cytoplasm:'''

''The cytoplasm (of both eukaryotes and prokaryotes) is where the functions for cell expansion, growth, metabolism, and replication are carried out''

* '''Epiboly:'''
''The expansion of one cell sheet over other cells, as takes place during gastrulation''

*'''Fertilization:'''

''A process in sexual reproduction that involves the union of male (sperm) and female (ovum) gametes (each with a single, haploid set of chromosomes) to produce a diploid zygote.''

*'''Gamete:'''
''A reproductive cell (male (sperm) or female (egg)) that has only half the usual number of chromosomes''

*'''Gametogenesis:'''

''process leading to the production of gametes. The development and maturation of sex cells through meiosis.Another name for meiosis where a diploid cell is divided into two haploid cells with half the chromosome content of the diploid parent cell.''

*'''Herbivorous:'''

''eating plants; of or pertaining to the herbivora.''

*'''Holoblastic:'''

''The complete division of an isolecithal or microlecithal egg into blastomeres''

*'''Invagination:'''

''One of the methods by which the various germinal layers of the ovum are differentiated.''

*'''Isoenzymes:'''

''Isozymes (also known as isoenzymes) are enzymes that differ in amino acid sequence but catalyze the same chemical reaction.''

*'''Mesentery:'''

'' membranous fold attaching various organs to the body wall.''

*'''Metamorphosis:'''

''A change in the form and often habits of an animal after the embryonic stage during normal development.''

*'''Neuroendocrine:'''

''Neuroendocrine [IPA nʊəroʊˈɛndəkrɪn] cells are cells that release a hormone into the circulating blood in response to a neural stimulus.''

*'''Organogenesis:'''

''The part of embryonic development where the body's main organs develop.''

*'''Peritoneum:'''

''The smooth serous membrane which lines the cavity of the abdomen, or the whole body cavity when there is no diaphragm, and, turning back, surrounds the viscera, forming a closed, or nearly closed, sac.''

*'''Perivitelline space:'''

''The perivitelline space is the space between the zona pellucida and the plasma membrane (sometimes called the vitelline membrane) in a fertilized ovum.''

*'''Polyploidy:'''

''Cells with three or more sets of chromosomes.''

*'''Pronucleus:'''

''the nucleus of the ovum or sperm after fertilization but before they fuse to form the nucleus of the zygote ''

*'''Protoplasm:'''

''The fluid living content of the cell that consists of two major divisions, the cytoplasm and the nucleoplasm (cell nucleus). It is composed mainly of nucleic acids, proteins, lipids, carbohydrates, and inorganic salts''

*'''Segmentation:'''

''division of some metazoan bodies (such as annelida and Arthropoda) into repeated parts, segments. Segmentation can be homomeric (more or less the same) or heteromeric(different from each other).''

*'''Terrestrial:'''

''Of or on the ground, of the habitat of a plant, on land as opposed to in water, or on the ground as opposed to on another plant.''

*'''Transgenesis:'''

''Transgenesis is the process of introducing an exogenous gene - called a transgene - into a living organism so that the organism will exhibit a new property and transmit that property to its offspring.''

*'''Yolk:'''

''nutritive material of an ovum stored for the nutrition of an embryo''

*'''Zygote:'''

''The cell from which an organism develops, that results from the fertilization of the egg by the sperm.''

''Primary Resource "Biology- Online Dictionary''[http://www.biology-online.org/dictionary/Main_Page]

== References - Frog Embryology: ==

[[Image:Frog Research.jpg|thumb|left|Image details:[http://images.google.com.au/imgres?imgurl=http://www.odt.co.nz/files/story/2008/09/university_of_otago_zoology_senior_lecturer_phil_b_3343259744.jpg&imgrefurl=http://www.odt.co.nz/on-campus/university-otago/21670/dunedin-frog-man-wins-zoo-award&usg=__JvJJU5QfOnIwY2bk4xo64UXuJRs=&h=600&w=404&sz=22&hl=en&start=14&um=1&tbnid=AbsP89yWcUiilM:&tbnh=135&tbnw=91&prev=/images%3Fq%3Dfrog%2Bresearch%26hl%3Den%26um%3D1].jpg]]

1. Savage, J. M. (2002). The Amphibians and Reptiles of Costa Rica. University of Chicago Press, Chicago [http://www.springerlink.com/content/vv015277w1746llw/]

2. Ford, L.S.; D.C. Cannatella (1993). "The major clades of frogs". Herpetological Monographs 7: 94–117 [http://digimorph.org/specimens/Xenopus_laevis/]

3. Tyler, M. J. (1994). Australian Frogs A Natural History. Reed Books [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.gracilenta.html]

4. Cogger, H.G.; R.G. Zweifel, and D. Kirschner (2004). Encyclopedia of Reptiles & Amphibians Second Edition. Fog City Press [http://en.wikipedia.org/wiki/Microhylidae]

5. Beltz, Ellin (2005). Frogs: Inside their Remarkable World. Firefly Books [http://unjobs.org/authors/ellin-beltz]

6. Tyler, M. J. (1994). Australian Frogs A Natural History. Reed Books [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

7. Moury JD, Hanken J (1995) Early cranial neural crest migration in the direct-developing frog, Eleutherodactylus coqui. Acta
Anatomica (Basel) 153, 243-253.

8.Raynaud A (1985) Development of limbs and embryonic limb reduction. In Biology of the Reptilia (ed. Gans C, Billett F), pp.
59-148. New York: John Wiley.[http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=9309]

9. Hanken J (1986) Developmental evidence for amphibian origins. In Evolutionary Biology (ed. Hecht MK, Wallace B, Prance GT), 20, pp. 389-417. New York: Plenum Press. [Hanken J (1986) Developmental evidence for amphibian origins. In Evolutionary Biology (ed. Hecht MK, Wallace B, Prance GT), 20, pp. 389-417. New York: Plenum Press.]

10. Elinson RP (1990) Direct development in frogs : wiping the recapitulationist slate clean. Seminars in Developmental Biology
1, 263-270.

11. Beebee, T. J. C. 1996. Ecology and Conservation of Amphibians. Chapman and Hall. London. [http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V5X-3SVHMKH-1X&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=1021245355&_rerunOrigin=google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=825868e10cd178d16a8a0e5ad14dc5ef]

12. Lehtinen, R. M. 2002. The use of screw pines (Pandanus spp.) by amphibians and reptiles in Madagascar. Herpetological Bulletin 2002:20–25.

13. Parris, K. M. and M. A. McCarthy. 1999. What influences the structure of frog assemblages at forest streams. Australian Journal of Ecology 24:495–502. CrossRef

14. Zug, G. R. 1993. Herpetology: An Introductory Biology of Amphibians and Reptiles. Academic Press. San Diego, CA.

15. Slack,J.M.W., Darlington,B.G., Heath,J.K. and Godsave,S.F. (1987)Mesoderm induction in early Xenopus embryos by heparin-binding growth factors. Nature, 326, 197-200.

16. Melton,D.A. (1990) Activins are expressed early in Xenopus embryogenesis and can induce axial mesoderm and anterior structures. Cell, 63, 485-493.

17. Harland,R.M. and Misher,L. (1988) Stability of RNA in developing Xenopus embryos and identification of a destabilizing sequence in TFIIIA RNA. Development, 102, 837-852.

18. Cunliffe,V. and Smith,J.C. (1992) Ectopic mesoderm formation in Xenopus embryos caused by widespread expression of a Brachyury homologue. Nature, 358, 427-430.

19. Kinoshita,K., Bessho,T. and Asashima,M. (1993) Competence prepattern in the animal hemisphere of the 8-cell-stage Xenopus embryo. Devel. Biol., 160, 276-284.

20. LaBonne,C., Burke,B. and Whitman,M. (1995) Role of MAP kinase in mesoderm induction and axial patterning in Xenopus development. Development, 121, 1475-1486.

21. Green,J.B.A., New,H.V. and Smith,J.C. (1992) Responses of embryonic Xenopus cells to activin and FGF are separated by multiple dose thresholds and correspond to distinct axes of the mesoderm. Cell, 71, 731-739.

22. Grainger R., Blumberg B., Harland R., Amemiya C., Importance of Xenopus Tropicalis to biomedical and biological research, Benaroya Research Institute, Virginia Mason Research Center [http://www.genome.gov/Pages/Research/Sequencing/BACLibrary/xenopusTropicalis.pdf ]

23. Gregory, T.R. (2005). Animal Genome Size Database. [http://www.genomesize.com]

24. U.S Fish and Wildlife Services, ABNORMALITY CLASSIFICATION SOP, [http://www.fws.gov/contaminants/Amphibian/pdfs/AbnormalitySOP_woutpics_Jan08.pdf ]

25. Donald D. Brown*, Liquan Cai*, Biswajit Das*, Nicholas Marsh-Armstrong‡, Alexander M. Schreiber*, and Rejeanne Juste*(2005), Thyroid hormone controls multiple independent programs required for limb development in Xenopus laevis metamorphosis [http://www.pnas.org/content/102/35/12455.full]

26. Ogino, Hajime; Ochi, Haruki, Resources and transgenesis techniques for functional genomics in Xenopus, Development Growth & Differentiation, Volume 51, Number 4, May 2009 , pp. 387-401(15) [http://www.ingentaconnect.com/content/bsc/dgd/2009/00000051/00000004/art00001%3Bjsessionid=4ah96rms73gcu.alexandra]

27. Giles Newton (2004) Why the frog? The Human Genome, [http://genome.wellcome.ac.uk/doc_WTD020799.html]

28. Xenbase, [http://www.xenbase.org/common/]

29. Donders Center for Neuroscience & Nijmegen Center for Molecular Life Sciences (NCMLS), Beyond the genome (Xenopus transgenesis for functional genomics),Faculty of Science, Radboud University [http://molanphys.ruhosting.nl/transgenesis.htm]

== External Links ==
[[Image:Frog links.jpg|thumb|left|Image details:[http://images.google.com.au/imgres?imgurl=http://2.bp.blogspot.com/_o93AaY0GzH4/SjY_ZYv0PII/AAAAAAAAAgk/skruNc2yN78/s400/computer%2Bfrog.jpg&imgrefurl=http://hellaheaven-ana.blogspot.com/2009/06/talking-frog-contemporary-fairy-tale.html&usg=__oxji1TGLV2Fi7xe0dnlmuYk8gDo=&h=288&w=288&sz=16&hl=en&start=2&um=1&tbnid=ywZd4zpdxC5plM:&tbnh=115&tbnw=115&prev=/images%3Fq%3Dfrog%2Bon%2Bcomputer%26hl%3Den%26um%3D1].jpg]]

1. Frog embryology [http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/F/FrogEmbryology.html Frog Embryology]

2. Frog cellular materials [http://www.xenbase.org/xenbase/original/cell/cell.html xenbase]

3. The zoology of frog species [http://worms.zoology.wisc.edu/frogs/mainmenu.html zoology frogs]

4. Frog cycle [http://www.bioethics.gov/images/sc_images/frog_dev.gif bioethics frog] Just a little cycle of FROG'S life cycle

5. Frog Embryology [http://embryology.med.unsw.edu.au/OtherEmb/Frog.htm UNSW Embryology]

6. Frog Research [http://apps.carleton.edu/campus/library/now/exhibits/wallcharts/frog/ carleton library exhibit]

{{Template:Projects09}}
[[Category:Frog]]

2009 Group Project 5

2009-10-14T22:45:18Z

Z3258567: /* Structures derived from Germ-layers of frog species */

== The Embryology of Frogs ==

== The Frog ==

[[Image: Frog species .jpg|thumb|left|Image details: Wikipedia (2009) Frog species[http://en.wikipedia.org/wiki/Frog#Uses_in_agriculture_and_research].jpg]]

Frogs are scientifically identified by the structure of their long posterior limbs, a petite framework, webbed fingers and feet, budged eyes and the lack of a tail. The majority of frog species are extensively recognized as outstanding jumpers, due to their long, dominant legs, which are adaptations to progress jumping performance during activities. The Frog is one of the most frequently studied species in experimental embryology and most anatomical sciences. ''The Frog is a practically effective model for human embryological development given that the Frog:''

- Comprises of genes which can be effectively manipulated.

- Comprises of similar homogeny with humans species.

- Reproduces a large quantity of offspring in a short period of time.

- Are small species which can be simply sustained.

- Are not extremely luxurious and expensive.

== The History of the uses in agriculture and research ==

[[Image: Frog experiments .jpg|thumb|right|Image details: Scans of chemically cleared and dyed preserved deformed frogs and toads [http://www.sat.qc.ca/upload/residence/frog-04.jpg].jpg]]

There are numerous types of frog species that have been manipulated in many developmental experiments. The frog was traditionally used by countless of the early embryology investigators and presently there are several diverse molecular mechanisms regarding progression of the frog. Theses include:

'''1.''' Food source; frog legs are a delicacy and are eaten in European countries and in many parts of South American regions.

'''2.''' Frogs have the finest biochemical dissection of phenomena that take place in the egg and oocyte. Frogs are the evolutionarily closest to mammals, commonly used as a vertebrate model.

'''3.''' Frogs lay thousands of outsized eggs, from which cell extracts can be readily prepared that is capable of recapitulating most molecular phenomena in a test tube.

'''4.''' Frogs have been commonly used as a laboratory system for a very long period, and have an extensive history of producing crucial observations in countless fields of biology.

'''5.''' Frogs have a important historical connection to the study of epigenetics (John Gurdon-vertebrate cloning and reprogramming) which has been mostly performed on frog species.

'''6.''' Frogs also have very strong evidence of pattern formation and early development, as the embryos are large in size and experimentally manipulative.

'''7.''' Recent research into the biochemistry of chromatin and epigenetics has been performed with frog species and mammalian cultured cells.

'''8.''' The biggest weakness of the Frog model system is the difficulty of performing genetic experiments and analysis, as frogs are allotetraploid, meaning they take approximately a year to fully develop to sexual maturity, and the genome has not been completely sequenced. Nevertheless, biochemical manipulations of cell extracts, such as immunodepletions and application of heterologous DNAs and nuclei can avoid the need for genetic exploitation.

----

== Growth and development of the Frog ==

[[Image: Mature develop frog.jpg|thumb|Image details: Wikipedia (2009) Red Eyed Tree Frog Figure 1 Primary source:[http://en.wikipedia.org/wiki/File:Red-eyed_Tree_Frog_-_Litoria_chloris_edit1].jpg]]

* The frog is a well recognised species, abundant predominantly in ponds, swamps, though various species may also exist in damp or shady environments distant from moist habitats.

* Eggs of specific frogs are easily obtained and may be examined in from the beginning of fertilization onwards. The phases of embryonic development differs in various chordates, yet the typical phases are basically apparent in all frog species. The differences are associated principally to the amount of yolk particles present in an egg.

* The yolk particles offer nourishment of the developing embryo. The process of frog development will be discussed from the phases of gametogenesis to the adult stage.

----

== The Egg ==
[[Image:Development of Poles in frog Fertilization.jpg|thumb|left|Development of Poles in Frog Fertilisation:J,Nassif 2009.jpg]]

- The embryology of a frog egg is a vast cell; its dimensions are approximately 1.4-1.6 million times larger than a typical aquatic species egg cell. Throughout the frog’s embryonic maturation period, the egg will be transformed into a tadpole encompassing millions of cells but still remains with its constant volume of genetic material, the vast prodction of cell have been illusttrated in the figure on the right revealing the production of eggs from female frogs. [http://en.wikipedia.org/wiki/Microhylidae]

- The early embryonic frog structure consists of three main segments the superior hemisphere known as the animal pole which is usually visible as a grey coloured area. The innermost layer appears to be between the outer two sections known as the gray crescent represented in black. Inferiorly, represents the vegetal pole typically lighter than the superior compartment illustrated in gold.

VIDEO RESOURCE: [http://www.youtube.com/watch?v=GO5YN_t1fqw&feature=related]

[[Image:Early Development of Frogs.jpg|thumb|left|Early Development of Frog:J,Nassif 2009.jpg]]

==History of frog embryology use ==

*'''1851''' - ''Henby Nelson''(MD): He identified a remarkable fact through the frog embryo. Henby observed the first cleavage of the yolk, in the egg of the frog. And cleaved structure corresponds in line of direction to the longitudinal axis of the body of the embryo of the frog species.

[[Image:Wilhelm Roux.jpg|thumb|right|Wilhelm Roux[http://images.google.com.au/imgres?imgurl=http://www.todayinsci.com/R/Roux_Wilhelm/RouxWilhelmThm.jpg&imgrefurl=http://www.todayinsci.com/6/6_09.htm&usg=__qRLTEMTHdZpAHxiNX12hWjcm9tA=&h=125&w=100&sz=4&hl=en&start=2&um=1&tbnid=LIKIwZTqCpk7MM:&tbnh=90&tbnw=72&prev=/images%3Fq%3DWilhelm%2BRoux%26gbv%3D2%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

*'''1888''' - ''Wilhelm Roux'': Wilhelm Roux attempted to solve the above observation by damaging one cell of a two-cell frog embryo with a hot needle. The cell stayed in place. However, it did not develop further. Its partner developed into a left or right half-embryo;

*'''1907''' - ''John Hopkins'' hospital: In order to identify the cellular source of neuronal fibres. Scientist placed small portions of frog embryo spinal cords in lymph on a microscope slide and was able to observe clear cut neuronal sprouting.

*'''1951''' - ''Robert Briggs'': Robert Briggs was able to clone a frog embryo by substituting the nucleus of an unfertilized frog egg cell with the nucleus of a frog embryo cell. This process is known as nuclear transplant, has formed the basis for all cloning.

*'''1952''' - ''Robert Briggs and T.J. King'': Robert Briggs and T.J. King used frog for test experiment. Because the size of the eggs in the frogs are enormous compared with those of mammals, which make them easier to manipulate.

*'''1976'''- Using the technique that had been successful in cloning frog embryos, the doctor transferred the nucleus of one cells into a donated egg cell. As an embryo began to develop, it was implanted into the uterus of a young woman.

*'''1997''' - ''Wilmut and Campbell'': Utilizing the cloning technique from frog embryo, Drs. Wilmut and Campbell tried the starvation technique on embryo cells to produce Megan and Morag, the world's first cloned sheep and, until now, the most famous sheep in history.

*'''2000''' - ''Tokyo University'': Scientists at Tokyo University have grown artificial eyeballs. Scientists formed them in tadpoles by using frog embryo cells.

*'''2001''' - ''Advanced Cell Technology'': Scientists from Advanced Cell Technology announced production of a human embryo clone. This is significant as its parthenogenesis has been artificially induced in frogs.

[[Image:John Gurdon .jpg|thumb|right|John Gurdon [http://images.google.com.au/imgres?imgurl=http://www.pnas.org/site/misc/images/gurdon.jpg&imgrefurl=http://www.pnas.org/site/misc/classics4.shtml&usg=__1p-GA1PdOYsxKL-cznMb3RHCm98=&h=526&w=400&sz=223&hl=en&start=1&um=1&tbnid=9k4lhuLssiWCAM:&tbnh=132&tbnw=100&prev=/images%3Fq%3DJohn%2BGurdon%26gbv%3D2%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

*'''2002''' - ''John Gurdon'': John Gurdon from Wellcome Cancer Research Institute in Cambridge experimented on cloned frog embryo.

== Gametogenesis ==

* The sexual reproduction occurs through the fusion of either mature reproductive cells or germ cells known as gametes, which include the sperm from the male frog and ova from female frog species so as to form a single cell, the fertilized zygote. The gametes are typically developed in parents of different sexes . [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

* Males gametes is a spermatozoon , the female frog gamete is an ovum. Each gamete is formed by a process, recognised as maturation or gametogenesis in gonads. The typical male frog gonads are testies in male, while the female gonads are ovaries. The synthesis of both gonads is associated with the process of fertilization. [http://en.wikipedia.org/wiki/Microhylidae]

* The zygote changes into a mature frog through the process of embryology and metamorphosis. Gametogenesis is a in progression which frog gametes are established from germ cells. Initial germ cells are called primordial germ cells, which can be recognised extremely early in the life of frog species.

----

== The Egg & Fertilization ==

[[Image:Fertilized and Unfertilised Eggs.jpg|thumb|left|Fertilized and Unfertilized Eggs:J,Nassif 2009.jpg]]

[[Image:Egg Development.jpg|thumb|left|Egg Development:J,Nassif 2009.jpg]]

- This occurs once the sperm cell has inserted, following the insertion of the sperm cells meiosis II is completed, there is a 30 degree position change of the cytoplasm, gray crescent allows this change to be visible in some amphibians, the gray crescent is able what determines the expect ted outline of how the frog will form. The sperm cell joins with the nuclei of the egg which forms the diploid zygote nucleus. --Sando Rashed 10:09, 24 September 2009 (EST)

- The early phases in the development of the egg is visible, but must be studied in tadpoles throughout maturation. In embryonic tadpoles of about 10 millimetres in length, soon after the opening of the oral cavity, a pair of longitudinal ridge-like thickenings of peritoneum becomes apparent along the posterior surface of the body cavity situated near to the mesentery and along the inner boundaries of the kidneys. Genital ridges are established in all tadpoles of this age, sex is not distinct until a later period. The development of the egg is illustrated in the figure on the left revealing the structure of a developed egg and a mature of egg.

[[Image:Fertilisation life cyle.jpg|thumb|Fertilization of Life cycle:Derived from primary source:[http://en.wikipedia.org/wiki/Frog]]]

== Maturation of the Egg ==

- The eggs have currently accomplished their full size, and develop from the exterior of the ovaries like a small shot, but they still have to pass through the course of maturation before they are prepared to be fertilised. This progression of maturation relates to the nucleus almost completely.

- The nucleus component, containing the nuclear fluid that excludes through the nuclear membrane into the substance of the egg, a great segment of the nuclear reticulum vanishes and becomes degraded into separate globules known as nucleoli, but a extremely small division remains in the midpoint as a slender intricately thread recognised as the nuclear skets.
Relative to the egg getting discharged from the ovary, the follicles shatter allowing the eggs to fall into the abdominal cavity of the frog species, the egg then passes forwards, directly by the contraction of the muscular wall, somewhat by the movement of the cilia of the peritoneum, to the apex of the oviduct, which positioned at the anterior compartment of the body cavity opposite to the roots of the respiratory organs.

- The terminal part of the oviduct establishes a thin-walled pouch capable of great swelling, inside which the eggs gathers in large numbers. In conclusion, the eggs are migrated out through the cloaca into water which the albuminous investments of the eggs rapidly augment to form the gelatinous mass of the frogs spawn.

== Maturation phases ==

'''1. Nuclear skein''', moves from the midpoint of the egg to its outer surface, which it reaches opposite the midpoint of the black pole. The skein, subsequently an unevenly twisted thread, now presumes the specific arrangement of a nuclear spindle, for instance may be visible in the nucleus of an epithelial or additional cell instantly prior to division of the cell occurs.[http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

'''2. The first Polar Body,''' regarding the instance the egg is laid, but prior to its fertilistion, the egg develops a considerably flattened appearance at its upper or black pole, a definite sum of fluid being exuded among the egg and the vitelline membrane. The nuclear spindle currently separate into two identical segments, one of which remains with the egg, and the supplementary is extruded as the first polar body, a small ovoidal white globule, which is situated on the surface of the egg surrounding the exuded peri-vitellline fluid.

'''3. The Second Polar Body''', half of the nuclear spindle that stay behind then splits into two equivalent divisions, one of which remains inside the egg as the female pronucleus, whereas the other segment is extruded as the second polar body, a small white globule extremely related to the first polar body, and like this positioned in the perivitelline fluid on the superior portion of the egg.

'''4. Fertilisation of the egg''', includes the synthesis of the spermatozoon with to egg, specifically, synthesis of the nuclei of these two bodies. The spermatozoa, subsequent to being shed over the seed by the male, distribute vigorously by means of their extended tails, break through the gelatinous investment of the female eggs, bore their way through the vitelline membrane and so go through into the eggs themselves, which they penetrate relative to the superior or black hemispheres.
* Subsequently, an hour following the spermatozoon has entered; a progression may be visible projecting within from the exterior segement of the egg, with a liquid spot in the mid point. This liquid centre is the nucleus of the spermatozoon, and is said to be the male pronucleus, it break through beyond into the female egg, transporting the specialised pigment into it, so that it appears bounded by a pigmented capsule linked with the exterior of the egg by a pigmented stalk.

* By this instance, the second polar body has been established and extruded, and the female pronucleus is merely the only component of the primary egg nucleus still present. Both the male and female pronuceli, which are at initially distance separate to each other, merge and after having enlarged significantly in size then fuse mutually about two and half hours after fertilisation has originated to produce the segmentation nucleus.
* The segmentation nucleus is a huge sphere-shaped vesicle embedded in delicately granular protoplasm, and bounded by a distinct capsule of pigment, its arrangement by the synthesis of the male and female pronuclei completes the action of fertilisation. Specifically female pronucleus may be observe as an imperfect nucleus, and consequently result in the course of fertilisation. The nucleus of the spermatozoon or male pronucleus, replaces the component of the egg- nucleus which has been misplaced as the polar bodies.

'''5. Segmentation of the Egg''', the initial phase of growth consist in constant separation of the egg, whereby it becomes transformed from the unicellular state, which is everlasting only in the lowest species, to muliticelluar state charactertics of all higher species. To these early processes of growth the names segmentation is specified. Shorty subsequent to the competition of fertilisation and arrangement of the segmentation nucleus this later misplaces its sphere-shaped appearance and develops to be spindle-shaped, the yolk granules at the equivalent instance showing a tendency to develop into lines distributing outwards from the distal segment of the spindle.
* The nucleus now split into two halves, which shift away from one another, the yolk granules are likely to combined themselves around the two nuclei, and a slender vertical plate of delicately granular substance is left, dividing the egg.[http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

* Superiorly the eggs depression now becomes visible, initially as a small cavity and then develops as a groove, which almost immediately extends all round, and speedily deepening, splits the egg into two entirely separate halves along a plane equivalent with the vertical plane.

* Shorty after, the two nuclei soon separate again into two, and therefore a second cleft is created in the same state as before, its additionally in the vertical plane, however in a plane at 90 degrees to the initial one, and on its finishing point the egg comprises of four accurately similar segments, each containing a nucleus. The third cleft is horizontal in shape, but not equal, lying closer to the superior than the lower pole, it segregates each of the four cells into, an superior smaller and a inferior larger pole

----

== Cleavage ==

[[Image: Frog Cleavage development.jpg|thumb|left|Cleavage Process details:[http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/F/FrogEmbryology.html].jpg]]

* The egg of the frog is scientifically identified as’ telolecithal’ meaning there is a outsized amount of yolk concentrated at a single pole, in contrast to the concentration of cytoplasm and the site of the nucleus. The cleavage phases are holoblastic, therefore the total and after the second cleavage they are asymmetrical .The initial cleavage stage appears about two and half to three hours after fertilization. It commences as a minor depression in close proximity to the centre of the animal hemisphere. It appears as if some interior force is pushing the surface the egg towards the centre. This small upturned fold steadily continues in the form of a channel until it surrounds the egg. This groove is shallow in the commencement, but develop into deeper eventually separating the fertilized egg into two halves recognised as the blastomeres. [The figure on the left symbolise the development and growth of the frog embryo during cleavage].

* Internally the separation is mitotic, consequently each daughter cell contains a nucleus resulting from the copulation nucleus of the fertilised egg. This cleavage is vertical, the two cells are indistinguishable in respect of cytoplasm, pigment and yolk. The subsequent cleavage appears about an hour after the first. The channel of this cleavage begins at the centre of the animal hemisphere, is at right angles to the first and is vertical. This divides the egg into four blastomeres. The fourth blastomere so produced are not qualitatively equal, since of these only two contain the material from the gray crescent. The cleavage begins about thirty minutes after the second is completed or four hours after fertilisation. the cleavage plane of the third furrow is horizontal and slightly above the equator. Thus the four upper cells are a little smaller than the four lower cells. The smaller blastomeres are called micromeres and the larger blastomeres are called macromeres. The fourth cleavages follow 20 minutes after the third and tend to be vertical. This is usually a double furrow.

* The cleavage rate is accelerated with each of the early divisions and since the blastomeres are of unequal size and have varying amounts of cytoplasm and yolk, synchronous cleavage is lost and there is an obvious overlapping of the division. The upper most cells divide more rapidly than the lowermost cells. From this point onwards perfect symmetry in cleavage and in blastomere is very rare, although the embryo developed perfectly. The fifth cleavage is also doubled, appearing first in the upper hemisphere and then in the lower.

* The cleavage thus far follows the rule that each cleavage plane comes in at right angles to the previous one. The subsequent divisions become so irregular that it is previous one. The subsequent division become so irregular that it is impossible to trace out any plan or procedure. The segmentation continues more rapidly in the pigmented regions, since at that place the protoplasm is most dense, whereas, yolk which is very abundant in the vegetal side delays cell division. The multicelluar embryo at this stage is called morula by some biologists.

----

== Gastrulation ==

[[Image:FROG GASTRULATION .jpg|thumb|left|Frog Gastrulation Image details:[http://www.google.com.au/imgres?imgurl=http://bio1903.nicerweb.com/Locked/media/ch47/47_12FrogGastrulation.jpg&imgrefurl=http://bio1903.nicerweb.com/Locked/media/ch47/gastrulation-frog.html&h=540&w=480&sz=46&tbnid=N78sHjELreGGSM:&tbnh=132&tbnw=117&prev=/images%3Fq%3Dfrog%2B-%2Bgastrulation&hl=en&usg=__4VK9FYLft0W-4lBe6p5EtQAMiaI=&ei=qPy5SurtMJvE6wON8JmdAg&sa=X&oi=image_result&resnum=4&ct=image].jpg]]

''The phase of Blastulation is followed by the unique developmental progression of gastrulation. The process of frog gastrulation involves the following processes.''

'''1. Epiboly Phase'''

The pigmented cellular materials of blastula have the propensity to overgrow the yolk cells within the developing content. This course which is known as epiboly commences gradually in the final blastula and rapidly accelerates with advancing gastrulation development. The cellular matter within the animal pole reproduces and matures on all sides except in area surrounding the dorsal lip of the blastopore has been established.

'''2. Convergence'''

Scientists suggested that the unfolding was thought to result in spreading of the superficial cells over a substrate with suitable absorption properties. Consequently epiboly and convergence are an outcome to this spreading tendency, which is actually increased by a reduction in surface tension of the distributing cells.

'''3. Rotation'''

The epiboly phase is maintained until the region of the dorsal lip has migrated and is a to some extent greater than 90 degrees and the region of the white blastopore is reduced to small circular rings. This section will be positioned away from the developing vegetal pole. Laterally the complete developing gastrula has been rotated to a horizontal axis, allowing it to lie at right angles to the original median plane of the egg. Therefore, the course of rotation is such that the dorsal lip is practically pushed backwards in one direction as rapid or quicker than epiboly moves it forward in the other. The outcome will be that the blastopore produced at roughly the vegetal pole is posterior, and the dorsal and ventral lips are essentially dorsal and ventral. This in addition allows the eggs to form the antero-ventral side of the potential embryo whilst the area marked by the grey crescent is to develop the dorsal segment.

'''4. Invagination'''

Visible is a small fissure- like invagination which is apparent in the middle between the equator and the vegetal segment. The most superior or dorsal border of the cleft produce the dorsal lip of the blastopore. This imput move back and forth on the dorsal plane near the dorsal lip and migrates around the boundaries of the blastocoel in company with the extension of the lateral lips. This adapted invagination is maintained until the blastocoel cavity has been almost abolished; excluding the slender opening separating epiblasts from the hypoblast, the new segment formed is known as the archenteron cavity.

'''5. Involution'''

- Additional to previous course of action a distinct involution also occurs at the blastoporal borders. This is mainly dynamic at the median dorsal lip and gradually more less as it shifts across either side until it reaches the ventral lip where it constant.Throughout this progression, cells positioned beside the superior boundaries of the blastoporal lip migrate over the lip to the interior portion of the lip. These cells are remained within the embryo along the internal edge of the blastopore. This indicates the root of archenteron is composed of involuted cells and beyond this the external layer known as the ectoderm. The base and lateral sides are enclosed mainly of endodermal cellular material, which have been established from larger yolk cells, situated in the vegetal pole of the blastula.

- In the final phases of the gastrula development, the cells contributing to the floor of the archenteron, thin out significantly where they surround the blastocoel.
The hemispherical shaped dorsal lip of blastopore which become visible at the commencement of the gastruation stage carry on to augment, initially becoming semicircular, then transform into a horse shoe shaped and then finally forming into circular band. The band is the accomplished by the blastopore. Various yolk cells of vegetal pole present in the section are crowed into the blastoporal cavity where they form a gathering identified as a yolk plug. Blastopore rapidly reduces in size while the archenteron is still developing and becomes completely formed in the final stage; the yolk plug appears as only a small oval on the gastrula.

==Growth and Modification of Frog Species==

'''1. Changes in habits and habitats:'''

'''a)''' In frogs, metamorphosis is related with to the modifications and adaptations as a frog changes environmental habitats from an aquatic to a terrestrial mode. Metamorphosis has modified the adaption of frogs as this alteration it began during the aquatic adaptations in the surface of water to breathe air. Subsequently, it continues the terrestrial surroundings, therefore the frog species become abundant in vegetation area allowing the frog to transform in to amphibious species.

'''b)''' The transition during metamorphosis is linked with a change in food chain. The tadpoles being the embryonic origin of frogs are herbivorous, feeding on algae and green matter, which they collect by the adapted feature such as their teeth surrounding their mouths. Adult frogs, alternatively, are classified as carnivorous feeding on insects and worms. Occasionally, they also consume larger prey, for instance smaller frogs species and even little birds and rodents which they dominant and ingest.

[[Image:Development of frog from sperm to mature structure.jpg|thumb|left|Development of Frog from sperm to mature structure Image details:J,Nassif 2009.jpg]]

'''2. Changes in Morphology'''

These include the decrease or complete absence of specific organs or structures which are essential during development of early frog embryology, but not critical in the mature frog species. The significant alterations of this nature include the following developmental structures.

'''a)''' The long tail of the tadpole alongside the fin folds is absorbed again during metamorphosis and becomes absent at the final stage of the metamorphosis.

'''b) '''The developing gills are resorted, the gill clefts are congested and the branchial cavities start to become absent. The reabsorbtion of gills also takes place by autolysis.

'''c)''' The teeth of the perioral disc additionally the homey lining of the jaws are shed.

'''d)''' The lateral line sense organs within the skin of tadpoles vanish throughout metamorphosis.

'''e)''' The cloacal tube begins to condensed and reduced.

'''f)''' Various blood vessels, together with parts of the aortic arches, are reduced during mature development.

(The figure on the left represents the transformation from a tadpole to a developing structure.)[http://science.jrank.org/pages/2862/Frogs-Adult-morphology.html]

'''3. Progressive or constructive changes'''

This process comprises of the development of specific organs which mature into functional systems only during metamorphosis.

'''a)''' During development the limbs continue to augment in size and differentiation. The forelimbs, which in the tadpole mature under the opercular membrane, which then break through to the exterior. Simultaneously there is a increase in the length and strength of the hind limbs, joints develop in them and the toes become visible.

'''b)''' The middle ear becomes apparent in relation with the first pharyngeal pouch. The tympanic membrane matures. It is bounded by circular tympanic cartilage which allows the frog to retain air.

'''c)''' The visual organs bulge up on the dorsal surface of the head developing the nictitating membrane.

'''d)''' There is augmentation of the tongue and the formation of thevomerina teeth.

[[Image: Growth model.jpg|thumb|Growth Model Image details:J,Nassif2009:]]

'''4. Remodelling of some structures'''

Systematic organs which operate both in the early embryonic larva and the mature adult change their differentiation during metamorphosis so as to meet the requirements of the adult mode of life and due to the habitat adaptations. The figure on the right illustrates structures developing from specic germ cell layers.

'''a)''' The skin of the embryonic tadpole is lined with a double-layered epidermis. The number of layers of cells in the epidermis augments throughout metamorphosis. Superficial surface layers become cornified. Multicellular mucous and serous glands originate in the skin. The pigmentation of the skin continuously changes, new patterns and colour start to form.

'''b)''' There is a lengthening of the mouth gap as a result of rotation of the quadrate cartilage and the true jaws become functional.

'''c)''' The tongue rapidly progresses and becomes larger and more muscular.

'''d)''' The eyes become more specialised.

'''e)''' In early tadpoles, the GIT is extremely long and wound up into a spiral folds. The intestine become greatly lengthened in herbivorous species due to the vegetables food chain.[http://en.wikipedia.org/wiki/Frog]

'''5. Development of the reproductive system'''

(The figure below represents the reproductive and development cycle of a frog as it transform from egg to frog specie.)

In tadpoles, right after the mouth is being formed, two indentation like thickenings of peritoneum begin to appear near the body cavity (dorsal surface), which is nearest to the mesentery which is near the developing kidneys. These appear in all tadpoles.

These indentations appear here because of a change in the endothelial cells, everywhere else they are usually flat looking cells but they undergo a change and in this particular area become somewhat cuboidal/columnar.

Later on the indentations become more obvious due to the epithelial cells replicating numerously to form a thick layer. The posterior two thirds of the indentation for the female is the ovary and for the male it is the testis. The third that is left differentiates and becomes fat for the body.

[[Image: Mature frog life cyle.jpg|thumb|200px|left|Mature from life cycle Image details:Derived from primary source:http://www.scienceclarified.com/images/uesc_01_img0038.jpg]]

[[Image: Developing frog.jpg|thumb|Developing Frog Image details:
[[Image: Mature develop frog.jpg|thumb|Image details: Red eyed tree frog litoria chloris source:[http://en.wikipedia.org/wiki/File:Red-eyed_Tree_Frog_-_Litoria_chloris_edit1.jpg]].jpg]]

===Delamination===

Delamination indicates a mass separating a group of cellular matter from other cellular groups. It has been illustrated that the division of notochord, mesoderm and endoderm tissues from each other to form distinct cellular masses is completed by the progression of delamination, subsequent to these materials moving to the inside throughout gastrulation. During the developing gastrula, the germ layers are all recognized. These distinct segments of the embryo develop from these germ tissue layers.

===Polarity and Rotation===

Throughout fertilisation to the beginning of gastrulation, the frog’s egg continues in the original location in relation to its polarity. Subsequent to gastrulation its polarity begins to differentiate. This progression is linked with migration of materials within the gastrula and can be responsible for the alterations of the centre of gravity.

===Closing of Blastopore===

Subsequent to the formation of the gastrula, the blastopore is visible as a tiny round circular filled cavity containing the yolk plug. As it continues to reduce in dimension, it represented as a pear-shaped outline through the mutual approach of its lateral lips. Through it final progression these fuse entirely to produce a longitudinal groove, the streak which continue dorsally and ventrally in a small aperture. The inferior aperture closes, resulting in a depression called the anal pit. The superior region remains open for some period and begins to as the neural groove is laid down.

===Post Gastrulation or Organogenesis===

Throughout the duration of pre-gastrulation, all tissues for different organs vanish from the surface of blastula and migrate inside to take their final arrangement in the embryo structure where organs are developed from their potential regions. Consequently organogenesis transfers an embryo into free larva structure.

----

==Germ-layer origin of various body tissues==
[[Image: Development Models of Frog.jpg|thumb|right|Figure 13 Image details:Vertebrate Structure and Development.jpg]]

Ectoderm will give raise to structures such as skin, brain, spinal cord, neurons and sense receptors.
Mesoderm will give raise to structrues such as notochord, muscles, blood, bone and sex organs.
Endoderm will give raise to sturctures such as inner lining of gut, liver, pancreas, lungs and bladder, thyroid and parathyroid glands and thymus.

== Structures derived from Germ-layers of frog species ==

[[Image:Development of Frog Layers.jpg|thumb|left|Development of Frog Layers Primary source[http://www.bio.miami.edu/~cmallery/150/physiol/sf19x11b.jpg]Image details:J,Nassif 2009.jpg]]

[[Image:Development of frog layers.jpg|thumb|left|Development of Frog Layers Primary source [http://www.bio.miami.edu/~cmallery/150/physiol/sf19x11b.jpg]Image details:J,Nassif 2009.jpg]]

'''Ectoderm '''

''Establishes the epidermal segments and its derivatives, to the frog’s nervous system. The ectoderm also contributes to :''

1. The olfactory and auditory epithelium.

2. The retina and lens of the eye.

3. Sensory organs.

4. The epithelial lining of the oral cavity and the anus.

5. The pineal and pituitary body.

'''Mesoderm'''

''Mesoderm originates:''

1. Connective tissue.

2. Muscles, except the notochord.

3. Blood vessels.

4. Lymphatics.

5. The peritoneum and the urinary and reproductive system.

6. The dermis, parts of the eye excluding lens, cornea, and conjunctiva.

'''Endoderm'''

''From the endoderm arises:''

1. The epithelial lining to the gut and oesophagus, stomach, intestine, bile duct.

2. The hepatic cells of the liver, respiratory tract, larynx, trachea and lungs.

3. The lining of the urinary bladder, pancreas thyroid and thymus.

[The two figures reveal the development of structures deriving from the celluar components of the embryology of the frog].[Structures derived from Germ-layers of frog species ]

==Life cycle of a frog==

'''Fertilization-egg''':

The female lays eggs in the spring. A group of fertilized eggs is called spawn;

'''7-10 days''':

Fertilized egg feed on remaining yolk which is in its gut. Their gills, mouth and tail have poorly developed. Begin to swim and feed on algae;

'''10-30 days(4 weeks):'''

A layer of skin grows over gills. Teeth begin to appear. A coiled gut start to develop. This is aid in digestion;

'''30-60 days(6-9 weeks):'''

Legs being to grow and head is more distinct. Start to eat insects. Arms begin to grow;

'''60-80 days(12 weeks):'''

Resemble a frog. Still have remaining tail;

'''80-140 days(20 weeks):'''

Fully developed, spend most of time out of water. Majority of frog live between 4-15 years.

==Timeline of frog development==

Development of egg and embryo at temperature 18 degree celsius.

'''0 hours''' - fertilization of the egg

'''1 hours''' - formation of the gray crescent due to pigment migration

'''3.5 hours''' - early cleavage

'''4.5 hours''' - blastula stage(coeloblastula with eccentric blastocoel

'''26 hours''' - gastrulation

'''26 hours''' -'' early'' - crescent shaped dorsal lip

'''34 hours''' - ''middle''- semicircular blastoporal lip

'''42 hours''' - ''late'' - circular blastoporal lip

'''50 hours''' - neurulation

'''50 hours''' - ''early'' - medullary plate

'''62 hours''' -'' middle''- neural folds converging

'''67 hours''' - ''late'' - neural tube formed and ciliation of embryo

'''84 hours''' - tail bud stage(early organogeny)

'''96 hours''' - muscular response to tactile stimulation

'''118 hours''' - early heart beat, development of gill buds

'''140 hours''' - hatching and gill circulation

'''162 hours''' - mouth opens and cornea becomes transparent

'''192 hours''' - tail fin circulation established

'''216 hours''' - degeneration of external gills, formation of operculum, development of embryonic teeth

'''240 hours''' - opercular fold over brachial chamber except for spiracle and internal gills

'''255 hours''' - prolonged larval stage with refinement of organs

'''270 hours''' - development of hindlimbs, internal development of forelimbs in opercular cavity

'''275 hours''' - projection of forelimbs through operculum, left side first

'''280 hours''' - absorption of the tail and reduction in size of the gut

'''284 hours''' - metamorphosis complete, emergence from water as miniature, air breathing frog

==Stages of frog embryology==
--[[User:S8600021|Mark Hill]] 08:40, 9 October 2009 (EST) [[Talk:2009_Group_Project_5#Constructive_Criticism_of_Coordinator|see my comment on images]]

The rate of development of the egg and embryo will depend upon the temperature at which they are kept. The approximate schedule of development at 23 degree celsius is provided below.

{| border='1px'
|+ Table 1: Stages of frog development
!Stage !!Time since fertilisation (hours)!!Stage Characteristic !!Embryo characteristic !!Image of frog stage
|-
|1
|0.00-1.30
|fertilization of the egg, post fertilization
|animal hemisphere, gray crescent and vegetal hemisphere are present
|[[File:Stage01ventral.jpg|100px]]
|-
|2
|1.30-2.00
|splits into two cells
|appearance of first cleavage furrow
|[[File:Stage02ventral.jpg|100px]]
|-
|3
|2.00-2.15
|becomes four cells
|appearance of second cleavage furrow
|[[File:Stage03dorsolat.jpg|100px]]
|-
|4
|2.15-2.45
|becomes eight cells
|appearance of third cleavage furrow
|[[File:Stage04dorsolat.jpg|100px]]
|-
|5
|2.45-3.00
|becomes sixteen cells
|appearance of fourth cleavage furrow
|[[File:Stage05dorsal.jpg|100px]]
|-
|6
|3.00-3.30
|becomes thirty-two cells
|appearance of fifth cleavage furrow
|[[File:Stage06animal.jpg|100px]]
|-
|6.5
|3.30-4.00
|blastula stage
|Three dorsal folds become visible as a result of endoderm invagination. Pole cells no longer visible on surface
|[[File:Stage065dorsal.jpg|100px]]
|-
|7
|4.00-5.00
|Gastrulation stage
|two primary germ layers. epiblast and endoderm
|[[File:Stage07ventral.jpg|100px]]
|-
|8
|5.00-7.00
|neurulation
|medullary plate, neural folds and neural tube
|[[File:Stage08animal.jpg|100px]]
|-
|9
|7.00-9.00
|germ layer
|complete lip involution encircling yolk
|[[File:Stage09veg.jpg|100px]]
|-
|10
|9.00-11.00
|early gastrula
|two primary germ layers
|[[File:Stage10veg.jpg|100px]]
|-
|10.5
|11.00-11.45
|gastrula
|two germ layers
|[[File:Stage105vegb.jpg|100px]]
|-
|11
|11.45-12.30
|medulla plate
|Yolk sac protrudes dorsally, labium moves to midline on ventral side
|[[File:Stage11veg.jpg|100px]]
|-
|11.5
|12.30-13.15
|continuation of medulla plate
|start closing the plate
|[[File:Stage115veg.jpg|100px]]
|-
|12
|13.15-14.15
|early neurula
|thickened ectoderm give rise to CNS
|[[File:Stage12veg.jpg|100px]]
|-
|12.5
|14.15-14.45
|neural folds
|expansion of cavity
|[[File:Stage125postdors.jpg|100px]]
|-
|13
|14.45-16.15
|neural folds
|continue expanding cavity
|[[File:Stage13postdors.jpg|100px]]
|-
|14
|16.15-17.30
|neural folds
|continuation of cavity
|[[File:Stage14postdors.jpg|100px]]
|-
|15
|17.30-18.15
|tail bud stage
|early organogeny
|[[File:Stage15postdors.jpg|100px]]
|-
|16
|18.15-18.45
|tail bud stage
|posterior ventral view
|[[File:Stage16ant.jpg|100px]]
|-
|17
|18.45-19.45
|tail bud stage
|anterior view
|[[File:Stage17ant.jpg|100px]]
|-
|19
|20.45-21.45
|neural fold close complete
|dorsal view
|[[File:Stage19dorsal.jpg|100px]]
|-
|20
|21.45-22.30
|early tail bud
|anterior view
|[[File:Stage20dorsal.jpg|100px]]
|-
|21
|22.30-24.00
|termination of neural crest
|progress to next stage
|[[File:Stage21ant.jpg|100px]]
|-
|22
|24.00-24.45
|prolonged development
|elongation
|[[File:Stage22lat.jpg|100px]]
|-
|23
|24.45-26.15
|elongation of embryo
|later view
|[[File:Stage23lat.jpg|100px]]
|-
|24
|26.15-27.30
|continuation of elongation of embryo
|dorsal view
|[[File:Stage24latsmall.jpg|50px]]
|-
|25
|27.30-29.30
|organs development
|embryo elongates and develops dorsal thickening
|[[File:Stage25dorsal.jpg|50px]]
|-
|26
|29.30-31.15
|elongation
|dorsally forms neural and brain cavity
|[[File:Stage26lat.jpg|50px]]
|-
|27
|31.15-32.30
|elongation of embryo
|dorsal view
|[[File:Stage27lat.jpg|50px]]
|-
|28
|32.30-35.00
|further development
|lateral view
|[[File:Stage28lat.jpg|50px]]
|-
|29-30
|35.00-37.30
|tail bud
|growth
|[[File:Stage29-30lat.jpg|50px]]
|-
|31
|37.30-40.00
|prolonged development
|bud development
|[[File:Stage31lat.jpg|50px]]
|-
|32
|40.00-44.30
|early muscular development
|elongation
|[[File:Stage32lat.jpg|50px]]
|-
|33-34
|44.30-50.00
|muscular movement
|apparatus for locomotion
|[[File:Stage33-34lat.jpg|50px]]
|-
|35-36
|50.00-53.30
|muscular movement
|apparatus for locomotion
|[[File:Stage35-36lat.jpg|50px]]
|-
|37-38
|53.30-56.30
|heart beat
|develops apparatus
|[[File:Stage37-38lat.jpg|50px]]
|-
|39
|56.30-66.00
|mouth opens
|cornea transparent
|[[File:Stage39latsmall.jpg|50px]]
|-
|40
|66.00-76.00
|gill circulation
|hatching
|[[File:Stage40lat.jpg|50px]]
|-
|41
|76.00-80.00
|tail, fin circulation
|circulation
|[[File:Stage41lat.jpg|50px]]
|-
|42
|80.00-86.00
|internal gills, operculum
|opercular fold, teeth
|[[File:Stage42lat.jpg|50px]]
|-
|43
|86.00-98.00
|operculum complete
|operculum closed on right
|[[File:Stage43lat.jpg|50px]]
|-
|46
|98.00-106.00
|metamorphosis
|emergence from water as miniature, operculum complete|
|[[File:Stage46lat.jpg|50px]]
|-
|}

==Abnormalities of frog==

Abnormalities of frog could be caused by multiple factors. These include change in climate, predators, parasites, bacteria, fungi, viruses or pollution and contaminants such as pesticides, metals and fertilizer.[http://www.fws.gov/contaminants/documents/frogsrefup_septoct_2006.pdf]

The Abnormalities are further classified into different categories. These categories are:

===1. Infectious Diseases:===

'''Perkinsus Symptoms-''' caused by perkinsus-like protozoan organism. Symptoms include swollen viscera that leads to a bloated body and and infected swollen heart

'''Ichthyophonus symptoms-''' cause by parasitic genus, where symptoms include a swollen tail resorption site that matches the surrounding skin in color and translucency.

[[Image:Abnormalities of Frog species.jpg|thumb|left|Figure A Image details[waterwatchadelaide.net.au].jpg]]

===2. Surficial Abnormalities:===

Surficial abnormalities as the one that are visible on the surface of the skin. This includes abnormal pigmentation, , subcutaneous hemorrhaging, wounds due to trauma or from a predator
Edema is a fluid-filled swelling under skin whihc is also a surficial abnormality.

===3. Skeletal Abnormalities:===

This is further classified into three more categories:

'''a. Skeletal Malformations-'''

* Microcephaly (small head or blunt snout)
*Scoliosis (Curved spine in lateral direction)
*Shrunken Limb (Micromelia)
*Amelia (Completely missing limb with no stump)

'''b. Skeletal Abnormalities of Unclear Etiology-'''

This condition arises when a frog has ectromelia (missing limb), brachydactyly (missing digits) or other such condition with no visible trauma or external damage, then this will be classified as the Skeletal abnormality of unclear etiology.

'''c. Skeletal Injuries-'''

Any limb missing or broken due to trauma or other related reason which shows clear evidence of it is classified as skeletal injury

===4. Eye Abnormalities:===

Most common includes-

'''i. Anophthalmia:''' Skin covers the eye socket as there is no eye

'''ii. Abnormal Iris Coloration:''' Reduced pigment in either one eye or both resulting in two different colours of the iris at times

'''iii. Abnormal size or shape:''' Both eyes either deviating from each other or size of pupil or iris is different than the other eye

[http://www.fws.gov/contaminants/Amphibian/pdfs/AbnormalitySOP_woutpics_Jan08.pdf ]

==Genetics==

There are a wide variety of species that differ from each other when it comes to genetics and their functioning.

'''TAXONOMY:''' '''Phylum''' ''Chordata'' / '''Sub Phylum''' ''Vertebrata'' / '''Class''' ''Amphibia'' / '''Order''' ''Anura''

Their are more than two dozen different families of frogs, where suborders are:

'''1. ARCHAEBATRACHIA-''' most primitive frogs

'''2. MESOBATRACHIA-''' linked between the Archaebatrachia and Neobatrachia

'''3. NEOBATRACHIA-''' most modern frogs

{| border='4px'
|+ '''General Info:'''
! !!
|-
| '''Number of frogs' species'''
| 5280
|-
| '''Smallest frog genome size:'''
| 0.95pg, Ornate burrowing frog
|-
| '''Largest frog genome size:'''
| 13.40pg, Ornate horned frog
|-
| '''Mean of frogs' genome'''
| 4.68pg ± 0.13
|-
|}

[http://www.genomesize.com]

*Majority of frogs have only 22 to 26 chromosomes and polyploid is very common where they are almost bisexual.

*Polyploid Amphibians reduce their total cell number such that they acheive the same body size as diploids. One of the most unsual forms of polypoidy in amphibians is the water frog ''Rana esculenta'' from Europe and Western Asia.

* The species with larger genomes have more genes for e.g. the frog genus ''Xenopus'' includes 16 species, with genome sizes ranging from 3.5 x 10^9 bp to 1.6 x 10^10 bp. These differences have arisen by numerous events of polyploidization within the past 40 million years or so. The ancestral chromosome number for the genus seems to have been 18, but there are species with 36, 72 and 105 chromosomes [http://www.xenbase.org/common/]

{| border='4px'
|+ '''Difference within two families'''
! '''SPECIES''' !! ''X.LAEVIS'' !! ''X.TROPICALIS''
|-
| '''PLOIDY'''
| Allotetraploid
| Diploid
|-
| '''NO. OF CHROMOSOMES'''
| 36 chromosomes
| 20 chromosomes
|-
| '''GENOME SIZE'''
| 3.1 x 10^9 bp
| 1.7 x 10^9 bp
|-
| '''EGG SIZE'''
| 1-1.3 mm
| 0.7-0.8 mm
|-
| '''GENERATION TIME'''
| 1-2 years
| 4 months
|-
|}
[http://www.xenbase.org/common/]

===Genome Sequencing===

Since Frog has a huge family with many different species, only few main species that are used widely for the purposes of experiments have their genome sequenced.

''Xenopus tropicalis'' has one of the smallest genomes among amphibians and has the shortest generation time- four to six months and the only diploid genome among the 14 Xenopus species. This means it has no more than two copies of most genes, whereas the other species of Xenopus have four copies of most genes (pseudotetraploid). US Department of Energy's Joint Genome Institute (JGI) in Walnut Creek, California, initiated the X. tropicalis Genome Project, finding 1,700 million base pairs.
[http://www.genome.gov/Pages/Research/Sequencing/BACLibrary/xenopusTropicalis.pdf]

===Xenopus oocytes===

* The oocytes provide an important expression system for molecular biology.

* By injecting DNA or mRNA into the oocyte or developing embryo, scientists can study the protein products in a controlled system. This allows rapid functional expression of manipulated DNAs (or mRNA). This is particularly useful in electrophysiology, where the ease of recording from the oocyte makes expression of membrane channels attractive.

* One challenge of oocyte work is eliminating native proteins that might confound results, such as membrane channels native to the oocyte.

* Translation of proteins can be blocked or splicing of pre-mRNA can be modified by injection of Morpholino antisense oligos into the oocyte (for distribution throughout the embryo) or early embryo (for distribution only into daughter cells of the injected cell).
[http://www.staff.unibe.ch/sigel/xenopus.html]

===Xenopus Laevis===

* ''Xenopus Laevis'' is an important model organism in developmental biology. X. laevis is tetraploid and reaches sexual maturity in 1 to 2 years. What makes it important in developmental biology is its large and easily manipulable embryo.

* Extracts from the eggs of X. laevis frogs are also commonly used for biochemical studies of DNA replication and repair, as these extracts fully support DNA replication and other related processes in a cell-free environment which allows easier manipulation.

* The Human chorionic gonadotropin hormone (hCG) is present in the urine of the pregnant women in large quantities only. This hormone in the urine induces X.laevis oocyte production which formed the basis of first well-documented method of pregnancy testing X. laevis is also notable for its use as the first well-documented method of pregnancy testing when it was discovered. Today, commercially available HCG is injected into Xenopus males and females to induce mating behavior and breed these frogs in captivity at any time of the year.

===Gene cluster===

* The alpha and beta globin genes are closely linked in small cluster of frogs compared to human and chicken

* The similarity of architecture of two clusters found in X.laevis supports the tetraploid origin

* The two loci encoding the muscle specific creatine kinase isoenzymes and have large differences in developmental profile, therefore suggesting that duplicate loci that have not undergone silencing are not simply redundant copies but have acquired specialization.

* Contains twice number of genes for proteins i.e. haemoglobin and sarcomeric actin serum albumin compared with other species

----

==Current Embrology Research==

Currently, a number of fields have benefited from the development of frog embrology. These include cloning, verification of messenger RNA, and Cell cycle.

===Cloning===
[[Image:Robert Briggs.jpg|thumb|left|Figure 16 Image details:Robert Briggs.jpg]]

In 1952, Robert Briggs and Thomas J King cloned northern leopard frogs using a method of nuclear transfer. Briggs and King's experiment was similar to that envisioned - and piloted using salamanders - by Hans Spemann in his 1938 proposal for a 'fantastical experiment'. Later, John Gurdon extended this work and showed that nuclei from differentiated cells could support development, although less well than those from early embryos. [http://genome.wellcome.ac.uk/doc_WTD020799.html]

Lemaitre et a. (2005) from MRC Cancer Cell Unit, Cambridge, U.K. worked on experiments that demonstrated that importance of serial nuclear transplantation for the sucessful cloning of frogs. He demonstrated that exposure of somatic-cell nuclei (erythrocyte nuclei) and sperm nuclei to an extract of mitotic cell extract reorganizes the chromatin into shorter loops and allows replication at much shorter intervals along the DNA. This increases the efficiency of DNA replication in mammalian cell-free systems.

===Transgenesis techniques for functional genomics in Xenopus===

Transgenesis in Xenopus is made possible due to large embryos, a reliable fate map, ease of microinjection, ease of dissection/micromanipulation and existence of the neuroendocrine reflex of background adaptation as a model for activation/inact.

Recently, Hajime Ogino and Haruki Ochi from Nura Institute of Science and Technology in Japan focused on the genomic resources and principles of the transgenesis techniques in Xenopus, and discusses their applications to genome wide network analysis, with emphasis on the use of bioinformatics tools. This is will to understand the gene regulatory networks that control vertebrate development. [http://www.ingentaconnect.com/content/bsc/dgd/2009/00000051/00000004/art00001%3Bjsessionid=4ah96rms73gcu.alexandra]

Xenopus used to be a problem in earlier days when it came to transgenesis. Current methods involves isolated sperm nuclei from Xenopus testis that are microinjected into unfertilized eggs. The generated transgenic tadpoles contain 5-35 copies of the integrated plasmid that are expressed in all cells. If desired, expression of the transgene can be directed to the appropriate tissue and at the appropriate time by using specific promoters, mostly the Xenopus POMC gene promoter (isolated from a Xenopus genomic DNA library) to specifically direct expression of green fluorescent protein (GFP) at high levels to the intermediate pituitary cells, which can either be over expressed or inhibited.[http://molanphys.ruhosting.nl/transgenesis.htm]

[[File:Transgenesis.JPG]]

===Verification of messenger RNA===

While the existence and role of messenger RNA (mRNA) was known in bacteria, in the 1960s it was still debated whether it also existed in vertebrates. Taking haemoglobin mRNA from immature red blood cells and injecting it into a Xenopus oocyte, John Gurdon showed that the haemoglobin protein was indeed produced. Producing proteins in Xenopus oocytes has proved to be extremely useful in cell biology, in particular for the study of receptor proteins.[http://genome.wellcome.ac.uk/doc_WTD020799.html]

===Cell Cycle===

As they develop outside the mother, frog eggs are well stocked with the proteins needed to drive the development of the embryo. Studies of these processes has shed considerable light on the processes involved in cell division - termed the cell cycle. [http://genome.wellcome.ac.uk/doc_WTD020799.html]

===Limb development in Xenopus Laevis===

[[Image: Frog Limb development.jpg|thumb|right|Image details:Primary source:[http://images.google.com.au/imgres?imgurl=http://www.sciencedaily.com/images/2006/06/060616130718.jpg&imgrefurl=http://www.sciencedaily.com/releases/2006/06/060616130718.htm&usg=__xliPsPAvheUBME_kjv_q7auiFbo=&h=333&w=300&sz=11&hl=en&start=2&um=1&tbnid=y_ntJtmkRSK7WM:&tbnh=119&tbnw=107&prev=/images%3Fq%3DLimb%2Bdevelopment%2Bin%2BXenopus%2BLaevis%26ndsp%3D18%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

Donald D. Brown (2005),Department of Embryology, Carnegie Institution of Washington demonstrated factors related to limb development of Xenopus Laevis. Thyroid hormone (TH) is found to be required for limb development in this frog. Specific cell types in the growing limb were targeted for expression of a dominant negative form of the TH receptor by sperm-mediated transgenesis. Limb muscle development, the innervation of muscle from the spinal cord, and cartilage growth can be inhibited without affecting patterning of the limb or differentiation of other cell types. Remodeling of the skin occurs late in metamorphosis after the limb has formed. The coordination of these independent programs is affected in part by the control that TH exerts over DNA replication in all cell types of the limb. [http://www.pnas.org/content/102/35/12455.full]

----

== Glossary ==

[[Image: Frog species.jpg|thumb|left|Image details:Primary source:www.olympus.co.jp/.../080925/large/p02L.jpg].jpg]]

*'''Amphibian:'''

''Relating to or characteristic of animals of the class amphibia.Amphibians are found in the taxonomic class of amphibia, amphibians are capable of both occupying and successfully living in both land and aquatic communities.amphibian''

*'''Augmentation:'''

''Enlargement/Increase in cellular size.''

*'''Autolysis:'''

''breakdown of a part or whole cell or tissue by self-produced enzymes''

*'''Blastomeres:'''

''The undifferentiated cells formed by cleavage of the fertilised ovum. This includes cells in the cleavage, morula, and blastula stages of the embryo''

*'''Carnivorous:'''
''
Flesh-eating; subsisting on animals as food.''

*'''Cleavage:'''

''he repeated division of a fertilised ovum ''

* '''Cleft:'''

''an opening, fissure, or V-shaped indentation made by or as if by splitting''

*'''Chordate:'''

''Members of a diverse phylum of animals that, as embryos, possess a (1) notochord; (2) a dorsal, hollow nerve cord, (3) pharyngeal gill slits; and (4) a post-anal tail''

''The act or state of splitting or dividing of a cell, particularly during the telophase of (animal) cell division.''

*'''Cytoplasm:'''

''The cytoplasm (of both eukaryotes and prokaryotes) is where the functions for cell expansion, growth, metabolism, and replication are carried out''

* '''Epiboly:'''
''The expansion of one cell sheet over other cells, as takes place during gastrulation''

*'''Fertilization:'''

''A process in sexual reproduction that involves the union of male (sperm) and female (ovum) gametes (each with a single, haploid set of chromosomes) to produce a diploid zygote.''

*'''Gamete:'''
''A reproductive cell (male (sperm) or female (egg)) that has only half the usual number of chromosomes''

*'''Gametogenesis:'''

''process leading to the production of gametes. The development and maturation of sex cells through meiosis.Another name for meiosis where a diploid cell is divided into two haploid cells with half the chromosome content of the diploid parent cell.''

*'''Herbivorous:'''

''eating plants; of or pertaining to the herbivora.''

*'''Holoblastic:'''

''The complete division of an isolecithal or microlecithal egg into blastomeres''

*'''Invagination:'''

''One of the methods by which the various germinal layers of the ovum are differentiated.''

*'''Isoenzymes:'''

''Isozymes (also known as isoenzymes) are enzymes that differ in amino acid sequence but catalyze the same chemical reaction.''

*'''Mesentery:'''

'' membranous fold attaching various organs to the body wall.''

*'''Metamorphosis:'''

''A change in the form and often habits of an animal after the embryonic stage during normal development.''

*'''Neuroendocrine:'''

''Neuroendocrine [IPA nʊəroʊˈɛndəkrɪn] cells are cells that release a hormone into the circulating blood in response to a neural stimulus.''

*'''Organogenesis:'''

''The part of embryonic development where the body's main organs develop.''

*'''Peritoneum:'''

''The smooth serous membrane which lines the cavity of the abdomen, or the whole body cavity when there is no diaphragm, and, turning back, surrounds the viscera, forming a closed, or nearly closed, sac.''

*'''Perivitelline space:'''

''The perivitelline space is the space between the zona pellucida and the plasma membrane (sometimes called the vitelline membrane) in a fertilized ovum.''

*'''Polyploidy:'''

''Cells with three or more sets of chromosomes.''

*'''Pronucleus:'''

''the nucleus of the ovum or sperm after fertilization but before they fuse to form the nucleus of the zygote ''

*'''Protoplasm:'''

''The fluid living content of the cell that consists of two major divisions, the cytoplasm and the nucleoplasm (cell nucleus). It is composed mainly of nucleic acids, proteins, lipids, carbohydrates, and inorganic salts''

*'''Segmentation:'''

''division of some metazoan bodies (such as annelida and Arthropoda) into repeated parts, segments. Segmentation can be homomeric (more or less the same) or heteromeric(different from each other).''

*'''Terrestrial:'''

''Of or on the ground, of the habitat of a plant, on land as opposed to in water, or on the ground as opposed to on another plant.''

*'''Transgenesis:'''

''Transgenesis is the process of introducing an exogenous gene - called a transgene - into a living organism so that the organism will exhibit a new property and transmit that property to its offspring.''

*'''Yolk:'''

''nutritive material of an ovum stored for the nutrition of an embryo''

*'''Zygote:'''

''The cell from which an organism develops, that results from the fertilization of the egg by the sperm.''

''Primary Resource "Biology- Online Dictionary''[http://www.biology-online.org/dictionary/Main_Page]

== References - Frog Embryology: ==

[[Image:Frog Research.jpg|thumb|left|Image details:[http://images.google.com.au/imgres?imgurl=http://www.odt.co.nz/files/story/2008/09/university_of_otago_zoology_senior_lecturer_phil_b_3343259744.jpg&imgrefurl=http://www.odt.co.nz/on-campus/university-otago/21670/dunedin-frog-man-wins-zoo-award&usg=__JvJJU5QfOnIwY2bk4xo64UXuJRs=&h=600&w=404&sz=22&hl=en&start=14&um=1&tbnid=AbsP89yWcUiilM:&tbnh=135&tbnw=91&prev=/images%3Fq%3Dfrog%2Bresearch%26hl%3Den%26um%3D1].jpg]]

1. Savage, J. M. (2002). The Amphibians and Reptiles of Costa Rica. University of Chicago Press, Chicago [http://www.springerlink.com/content/vv015277w1746llw/]

2. Ford, L.S.; D.C. Cannatella (1993). "The major clades of frogs". Herpetological Monographs 7: 94–117 [http://digimorph.org/specimens/Xenopus_laevis/]

3. Tyler, M. J. (1994). Australian Frogs A Natural History. Reed Books [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.gracilenta.html]

4. Cogger, H.G.; R.G. Zweifel, and D. Kirschner (2004). Encyclopedia of Reptiles & Amphibians Second Edition. Fog City Press [http://en.wikipedia.org/wiki/Microhylidae]

5. Beltz, Ellin (2005). Frogs: Inside their Remarkable World. Firefly Books [http://unjobs.org/authors/ellin-beltz]

6. Tyler, M. J. (1994). Australian Frogs A Natural History. Reed Books [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

7. Moury JD, Hanken J (1995) Early cranial neural crest migration in the direct-developing frog, Eleutherodactylus coqui. Acta
Anatomica (Basel) 153, 243-253.

8.Raynaud A (1985) Development of limbs and embryonic limb reduction. In Biology of the Reptilia (ed. Gans C, Billett F), pp.
59-148. New York: John Wiley.[http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=9309]

9. Hanken J (1986) Developmental evidence for amphibian origins. In Evolutionary Biology (ed. Hecht MK, Wallace B, Prance GT), 20, pp. 389-417. New York: Plenum Press. [Hanken J (1986) Developmental evidence for amphibian origins. In Evolutionary Biology (ed. Hecht MK, Wallace B, Prance GT), 20, pp. 389-417. New York: Plenum Press.]

10. Elinson RP (1990) Direct development in frogs : wiping the recapitulationist slate clean. Seminars in Developmental Biology
1, 263-270.

11. Beebee, T. J. C. 1996. Ecology and Conservation of Amphibians. Chapman and Hall. London. [http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V5X-3SVHMKH-1X&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=1021245355&_rerunOrigin=google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=825868e10cd178d16a8a0e5ad14dc5ef]

12. Lehtinen, R. M. 2002. The use of screw pines (Pandanus spp.) by amphibians and reptiles in Madagascar. Herpetological Bulletin 2002:20–25.

13. Parris, K. M. and M. A. McCarthy. 1999. What influences the structure of frog assemblages at forest streams. Australian Journal of Ecology 24:495–502. CrossRef

14. Zug, G. R. 1993. Herpetology: An Introductory Biology of Amphibians and Reptiles. Academic Press. San Diego, CA.

15. Slack,J.M.W., Darlington,B.G., Heath,J.K. and Godsave,S.F. (1987)Mesoderm induction in early Xenopus embryos by heparin-binding growth factors. Nature, 326, 197-200.

16. Melton,D.A. (1990) Activins are expressed early in Xenopus embryogenesis and can induce axial mesoderm and anterior structures. Cell, 63, 485-493.

17. Harland,R.M. and Misher,L. (1988) Stability of RNA in developing Xenopus embryos and identification of a destabilizing sequence in TFIIIA RNA. Development, 102, 837-852.

18. Cunliffe,V. and Smith,J.C. (1992) Ectopic mesoderm formation in Xenopus embryos caused by widespread expression of a Brachyury homologue. Nature, 358, 427-430.

19. Kinoshita,K., Bessho,T. and Asashima,M. (1993) Competence prepattern in the animal hemisphere of the 8-cell-stage Xenopus embryo. Devel. Biol., 160, 276-284.

20. LaBonne,C., Burke,B. and Whitman,M. (1995) Role of MAP kinase in mesoderm induction and axial patterning in Xenopus development. Development, 121, 1475-1486.

21. Green,J.B.A., New,H.V. and Smith,J.C. (1992) Responses of embryonic Xenopus cells to activin and FGF are separated by multiple dose thresholds and correspond to distinct axes of the mesoderm. Cell, 71, 731-739.

22. Grainger R., Blumberg B., Harland R., Amemiya C., Importance of Xenopus Tropicalis to biomedical and biological research, Benaroya Research Institute, Virginia Mason Research Center [http://www.genome.gov/Pages/Research/Sequencing/BACLibrary/xenopusTropicalis.pdf ]

23. Gregory, T.R. (2005). Animal Genome Size Database. [http://www.genomesize.com]

24. U.S Fish and Wildlife Services, ABNORMALITY CLASSIFICATION SOP, [http://www.fws.gov/contaminants/Amphibian/pdfs/AbnormalitySOP_woutpics_Jan08.pdf ]

25. Donald D. Brown*, Liquan Cai*, Biswajit Das*, Nicholas Marsh-Armstrong‡, Alexander M. Schreiber*, and Rejeanne Juste*(2005), Thyroid hormone controls multiple independent programs required for limb development in Xenopus laevis metamorphosis [http://www.pnas.org/content/102/35/12455.full]

26. Ogino, Hajime; Ochi, Haruki, Resources and transgenesis techniques for functional genomics in Xenopus, Development Growth & Differentiation, Volume 51, Number 4, May 2009 , pp. 387-401(15) [http://www.ingentaconnect.com/content/bsc/dgd/2009/00000051/00000004/art00001%3Bjsessionid=4ah96rms73gcu.alexandra]

27. Giles Newton (2004) Why the frog? The Human Genome, [http://genome.wellcome.ac.uk/doc_WTD020799.html]

28. Xenbase, [http://www.xenbase.org/common/]

29. Donders Center for Neuroscience & Nijmegen Center for Molecular Life Sciences (NCMLS), Beyond the genome (Xenopus transgenesis for functional genomics),Faculty of Science, Radboud University [http://molanphys.ruhosting.nl/transgenesis.htm]

== External Links ==
[[Image:Frog links.jpg|thumb|left|Image details:[http://images.google.com.au/imgres?imgurl=http://2.bp.blogspot.com/_o93AaY0GzH4/SjY_ZYv0PII/AAAAAAAAAgk/skruNc2yN78/s400/computer%2Bfrog.jpg&imgrefurl=http://hellaheaven-ana.blogspot.com/2009/06/talking-frog-contemporary-fairy-tale.html&usg=__oxji1TGLV2Fi7xe0dnlmuYk8gDo=&h=288&w=288&sz=16&hl=en&start=2&um=1&tbnid=ywZd4zpdxC5plM:&tbnh=115&tbnw=115&prev=/images%3Fq%3Dfrog%2Bon%2Bcomputer%26hl%3Den%26um%3D1].jpg]]

1. Frog embryology [http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/F/FrogEmbryology.html Frog Embryology]

2. Frog cellular materials [http://www.xenbase.org/xenbase/original/cell/cell.html xenbase]

3. The zoology of frog species [http://worms.zoology.wisc.edu/frogs/mainmenu.html zoology frogs]

4. Frog cycle [http://www.bioethics.gov/images/sc_images/frog_dev.gif bioethics frog] Just a little cycle of FROG'S life cycle

5. Frog Embryology [http://embryology.med.unsw.edu.au/OtherEmb/Frog.htm UNSW Embryology]

6. Frog Research [http://apps.carleton.edu/campus/library/now/exhibits/wallcharts/frog/ carleton library exhibit]

{{Template:Projects09}}
[[Category:Frog]]

2009 Group Project 5

2009-10-14T22:43:59Z

Z3258567: /* Growth and Modification of Frog Species */

== The Embryology of Frogs ==

== The Frog ==

[[Image: Frog species .jpg|thumb|left|Image details: Wikipedia (2009) Frog species[http://en.wikipedia.org/wiki/Frog#Uses_in_agriculture_and_research].jpg]]

Frogs are scientifically identified by the structure of their long posterior limbs, a petite framework, webbed fingers and feet, budged eyes and the lack of a tail. The majority of frog species are extensively recognized as outstanding jumpers, due to their long, dominant legs, which are adaptations to progress jumping performance during activities. The Frog is one of the most frequently studied species in experimental embryology and most anatomical sciences. ''The Frog is a practically effective model for human embryological development given that the Frog:''

- Comprises of genes which can be effectively manipulated.

- Comprises of similar homogeny with humans species.

- Reproduces a large quantity of offspring in a short period of time.

- Are small species which can be simply sustained.

- Are not extremely luxurious and expensive.

== The History of the uses in agriculture and research ==

[[Image: Frog experiments .jpg|thumb|right|Image details: Scans of chemically cleared and dyed preserved deformed frogs and toads [http://www.sat.qc.ca/upload/residence/frog-04.jpg].jpg]]

There are numerous types of frog species that have been manipulated in many developmental experiments. The frog was traditionally used by countless of the early embryology investigators and presently there are several diverse molecular mechanisms regarding progression of the frog. Theses include:

'''1.''' Food source; frog legs are a delicacy and are eaten in European countries and in many parts of South American regions.

'''2.''' Frogs have the finest biochemical dissection of phenomena that take place in the egg and oocyte. Frogs are the evolutionarily closest to mammals, commonly used as a vertebrate model.

'''3.''' Frogs lay thousands of outsized eggs, from which cell extracts can be readily prepared that is capable of recapitulating most molecular phenomena in a test tube.

'''4.''' Frogs have been commonly used as a laboratory system for a very long period, and have an extensive history of producing crucial observations in countless fields of biology.

'''5.''' Frogs have a important historical connection to the study of epigenetics (John Gurdon-vertebrate cloning and reprogramming) which has been mostly performed on frog species.

'''6.''' Frogs also have very strong evidence of pattern formation and early development, as the embryos are large in size and experimentally manipulative.

'''7.''' Recent research into the biochemistry of chromatin and epigenetics has been performed with frog species and mammalian cultured cells.

'''8.''' The biggest weakness of the Frog model system is the difficulty of performing genetic experiments and analysis, as frogs are allotetraploid, meaning they take approximately a year to fully develop to sexual maturity, and the genome has not been completely sequenced. Nevertheless, biochemical manipulations of cell extracts, such as immunodepletions and application of heterologous DNAs and nuclei can avoid the need for genetic exploitation.

----

== Growth and development of the Frog ==

[[Image: Mature develop frog.jpg|thumb|Image details: Wikipedia (2009) Red Eyed Tree Frog Figure 1 Primary source:[http://en.wikipedia.org/wiki/File:Red-eyed_Tree_Frog_-_Litoria_chloris_edit1].jpg]]

* The frog is a well recognised species, abundant predominantly in ponds, swamps, though various species may also exist in damp or shady environments distant from moist habitats.

* Eggs of specific frogs are easily obtained and may be examined in from the beginning of fertilization onwards. The phases of embryonic development differs in various chordates, yet the typical phases are basically apparent in all frog species. The differences are associated principally to the amount of yolk particles present in an egg.

* The yolk particles offer nourishment of the developing embryo. The process of frog development will be discussed from the phases of gametogenesis to the adult stage.

----

== The Egg ==
[[Image:Development of Poles in frog Fertilization.jpg|thumb|left|Development of Poles in Frog Fertilisation:J,Nassif 2009.jpg]]

- The embryology of a frog egg is a vast cell; its dimensions are approximately 1.4-1.6 million times larger than a typical aquatic species egg cell. Throughout the frog’s embryonic maturation period, the egg will be transformed into a tadpole encompassing millions of cells but still remains with its constant volume of genetic material, the vast prodction of cell have been illusttrated in the figure on the right revealing the production of eggs from female frogs. [http://en.wikipedia.org/wiki/Microhylidae]

- The early embryonic frog structure consists of three main segments the superior hemisphere known as the animal pole which is usually visible as a grey coloured area. The innermost layer appears to be between the outer two sections known as the gray crescent represented in black. Inferiorly, represents the vegetal pole typically lighter than the superior compartment illustrated in gold.

VIDEO RESOURCE: [http://www.youtube.com/watch?v=GO5YN_t1fqw&feature=related]

[[Image:Early Development of Frogs.jpg|thumb|left|Early Development of Frog:J,Nassif 2009.jpg]]

==History of frog embryology use ==

*'''1851''' - ''Henby Nelson''(MD): He identified a remarkable fact through the frog embryo. Henby observed the first cleavage of the yolk, in the egg of the frog. And cleaved structure corresponds in line of direction to the longitudinal axis of the body of the embryo of the frog species.

[[Image:Wilhelm Roux.jpg|thumb|right|Wilhelm Roux[http://images.google.com.au/imgres?imgurl=http://www.todayinsci.com/R/Roux_Wilhelm/RouxWilhelmThm.jpg&imgrefurl=http://www.todayinsci.com/6/6_09.htm&usg=__qRLTEMTHdZpAHxiNX12hWjcm9tA=&h=125&w=100&sz=4&hl=en&start=2&um=1&tbnid=LIKIwZTqCpk7MM:&tbnh=90&tbnw=72&prev=/images%3Fq%3DWilhelm%2BRoux%26gbv%3D2%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

*'''1888''' - ''Wilhelm Roux'': Wilhelm Roux attempted to solve the above observation by damaging one cell of a two-cell frog embryo with a hot needle. The cell stayed in place. However, it did not develop further. Its partner developed into a left or right half-embryo;

*'''1907''' - ''John Hopkins'' hospital: In order to identify the cellular source of neuronal fibres. Scientist placed small portions of frog embryo spinal cords in lymph on a microscope slide and was able to observe clear cut neuronal sprouting.

*'''1951''' - ''Robert Briggs'': Robert Briggs was able to clone a frog embryo by substituting the nucleus of an unfertilized frog egg cell with the nucleus of a frog embryo cell. This process is known as nuclear transplant, has formed the basis for all cloning.

*'''1952''' - ''Robert Briggs and T.J. King'': Robert Briggs and T.J. King used frog for test experiment. Because the size of the eggs in the frogs are enormous compared with those of mammals, which make them easier to manipulate.

*'''1976'''- Using the technique that had been successful in cloning frog embryos, the doctor transferred the nucleus of one cells into a donated egg cell. As an embryo began to develop, it was implanted into the uterus of a young woman.

*'''1997''' - ''Wilmut and Campbell'': Utilizing the cloning technique from frog embryo, Drs. Wilmut and Campbell tried the starvation technique on embryo cells to produce Megan and Morag, the world's first cloned sheep and, until now, the most famous sheep in history.

*'''2000''' - ''Tokyo University'': Scientists at Tokyo University have grown artificial eyeballs. Scientists formed them in tadpoles by using frog embryo cells.

*'''2001''' - ''Advanced Cell Technology'': Scientists from Advanced Cell Technology announced production of a human embryo clone. This is significant as its parthenogenesis has been artificially induced in frogs.

[[Image:John Gurdon .jpg|thumb|right|John Gurdon [http://images.google.com.au/imgres?imgurl=http://www.pnas.org/site/misc/images/gurdon.jpg&imgrefurl=http://www.pnas.org/site/misc/classics4.shtml&usg=__1p-GA1PdOYsxKL-cznMb3RHCm98=&h=526&w=400&sz=223&hl=en&start=1&um=1&tbnid=9k4lhuLssiWCAM:&tbnh=132&tbnw=100&prev=/images%3Fq%3DJohn%2BGurdon%26gbv%3D2%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

*'''2002''' - ''John Gurdon'': John Gurdon from Wellcome Cancer Research Institute in Cambridge experimented on cloned frog embryo.

== Gametogenesis ==

* The sexual reproduction occurs through the fusion of either mature reproductive cells or germ cells known as gametes, which include the sperm from the male frog and ova from female frog species so as to form a single cell, the fertilized zygote. The gametes are typically developed in parents of different sexes . [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

* Males gametes is a spermatozoon , the female frog gamete is an ovum. Each gamete is formed by a process, recognised as maturation or gametogenesis in gonads. The typical male frog gonads are testies in male, while the female gonads are ovaries. The synthesis of both gonads is associated with the process of fertilization. [http://en.wikipedia.org/wiki/Microhylidae]

* The zygote changes into a mature frog through the process of embryology and metamorphosis. Gametogenesis is a in progression which frog gametes are established from germ cells. Initial germ cells are called primordial germ cells, which can be recognised extremely early in the life of frog species.

----

== The Egg & Fertilization ==

[[Image:Fertilized and Unfertilised Eggs.jpg|thumb|left|Fertilized and Unfertilized Eggs:J,Nassif 2009.jpg]]

[[Image:Egg Development.jpg|thumb|left|Egg Development:J,Nassif 2009.jpg]]

- This occurs once the sperm cell has inserted, following the insertion of the sperm cells meiosis II is completed, there is a 30 degree position change of the cytoplasm, gray crescent allows this change to be visible in some amphibians, the gray crescent is able what determines the expect ted outline of how the frog will form. The sperm cell joins with the nuclei of the egg which forms the diploid zygote nucleus. --Sando Rashed 10:09, 24 September 2009 (EST)

- The early phases in the development of the egg is visible, but must be studied in tadpoles throughout maturation. In embryonic tadpoles of about 10 millimetres in length, soon after the opening of the oral cavity, a pair of longitudinal ridge-like thickenings of peritoneum becomes apparent along the posterior surface of the body cavity situated near to the mesentery and along the inner boundaries of the kidneys. Genital ridges are established in all tadpoles of this age, sex is not distinct until a later period. The development of the egg is illustrated in the figure on the left revealing the structure of a developed egg and a mature of egg.

[[Image:Fertilisation life cyle.jpg|thumb|Fertilization of Life cycle:Derived from primary source:[http://en.wikipedia.org/wiki/Frog]]]

== Maturation of the Egg ==

- The eggs have currently accomplished their full size, and develop from the exterior of the ovaries like a small shot, but they still have to pass through the course of maturation before they are prepared to be fertilised. This progression of maturation relates to the nucleus almost completely.

- The nucleus component, containing the nuclear fluid that excludes through the nuclear membrane into the substance of the egg, a great segment of the nuclear reticulum vanishes and becomes degraded into separate globules known as nucleoli, but a extremely small division remains in the midpoint as a slender intricately thread recognised as the nuclear skets.
Relative to the egg getting discharged from the ovary, the follicles shatter allowing the eggs to fall into the abdominal cavity of the frog species, the egg then passes forwards, directly by the contraction of the muscular wall, somewhat by the movement of the cilia of the peritoneum, to the apex of the oviduct, which positioned at the anterior compartment of the body cavity opposite to the roots of the respiratory organs.

- The terminal part of the oviduct establishes a thin-walled pouch capable of great swelling, inside which the eggs gathers in large numbers. In conclusion, the eggs are migrated out through the cloaca into water which the albuminous investments of the eggs rapidly augment to form the gelatinous mass of the frogs spawn.

== Maturation phases ==

'''1. Nuclear skein''', moves from the midpoint of the egg to its outer surface, which it reaches opposite the midpoint of the black pole. The skein, subsequently an unevenly twisted thread, now presumes the specific arrangement of a nuclear spindle, for instance may be visible in the nucleus of an epithelial or additional cell instantly prior to division of the cell occurs.[http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

'''2. The first Polar Body,''' regarding the instance the egg is laid, but prior to its fertilistion, the egg develops a considerably flattened appearance at its upper or black pole, a definite sum of fluid being exuded among the egg and the vitelline membrane. The nuclear spindle currently separate into two identical segments, one of which remains with the egg, and the supplementary is extruded as the first polar body, a small ovoidal white globule, which is situated on the surface of the egg surrounding the exuded peri-vitellline fluid.

'''3. The Second Polar Body''', half of the nuclear spindle that stay behind then splits into two equivalent divisions, one of which remains inside the egg as the female pronucleus, whereas the other segment is extruded as the second polar body, a small white globule extremely related to the first polar body, and like this positioned in the perivitelline fluid on the superior portion of the egg.

'''4. Fertilisation of the egg''', includes the synthesis of the spermatozoon with to egg, specifically, synthesis of the nuclei of these two bodies. The spermatozoa, subsequent to being shed over the seed by the male, distribute vigorously by means of their extended tails, break through the gelatinous investment of the female eggs, bore their way through the vitelline membrane and so go through into the eggs themselves, which they penetrate relative to the superior or black hemispheres.
* Subsequently, an hour following the spermatozoon has entered; a progression may be visible projecting within from the exterior segement of the egg, with a liquid spot in the mid point. This liquid centre is the nucleus of the spermatozoon, and is said to be the male pronucleus, it break through beyond into the female egg, transporting the specialised pigment into it, so that it appears bounded by a pigmented capsule linked with the exterior of the egg by a pigmented stalk.

* By this instance, the second polar body has been established and extruded, and the female pronucleus is merely the only component of the primary egg nucleus still present. Both the male and female pronuceli, which are at initially distance separate to each other, merge and after having enlarged significantly in size then fuse mutually about two and half hours after fertilisation has originated to produce the segmentation nucleus.
* The segmentation nucleus is a huge sphere-shaped vesicle embedded in delicately granular protoplasm, and bounded by a distinct capsule of pigment, its arrangement by the synthesis of the male and female pronuclei completes the action of fertilisation. Specifically female pronucleus may be observe as an imperfect nucleus, and consequently result in the course of fertilisation. The nucleus of the spermatozoon or male pronucleus, replaces the component of the egg- nucleus which has been misplaced as the polar bodies.

'''5. Segmentation of the Egg''', the initial phase of growth consist in constant separation of the egg, whereby it becomes transformed from the unicellular state, which is everlasting only in the lowest species, to muliticelluar state charactertics of all higher species. To these early processes of growth the names segmentation is specified. Shorty subsequent to the competition of fertilisation and arrangement of the segmentation nucleus this later misplaces its sphere-shaped appearance and develops to be spindle-shaped, the yolk granules at the equivalent instance showing a tendency to develop into lines distributing outwards from the distal segment of the spindle.
* The nucleus now split into two halves, which shift away from one another, the yolk granules are likely to combined themselves around the two nuclei, and a slender vertical plate of delicately granular substance is left, dividing the egg.[http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

* Superiorly the eggs depression now becomes visible, initially as a small cavity and then develops as a groove, which almost immediately extends all round, and speedily deepening, splits the egg into two entirely separate halves along a plane equivalent with the vertical plane.

* Shorty after, the two nuclei soon separate again into two, and therefore a second cleft is created in the same state as before, its additionally in the vertical plane, however in a plane at 90 degrees to the initial one, and on its finishing point the egg comprises of four accurately similar segments, each containing a nucleus. The third cleft is horizontal in shape, but not equal, lying closer to the superior than the lower pole, it segregates each of the four cells into, an superior smaller and a inferior larger pole

----

== Cleavage ==

[[Image: Frog Cleavage development.jpg|thumb|left|Cleavage Process details:[http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/F/FrogEmbryology.html].jpg]]

* The egg of the frog is scientifically identified as’ telolecithal’ meaning there is a outsized amount of yolk concentrated at a single pole, in contrast to the concentration of cytoplasm and the site of the nucleus. The cleavage phases are holoblastic, therefore the total and after the second cleavage they are asymmetrical .The initial cleavage stage appears about two and half to three hours after fertilization. It commences as a minor depression in close proximity to the centre of the animal hemisphere. It appears as if some interior force is pushing the surface the egg towards the centre. This small upturned fold steadily continues in the form of a channel until it surrounds the egg. This groove is shallow in the commencement, but develop into deeper eventually separating the fertilized egg into two halves recognised as the blastomeres. [The figure on the left symbolise the development and growth of the frog embryo during cleavage].

* Internally the separation is mitotic, consequently each daughter cell contains a nucleus resulting from the copulation nucleus of the fertilised egg. This cleavage is vertical, the two cells are indistinguishable in respect of cytoplasm, pigment and yolk. The subsequent cleavage appears about an hour after the first. The channel of this cleavage begins at the centre of the animal hemisphere, is at right angles to the first and is vertical. This divides the egg into four blastomeres. The fourth blastomere so produced are not qualitatively equal, since of these only two contain the material from the gray crescent. The cleavage begins about thirty minutes after the second is completed or four hours after fertilisation. the cleavage plane of the third furrow is horizontal and slightly above the equator. Thus the four upper cells are a little smaller than the four lower cells. The smaller blastomeres are called micromeres and the larger blastomeres are called macromeres. The fourth cleavages follow 20 minutes after the third and tend to be vertical. This is usually a double furrow.

* The cleavage rate is accelerated with each of the early divisions and since the blastomeres are of unequal size and have varying amounts of cytoplasm and yolk, synchronous cleavage is lost and there is an obvious overlapping of the division. The upper most cells divide more rapidly than the lowermost cells. From this point onwards perfect symmetry in cleavage and in blastomere is very rare, although the embryo developed perfectly. The fifth cleavage is also doubled, appearing first in the upper hemisphere and then in the lower.

* The cleavage thus far follows the rule that each cleavage plane comes in at right angles to the previous one. The subsequent divisions become so irregular that it is previous one. The subsequent division become so irregular that it is impossible to trace out any plan or procedure. The segmentation continues more rapidly in the pigmented regions, since at that place the protoplasm is most dense, whereas, yolk which is very abundant in the vegetal side delays cell division. The multicelluar embryo at this stage is called morula by some biologists.

----

== Gastrulation ==

[[Image:FROG GASTRULATION .jpg|thumb|left|Frog Gastrulation Image details:[http://www.google.com.au/imgres?imgurl=http://bio1903.nicerweb.com/Locked/media/ch47/47_12FrogGastrulation.jpg&imgrefurl=http://bio1903.nicerweb.com/Locked/media/ch47/gastrulation-frog.html&h=540&w=480&sz=46&tbnid=N78sHjELreGGSM:&tbnh=132&tbnw=117&prev=/images%3Fq%3Dfrog%2B-%2Bgastrulation&hl=en&usg=__4VK9FYLft0W-4lBe6p5EtQAMiaI=&ei=qPy5SurtMJvE6wON8JmdAg&sa=X&oi=image_result&resnum=4&ct=image].jpg]]

''The phase of Blastulation is followed by the unique developmental progression of gastrulation. The process of frog gastrulation involves the following processes.''

'''1. Epiboly Phase'''

The pigmented cellular materials of blastula have the propensity to overgrow the yolk cells within the developing content. This course which is known as epiboly commences gradually in the final blastula and rapidly accelerates with advancing gastrulation development. The cellular matter within the animal pole reproduces and matures on all sides except in area surrounding the dorsal lip of the blastopore has been established.

'''2. Convergence'''

Scientists suggested that the unfolding was thought to result in spreading of the superficial cells over a substrate with suitable absorption properties. Consequently epiboly and convergence are an outcome to this spreading tendency, which is actually increased by a reduction in surface tension of the distributing cells.

'''3. Rotation'''

The epiboly phase is maintained until the region of the dorsal lip has migrated and is a to some extent greater than 90 degrees and the region of the white blastopore is reduced to small circular rings. This section will be positioned away from the developing vegetal pole. Laterally the complete developing gastrula has been rotated to a horizontal axis, allowing it to lie at right angles to the original median plane of the egg. Therefore, the course of rotation is such that the dorsal lip is practically pushed backwards in one direction as rapid or quicker than epiboly moves it forward in the other. The outcome will be that the blastopore produced at roughly the vegetal pole is posterior, and the dorsal and ventral lips are essentially dorsal and ventral. This in addition allows the eggs to form the antero-ventral side of the potential embryo whilst the area marked by the grey crescent is to develop the dorsal segment.

'''4. Invagination'''

Visible is a small fissure- like invagination which is apparent in the middle between the equator and the vegetal segment. The most superior or dorsal border of the cleft produce the dorsal lip of the blastopore. This imput move back and forth on the dorsal plane near the dorsal lip and migrates around the boundaries of the blastocoel in company with the extension of the lateral lips. This adapted invagination is maintained until the blastocoel cavity has been almost abolished; excluding the slender opening separating epiblasts from the hypoblast, the new segment formed is known as the archenteron cavity.

'''5. Involution'''

- Additional to previous course of action a distinct involution also occurs at the blastoporal borders. This is mainly dynamic at the median dorsal lip and gradually more less as it shifts across either side until it reaches the ventral lip where it constant.Throughout this progression, cells positioned beside the superior boundaries of the blastoporal lip migrate over the lip to the interior portion of the lip. These cells are remained within the embryo along the internal edge of the blastopore. This indicates the root of archenteron is composed of involuted cells and beyond this the external layer known as the ectoderm. The base and lateral sides are enclosed mainly of endodermal cellular material, which have been established from larger yolk cells, situated in the vegetal pole of the blastula.

- In the final phases of the gastrula development, the cells contributing to the floor of the archenteron, thin out significantly where they surround the blastocoel.
The hemispherical shaped dorsal lip of blastopore which become visible at the commencement of the gastruation stage carry on to augment, initially becoming semicircular, then transform into a horse shoe shaped and then finally forming into circular band. The band is the accomplished by the blastopore. Various yolk cells of vegetal pole present in the section are crowed into the blastoporal cavity where they form a gathering identified as a yolk plug. Blastopore rapidly reduces in size while the archenteron is still developing and becomes completely formed in the final stage; the yolk plug appears as only a small oval on the gastrula.

==Growth and Modification of Frog Species==

'''1. Changes in habits and habitats:'''

'''a)''' In frogs, metamorphosis is related with to the modifications and adaptations as a frog changes environmental habitats from an aquatic to a terrestrial mode. Metamorphosis has modified the adaption of frogs as this alteration it began during the aquatic adaptations in the surface of water to breathe air. Subsequently, it continues the terrestrial surroundings, therefore the frog species become abundant in vegetation area allowing the frog to transform in to amphibious species.

'''b)''' The transition during metamorphosis is linked with a change in food chain. The tadpoles being the embryonic origin of frogs are herbivorous, feeding on algae and green matter, which they collect by the adapted feature such as their teeth surrounding their mouths. Adult frogs, alternatively, are classified as carnivorous feeding on insects and worms. Occasionally, they also consume larger prey, for instance smaller frogs species and even little birds and rodents which they dominant and ingest.

[[Image:Development of frog from sperm to mature structure.jpg|thumb|left|Development of Frog from sperm to mature structure Image details:J,Nassif 2009.jpg]]

'''2. Changes in Morphology'''

These include the decrease or complete absence of specific organs or structures which are essential during development of early frog embryology, but not critical in the mature frog species. The significant alterations of this nature include the following developmental structures.

'''a)''' The long tail of the tadpole alongside the fin folds is absorbed again during metamorphosis and becomes absent at the final stage of the metamorphosis.

'''b) '''The developing gills are resorted, the gill clefts are congested and the branchial cavities start to become absent. The reabsorbtion of gills also takes place by autolysis.

'''c)''' The teeth of the perioral disc additionally the homey lining of the jaws are shed.

'''d)''' The lateral line sense organs within the skin of tadpoles vanish throughout metamorphosis.

'''e)''' The cloacal tube begins to condensed and reduced.

'''f)''' Various blood vessels, together with parts of the aortic arches, are reduced during mature development.

(The figure on the left represents the transformation from a tadpole to a developing structure.)[http://science.jrank.org/pages/2862/Frogs-Adult-morphology.html]

'''3. Progressive or constructive changes'''

This process comprises of the development of specific organs which mature into functional systems only during metamorphosis.

'''a)''' During development the limbs continue to augment in size and differentiation. The forelimbs, which in the tadpole mature under the opercular membrane, which then break through to the exterior. Simultaneously there is a increase in the length and strength of the hind limbs, joints develop in them and the toes become visible.

'''b)''' The middle ear becomes apparent in relation with the first pharyngeal pouch. The tympanic membrane matures. It is bounded by circular tympanic cartilage which allows the frog to retain air.

'''c)''' The visual organs bulge up on the dorsal surface of the head developing the nictitating membrane.

'''d)''' There is augmentation of the tongue and the formation of thevomerina teeth.

[[Image: Growth model.jpg|thumb|Growth Model Image details:J,Nassif2009:]]

'''4. Remodelling of some structures'''

Systematic organs which operate both in the early embryonic larva and the mature adult change their differentiation during metamorphosis so as to meet the requirements of the adult mode of life and due to the habitat adaptations. The figure on the right illustrates structures developing from specic germ cell layers.

'''a)''' The skin of the embryonic tadpole is lined with a double-layered epidermis. The number of layers of cells in the epidermis augments throughout metamorphosis. Superficial surface layers become cornified. Multicellular mucous and serous glands originate in the skin. The pigmentation of the skin continuously changes, new patterns and colour start to form.

'''b)''' There is a lengthening of the mouth gap as a result of rotation of the quadrate cartilage and the true jaws become functional.

'''c)''' The tongue rapidly progresses and becomes larger and more muscular.

'''d)''' The eyes become more specialised.

'''e)''' In early tadpoles, the GIT is extremely long and wound up into a spiral folds. The intestine become greatly lengthened in herbivorous species due to the vegetables food chain.[http://en.wikipedia.org/wiki/Frog]

'''5. Development of the reproductive system'''

(The figure below represents the reproductive and development cycle of a frog as it transform from egg to frog specie.)

In tadpoles, right after the mouth is being formed, two indentation like thickenings of peritoneum begin to appear near the body cavity (dorsal surface), which is nearest to the mesentery which is near the developing kidneys. These appear in all tadpoles.

These indentations appear here because of a change in the endothelial cells, everywhere else they are usually flat looking cells but they undergo a change and in this particular area become somewhat cuboidal/columnar.

Later on the indentations become more obvious due to the epithelial cells replicating numerously to form a thick layer. The posterior two thirds of the indentation for the female is the ovary and for the male it is the testis. The third that is left differentiates and becomes fat for the body.

[[Image: Mature frog life cyle.jpg|thumb|200px|left|Mature from life cycle Image details:Derived from primary source:http://www.scienceclarified.com/images/uesc_01_img0038.jpg]]

[[Image: Developing frog.jpg|thumb|Developing Frog Image details:
[[Image: Mature develop frog.jpg|thumb|Image details: Red eyed tree frog litoria chloris source:[http://en.wikipedia.org/wiki/File:Red-eyed_Tree_Frog_-_Litoria_chloris_edit1.jpg]].jpg]]

===Delamination===

Delamination indicates a mass separating a group of cellular matter from other cellular groups. It has been illustrated that the division of notochord, mesoderm and endoderm tissues from each other to form distinct cellular masses is completed by the progression of delamination, subsequent to these materials moving to the inside throughout gastrulation. During the developing gastrula, the germ layers are all recognized. These distinct segments of the embryo develop from these germ tissue layers.

===Polarity and Rotation===

Throughout fertilisation to the beginning of gastrulation, the frog’s egg continues in the original location in relation to its polarity. Subsequent to gastrulation its polarity begins to differentiate. This progression is linked with migration of materials within the gastrula and can be responsible for the alterations of the centre of gravity.

===Closing of Blastopore===

Subsequent to the formation of the gastrula, the blastopore is visible as a tiny round circular filled cavity containing the yolk plug. As it continues to reduce in dimension, it represented as a pear-shaped outline through the mutual approach of its lateral lips. Through it final progression these fuse entirely to produce a longitudinal groove, the streak which continue dorsally and ventrally in a small aperture. The inferior aperture closes, resulting in a depression called the anal pit. The superior region remains open for some period and begins to as the neural groove is laid down.

===Post Gastrulation or Organogenesis===

Throughout the duration of pre-gastrulation, all tissues for different organs vanish from the surface of blastula and migrate inside to take their final arrangement in the embryo structure where organs are developed from their potential regions. Consequently organogenesis transfers an embryo into free larva structure.

----

==Germ-layer origin of various body tissues==
[[Image: Development Models of Frog.jpg|thumb|right|Figure 13 Image details:Vertebrate Structure and Development.jpg]]

Ectoderm will give raise to structures such as skin, brain, spinal cord, neurons and sense receptors.
Mesoderm will give raise to structrues such as notochord, muscles, blood, bone and sex organs.
Endoderm will give raise to sturctures such as inner lining of gut, liver, pancreas, lungs and bladder, thyroid and parathyroid glands and thymus.

== Structures derived from Germ-layers of frog species ==

[[Image:Development of Frog Layers.jpg|thumb|left|Figure 14 Primary source[http://www.bio.miami.edu/~cmallery/150/physiol/sf19x11b.jpg]Image details:J,Nassif 2009.jpg]]

[[Image:Development of frog layers.jpg|thumb|left|Figure 15 Primary source [http://www.bio.miami.edu/~cmallery/150/physiol/sf19x11b.jpg]Image details:J,Nassif 2009.jpg]]

'''Ectoderm '''

''Establishes the epidermal segments and its derivatives, to the frog’s nervous system. The ectoderm also contributes to :''

1. The olfactory and auditory epithelium.

2. The retina and lens of the eye.

3. Sensory organs.

4. The epithelial lining of the oral cavity and the anus.

5. The pineal and pituitary body.

'''Mesoderm'''

''Mesoderm originates:''

1. Connective tissue.

2. Muscles, except the notochord.

3. Blood vessels.

4. Lymphatics.

5. The peritoneum and the urinary and reproductive system.

6. The dermis, parts of the eye excluding lens, cornea, and conjunctiva.

'''Endoderm'''

''From the endoderm arises:''

1. The epithelial lining to the gut and oesophagus, stomach, intestine, bile duct.

2. The hepatic cells of the liver, respiratory tract, larynx, trachea and lungs.

3. The lining of the urinary bladder, pancreas thyroid and thymus.

[The two figures reveal the development of structures deriving from the celluar components of the embryology of the frog].[Structures derived from Germ-layers of frog species ]

==Life cycle of a frog==

'''Fertilization-egg''':

The female lays eggs in the spring. A group of fertilized eggs is called spawn;

'''7-10 days''':

Fertilized egg feed on remaining yolk which is in its gut. Their gills, mouth and tail have poorly developed. Begin to swim and feed on algae;

'''10-30 days(4 weeks):'''

A layer of skin grows over gills. Teeth begin to appear. A coiled gut start to develop. This is aid in digestion;

'''30-60 days(6-9 weeks):'''

Legs being to grow and head is more distinct. Start to eat insects. Arms begin to grow;

'''60-80 days(12 weeks):'''

Resemble a frog. Still have remaining tail;

'''80-140 days(20 weeks):'''

Fully developed, spend most of time out of water. Majority of frog live between 4-15 years.

==Timeline of frog development==

Development of egg and embryo at temperature 18 degree celsius.

'''0 hours''' - fertilization of the egg

'''1 hours''' - formation of the gray crescent due to pigment migration

'''3.5 hours''' - early cleavage

'''4.5 hours''' - blastula stage(coeloblastula with eccentric blastocoel

'''26 hours''' - gastrulation

'''26 hours''' -'' early'' - crescent shaped dorsal lip

'''34 hours''' - ''middle''- semicircular blastoporal lip

'''42 hours''' - ''late'' - circular blastoporal lip

'''50 hours''' - neurulation

'''50 hours''' - ''early'' - medullary plate

'''62 hours''' -'' middle''- neural folds converging

'''67 hours''' - ''late'' - neural tube formed and ciliation of embryo

'''84 hours''' - tail bud stage(early organogeny)

'''96 hours''' - muscular response to tactile stimulation

'''118 hours''' - early heart beat, development of gill buds

'''140 hours''' - hatching and gill circulation

'''162 hours''' - mouth opens and cornea becomes transparent

'''192 hours''' - tail fin circulation established

'''216 hours''' - degeneration of external gills, formation of operculum, development of embryonic teeth

'''240 hours''' - opercular fold over brachial chamber except for spiracle and internal gills

'''255 hours''' - prolonged larval stage with refinement of organs

'''270 hours''' - development of hindlimbs, internal development of forelimbs in opercular cavity

'''275 hours''' - projection of forelimbs through operculum, left side first

'''280 hours''' - absorption of the tail and reduction in size of the gut

'''284 hours''' - metamorphosis complete, emergence from water as miniature, air breathing frog

==Stages of frog embryology==
--[[User:S8600021|Mark Hill]] 08:40, 9 October 2009 (EST) [[Talk:2009_Group_Project_5#Constructive_Criticism_of_Coordinator|see my comment on images]]

The rate of development of the egg and embryo will depend upon the temperature at which they are kept. The approximate schedule of development at 23 degree celsius is provided below.

{| border='1px'
|+ Table 1: Stages of frog development
!Stage !!Time since fertilisation (hours)!!Stage Characteristic !!Embryo characteristic !!Image of frog stage
|-
|1
|0.00-1.30
|fertilization of the egg, post fertilization
|animal hemisphere, gray crescent and vegetal hemisphere are present
|[[File:Stage01ventral.jpg|100px]]
|-
|2
|1.30-2.00
|splits into two cells
|appearance of first cleavage furrow
|[[File:Stage02ventral.jpg|100px]]
|-
|3
|2.00-2.15
|becomes four cells
|appearance of second cleavage furrow
|[[File:Stage03dorsolat.jpg|100px]]
|-
|4
|2.15-2.45
|becomes eight cells
|appearance of third cleavage furrow
|[[File:Stage04dorsolat.jpg|100px]]
|-
|5
|2.45-3.00
|becomes sixteen cells
|appearance of fourth cleavage furrow
|[[File:Stage05dorsal.jpg|100px]]
|-
|6
|3.00-3.30
|becomes thirty-two cells
|appearance of fifth cleavage furrow
|[[File:Stage06animal.jpg|100px]]
|-
|6.5
|3.30-4.00
|blastula stage
|Three dorsal folds become visible as a result of endoderm invagination. Pole cells no longer visible on surface
|[[File:Stage065dorsal.jpg|100px]]
|-
|7
|4.00-5.00
|Gastrulation stage
|two primary germ layers. epiblast and endoderm
|[[File:Stage07ventral.jpg|100px]]
|-
|8
|5.00-7.00
|neurulation
|medullary plate, neural folds and neural tube
|[[File:Stage08animal.jpg|100px]]
|-
|9
|7.00-9.00
|germ layer
|complete lip involution encircling yolk
|[[File:Stage09veg.jpg|100px]]
|-
|10
|9.00-11.00
|early gastrula
|two primary germ layers
|[[File:Stage10veg.jpg|100px]]
|-
|10.5
|11.00-11.45
|gastrula
|two germ layers
|[[File:Stage105vegb.jpg|100px]]
|-
|11
|11.45-12.30
|medulla plate
|Yolk sac protrudes dorsally, labium moves to midline on ventral side
|[[File:Stage11veg.jpg|100px]]
|-
|11.5
|12.30-13.15
|continuation of medulla plate
|start closing the plate
|[[File:Stage115veg.jpg|100px]]
|-
|12
|13.15-14.15
|early neurula
|thickened ectoderm give rise to CNS
|[[File:Stage12veg.jpg|100px]]
|-
|12.5
|14.15-14.45
|neural folds
|expansion of cavity
|[[File:Stage125postdors.jpg|100px]]
|-
|13
|14.45-16.15
|neural folds
|continue expanding cavity
|[[File:Stage13postdors.jpg|100px]]
|-
|14
|16.15-17.30
|neural folds
|continuation of cavity
|[[File:Stage14postdors.jpg|100px]]
|-
|15
|17.30-18.15
|tail bud stage
|early organogeny
|[[File:Stage15postdors.jpg|100px]]
|-
|16
|18.15-18.45
|tail bud stage
|posterior ventral view
|[[File:Stage16ant.jpg|100px]]
|-
|17
|18.45-19.45
|tail bud stage
|anterior view
|[[File:Stage17ant.jpg|100px]]
|-
|19
|20.45-21.45
|neural fold close complete
|dorsal view
|[[File:Stage19dorsal.jpg|100px]]
|-
|20
|21.45-22.30
|early tail bud
|anterior view
|[[File:Stage20dorsal.jpg|100px]]
|-
|21
|22.30-24.00
|termination of neural crest
|progress to next stage
|[[File:Stage21ant.jpg|100px]]
|-
|22
|24.00-24.45
|prolonged development
|elongation
|[[File:Stage22lat.jpg|100px]]
|-
|23
|24.45-26.15
|elongation of embryo
|later view
|[[File:Stage23lat.jpg|100px]]
|-
|24
|26.15-27.30
|continuation of elongation of embryo
|dorsal view
|[[File:Stage24latsmall.jpg|50px]]
|-
|25
|27.30-29.30
|organs development
|embryo elongates and develops dorsal thickening
|[[File:Stage25dorsal.jpg|50px]]
|-
|26
|29.30-31.15
|elongation
|dorsally forms neural and brain cavity
|[[File:Stage26lat.jpg|50px]]
|-
|27
|31.15-32.30
|elongation of embryo
|dorsal view
|[[File:Stage27lat.jpg|50px]]
|-
|28
|32.30-35.00
|further development
|lateral view
|[[File:Stage28lat.jpg|50px]]
|-
|29-30
|35.00-37.30
|tail bud
|growth
|[[File:Stage29-30lat.jpg|50px]]
|-
|31
|37.30-40.00
|prolonged development
|bud development
|[[File:Stage31lat.jpg|50px]]
|-
|32
|40.00-44.30
|early muscular development
|elongation
|[[File:Stage32lat.jpg|50px]]
|-
|33-34
|44.30-50.00
|muscular movement
|apparatus for locomotion
|[[File:Stage33-34lat.jpg|50px]]
|-
|35-36
|50.00-53.30
|muscular movement
|apparatus for locomotion
|[[File:Stage35-36lat.jpg|50px]]
|-
|37-38
|53.30-56.30
|heart beat
|develops apparatus
|[[File:Stage37-38lat.jpg|50px]]
|-
|39
|56.30-66.00
|mouth opens
|cornea transparent
|[[File:Stage39latsmall.jpg|50px]]
|-
|40
|66.00-76.00
|gill circulation
|hatching
|[[File:Stage40lat.jpg|50px]]
|-
|41
|76.00-80.00
|tail, fin circulation
|circulation
|[[File:Stage41lat.jpg|50px]]
|-
|42
|80.00-86.00
|internal gills, operculum
|opercular fold, teeth
|[[File:Stage42lat.jpg|50px]]
|-
|43
|86.00-98.00
|operculum complete
|operculum closed on right
|[[File:Stage43lat.jpg|50px]]
|-
|46
|98.00-106.00
|metamorphosis
|emergence from water as miniature, operculum complete|
|[[File:Stage46lat.jpg|50px]]
|-
|}

==Abnormalities of frog==

Abnormalities of frog could be caused by multiple factors. These include change in climate, predators, parasites, bacteria, fungi, viruses or pollution and contaminants such as pesticides, metals and fertilizer.[http://www.fws.gov/contaminants/documents/frogsrefup_septoct_2006.pdf]

The Abnormalities are further classified into different categories. These categories are:

===1. Infectious Diseases:===

'''Perkinsus Symptoms-''' caused by perkinsus-like protozoan organism. Symptoms include swollen viscera that leads to a bloated body and and infected swollen heart

'''Ichthyophonus symptoms-''' cause by parasitic genus, where symptoms include a swollen tail resorption site that matches the surrounding skin in color and translucency.

[[Image:Abnormalities of Frog species.jpg|thumb|left|Figure A Image details[waterwatchadelaide.net.au].jpg]]

===2. Surficial Abnormalities:===

Surficial abnormalities as the one that are visible on the surface of the skin. This includes abnormal pigmentation, , subcutaneous hemorrhaging, wounds due to trauma or from a predator
Edema is a fluid-filled swelling under skin whihc is also a surficial abnormality.

===3. Skeletal Abnormalities:===

This is further classified into three more categories:

'''a. Skeletal Malformations-'''

* Microcephaly (small head or blunt snout)
*Scoliosis (Curved spine in lateral direction)
*Shrunken Limb (Micromelia)
*Amelia (Completely missing limb with no stump)

'''b. Skeletal Abnormalities of Unclear Etiology-'''

This condition arises when a frog has ectromelia (missing limb), brachydactyly (missing digits) or other such condition with no visible trauma or external damage, then this will be classified as the Skeletal abnormality of unclear etiology.

'''c. Skeletal Injuries-'''

Any limb missing or broken due to trauma or other related reason which shows clear evidence of it is classified as skeletal injury

===4. Eye Abnormalities:===

Most common includes-

'''i. Anophthalmia:''' Skin covers the eye socket as there is no eye

'''ii. Abnormal Iris Coloration:''' Reduced pigment in either one eye or both resulting in two different colours of the iris at times

'''iii. Abnormal size or shape:''' Both eyes either deviating from each other or size of pupil or iris is different than the other eye

[http://www.fws.gov/contaminants/Amphibian/pdfs/AbnormalitySOP_woutpics_Jan08.pdf ]

==Genetics==

There are a wide variety of species that differ from each other when it comes to genetics and their functioning.

'''TAXONOMY:''' '''Phylum''' ''Chordata'' / '''Sub Phylum''' ''Vertebrata'' / '''Class''' ''Amphibia'' / '''Order''' ''Anura''

Their are more than two dozen different families of frogs, where suborders are:

'''1. ARCHAEBATRACHIA-''' most primitive frogs

'''2. MESOBATRACHIA-''' linked between the Archaebatrachia and Neobatrachia

'''3. NEOBATRACHIA-''' most modern frogs

{| border='4px'
|+ '''General Info:'''
! !!
|-
| '''Number of frogs' species'''
| 5280
|-
| '''Smallest frog genome size:'''
| 0.95pg, Ornate burrowing frog
|-
| '''Largest frog genome size:'''
| 13.40pg, Ornate horned frog
|-
| '''Mean of frogs' genome'''
| 4.68pg ± 0.13
|-
|}

[http://www.genomesize.com]

*Majority of frogs have only 22 to 26 chromosomes and polyploid is very common where they are almost bisexual.

*Polyploid Amphibians reduce their total cell number such that they acheive the same body size as diploids. One of the most unsual forms of polypoidy in amphibians is the water frog ''Rana esculenta'' from Europe and Western Asia.

* The species with larger genomes have more genes for e.g. the frog genus ''Xenopus'' includes 16 species, with genome sizes ranging from 3.5 x 10^9 bp to 1.6 x 10^10 bp. These differences have arisen by numerous events of polyploidization within the past 40 million years or so. The ancestral chromosome number for the genus seems to have been 18, but there are species with 36, 72 and 105 chromosomes [http://www.xenbase.org/common/]

{| border='4px'
|+ '''Difference within two families'''
! '''SPECIES''' !! ''X.LAEVIS'' !! ''X.TROPICALIS''
|-
| '''PLOIDY'''
| Allotetraploid
| Diploid
|-
| '''NO. OF CHROMOSOMES'''
| 36 chromosomes
| 20 chromosomes
|-
| '''GENOME SIZE'''
| 3.1 x 10^9 bp
| 1.7 x 10^9 bp
|-
| '''EGG SIZE'''
| 1-1.3 mm
| 0.7-0.8 mm
|-
| '''GENERATION TIME'''
| 1-2 years
| 4 months
|-
|}
[http://www.xenbase.org/common/]

===Genome Sequencing===

Since Frog has a huge family with many different species, only few main species that are used widely for the purposes of experiments have their genome sequenced.

''Xenopus tropicalis'' has one of the smallest genomes among amphibians and has the shortest generation time- four to six months and the only diploid genome among the 14 Xenopus species. This means it has no more than two copies of most genes, whereas the other species of Xenopus have four copies of most genes (pseudotetraploid). US Department of Energy's Joint Genome Institute (JGI) in Walnut Creek, California, initiated the X. tropicalis Genome Project, finding 1,700 million base pairs.
[http://www.genome.gov/Pages/Research/Sequencing/BACLibrary/xenopusTropicalis.pdf]

===Xenopus oocytes===

* The oocytes provide an important expression system for molecular biology.

* By injecting DNA or mRNA into the oocyte or developing embryo, scientists can study the protein products in a controlled system. This allows rapid functional expression of manipulated DNAs (or mRNA). This is particularly useful in electrophysiology, where the ease of recording from the oocyte makes expression of membrane channels attractive.

* One challenge of oocyte work is eliminating native proteins that might confound results, such as membrane channels native to the oocyte.

* Translation of proteins can be blocked or splicing of pre-mRNA can be modified by injection of Morpholino antisense oligos into the oocyte (for distribution throughout the embryo) or early embryo (for distribution only into daughter cells of the injected cell).
[http://www.staff.unibe.ch/sigel/xenopus.html]

===Xenopus Laevis===

* ''Xenopus Laevis'' is an important model organism in developmental biology. X. laevis is tetraploid and reaches sexual maturity in 1 to 2 years. What makes it important in developmental biology is its large and easily manipulable embryo.

* Extracts from the eggs of X. laevis frogs are also commonly used for biochemical studies of DNA replication and repair, as these extracts fully support DNA replication and other related processes in a cell-free environment which allows easier manipulation.

* The Human chorionic gonadotropin hormone (hCG) is present in the urine of the pregnant women in large quantities only. This hormone in the urine induces X.laevis oocyte production which formed the basis of first well-documented method of pregnancy testing X. laevis is also notable for its use as the first well-documented method of pregnancy testing when it was discovered. Today, commercially available HCG is injected into Xenopus males and females to induce mating behavior and breed these frogs in captivity at any time of the year.

===Gene cluster===

* The alpha and beta globin genes are closely linked in small cluster of frogs compared to human and chicken

* The similarity of architecture of two clusters found in X.laevis supports the tetraploid origin

* The two loci encoding the muscle specific creatine kinase isoenzymes and have large differences in developmental profile, therefore suggesting that duplicate loci that have not undergone silencing are not simply redundant copies but have acquired specialization.

* Contains twice number of genes for proteins i.e. haemoglobin and sarcomeric actin serum albumin compared with other species

----

==Current Embrology Research==

Currently, a number of fields have benefited from the development of frog embrology. These include cloning, verification of messenger RNA, and Cell cycle.

===Cloning===
[[Image:Robert Briggs.jpg|thumb|left|Figure 16 Image details:Robert Briggs.jpg]]

In 1952, Robert Briggs and Thomas J King cloned northern leopard frogs using a method of nuclear transfer. Briggs and King's experiment was similar to that envisioned - and piloted using salamanders - by Hans Spemann in his 1938 proposal for a 'fantastical experiment'. Later, John Gurdon extended this work and showed that nuclei from differentiated cells could support development, although less well than those from early embryos. [http://genome.wellcome.ac.uk/doc_WTD020799.html]

Lemaitre et a. (2005) from MRC Cancer Cell Unit, Cambridge, U.K. worked on experiments that demonstrated that importance of serial nuclear transplantation for the sucessful cloning of frogs. He demonstrated that exposure of somatic-cell nuclei (erythrocyte nuclei) and sperm nuclei to an extract of mitotic cell extract reorganizes the chromatin into shorter loops and allows replication at much shorter intervals along the DNA. This increases the efficiency of DNA replication in mammalian cell-free systems.

===Transgenesis techniques for functional genomics in Xenopus===

Transgenesis in Xenopus is made possible due to large embryos, a reliable fate map, ease of microinjection, ease of dissection/micromanipulation and existence of the neuroendocrine reflex of background adaptation as a model for activation/inact.

Recently, Hajime Ogino and Haruki Ochi from Nura Institute of Science and Technology in Japan focused on the genomic resources and principles of the transgenesis techniques in Xenopus, and discusses their applications to genome wide network analysis, with emphasis on the use of bioinformatics tools. This is will to understand the gene regulatory networks that control vertebrate development. [http://www.ingentaconnect.com/content/bsc/dgd/2009/00000051/00000004/art00001%3Bjsessionid=4ah96rms73gcu.alexandra]

Xenopus used to be a problem in earlier days when it came to transgenesis. Current methods involves isolated sperm nuclei from Xenopus testis that are microinjected into unfertilized eggs. The generated transgenic tadpoles contain 5-35 copies of the integrated plasmid that are expressed in all cells. If desired, expression of the transgene can be directed to the appropriate tissue and at the appropriate time by using specific promoters, mostly the Xenopus POMC gene promoter (isolated from a Xenopus genomic DNA library) to specifically direct expression of green fluorescent protein (GFP) at high levels to the intermediate pituitary cells, which can either be over expressed or inhibited.[http://molanphys.ruhosting.nl/transgenesis.htm]

[[File:Transgenesis.JPG]]

===Verification of messenger RNA===

While the existence and role of messenger RNA (mRNA) was known in bacteria, in the 1960s it was still debated whether it also existed in vertebrates. Taking haemoglobin mRNA from immature red blood cells and injecting it into a Xenopus oocyte, John Gurdon showed that the haemoglobin protein was indeed produced. Producing proteins in Xenopus oocytes has proved to be extremely useful in cell biology, in particular for the study of receptor proteins.[http://genome.wellcome.ac.uk/doc_WTD020799.html]

===Cell Cycle===

As they develop outside the mother, frog eggs are well stocked with the proteins needed to drive the development of the embryo. Studies of these processes has shed considerable light on the processes involved in cell division - termed the cell cycle. [http://genome.wellcome.ac.uk/doc_WTD020799.html]

===Limb development in Xenopus Laevis===

[[Image: Frog Limb development.jpg|thumb|right|Image details:Primary source:[http://images.google.com.au/imgres?imgurl=http://www.sciencedaily.com/images/2006/06/060616130718.jpg&imgrefurl=http://www.sciencedaily.com/releases/2006/06/060616130718.htm&usg=__xliPsPAvheUBME_kjv_q7auiFbo=&h=333&w=300&sz=11&hl=en&start=2&um=1&tbnid=y_ntJtmkRSK7WM:&tbnh=119&tbnw=107&prev=/images%3Fq%3DLimb%2Bdevelopment%2Bin%2BXenopus%2BLaevis%26ndsp%3D18%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

Donald D. Brown (2005),Department of Embryology, Carnegie Institution of Washington demonstrated factors related to limb development of Xenopus Laevis. Thyroid hormone (TH) is found to be required for limb development in this frog. Specific cell types in the growing limb were targeted for expression of a dominant negative form of the TH receptor by sperm-mediated transgenesis. Limb muscle development, the innervation of muscle from the spinal cord, and cartilage growth can be inhibited without affecting patterning of the limb or differentiation of other cell types. Remodeling of the skin occurs late in metamorphosis after the limb has formed. The coordination of these independent programs is affected in part by the control that TH exerts over DNA replication in all cell types of the limb. [http://www.pnas.org/content/102/35/12455.full]

----

== Glossary ==

[[Image: Frog species.jpg|thumb|left|Image details:Primary source:www.olympus.co.jp/.../080925/large/p02L.jpg].jpg]]

*'''Amphibian:'''

''Relating to or characteristic of animals of the class amphibia.Amphibians are found in the taxonomic class of amphibia, amphibians are capable of both occupying and successfully living in both land and aquatic communities.amphibian''

*'''Augmentation:'''

''Enlargement/Increase in cellular size.''

*'''Autolysis:'''

''breakdown of a part or whole cell or tissue by self-produced enzymes''

*'''Blastomeres:'''

''The undifferentiated cells formed by cleavage of the fertilised ovum. This includes cells in the cleavage, morula, and blastula stages of the embryo''

*'''Carnivorous:'''
''
Flesh-eating; subsisting on animals as food.''

*'''Cleavage:'''

''he repeated division of a fertilised ovum ''

* '''Cleft:'''

''an opening, fissure, or V-shaped indentation made by or as if by splitting''

*'''Chordate:'''

''Members of a diverse phylum of animals that, as embryos, possess a (1) notochord; (2) a dorsal, hollow nerve cord, (3) pharyngeal gill slits; and (4) a post-anal tail''

''The act or state of splitting or dividing of a cell, particularly during the telophase of (animal) cell division.''

*'''Cytoplasm:'''

''The cytoplasm (of both eukaryotes and prokaryotes) is where the functions for cell expansion, growth, metabolism, and replication are carried out''

* '''Epiboly:'''
''The expansion of one cell sheet over other cells, as takes place during gastrulation''

*'''Fertilization:'''

''A process in sexual reproduction that involves the union of male (sperm) and female (ovum) gametes (each with a single, haploid set of chromosomes) to produce a diploid zygote.''

*'''Gamete:'''
''A reproductive cell (male (sperm) or female (egg)) that has only half the usual number of chromosomes''

*'''Gametogenesis:'''

''process leading to the production of gametes. The development and maturation of sex cells through meiosis.Another name for meiosis where a diploid cell is divided into two haploid cells with half the chromosome content of the diploid parent cell.''

*'''Herbivorous:'''

''eating plants; of or pertaining to the herbivora.''

*'''Holoblastic:'''

''The complete division of an isolecithal or microlecithal egg into blastomeres''

*'''Invagination:'''

''One of the methods by which the various germinal layers of the ovum are differentiated.''

*'''Isoenzymes:'''

''Isozymes (also known as isoenzymes) are enzymes that differ in amino acid sequence but catalyze the same chemical reaction.''

*'''Mesentery:'''

'' membranous fold attaching various organs to the body wall.''

*'''Metamorphosis:'''

''A change in the form and often habits of an animal after the embryonic stage during normal development.''

*'''Neuroendocrine:'''

''Neuroendocrine [IPA nʊəroʊˈɛndəkrɪn] cells are cells that release a hormone into the circulating blood in response to a neural stimulus.''

*'''Organogenesis:'''

''The part of embryonic development where the body's main organs develop.''

*'''Peritoneum:'''

''The smooth serous membrane which lines the cavity of the abdomen, or the whole body cavity when there is no diaphragm, and, turning back, surrounds the viscera, forming a closed, or nearly closed, sac.''

*'''Perivitelline space:'''

''The perivitelline space is the space between the zona pellucida and the plasma membrane (sometimes called the vitelline membrane) in a fertilized ovum.''

*'''Polyploidy:'''

''Cells with three or more sets of chromosomes.''

*'''Pronucleus:'''

''the nucleus of the ovum or sperm after fertilization but before they fuse to form the nucleus of the zygote ''

*'''Protoplasm:'''

''The fluid living content of the cell that consists of two major divisions, the cytoplasm and the nucleoplasm (cell nucleus). It is composed mainly of nucleic acids, proteins, lipids, carbohydrates, and inorganic salts''

*'''Segmentation:'''

''division of some metazoan bodies (such as annelida and Arthropoda) into repeated parts, segments. Segmentation can be homomeric (more or less the same) or heteromeric(different from each other).''

*'''Terrestrial:'''

''Of or on the ground, of the habitat of a plant, on land as opposed to in water, or on the ground as opposed to on another plant.''

*'''Transgenesis:'''

''Transgenesis is the process of introducing an exogenous gene - called a transgene - into a living organism so that the organism will exhibit a new property and transmit that property to its offspring.''

*'''Yolk:'''

''nutritive material of an ovum stored for the nutrition of an embryo''

*'''Zygote:'''

''The cell from which an organism develops, that results from the fertilization of the egg by the sperm.''

''Primary Resource "Biology- Online Dictionary''[http://www.biology-online.org/dictionary/Main_Page]

== References - Frog Embryology: ==

[[Image:Frog Research.jpg|thumb|left|Image details:[http://images.google.com.au/imgres?imgurl=http://www.odt.co.nz/files/story/2008/09/university_of_otago_zoology_senior_lecturer_phil_b_3343259744.jpg&imgrefurl=http://www.odt.co.nz/on-campus/university-otago/21670/dunedin-frog-man-wins-zoo-award&usg=__JvJJU5QfOnIwY2bk4xo64UXuJRs=&h=600&w=404&sz=22&hl=en&start=14&um=1&tbnid=AbsP89yWcUiilM:&tbnh=135&tbnw=91&prev=/images%3Fq%3Dfrog%2Bresearch%26hl%3Den%26um%3D1].jpg]]

1. Savage, J. M. (2002). The Amphibians and Reptiles of Costa Rica. University of Chicago Press, Chicago [http://www.springerlink.com/content/vv015277w1746llw/]

2. Ford, L.S.; D.C. Cannatella (1993). "The major clades of frogs". Herpetological Monographs 7: 94–117 [http://digimorph.org/specimens/Xenopus_laevis/]

3. Tyler, M. J. (1994). Australian Frogs A Natural History. Reed Books [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.gracilenta.html]

4. Cogger, H.G.; R.G. Zweifel, and D. Kirschner (2004). Encyclopedia of Reptiles & Amphibians Second Edition. Fog City Press [http://en.wikipedia.org/wiki/Microhylidae]

5. Beltz, Ellin (2005). Frogs: Inside their Remarkable World. Firefly Books [http://unjobs.org/authors/ellin-beltz]

6. Tyler, M. J. (1994). Australian Frogs A Natural History. Reed Books [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

7. Moury JD, Hanken J (1995) Early cranial neural crest migration in the direct-developing frog, Eleutherodactylus coqui. Acta
Anatomica (Basel) 153, 243-253.

8.Raynaud A (1985) Development of limbs and embryonic limb reduction. In Biology of the Reptilia (ed. Gans C, Billett F), pp.
59-148. New York: John Wiley.[http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=9309]

9. Hanken J (1986) Developmental evidence for amphibian origins. In Evolutionary Biology (ed. Hecht MK, Wallace B, Prance GT), 20, pp. 389-417. New York: Plenum Press. [Hanken J (1986) Developmental evidence for amphibian origins. In Evolutionary Biology (ed. Hecht MK, Wallace B, Prance GT), 20, pp. 389-417. New York: Plenum Press.]

10. Elinson RP (1990) Direct development in frogs : wiping the recapitulationist slate clean. Seminars in Developmental Biology
1, 263-270.

11. Beebee, T. J. C. 1996. Ecology and Conservation of Amphibians. Chapman and Hall. London. [http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V5X-3SVHMKH-1X&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=1021245355&_rerunOrigin=google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=825868e10cd178d16a8a0e5ad14dc5ef]

12. Lehtinen, R. M. 2002. The use of screw pines (Pandanus spp.) by amphibians and reptiles in Madagascar. Herpetological Bulletin 2002:20–25.

13. Parris, K. M. and M. A. McCarthy. 1999. What influences the structure of frog assemblages at forest streams. Australian Journal of Ecology 24:495–502. CrossRef

14. Zug, G. R. 1993. Herpetology: An Introductory Biology of Amphibians and Reptiles. Academic Press. San Diego, CA.

15. Slack,J.M.W., Darlington,B.G., Heath,J.K. and Godsave,S.F. (1987)Mesoderm induction in early Xenopus embryos by heparin-binding growth factors. Nature, 326, 197-200.

16. Melton,D.A. (1990) Activins are expressed early in Xenopus embryogenesis and can induce axial mesoderm and anterior structures. Cell, 63, 485-493.

17. Harland,R.M. and Misher,L. (1988) Stability of RNA in developing Xenopus embryos and identification of a destabilizing sequence in TFIIIA RNA. Development, 102, 837-852.

18. Cunliffe,V. and Smith,J.C. (1992) Ectopic mesoderm formation in Xenopus embryos caused by widespread expression of a Brachyury homologue. Nature, 358, 427-430.

19. Kinoshita,K., Bessho,T. and Asashima,M. (1993) Competence prepattern in the animal hemisphere of the 8-cell-stage Xenopus embryo. Devel. Biol., 160, 276-284.

20. LaBonne,C., Burke,B. and Whitman,M. (1995) Role of MAP kinase in mesoderm induction and axial patterning in Xenopus development. Development, 121, 1475-1486.

21. Green,J.B.A., New,H.V. and Smith,J.C. (1992) Responses of embryonic Xenopus cells to activin and FGF are separated by multiple dose thresholds and correspond to distinct axes of the mesoderm. Cell, 71, 731-739.

22. Grainger R., Blumberg B., Harland R., Amemiya C., Importance of Xenopus Tropicalis to biomedical and biological research, Benaroya Research Institute, Virginia Mason Research Center [http://www.genome.gov/Pages/Research/Sequencing/BACLibrary/xenopusTropicalis.pdf ]

23. Gregory, T.R. (2005). Animal Genome Size Database. [http://www.genomesize.com]

24. U.S Fish and Wildlife Services, ABNORMALITY CLASSIFICATION SOP, [http://www.fws.gov/contaminants/Amphibian/pdfs/AbnormalitySOP_woutpics_Jan08.pdf ]

25. Donald D. Brown*, Liquan Cai*, Biswajit Das*, Nicholas Marsh-Armstrong‡, Alexander M. Schreiber*, and Rejeanne Juste*(2005), Thyroid hormone controls multiple independent programs required for limb development in Xenopus laevis metamorphosis [http://www.pnas.org/content/102/35/12455.full]

26. Ogino, Hajime; Ochi, Haruki, Resources and transgenesis techniques for functional genomics in Xenopus, Development Growth & Differentiation, Volume 51, Number 4, May 2009 , pp. 387-401(15) [http://www.ingentaconnect.com/content/bsc/dgd/2009/00000051/00000004/art00001%3Bjsessionid=4ah96rms73gcu.alexandra]

27. Giles Newton (2004) Why the frog? The Human Genome, [http://genome.wellcome.ac.uk/doc_WTD020799.html]

28. Xenbase, [http://www.xenbase.org/common/]

29. Donders Center for Neuroscience & Nijmegen Center for Molecular Life Sciences (NCMLS), Beyond the genome (Xenopus transgenesis for functional genomics),Faculty of Science, Radboud University [http://molanphys.ruhosting.nl/transgenesis.htm]

== External Links ==
[[Image:Frog links.jpg|thumb|left|Image details:[http://images.google.com.au/imgres?imgurl=http://2.bp.blogspot.com/_o93AaY0GzH4/SjY_ZYv0PII/AAAAAAAAAgk/skruNc2yN78/s400/computer%2Bfrog.jpg&imgrefurl=http://hellaheaven-ana.blogspot.com/2009/06/talking-frog-contemporary-fairy-tale.html&usg=__oxji1TGLV2Fi7xe0dnlmuYk8gDo=&h=288&w=288&sz=16&hl=en&start=2&um=1&tbnid=ywZd4zpdxC5plM:&tbnh=115&tbnw=115&prev=/images%3Fq%3Dfrog%2Bon%2Bcomputer%26hl%3Den%26um%3D1].jpg]]

1. Frog embryology [http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/F/FrogEmbryology.html Frog Embryology]

2. Frog cellular materials [http://www.xenbase.org/xenbase/original/cell/cell.html xenbase]

3. The zoology of frog species [http://worms.zoology.wisc.edu/frogs/mainmenu.html zoology frogs]

4. Frog cycle [http://www.bioethics.gov/images/sc_images/frog_dev.gif bioethics frog] Just a little cycle of FROG'S life cycle

5. Frog Embryology [http://embryology.med.unsw.edu.au/OtherEmb/Frog.htm UNSW Embryology]

6. Frog Research [http://apps.carleton.edu/campus/library/now/exhibits/wallcharts/frog/ carleton library exhibit]

{{Template:Projects09}}
[[Category:Frog]]

2009 Group Project 5

2009-10-14T22:42:20Z

Z3258567: /* Growth and Modification of Frog Species */

== The Embryology of Frogs ==

== The Frog ==

[[Image: Frog species .jpg|thumb|left|Image details: Wikipedia (2009) Frog species[http://en.wikipedia.org/wiki/Frog#Uses_in_agriculture_and_research].jpg]]

Frogs are scientifically identified by the structure of their long posterior limbs, a petite framework, webbed fingers and feet, budged eyes and the lack of a tail. The majority of frog species are extensively recognized as outstanding jumpers, due to their long, dominant legs, which are adaptations to progress jumping performance during activities. The Frog is one of the most frequently studied species in experimental embryology and most anatomical sciences. ''The Frog is a practically effective model for human embryological development given that the Frog:''

- Comprises of genes which can be effectively manipulated.

- Comprises of similar homogeny with humans species.

- Reproduces a large quantity of offspring in a short period of time.

- Are small species which can be simply sustained.

- Are not extremely luxurious and expensive.

== The History of the uses in agriculture and research ==

[[Image: Frog experiments .jpg|thumb|right|Image details: Scans of chemically cleared and dyed preserved deformed frogs and toads [http://www.sat.qc.ca/upload/residence/frog-04.jpg].jpg]]

There are numerous types of frog species that have been manipulated in many developmental experiments. The frog was traditionally used by countless of the early embryology investigators and presently there are several diverse molecular mechanisms regarding progression of the frog. Theses include:

'''1.''' Food source; frog legs are a delicacy and are eaten in European countries and in many parts of South American regions.

'''2.''' Frogs have the finest biochemical dissection of phenomena that take place in the egg and oocyte. Frogs are the evolutionarily closest to mammals, commonly used as a vertebrate model.

'''3.''' Frogs lay thousands of outsized eggs, from which cell extracts can be readily prepared that is capable of recapitulating most molecular phenomena in a test tube.

'''4.''' Frogs have been commonly used as a laboratory system for a very long period, and have an extensive history of producing crucial observations in countless fields of biology.

'''5.''' Frogs have a important historical connection to the study of epigenetics (John Gurdon-vertebrate cloning and reprogramming) which has been mostly performed on frog species.

'''6.''' Frogs also have very strong evidence of pattern formation and early development, as the embryos are large in size and experimentally manipulative.

'''7.''' Recent research into the biochemistry of chromatin and epigenetics has been performed with frog species and mammalian cultured cells.

'''8.''' The biggest weakness of the Frog model system is the difficulty of performing genetic experiments and analysis, as frogs are allotetraploid, meaning they take approximately a year to fully develop to sexual maturity, and the genome has not been completely sequenced. Nevertheless, biochemical manipulations of cell extracts, such as immunodepletions and application of heterologous DNAs and nuclei can avoid the need for genetic exploitation.

----

== Growth and development of the Frog ==

[[Image: Mature develop frog.jpg|thumb|Image details: Wikipedia (2009) Red Eyed Tree Frog Figure 1 Primary source:[http://en.wikipedia.org/wiki/File:Red-eyed_Tree_Frog_-_Litoria_chloris_edit1].jpg]]

* The frog is a well recognised species, abundant predominantly in ponds, swamps, though various species may also exist in damp or shady environments distant from moist habitats.

* Eggs of specific frogs are easily obtained and may be examined in from the beginning of fertilization onwards. The phases of embryonic development differs in various chordates, yet the typical phases are basically apparent in all frog species. The differences are associated principally to the amount of yolk particles present in an egg.

* The yolk particles offer nourishment of the developing embryo. The process of frog development will be discussed from the phases of gametogenesis to the adult stage.

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== The Egg ==
[[Image:Development of Poles in frog Fertilization.jpg|thumb|left|Development of Poles in Frog Fertilisation:J,Nassif 2009.jpg]]

- The embryology of a frog egg is a vast cell; its dimensions are approximately 1.4-1.6 million times larger than a typical aquatic species egg cell. Throughout the frog’s embryonic maturation period, the egg will be transformed into a tadpole encompassing millions of cells but still remains with its constant volume of genetic material, the vast prodction of cell have been illusttrated in the figure on the right revealing the production of eggs from female frogs. [http://en.wikipedia.org/wiki/Microhylidae]

- The early embryonic frog structure consists of three main segments the superior hemisphere known as the animal pole which is usually visible as a grey coloured area. The innermost layer appears to be between the outer two sections known as the gray crescent represented in black. Inferiorly, represents the vegetal pole typically lighter than the superior compartment illustrated in gold.

VIDEO RESOURCE: [http://www.youtube.com/watch?v=GO5YN_t1fqw&feature=related]

[[Image:Early Development of Frogs.jpg|thumb|left|Early Development of Frog:J,Nassif 2009.jpg]]

==History of frog embryology use ==

*'''1851''' - ''Henby Nelson''(MD): He identified a remarkable fact through the frog embryo. Henby observed the first cleavage of the yolk, in the egg of the frog. And cleaved structure corresponds in line of direction to the longitudinal axis of the body of the embryo of the frog species.

[[Image:Wilhelm Roux.jpg|thumb|right|Wilhelm Roux[http://images.google.com.au/imgres?imgurl=http://www.todayinsci.com/R/Roux_Wilhelm/RouxWilhelmThm.jpg&imgrefurl=http://www.todayinsci.com/6/6_09.htm&usg=__qRLTEMTHdZpAHxiNX12hWjcm9tA=&h=125&w=100&sz=4&hl=en&start=2&um=1&tbnid=LIKIwZTqCpk7MM:&tbnh=90&tbnw=72&prev=/images%3Fq%3DWilhelm%2BRoux%26gbv%3D2%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

*'''1888''' - ''Wilhelm Roux'': Wilhelm Roux attempted to solve the above observation by damaging one cell of a two-cell frog embryo with a hot needle. The cell stayed in place. However, it did not develop further. Its partner developed into a left or right half-embryo;

*'''1907''' - ''John Hopkins'' hospital: In order to identify the cellular source of neuronal fibres. Scientist placed small portions of frog embryo spinal cords in lymph on a microscope slide and was able to observe clear cut neuronal sprouting.

*'''1951''' - ''Robert Briggs'': Robert Briggs was able to clone a frog embryo by substituting the nucleus of an unfertilized frog egg cell with the nucleus of a frog embryo cell. This process is known as nuclear transplant, has formed the basis for all cloning.

*'''1952''' - ''Robert Briggs and T.J. King'': Robert Briggs and T.J. King used frog for test experiment. Because the size of the eggs in the frogs are enormous compared with those of mammals, which make them easier to manipulate.

*'''1976'''- Using the technique that had been successful in cloning frog embryos, the doctor transferred the nucleus of one cells into a donated egg cell. As an embryo began to develop, it was implanted into the uterus of a young woman.

*'''1997''' - ''Wilmut and Campbell'': Utilizing the cloning technique from frog embryo, Drs. Wilmut and Campbell tried the starvation technique on embryo cells to produce Megan and Morag, the world's first cloned sheep and, until now, the most famous sheep in history.

*'''2000''' - ''Tokyo University'': Scientists at Tokyo University have grown artificial eyeballs. Scientists formed them in tadpoles by using frog embryo cells.

*'''2001''' - ''Advanced Cell Technology'': Scientists from Advanced Cell Technology announced production of a human embryo clone. This is significant as its parthenogenesis has been artificially induced in frogs.

[[Image:John Gurdon .jpg|thumb|right|John Gurdon [http://images.google.com.au/imgres?imgurl=http://www.pnas.org/site/misc/images/gurdon.jpg&imgrefurl=http://www.pnas.org/site/misc/classics4.shtml&usg=__1p-GA1PdOYsxKL-cznMb3RHCm98=&h=526&w=400&sz=223&hl=en&start=1&um=1&tbnid=9k4lhuLssiWCAM:&tbnh=132&tbnw=100&prev=/images%3Fq%3DJohn%2BGurdon%26gbv%3D2%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

*'''2002''' - ''John Gurdon'': John Gurdon from Wellcome Cancer Research Institute in Cambridge experimented on cloned frog embryo.

== Gametogenesis ==

* The sexual reproduction occurs through the fusion of either mature reproductive cells or germ cells known as gametes, which include the sperm from the male frog and ova from female frog species so as to form a single cell, the fertilized zygote. The gametes are typically developed in parents of different sexes . [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

* Males gametes is a spermatozoon , the female frog gamete is an ovum. Each gamete is formed by a process, recognised as maturation or gametogenesis in gonads. The typical male frog gonads are testies in male, while the female gonads are ovaries. The synthesis of both gonads is associated with the process of fertilization. [http://en.wikipedia.org/wiki/Microhylidae]

* The zygote changes into a mature frog through the process of embryology and metamorphosis. Gametogenesis is a in progression which frog gametes are established from germ cells. Initial germ cells are called primordial germ cells, which can be recognised extremely early in the life of frog species.

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== The Egg & Fertilization ==

[[Image:Fertilized and Unfertilised Eggs.jpg|thumb|left|Fertilized and Unfertilized Eggs:J,Nassif 2009.jpg]]

[[Image:Egg Development.jpg|thumb|left|Egg Development:J,Nassif 2009.jpg]]

- This occurs once the sperm cell has inserted, following the insertion of the sperm cells meiosis II is completed, there is a 30 degree position change of the cytoplasm, gray crescent allows this change to be visible in some amphibians, the gray crescent is able what determines the expect ted outline of how the frog will form. The sperm cell joins with the nuclei of the egg which forms the diploid zygote nucleus. --Sando Rashed 10:09, 24 September 2009 (EST)

- The early phases in the development of the egg is visible, but must be studied in tadpoles throughout maturation. In embryonic tadpoles of about 10 millimetres in length, soon after the opening of the oral cavity, a pair of longitudinal ridge-like thickenings of peritoneum becomes apparent along the posterior surface of the body cavity situated near to the mesentery and along the inner boundaries of the kidneys. Genital ridges are established in all tadpoles of this age, sex is not distinct until a later period. The development of the egg is illustrated in the figure on the left revealing the structure of a developed egg and a mature of egg.

[[Image:Fertilisation life cyle.jpg|thumb|Fertilization of Life cycle:Derived from primary source:[http://en.wikipedia.org/wiki/Frog]]]

== Maturation of the Egg ==

- The eggs have currently accomplished their full size, and develop from the exterior of the ovaries like a small shot, but they still have to pass through the course of maturation before they are prepared to be fertilised. This progression of maturation relates to the nucleus almost completely.

- The nucleus component, containing the nuclear fluid that excludes through the nuclear membrane into the substance of the egg, a great segment of the nuclear reticulum vanishes and becomes degraded into separate globules known as nucleoli, but a extremely small division remains in the midpoint as a slender intricately thread recognised as the nuclear skets.
Relative to the egg getting discharged from the ovary, the follicles shatter allowing the eggs to fall into the abdominal cavity of the frog species, the egg then passes forwards, directly by the contraction of the muscular wall, somewhat by the movement of the cilia of the peritoneum, to the apex of the oviduct, which positioned at the anterior compartment of the body cavity opposite to the roots of the respiratory organs.

- The terminal part of the oviduct establishes a thin-walled pouch capable of great swelling, inside which the eggs gathers in large numbers. In conclusion, the eggs are migrated out through the cloaca into water which the albuminous investments of the eggs rapidly augment to form the gelatinous mass of the frogs spawn.

== Maturation phases ==

'''1. Nuclear skein''', moves from the midpoint of the egg to its outer surface, which it reaches opposite the midpoint of the black pole. The skein, subsequently an unevenly twisted thread, now presumes the specific arrangement of a nuclear spindle, for instance may be visible in the nucleus of an epithelial or additional cell instantly prior to division of the cell occurs.[http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

'''2. The first Polar Body,''' regarding the instance the egg is laid, but prior to its fertilistion, the egg develops a considerably flattened appearance at its upper or black pole, a definite sum of fluid being exuded among the egg and the vitelline membrane. The nuclear spindle currently separate into two identical segments, one of which remains with the egg, and the supplementary is extruded as the first polar body, a small ovoidal white globule, which is situated on the surface of the egg surrounding the exuded peri-vitellline fluid.

'''3. The Second Polar Body''', half of the nuclear spindle that stay behind then splits into two equivalent divisions, one of which remains inside the egg as the female pronucleus, whereas the other segment is extruded as the second polar body, a small white globule extremely related to the first polar body, and like this positioned in the perivitelline fluid on the superior portion of the egg.

'''4. Fertilisation of the egg''', includes the synthesis of the spermatozoon with to egg, specifically, synthesis of the nuclei of these two bodies. The spermatozoa, subsequent to being shed over the seed by the male, distribute vigorously by means of their extended tails, break through the gelatinous investment of the female eggs, bore their way through the vitelline membrane and so go through into the eggs themselves, which they penetrate relative to the superior or black hemispheres.
* Subsequently, an hour following the spermatozoon has entered; a progression may be visible projecting within from the exterior segement of the egg, with a liquid spot in the mid point. This liquid centre is the nucleus of the spermatozoon, and is said to be the male pronucleus, it break through beyond into the female egg, transporting the specialised pigment into it, so that it appears bounded by a pigmented capsule linked with the exterior of the egg by a pigmented stalk.

* By this instance, the second polar body has been established and extruded, and the female pronucleus is merely the only component of the primary egg nucleus still present. Both the male and female pronuceli, which are at initially distance separate to each other, merge and after having enlarged significantly in size then fuse mutually about two and half hours after fertilisation has originated to produce the segmentation nucleus.
* The segmentation nucleus is a huge sphere-shaped vesicle embedded in delicately granular protoplasm, and bounded by a distinct capsule of pigment, its arrangement by the synthesis of the male and female pronuclei completes the action of fertilisation. Specifically female pronucleus may be observe as an imperfect nucleus, and consequently result in the course of fertilisation. The nucleus of the spermatozoon or male pronucleus, replaces the component of the egg- nucleus which has been misplaced as the polar bodies.

'''5. Segmentation of the Egg''', the initial phase of growth consist in constant separation of the egg, whereby it becomes transformed from the unicellular state, which is everlasting only in the lowest species, to muliticelluar state charactertics of all higher species. To these early processes of growth the names segmentation is specified. Shorty subsequent to the competition of fertilisation and arrangement of the segmentation nucleus this later misplaces its sphere-shaped appearance and develops to be spindle-shaped, the yolk granules at the equivalent instance showing a tendency to develop into lines distributing outwards from the distal segment of the spindle.
* The nucleus now split into two halves, which shift away from one another, the yolk granules are likely to combined themselves around the two nuclei, and a slender vertical plate of delicately granular substance is left, dividing the egg.[http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

* Superiorly the eggs depression now becomes visible, initially as a small cavity and then develops as a groove, which almost immediately extends all round, and speedily deepening, splits the egg into two entirely separate halves along a plane equivalent with the vertical plane.

* Shorty after, the two nuclei soon separate again into two, and therefore a second cleft is created in the same state as before, its additionally in the vertical plane, however in a plane at 90 degrees to the initial one, and on its finishing point the egg comprises of four accurately similar segments, each containing a nucleus. The third cleft is horizontal in shape, but not equal, lying closer to the superior than the lower pole, it segregates each of the four cells into, an superior smaller and a inferior larger pole

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== Cleavage ==

[[Image: Frog Cleavage development.jpg|thumb|left|Cleavage Process details:[http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/F/FrogEmbryology.html].jpg]]

* The egg of the frog is scientifically identified as’ telolecithal’ meaning there is a outsized amount of yolk concentrated at a single pole, in contrast to the concentration of cytoplasm and the site of the nucleus. The cleavage phases are holoblastic, therefore the total and after the second cleavage they are asymmetrical .The initial cleavage stage appears about two and half to three hours after fertilization. It commences as a minor depression in close proximity to the centre of the animal hemisphere. It appears as if some interior force is pushing the surface the egg towards the centre. This small upturned fold steadily continues in the form of a channel until it surrounds the egg. This groove is shallow in the commencement, but develop into deeper eventually separating the fertilized egg into two halves recognised as the blastomeres. [The figure on the left symbolise the development and growth of the frog embryo during cleavage].

* Internally the separation is mitotic, consequently each daughter cell contains a nucleus resulting from the copulation nucleus of the fertilised egg. This cleavage is vertical, the two cells are indistinguishable in respect of cytoplasm, pigment and yolk. The subsequent cleavage appears about an hour after the first. The channel of this cleavage begins at the centre of the animal hemisphere, is at right angles to the first and is vertical. This divides the egg into four blastomeres. The fourth blastomere so produced are not qualitatively equal, since of these only two contain the material from the gray crescent. The cleavage begins about thirty minutes after the second is completed or four hours after fertilisation. the cleavage plane of the third furrow is horizontal and slightly above the equator. Thus the four upper cells are a little smaller than the four lower cells. The smaller blastomeres are called micromeres and the larger blastomeres are called macromeres. The fourth cleavages follow 20 minutes after the third and tend to be vertical. This is usually a double furrow.

* The cleavage rate is accelerated with each of the early divisions and since the blastomeres are of unequal size and have varying amounts of cytoplasm and yolk, synchronous cleavage is lost and there is an obvious overlapping of the division. The upper most cells divide more rapidly than the lowermost cells. From this point onwards perfect symmetry in cleavage and in blastomere is very rare, although the embryo developed perfectly. The fifth cleavage is also doubled, appearing first in the upper hemisphere and then in the lower.

* The cleavage thus far follows the rule that each cleavage plane comes in at right angles to the previous one. The subsequent divisions become so irregular that it is previous one. The subsequent division become so irregular that it is impossible to trace out any plan or procedure. The segmentation continues more rapidly in the pigmented regions, since at that place the protoplasm is most dense, whereas, yolk which is very abundant in the vegetal side delays cell division. The multicelluar embryo at this stage is called morula by some biologists.

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== Gastrulation ==

[[Image:FROG GASTRULATION .jpg|thumb|left|Frog Gastrulation Image details:[http://www.google.com.au/imgres?imgurl=http://bio1903.nicerweb.com/Locked/media/ch47/47_12FrogGastrulation.jpg&imgrefurl=http://bio1903.nicerweb.com/Locked/media/ch47/gastrulation-frog.html&h=540&w=480&sz=46&tbnid=N78sHjELreGGSM:&tbnh=132&tbnw=117&prev=/images%3Fq%3Dfrog%2B-%2Bgastrulation&hl=en&usg=__4VK9FYLft0W-4lBe6p5EtQAMiaI=&ei=qPy5SurtMJvE6wON8JmdAg&sa=X&oi=image_result&resnum=4&ct=image].jpg]]

''The phase of Blastulation is followed by the unique developmental progression of gastrulation. The process of frog gastrulation involves the following processes.''

'''1. Epiboly Phase'''

The pigmented cellular materials of blastula have the propensity to overgrow the yolk cells within the developing content. This course which is known as epiboly commences gradually in the final blastula and rapidly accelerates with advancing gastrulation development. The cellular matter within the animal pole reproduces and matures on all sides except in area surrounding the dorsal lip of the blastopore has been established.

'''2. Convergence'''

Scientists suggested that the unfolding was thought to result in spreading of the superficial cells over a substrate with suitable absorption properties. Consequently epiboly and convergence are an outcome to this spreading tendency, which is actually increased by a reduction in surface tension of the distributing cells.

'''3. Rotation'''

The epiboly phase is maintained until the region of the dorsal lip has migrated and is a to some extent greater than 90 degrees and the region of the white blastopore is reduced to small circular rings. This section will be positioned away from the developing vegetal pole. Laterally the complete developing gastrula has been rotated to a horizontal axis, allowing it to lie at right angles to the original median plane of the egg. Therefore, the course of rotation is such that the dorsal lip is practically pushed backwards in one direction as rapid or quicker than epiboly moves it forward in the other. The outcome will be that the blastopore produced at roughly the vegetal pole is posterior, and the dorsal and ventral lips are essentially dorsal and ventral. This in addition allows the eggs to form the antero-ventral side of the potential embryo whilst the area marked by the grey crescent is to develop the dorsal segment.

'''4. Invagination'''

Visible is a small fissure- like invagination which is apparent in the middle between the equator and the vegetal segment. The most superior or dorsal border of the cleft produce the dorsal lip of the blastopore. This imput move back and forth on the dorsal plane near the dorsal lip and migrates around the boundaries of the blastocoel in company with the extension of the lateral lips. This adapted invagination is maintained until the blastocoel cavity has been almost abolished; excluding the slender opening separating epiblasts from the hypoblast, the new segment formed is known as the archenteron cavity.

'''5. Involution'''

- Additional to previous course of action a distinct involution also occurs at the blastoporal borders. This is mainly dynamic at the median dorsal lip and gradually more less as it shifts across either side until it reaches the ventral lip where it constant.Throughout this progression, cells positioned beside the superior boundaries of the blastoporal lip migrate over the lip to the interior portion of the lip. These cells are remained within the embryo along the internal edge of the blastopore. This indicates the root of archenteron is composed of involuted cells and beyond this the external layer known as the ectoderm. The base and lateral sides are enclosed mainly of endodermal cellular material, which have been established from larger yolk cells, situated in the vegetal pole of the blastula.

- In the final phases of the gastrula development, the cells contributing to the floor of the archenteron, thin out significantly where they surround the blastocoel.
The hemispherical shaped dorsal lip of blastopore which become visible at the commencement of the gastruation stage carry on to augment, initially becoming semicircular, then transform into a horse shoe shaped and then finally forming into circular band. The band is the accomplished by the blastopore. Various yolk cells of vegetal pole present in the section are crowed into the blastoporal cavity where they form a gathering identified as a yolk plug. Blastopore rapidly reduces in size while the archenteron is still developing and becomes completely formed in the final stage; the yolk plug appears as only a small oval on the gastrula.

==Growth and Modification of Frog Species==

'''1. Changes in habits and habitats:'''

'''a)''' In frogs, metamorphosis is related with to the modifications and adaptations as a frog changes environmental habitats from an aquatic to a terrestrial mode. Metamorphosis has modified the adaption of frogs as this alteration it began during the aquatic adaptations in the surface of water to breathe air. Subsequently, it continues the terrestrial surroundings, therefore the frog species become abundant in vegetation area allowing the frog to transform in to amphibious species.

'''b)''' The transition during metamorphosis is linked with a change in food chain. The tadpoles being the embryonic origin of frogs are herbivorous, feeding on algae and green matter, which they collect by the adapted feature such as their teeth surrounding their mouths. Adult frogs, alternatively, are classified as carnivorous feeding on insects and worms. Occasionally, they also consume larger prey, for instance smaller frogs species and even little birds and rodents which they dominant and ingest.

[[Image:Development of frog from sperm to mature structure.jpg|thumb|left|Development of Frog from sperm to mature structure Image details:J,Nassif 2009.jpg]]

'''2. Changes in Morphology'''

These include the decrease or complete absence of specific organs or structures which are essential during development of early frog embryology, but not critical in the mature frog species. The significant alterations of this nature include the following developmental structures.

'''a)''' The long tail of the tadpole alongside the fin folds is absorbed again during metamorphosis and becomes absent at the final stage of the metamorphosis.

'''b) '''The developing gills are resorted, the gill clefts are congested and the branchial cavities start to become absent. The reabsorbtion of gills also takes place by autolysis.

'''c)''' The teeth of the perioral disc additionally the homey lining of the jaws are shed.

'''d)''' The lateral line sense organs within the skin of tadpoles vanish throughout metamorphosis.

'''e)''' The cloacal tube begins to condensed and reduced.

'''f)''' Various blood vessels, together with parts of the aortic arches, are reduced during mature development.

(The figure on the left represents the transformation from a tadpole to a developing structure.)[http://science.jrank.org/pages/2862/Frogs-Adult-morphology.html]

'''3. Progressive or constructive changes'''

This process comprises of the development of specific organs which mature into functional systems only during metamorphosis.

'''a)''' During development the limbs continue to augment in size and differentiation. The forelimbs, which in the tadpole mature under the opercular membrane, which then break through to the exterior. Simultaneously there is a increase in the length and strength of the hind limbs, joints develop in them and the toes become visible.

'''b)''' The middle ear becomes apparent in relation with the first pharyngeal pouch. The tympanic membrane matures. It is bounded by circular tympanic cartilage which allows the frog to retain air.

'''c)''' The visual organs bulge up on the dorsal surface of the head developing the nictitating membrane.

'''d)''' There is augmentation of the tongue and the formation of thevomerina teeth.

[[Image: Growth model.jpg|thumb|Growth Model Image details:J,Nassif2009:]]

'''4. Remodelling of some structures'''

Systematic organs which operate both in the early embryonic larva and the mature adult change their differentiation during metamorphosis so as to meet the requirements of the adult mode of life and due to the habitat adaptations. The figure on the right illustrates structures developing from specic germ cell layers.

'''a)''' The skin of the embryonic tadpole is lined with a double-layered epidermis. The number of layers of cells in the epidermis augments throughout metamorphosis. Superficial surface layers become cornified. Multicellular mucous and serous glands originate in the skin. The pigmentation of the skin continuously changes, new patterns and colour start to form.

'''b)''' There is a lengthening of the mouth gap as a result of rotation of the quadrate cartilage and the true jaws become functional.

'''c)''' The tongue rapidly progresses and becomes larger and more muscular.

'''d)''' The eyes become more specialised.

'''e)''' In early tadpoles, the GIT is extremely long and wound up into a spiral folds. The intestine become greatly lengthened in herbivorous species due to the vegetables food chain.[http://en.wikipedia.org/wiki/Frog]

'''5. Development of the reproductive system'''

(The figure below represents the reproductive and development cycle of a frog as it transform from egg to frog specie.)

In tadpoles, right after the mouth is being formed, two indentation like thickenings of peritoneum begin to appear near the body cavity (dorsal surface), which is nearest to the mesentery which is near the developing kidneys. These appear in all tadpoles.

These indentations appear here because of a change in the endothelial cells, everywhere else they are usually flat looking cells but they undergo a change and in this particular area become somewhat cuboidal/columnar.

Later on the indentations become more obvious due to the epithelial cells replicating numerously to form a thick layer. The posterior two thirds of the indentation for the female is the ovary and for the male it is the testis. The third that is left differentiates and becomes fat for the body.

[[Image: Mature frog life cyle.jpg|thumb|200px|left|Mature from life cycle Image details:Derived from primary source:http://www.scienceclarified.com/images/uesc_01_img0038.jpg]]

[[Image: Developing frog.jpg|thumb|Developing Frog Image details:
[[Image: Mature develop frog.jpg|thumb|Image details: Wikipedia (2009) TYPICAL FROG Primary source:[http://en.wikipedia.org/wiki/File:Red-eyed_Tree_Frog_-_Litoria_chloris_edit1.jpg]].jpg]]

===Delamination===

Delamination indicates a mass separating a group of cellular matter from other cellular groups. It has been illustrated that the division of notochord, mesoderm and endoderm tissues from each other to form distinct cellular masses is completed by the progression of delamination, subsequent to these materials moving to the inside throughout gastrulation. During the developing gastrula, the germ layers are all recognized. These distinct segments of the embryo develop from these germ tissue layers.

===Polarity and Rotation===

Throughout fertilisation to the beginning of gastrulation, the frog’s egg continues in the original location in relation to its polarity. Subsequent to gastrulation its polarity begins to differentiate. This progression is linked with migration of materials within the gastrula and can be responsible for the alterations of the centre of gravity.

===Closing of Blastopore===

Subsequent to the formation of the gastrula, the blastopore is visible as a tiny round circular filled cavity containing the yolk plug. As it continues to reduce in dimension, it represented as a pear-shaped outline through the mutual approach of its lateral lips. Through it final progression these fuse entirely to produce a longitudinal groove, the streak which continue dorsally and ventrally in a small aperture. The inferior aperture closes, resulting in a depression called the anal pit. The superior region remains open for some period and begins to as the neural groove is laid down.

===Post Gastrulation or Organogenesis===

Throughout the duration of pre-gastrulation, all tissues for different organs vanish from the surface of blastula and migrate inside to take their final arrangement in the embryo structure where organs are developed from their potential regions. Consequently organogenesis transfers an embryo into free larva structure.

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==Germ-layer origin of various body tissues==
[[Image: Development Models of Frog.jpg|thumb|right|Figure 13 Image details:Vertebrate Structure and Development.jpg]]

Ectoderm will give raise to structures such as skin, brain, spinal cord, neurons and sense receptors.
Mesoderm will give raise to structrues such as notochord, muscles, blood, bone and sex organs.
Endoderm will give raise to sturctures such as inner lining of gut, liver, pancreas, lungs and bladder, thyroid and parathyroid glands and thymus.

== Structures derived from Germ-layers of frog species ==

[[Image:Development of Frog Layers.jpg|thumb|left|Figure 14 Primary source[http://www.bio.miami.edu/~cmallery/150/physiol/sf19x11b.jpg]Image details:J,Nassif 2009.jpg]]

[[Image:Development of frog layers.jpg|thumb|left|Figure 15 Primary source [http://www.bio.miami.edu/~cmallery/150/physiol/sf19x11b.jpg]Image details:J,Nassif 2009.jpg]]

'''Ectoderm '''

''Establishes the epidermal segments and its derivatives, to the frog’s nervous system. The ectoderm also contributes to :''

1. The olfactory and auditory epithelium.

2. The retina and lens of the eye.

3. Sensory organs.

4. The epithelial lining of the oral cavity and the anus.

5. The pineal and pituitary body.

'''Mesoderm'''

''Mesoderm originates:''

1. Connective tissue.

2. Muscles, except the notochord.

3. Blood vessels.

4. Lymphatics.

5. The peritoneum and the urinary and reproductive system.

6. The dermis, parts of the eye excluding lens, cornea, and conjunctiva.

'''Endoderm'''

''From the endoderm arises:''

1. The epithelial lining to the gut and oesophagus, stomach, intestine, bile duct.

2. The hepatic cells of the liver, respiratory tract, larynx, trachea and lungs.

3. The lining of the urinary bladder, pancreas thyroid and thymus.

[The two figures reveal the development of structures deriving from the celluar components of the embryology of the frog].[Structures derived from Germ-layers of frog species ]

==Life cycle of a frog==

'''Fertilization-egg''':

The female lays eggs in the spring. A group of fertilized eggs is called spawn;

'''7-10 days''':

Fertilized egg feed on remaining yolk which is in its gut. Their gills, mouth and tail have poorly developed. Begin to swim and feed on algae;

'''10-30 days(4 weeks):'''

A layer of skin grows over gills. Teeth begin to appear. A coiled gut start to develop. This is aid in digestion;

'''30-60 days(6-9 weeks):'''

Legs being to grow and head is more distinct. Start to eat insects. Arms begin to grow;

'''60-80 days(12 weeks):'''

Resemble a frog. Still have remaining tail;

'''80-140 days(20 weeks):'''

Fully developed, spend most of time out of water. Majority of frog live between 4-15 years.

==Timeline of frog development==

Development of egg and embryo at temperature 18 degree celsius.

'''0 hours''' - fertilization of the egg

'''1 hours''' - formation of the gray crescent due to pigment migration

'''3.5 hours''' - early cleavage

'''4.5 hours''' - blastula stage(coeloblastula with eccentric blastocoel

'''26 hours''' - gastrulation

'''26 hours''' -'' early'' - crescent shaped dorsal lip

'''34 hours''' - ''middle''- semicircular blastoporal lip

'''42 hours''' - ''late'' - circular blastoporal lip

'''50 hours''' - neurulation

'''50 hours''' - ''early'' - medullary plate

'''62 hours''' -'' middle''- neural folds converging

'''67 hours''' - ''late'' - neural tube formed and ciliation of embryo

'''84 hours''' - tail bud stage(early organogeny)

'''96 hours''' - muscular response to tactile stimulation

'''118 hours''' - early heart beat, development of gill buds

'''140 hours''' - hatching and gill circulation

'''162 hours''' - mouth opens and cornea becomes transparent

'''192 hours''' - tail fin circulation established

'''216 hours''' - degeneration of external gills, formation of operculum, development of embryonic teeth

'''240 hours''' - opercular fold over brachial chamber except for spiracle and internal gills

'''255 hours''' - prolonged larval stage with refinement of organs

'''270 hours''' - development of hindlimbs, internal development of forelimbs in opercular cavity

'''275 hours''' - projection of forelimbs through operculum, left side first

'''280 hours''' - absorption of the tail and reduction in size of the gut

'''284 hours''' - metamorphosis complete, emergence from water as miniature, air breathing frog

==Stages of frog embryology==
--[[User:S8600021|Mark Hill]] 08:40, 9 October 2009 (EST) [[Talk:2009_Group_Project_5#Constructive_Criticism_of_Coordinator|see my comment on images]]

The rate of development of the egg and embryo will depend upon the temperature at which they are kept. The approximate schedule of development at 23 degree celsius is provided below.

{| border='1px'
|+ Table 1: Stages of frog development
!Stage !!Time since fertilisation (hours)!!Stage Characteristic !!Embryo characteristic !!Image of frog stage
|-
|1
|0.00-1.30
|fertilization of the egg, post fertilization
|animal hemisphere, gray crescent and vegetal hemisphere are present
|[[File:Stage01ventral.jpg|100px]]
|-
|2
|1.30-2.00
|splits into two cells
|appearance of first cleavage furrow
|[[File:Stage02ventral.jpg|100px]]
|-
|3
|2.00-2.15
|becomes four cells
|appearance of second cleavage furrow
|[[File:Stage03dorsolat.jpg|100px]]
|-
|4
|2.15-2.45
|becomes eight cells
|appearance of third cleavage furrow
|[[File:Stage04dorsolat.jpg|100px]]
|-
|5
|2.45-3.00
|becomes sixteen cells
|appearance of fourth cleavage furrow
|[[File:Stage05dorsal.jpg|100px]]
|-
|6
|3.00-3.30
|becomes thirty-two cells
|appearance of fifth cleavage furrow
|[[File:Stage06animal.jpg|100px]]
|-
|6.5
|3.30-4.00
|blastula stage
|Three dorsal folds become visible as a result of endoderm invagination. Pole cells no longer visible on surface
|[[File:Stage065dorsal.jpg|100px]]
|-
|7
|4.00-5.00
|Gastrulation stage
|two primary germ layers. epiblast and endoderm
|[[File:Stage07ventral.jpg|100px]]
|-
|8
|5.00-7.00
|neurulation
|medullary plate, neural folds and neural tube
|[[File:Stage08animal.jpg|100px]]
|-
|9
|7.00-9.00
|germ layer
|complete lip involution encircling yolk
|[[File:Stage09veg.jpg|100px]]
|-
|10
|9.00-11.00
|early gastrula
|two primary germ layers
|[[File:Stage10veg.jpg|100px]]
|-
|10.5
|11.00-11.45
|gastrula
|two germ layers
|[[File:Stage105vegb.jpg|100px]]
|-
|11
|11.45-12.30
|medulla plate
|Yolk sac protrudes dorsally, labium moves to midline on ventral side
|[[File:Stage11veg.jpg|100px]]
|-
|11.5
|12.30-13.15
|continuation of medulla plate
|start closing the plate
|[[File:Stage115veg.jpg|100px]]
|-
|12
|13.15-14.15
|early neurula
|thickened ectoderm give rise to CNS
|[[File:Stage12veg.jpg|100px]]
|-
|12.5
|14.15-14.45
|neural folds
|expansion of cavity
|[[File:Stage125postdors.jpg|100px]]
|-
|13
|14.45-16.15
|neural folds
|continue expanding cavity
|[[File:Stage13postdors.jpg|100px]]
|-
|14
|16.15-17.30
|neural folds
|continuation of cavity
|[[File:Stage14postdors.jpg|100px]]
|-
|15
|17.30-18.15
|tail bud stage
|early organogeny
|[[File:Stage15postdors.jpg|100px]]
|-
|16
|18.15-18.45
|tail bud stage
|posterior ventral view
|[[File:Stage16ant.jpg|100px]]
|-
|17
|18.45-19.45
|tail bud stage
|anterior view
|[[File:Stage17ant.jpg|100px]]
|-
|19
|20.45-21.45
|neural fold close complete
|dorsal view
|[[File:Stage19dorsal.jpg|100px]]
|-
|20
|21.45-22.30
|early tail bud
|anterior view
|[[File:Stage20dorsal.jpg|100px]]
|-
|21
|22.30-24.00
|termination of neural crest
|progress to next stage
|[[File:Stage21ant.jpg|100px]]
|-
|22
|24.00-24.45
|prolonged development
|elongation
|[[File:Stage22lat.jpg|100px]]
|-
|23
|24.45-26.15
|elongation of embryo
|later view
|[[File:Stage23lat.jpg|100px]]
|-
|24
|26.15-27.30
|continuation of elongation of embryo
|dorsal view
|[[File:Stage24latsmall.jpg|50px]]
|-
|25
|27.30-29.30
|organs development
|embryo elongates and develops dorsal thickening
|[[File:Stage25dorsal.jpg|50px]]
|-
|26
|29.30-31.15
|elongation
|dorsally forms neural and brain cavity
|[[File:Stage26lat.jpg|50px]]
|-
|27
|31.15-32.30
|elongation of embryo
|dorsal view
|[[File:Stage27lat.jpg|50px]]
|-
|28
|32.30-35.00
|further development
|lateral view
|[[File:Stage28lat.jpg|50px]]
|-
|29-30
|35.00-37.30
|tail bud
|growth
|[[File:Stage29-30lat.jpg|50px]]
|-
|31
|37.30-40.00
|prolonged development
|bud development
|[[File:Stage31lat.jpg|50px]]
|-
|32
|40.00-44.30
|early muscular development
|elongation
|[[File:Stage32lat.jpg|50px]]
|-
|33-34
|44.30-50.00
|muscular movement
|apparatus for locomotion
|[[File:Stage33-34lat.jpg|50px]]
|-
|35-36
|50.00-53.30
|muscular movement
|apparatus for locomotion
|[[File:Stage35-36lat.jpg|50px]]
|-
|37-38
|53.30-56.30
|heart beat
|develops apparatus
|[[File:Stage37-38lat.jpg|50px]]
|-
|39
|56.30-66.00
|mouth opens
|cornea transparent
|[[File:Stage39latsmall.jpg|50px]]
|-
|40
|66.00-76.00
|gill circulation
|hatching
|[[File:Stage40lat.jpg|50px]]
|-
|41
|76.00-80.00
|tail, fin circulation
|circulation
|[[File:Stage41lat.jpg|50px]]
|-
|42
|80.00-86.00
|internal gills, operculum
|opercular fold, teeth
|[[File:Stage42lat.jpg|50px]]
|-
|43
|86.00-98.00
|operculum complete
|operculum closed on right
|[[File:Stage43lat.jpg|50px]]
|-
|46
|98.00-106.00
|metamorphosis
|emergence from water as miniature, operculum complete|
|[[File:Stage46lat.jpg|50px]]
|-
|}

==Abnormalities of frog==

Abnormalities of frog could be caused by multiple factors. These include change in climate, predators, parasites, bacteria, fungi, viruses or pollution and contaminants such as pesticides, metals and fertilizer.[http://www.fws.gov/contaminants/documents/frogsrefup_septoct_2006.pdf]

The Abnormalities are further classified into different categories. These categories are:

===1. Infectious Diseases:===

'''Perkinsus Symptoms-''' caused by perkinsus-like protozoan organism. Symptoms include swollen viscera that leads to a bloated body and and infected swollen heart

'''Ichthyophonus symptoms-''' cause by parasitic genus, where symptoms include a swollen tail resorption site that matches the surrounding skin in color and translucency.

[[Image:Abnormalities of Frog species.jpg|thumb|left|Figure A Image details[waterwatchadelaide.net.au].jpg]]

===2. Surficial Abnormalities:===

Surficial abnormalities as the one that are visible on the surface of the skin. This includes abnormal pigmentation, , subcutaneous hemorrhaging, wounds due to trauma or from a predator
Edema is a fluid-filled swelling under skin whihc is also a surficial abnormality.

===3. Skeletal Abnormalities:===

This is further classified into three more categories:

'''a. Skeletal Malformations-'''

* Microcephaly (small head or blunt snout)
*Scoliosis (Curved spine in lateral direction)
*Shrunken Limb (Micromelia)
*Amelia (Completely missing limb with no stump)

'''b. Skeletal Abnormalities of Unclear Etiology-'''

This condition arises when a frog has ectromelia (missing limb), brachydactyly (missing digits) or other such condition with no visible trauma or external damage, then this will be classified as the Skeletal abnormality of unclear etiology.

'''c. Skeletal Injuries-'''

Any limb missing or broken due to trauma or other related reason which shows clear evidence of it is classified as skeletal injury

===4. Eye Abnormalities:===

Most common includes-

'''i. Anophthalmia:''' Skin covers the eye socket as there is no eye

'''ii. Abnormal Iris Coloration:''' Reduced pigment in either one eye or both resulting in two different colours of the iris at times

'''iii. Abnormal size or shape:''' Both eyes either deviating from each other or size of pupil or iris is different than the other eye

[http://www.fws.gov/contaminants/Amphibian/pdfs/AbnormalitySOP_woutpics_Jan08.pdf ]

==Genetics==

There are a wide variety of species that differ from each other when it comes to genetics and their functioning.

'''TAXONOMY:''' '''Phylum''' ''Chordata'' / '''Sub Phylum''' ''Vertebrata'' / '''Class''' ''Amphibia'' / '''Order''' ''Anura''

Their are more than two dozen different families of frogs, where suborders are:

'''1. ARCHAEBATRACHIA-''' most primitive frogs

'''2. MESOBATRACHIA-''' linked between the Archaebatrachia and Neobatrachia

'''3. NEOBATRACHIA-''' most modern frogs

{| border='4px'
|+ '''General Info:'''
! !!
|-
| '''Number of frogs' species'''
| 5280
|-
| '''Smallest frog genome size:'''
| 0.95pg, Ornate burrowing frog
|-
| '''Largest frog genome size:'''
| 13.40pg, Ornate horned frog
|-
| '''Mean of frogs' genome'''
| 4.68pg ± 0.13
|-
|}

[http://www.genomesize.com]

*Majority of frogs have only 22 to 26 chromosomes and polyploid is very common where they are almost bisexual.

*Polyploid Amphibians reduce their total cell number such that they acheive the same body size as diploids. One of the most unsual forms of polypoidy in amphibians is the water frog ''Rana esculenta'' from Europe and Western Asia.

* The species with larger genomes have more genes for e.g. the frog genus ''Xenopus'' includes 16 species, with genome sizes ranging from 3.5 x 10^9 bp to 1.6 x 10^10 bp. These differences have arisen by numerous events of polyploidization within the past 40 million years or so. The ancestral chromosome number for the genus seems to have been 18, but there are species with 36, 72 and 105 chromosomes [http://www.xenbase.org/common/]

{| border='4px'
|+ '''Difference within two families'''
! '''SPECIES''' !! ''X.LAEVIS'' !! ''X.TROPICALIS''
|-
| '''PLOIDY'''
| Allotetraploid
| Diploid
|-
| '''NO. OF CHROMOSOMES'''
| 36 chromosomes
| 20 chromosomes
|-
| '''GENOME SIZE'''
| 3.1 x 10^9 bp
| 1.7 x 10^9 bp
|-
| '''EGG SIZE'''
| 1-1.3 mm
| 0.7-0.8 mm
|-
| '''GENERATION TIME'''
| 1-2 years
| 4 months
|-
|}
[http://www.xenbase.org/common/]

===Genome Sequencing===

Since Frog has a huge family with many different species, only few main species that are used widely for the purposes of experiments have their genome sequenced.

''Xenopus tropicalis'' has one of the smallest genomes among amphibians and has the shortest generation time- four to six months and the only diploid genome among the 14 Xenopus species. This means it has no more than two copies of most genes, whereas the other species of Xenopus have four copies of most genes (pseudotetraploid). US Department of Energy's Joint Genome Institute (JGI) in Walnut Creek, California, initiated the X. tropicalis Genome Project, finding 1,700 million base pairs.
[http://www.genome.gov/Pages/Research/Sequencing/BACLibrary/xenopusTropicalis.pdf]

===Xenopus oocytes===

* The oocytes provide an important expression system for molecular biology.

* By injecting DNA or mRNA into the oocyte or developing embryo, scientists can study the protein products in a controlled system. This allows rapid functional expression of manipulated DNAs (or mRNA). This is particularly useful in electrophysiology, where the ease of recording from the oocyte makes expression of membrane channels attractive.

* One challenge of oocyte work is eliminating native proteins that might confound results, such as membrane channels native to the oocyte.

* Translation of proteins can be blocked or splicing of pre-mRNA can be modified by injection of Morpholino antisense oligos into the oocyte (for distribution throughout the embryo) or early embryo (for distribution only into daughter cells of the injected cell).
[http://www.staff.unibe.ch/sigel/xenopus.html]

===Xenopus Laevis===

* ''Xenopus Laevis'' is an important model organism in developmental biology. X. laevis is tetraploid and reaches sexual maturity in 1 to 2 years. What makes it important in developmental biology is its large and easily manipulable embryo.

* Extracts from the eggs of X. laevis frogs are also commonly used for biochemical studies of DNA replication and repair, as these extracts fully support DNA replication and other related processes in a cell-free environment which allows easier manipulation.

* The Human chorionic gonadotropin hormone (hCG) is present in the urine of the pregnant women in large quantities only. This hormone in the urine induces X.laevis oocyte production which formed the basis of first well-documented method of pregnancy testing X. laevis is also notable for its use as the first well-documented method of pregnancy testing when it was discovered. Today, commercially available HCG is injected into Xenopus males and females to induce mating behavior and breed these frogs in captivity at any time of the year.

===Gene cluster===

* The alpha and beta globin genes are closely linked in small cluster of frogs compared to human and chicken

* The similarity of architecture of two clusters found in X.laevis supports the tetraploid origin

* The two loci encoding the muscle specific creatine kinase isoenzymes and have large differences in developmental profile, therefore suggesting that duplicate loci that have not undergone silencing are not simply redundant copies but have acquired specialization.

* Contains twice number of genes for proteins i.e. haemoglobin and sarcomeric actin serum albumin compared with other species

----

==Current Embrology Research==

Currently, a number of fields have benefited from the development of frog embrology. These include cloning, verification of messenger RNA, and Cell cycle.

===Cloning===
[[Image:Robert Briggs.jpg|thumb|left|Figure 16 Image details:Robert Briggs.jpg]]

In 1952, Robert Briggs and Thomas J King cloned northern leopard frogs using a method of nuclear transfer. Briggs and King's experiment was similar to that envisioned - and piloted using salamanders - by Hans Spemann in his 1938 proposal for a 'fantastical experiment'. Later, John Gurdon extended this work and showed that nuclei from differentiated cells could support development, although less well than those from early embryos. [http://genome.wellcome.ac.uk/doc_WTD020799.html]

Lemaitre et a. (2005) from MRC Cancer Cell Unit, Cambridge, U.K. worked on experiments that demonstrated that importance of serial nuclear transplantation for the sucessful cloning of frogs. He demonstrated that exposure of somatic-cell nuclei (erythrocyte nuclei) and sperm nuclei to an extract of mitotic cell extract reorganizes the chromatin into shorter loops and allows replication at much shorter intervals along the DNA. This increases the efficiency of DNA replication in mammalian cell-free systems.

===Transgenesis techniques for functional genomics in Xenopus===

Transgenesis in Xenopus is made possible due to large embryos, a reliable fate map, ease of microinjection, ease of dissection/micromanipulation and existence of the neuroendocrine reflex of background adaptation as a model for activation/inact.

Recently, Hajime Ogino and Haruki Ochi from Nura Institute of Science and Technology in Japan focused on the genomic resources and principles of the transgenesis techniques in Xenopus, and discusses their applications to genome wide network analysis, with emphasis on the use of bioinformatics tools. This is will to understand the gene regulatory networks that control vertebrate development. [http://www.ingentaconnect.com/content/bsc/dgd/2009/00000051/00000004/art00001%3Bjsessionid=4ah96rms73gcu.alexandra]

Xenopus used to be a problem in earlier days when it came to transgenesis. Current methods involves isolated sperm nuclei from Xenopus testis that are microinjected into unfertilized eggs. The generated transgenic tadpoles contain 5-35 copies of the integrated plasmid that are expressed in all cells. If desired, expression of the transgene can be directed to the appropriate tissue and at the appropriate time by using specific promoters, mostly the Xenopus POMC gene promoter (isolated from a Xenopus genomic DNA library) to specifically direct expression of green fluorescent protein (GFP) at high levels to the intermediate pituitary cells, which can either be over expressed or inhibited.[http://molanphys.ruhosting.nl/transgenesis.htm]

[[File:Transgenesis.JPG]]

===Verification of messenger RNA===

While the existence and role of messenger RNA (mRNA) was known in bacteria, in the 1960s it was still debated whether it also existed in vertebrates. Taking haemoglobin mRNA from immature red blood cells and injecting it into a Xenopus oocyte, John Gurdon showed that the haemoglobin protein was indeed produced. Producing proteins in Xenopus oocytes has proved to be extremely useful in cell biology, in particular for the study of receptor proteins.[http://genome.wellcome.ac.uk/doc_WTD020799.html]

===Cell Cycle===

As they develop outside the mother, frog eggs are well stocked with the proteins needed to drive the development of the embryo. Studies of these processes has shed considerable light on the processes involved in cell division - termed the cell cycle. [http://genome.wellcome.ac.uk/doc_WTD020799.html]

===Limb development in Xenopus Laevis===

[[Image: Frog Limb development.jpg|thumb|right|Image details:Primary source:[http://images.google.com.au/imgres?imgurl=http://www.sciencedaily.com/images/2006/06/060616130718.jpg&imgrefurl=http://www.sciencedaily.com/releases/2006/06/060616130718.htm&usg=__xliPsPAvheUBME_kjv_q7auiFbo=&h=333&w=300&sz=11&hl=en&start=2&um=1&tbnid=y_ntJtmkRSK7WM:&tbnh=119&tbnw=107&prev=/images%3Fq%3DLimb%2Bdevelopment%2Bin%2BXenopus%2BLaevis%26ndsp%3D18%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

Donald D. Brown (2005),Department of Embryology, Carnegie Institution of Washington demonstrated factors related to limb development of Xenopus Laevis. Thyroid hormone (TH) is found to be required for limb development in this frog. Specific cell types in the growing limb were targeted for expression of a dominant negative form of the TH receptor by sperm-mediated transgenesis. Limb muscle development, the innervation of muscle from the spinal cord, and cartilage growth can be inhibited without affecting patterning of the limb or differentiation of other cell types. Remodeling of the skin occurs late in metamorphosis after the limb has formed. The coordination of these independent programs is affected in part by the control that TH exerts over DNA replication in all cell types of the limb. [http://www.pnas.org/content/102/35/12455.full]

----

== Glossary ==

[[Image: Frog species.jpg|thumb|left|Image details:Primary source:www.olympus.co.jp/.../080925/large/p02L.jpg].jpg]]

*'''Amphibian:'''

''Relating to or characteristic of animals of the class amphibia.Amphibians are found in the taxonomic class of amphibia, amphibians are capable of both occupying and successfully living in both land and aquatic communities.amphibian''

*'''Augmentation:'''

''Enlargement/Increase in cellular size.''

*'''Autolysis:'''

''breakdown of a part or whole cell or tissue by self-produced enzymes''

*'''Blastomeres:'''

''The undifferentiated cells formed by cleavage of the fertilised ovum. This includes cells in the cleavage, morula, and blastula stages of the embryo''

*'''Carnivorous:'''
''
Flesh-eating; subsisting on animals as food.''

*'''Cleavage:'''

''he repeated division of a fertilised ovum ''

* '''Cleft:'''

''an opening, fissure, or V-shaped indentation made by or as if by splitting''

*'''Chordate:'''

''Members of a diverse phylum of animals that, as embryos, possess a (1) notochord; (2) a dorsal, hollow nerve cord, (3) pharyngeal gill slits; and (4) a post-anal tail''

''The act or state of splitting or dividing of a cell, particularly during the telophase of (animal) cell division.''

*'''Cytoplasm:'''

''The cytoplasm (of both eukaryotes and prokaryotes) is where the functions for cell expansion, growth, metabolism, and replication are carried out''

* '''Epiboly:'''
''The expansion of one cell sheet over other cells, as takes place during gastrulation''

*'''Fertilization:'''

''A process in sexual reproduction that involves the union of male (sperm) and female (ovum) gametes (each with a single, haploid set of chromosomes) to produce a diploid zygote.''

*'''Gamete:'''
''A reproductive cell (male (sperm) or female (egg)) that has only half the usual number of chromosomes''

*'''Gametogenesis:'''

''process leading to the production of gametes. The development and maturation of sex cells through meiosis.Another name for meiosis where a diploid cell is divided into two haploid cells with half the chromosome content of the diploid parent cell.''

*'''Herbivorous:'''

''eating plants; of or pertaining to the herbivora.''

*'''Holoblastic:'''

''The complete division of an isolecithal or microlecithal egg into blastomeres''

*'''Invagination:'''

''One of the methods by which the various germinal layers of the ovum are differentiated.''

*'''Isoenzymes:'''

''Isozymes (also known as isoenzymes) are enzymes that differ in amino acid sequence but catalyze the same chemical reaction.''

*'''Mesentery:'''

'' membranous fold attaching various organs to the body wall.''

*'''Metamorphosis:'''

''A change in the form and often habits of an animal after the embryonic stage during normal development.''

*'''Neuroendocrine:'''

''Neuroendocrine [IPA nʊəroʊˈɛndəkrɪn] cells are cells that release a hormone into the circulating blood in response to a neural stimulus.''

*'''Organogenesis:'''

''The part of embryonic development where the body's main organs develop.''

*'''Peritoneum:'''

''The smooth serous membrane which lines the cavity of the abdomen, or the whole body cavity when there is no diaphragm, and, turning back, surrounds the viscera, forming a closed, or nearly closed, sac.''

*'''Perivitelline space:'''

''The perivitelline space is the space between the zona pellucida and the plasma membrane (sometimes called the vitelline membrane) in a fertilized ovum.''

*'''Polyploidy:'''

''Cells with three or more sets of chromosomes.''

*'''Pronucleus:'''

''the nucleus of the ovum or sperm after fertilization but before they fuse to form the nucleus of the zygote ''

*'''Protoplasm:'''

''The fluid living content of the cell that consists of two major divisions, the cytoplasm and the nucleoplasm (cell nucleus). It is composed mainly of nucleic acids, proteins, lipids, carbohydrates, and inorganic salts''

*'''Segmentation:'''

''division of some metazoan bodies (such as annelida and Arthropoda) into repeated parts, segments. Segmentation can be homomeric (more or less the same) or heteromeric(different from each other).''

*'''Terrestrial:'''

''Of or on the ground, of the habitat of a plant, on land as opposed to in water, or on the ground as opposed to on another plant.''

*'''Transgenesis:'''

''Transgenesis is the process of introducing an exogenous gene - called a transgene - into a living organism so that the organism will exhibit a new property and transmit that property to its offspring.''

*'''Yolk:'''

''nutritive material of an ovum stored for the nutrition of an embryo''

*'''Zygote:'''

''The cell from which an organism develops, that results from the fertilization of the egg by the sperm.''

''Primary Resource "Biology- Online Dictionary''[http://www.biology-online.org/dictionary/Main_Page]

== References - Frog Embryology: ==

[[Image:Frog Research.jpg|thumb|left|Image details:[http://images.google.com.au/imgres?imgurl=http://www.odt.co.nz/files/story/2008/09/university_of_otago_zoology_senior_lecturer_phil_b_3343259744.jpg&imgrefurl=http://www.odt.co.nz/on-campus/university-otago/21670/dunedin-frog-man-wins-zoo-award&usg=__JvJJU5QfOnIwY2bk4xo64UXuJRs=&h=600&w=404&sz=22&hl=en&start=14&um=1&tbnid=AbsP89yWcUiilM:&tbnh=135&tbnw=91&prev=/images%3Fq%3Dfrog%2Bresearch%26hl%3Den%26um%3D1].jpg]]

1. Savage, J. M. (2002). The Amphibians and Reptiles of Costa Rica. University of Chicago Press, Chicago [http://www.springerlink.com/content/vv015277w1746llw/]

2. Ford, L.S.; D.C. Cannatella (1993). "The major clades of frogs". Herpetological Monographs 7: 94–117 [http://digimorph.org/specimens/Xenopus_laevis/]

3. Tyler, M. J. (1994). Australian Frogs A Natural History. Reed Books [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.gracilenta.html]

4. Cogger, H.G.; R.G. Zweifel, and D. Kirschner (2004). Encyclopedia of Reptiles & Amphibians Second Edition. Fog City Press [http://en.wikipedia.org/wiki/Microhylidae]

5. Beltz, Ellin (2005). Frogs: Inside their Remarkable World. Firefly Books [http://unjobs.org/authors/ellin-beltz]

6. Tyler, M. J. (1994). Australian Frogs A Natural History. Reed Books [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

7. Moury JD, Hanken J (1995) Early cranial neural crest migration in the direct-developing frog, Eleutherodactylus coqui. Acta
Anatomica (Basel) 153, 243-253.

8.Raynaud A (1985) Development of limbs and embryonic limb reduction. In Biology of the Reptilia (ed. Gans C, Billett F), pp.
59-148. New York: John Wiley.[http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=9309]

9. Hanken J (1986) Developmental evidence for amphibian origins. In Evolutionary Biology (ed. Hecht MK, Wallace B, Prance GT), 20, pp. 389-417. New York: Plenum Press. [Hanken J (1986) Developmental evidence for amphibian origins. In Evolutionary Biology (ed. Hecht MK, Wallace B, Prance GT), 20, pp. 389-417. New York: Plenum Press.]

10. Elinson RP (1990) Direct development in frogs : wiping the recapitulationist slate clean. Seminars in Developmental Biology
1, 263-270.

11. Beebee, T. J. C. 1996. Ecology and Conservation of Amphibians. Chapman and Hall. London. [http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V5X-3SVHMKH-1X&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=1021245355&_rerunOrigin=google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=825868e10cd178d16a8a0e5ad14dc5ef]

12. Lehtinen, R. M. 2002. The use of screw pines (Pandanus spp.) by amphibians and reptiles in Madagascar. Herpetological Bulletin 2002:20–25.

13. Parris, K. M. and M. A. McCarthy. 1999. What influences the structure of frog assemblages at forest streams. Australian Journal of Ecology 24:495–502. CrossRef

14. Zug, G. R. 1993. Herpetology: An Introductory Biology of Amphibians and Reptiles. Academic Press. San Diego, CA.

15. Slack,J.M.W., Darlington,B.G., Heath,J.K. and Godsave,S.F. (1987)Mesoderm induction in early Xenopus embryos by heparin-binding growth factors. Nature, 326, 197-200.

16. Melton,D.A. (1990) Activins are expressed early in Xenopus embryogenesis and can induce axial mesoderm and anterior structures. Cell, 63, 485-493.

17. Harland,R.M. and Misher,L. (1988) Stability of RNA in developing Xenopus embryos and identification of a destabilizing sequence in TFIIIA RNA. Development, 102, 837-852.

18. Cunliffe,V. and Smith,J.C. (1992) Ectopic mesoderm formation in Xenopus embryos caused by widespread expression of a Brachyury homologue. Nature, 358, 427-430.

19. Kinoshita,K., Bessho,T. and Asashima,M. (1993) Competence prepattern in the animal hemisphere of the 8-cell-stage Xenopus embryo. Devel. Biol., 160, 276-284.

20. LaBonne,C., Burke,B. and Whitman,M. (1995) Role of MAP kinase in mesoderm induction and axial patterning in Xenopus development. Development, 121, 1475-1486.

21. Green,J.B.A., New,H.V. and Smith,J.C. (1992) Responses of embryonic Xenopus cells to activin and FGF are separated by multiple dose thresholds and correspond to distinct axes of the mesoderm. Cell, 71, 731-739.

22. Grainger R., Blumberg B., Harland R., Amemiya C., Importance of Xenopus Tropicalis to biomedical and biological research, Benaroya Research Institute, Virginia Mason Research Center [http://www.genome.gov/Pages/Research/Sequencing/BACLibrary/xenopusTropicalis.pdf ]

23. Gregory, T.R. (2005). Animal Genome Size Database. [http://www.genomesize.com]

24. U.S Fish and Wildlife Services, ABNORMALITY CLASSIFICATION SOP, [http://www.fws.gov/contaminants/Amphibian/pdfs/AbnormalitySOP_woutpics_Jan08.pdf ]

25. Donald D. Brown*, Liquan Cai*, Biswajit Das*, Nicholas Marsh-Armstrong‡, Alexander M. Schreiber*, and Rejeanne Juste*(2005), Thyroid hormone controls multiple independent programs required for limb development in Xenopus laevis metamorphosis [http://www.pnas.org/content/102/35/12455.full]

26. Ogino, Hajime; Ochi, Haruki, Resources and transgenesis techniques for functional genomics in Xenopus, Development Growth & Differentiation, Volume 51, Number 4, May 2009 , pp. 387-401(15) [http://www.ingentaconnect.com/content/bsc/dgd/2009/00000051/00000004/art00001%3Bjsessionid=4ah96rms73gcu.alexandra]

27. Giles Newton (2004) Why the frog? The Human Genome, [http://genome.wellcome.ac.uk/doc_WTD020799.html]

28. Xenbase, [http://www.xenbase.org/common/]

29. Donders Center for Neuroscience & Nijmegen Center for Molecular Life Sciences (NCMLS), Beyond the genome (Xenopus transgenesis for functional genomics),Faculty of Science, Radboud University [http://molanphys.ruhosting.nl/transgenesis.htm]

== External Links ==
[[Image:Frog links.jpg|thumb|left|Image details:[http://images.google.com.au/imgres?imgurl=http://2.bp.blogspot.com/_o93AaY0GzH4/SjY_ZYv0PII/AAAAAAAAAgk/skruNc2yN78/s400/computer%2Bfrog.jpg&imgrefurl=http://hellaheaven-ana.blogspot.com/2009/06/talking-frog-contemporary-fairy-tale.html&usg=__oxji1TGLV2Fi7xe0dnlmuYk8gDo=&h=288&w=288&sz=16&hl=en&start=2&um=1&tbnid=ywZd4zpdxC5plM:&tbnh=115&tbnw=115&prev=/images%3Fq%3Dfrog%2Bon%2Bcomputer%26hl%3Den%26um%3D1].jpg]]

1. Frog embryology [http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/F/FrogEmbryology.html Frog Embryology]

2. Frog cellular materials [http://www.xenbase.org/xenbase/original/cell/cell.html xenbase]

3. The zoology of frog species [http://worms.zoology.wisc.edu/frogs/mainmenu.html zoology frogs]

4. Frog cycle [http://www.bioethics.gov/images/sc_images/frog_dev.gif bioethics frog] Just a little cycle of FROG'S life cycle

5. Frog Embryology [http://embryology.med.unsw.edu.au/OtherEmb/Frog.htm UNSW Embryology]

6. Frog Research [http://apps.carleton.edu/campus/library/now/exhibits/wallcharts/frog/ carleton library exhibit]

{{Template:Projects09}}
[[Category:Frog]]

2009 Group Project 5

2009-10-14T22:41:09Z

Z3258567: /* Growth and Modification of Frog Species */

== The Embryology of Frogs ==

== The Frog ==

[[Image: Frog species .jpg|thumb|left|Image details: Wikipedia (2009) Frog species[http://en.wikipedia.org/wiki/Frog#Uses_in_agriculture_and_research].jpg]]

Frogs are scientifically identified by the structure of their long posterior limbs, a petite framework, webbed fingers and feet, budged eyes and the lack of a tail. The majority of frog species are extensively recognized as outstanding jumpers, due to their long, dominant legs, which are adaptations to progress jumping performance during activities. The Frog is one of the most frequently studied species in experimental embryology and most anatomical sciences. ''The Frog is a practically effective model for human embryological development given that the Frog:''

- Comprises of genes which can be effectively manipulated.

- Comprises of similar homogeny with humans species.

- Reproduces a large quantity of offspring in a short period of time.

- Are small species which can be simply sustained.

- Are not extremely luxurious and expensive.

== The History of the uses in agriculture and research ==

[[Image: Frog experiments .jpg|thumb|right|Image details: Scans of chemically cleared and dyed preserved deformed frogs and toads [http://www.sat.qc.ca/upload/residence/frog-04.jpg].jpg]]

There are numerous types of frog species that have been manipulated in many developmental experiments. The frog was traditionally used by countless of the early embryology investigators and presently there are several diverse molecular mechanisms regarding progression of the frog. Theses include:

'''1.''' Food source; frog legs are a delicacy and are eaten in European countries and in many parts of South American regions.

'''2.''' Frogs have the finest biochemical dissection of phenomena that take place in the egg and oocyte. Frogs are the evolutionarily closest to mammals, commonly used as a vertebrate model.

'''3.''' Frogs lay thousands of outsized eggs, from which cell extracts can be readily prepared that is capable of recapitulating most molecular phenomena in a test tube.

'''4.''' Frogs have been commonly used as a laboratory system for a very long period, and have an extensive history of producing crucial observations in countless fields of biology.

'''5.''' Frogs have a important historical connection to the study of epigenetics (John Gurdon-vertebrate cloning and reprogramming) which has been mostly performed on frog species.

'''6.''' Frogs also have very strong evidence of pattern formation and early development, as the embryos are large in size and experimentally manipulative.

'''7.''' Recent research into the biochemistry of chromatin and epigenetics has been performed with frog species and mammalian cultured cells.

'''8.''' The biggest weakness of the Frog model system is the difficulty of performing genetic experiments and analysis, as frogs are allotetraploid, meaning they take approximately a year to fully develop to sexual maturity, and the genome has not been completely sequenced. Nevertheless, biochemical manipulations of cell extracts, such as immunodepletions and application of heterologous DNAs and nuclei can avoid the need for genetic exploitation.

----

== Growth and development of the Frog ==

[[Image: Mature develop frog.jpg|thumb|Image details: Wikipedia (2009) Red Eyed Tree Frog Figure 1 Primary source:[http://en.wikipedia.org/wiki/File:Red-eyed_Tree_Frog_-_Litoria_chloris_edit1].jpg]]

* The frog is a well recognised species, abundant predominantly in ponds, swamps, though various species may also exist in damp or shady environments distant from moist habitats.

* Eggs of specific frogs are easily obtained and may be examined in from the beginning of fertilization onwards. The phases of embryonic development differs in various chordates, yet the typical phases are basically apparent in all frog species. The differences are associated principally to the amount of yolk particles present in an egg.

* The yolk particles offer nourishment of the developing embryo. The process of frog development will be discussed from the phases of gametogenesis to the adult stage.

----

== The Egg ==
[[Image:Development of Poles in frog Fertilization.jpg|thumb|left|Development of Poles in Frog Fertilisation:J,Nassif 2009.jpg]]

- The embryology of a frog egg is a vast cell; its dimensions are approximately 1.4-1.6 million times larger than a typical aquatic species egg cell. Throughout the frog’s embryonic maturation period, the egg will be transformed into a tadpole encompassing millions of cells but still remains with its constant volume of genetic material, the vast prodction of cell have been illusttrated in the figure on the right revealing the production of eggs from female frogs. [http://en.wikipedia.org/wiki/Microhylidae]

- The early embryonic frog structure consists of three main segments the superior hemisphere known as the animal pole which is usually visible as a grey coloured area. The innermost layer appears to be between the outer two sections known as the gray crescent represented in black. Inferiorly, represents the vegetal pole typically lighter than the superior compartment illustrated in gold.

VIDEO RESOURCE: [http://www.youtube.com/watch?v=GO5YN_t1fqw&feature=related]

[[Image:Early Development of Frogs.jpg|thumb|left|Early Development of Frog:J,Nassif 2009.jpg]]

==History of frog embryology use ==

*'''1851''' - ''Henby Nelson''(MD): He identified a remarkable fact through the frog embryo. Henby observed the first cleavage of the yolk, in the egg of the frog. And cleaved structure corresponds in line of direction to the longitudinal axis of the body of the embryo of the frog species.

[[Image:Wilhelm Roux.jpg|thumb|right|Wilhelm Roux[http://images.google.com.au/imgres?imgurl=http://www.todayinsci.com/R/Roux_Wilhelm/RouxWilhelmThm.jpg&imgrefurl=http://www.todayinsci.com/6/6_09.htm&usg=__qRLTEMTHdZpAHxiNX12hWjcm9tA=&h=125&w=100&sz=4&hl=en&start=2&um=1&tbnid=LIKIwZTqCpk7MM:&tbnh=90&tbnw=72&prev=/images%3Fq%3DWilhelm%2BRoux%26gbv%3D2%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

*'''1888''' - ''Wilhelm Roux'': Wilhelm Roux attempted to solve the above observation by damaging one cell of a two-cell frog embryo with a hot needle. The cell stayed in place. However, it did not develop further. Its partner developed into a left or right half-embryo;

*'''1907''' - ''John Hopkins'' hospital: In order to identify the cellular source of neuronal fibres. Scientist placed small portions of frog embryo spinal cords in lymph on a microscope slide and was able to observe clear cut neuronal sprouting.

*'''1951''' - ''Robert Briggs'': Robert Briggs was able to clone a frog embryo by substituting the nucleus of an unfertilized frog egg cell with the nucleus of a frog embryo cell. This process is known as nuclear transplant, has formed the basis for all cloning.

*'''1952''' - ''Robert Briggs and T.J. King'': Robert Briggs and T.J. King used frog for test experiment. Because the size of the eggs in the frogs are enormous compared with those of mammals, which make them easier to manipulate.

*'''1976'''- Using the technique that had been successful in cloning frog embryos, the doctor transferred the nucleus of one cells into a donated egg cell. As an embryo began to develop, it was implanted into the uterus of a young woman.

*'''1997''' - ''Wilmut and Campbell'': Utilizing the cloning technique from frog embryo, Drs. Wilmut and Campbell tried the starvation technique on embryo cells to produce Megan and Morag, the world's first cloned sheep and, until now, the most famous sheep in history.

*'''2000''' - ''Tokyo University'': Scientists at Tokyo University have grown artificial eyeballs. Scientists formed them in tadpoles by using frog embryo cells.

*'''2001''' - ''Advanced Cell Technology'': Scientists from Advanced Cell Technology announced production of a human embryo clone. This is significant as its parthenogenesis has been artificially induced in frogs.

[[Image:John Gurdon .jpg|thumb|right|John Gurdon [http://images.google.com.au/imgres?imgurl=http://www.pnas.org/site/misc/images/gurdon.jpg&imgrefurl=http://www.pnas.org/site/misc/classics4.shtml&usg=__1p-GA1PdOYsxKL-cznMb3RHCm98=&h=526&w=400&sz=223&hl=en&start=1&um=1&tbnid=9k4lhuLssiWCAM:&tbnh=132&tbnw=100&prev=/images%3Fq%3DJohn%2BGurdon%26gbv%3D2%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

*'''2002''' - ''John Gurdon'': John Gurdon from Wellcome Cancer Research Institute in Cambridge experimented on cloned frog embryo.

== Gametogenesis ==

* The sexual reproduction occurs through the fusion of either mature reproductive cells or germ cells known as gametes, which include the sperm from the male frog and ova from female frog species so as to form a single cell, the fertilized zygote. The gametes are typically developed in parents of different sexes . [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

* Males gametes is a spermatozoon , the female frog gamete is an ovum. Each gamete is formed by a process, recognised as maturation or gametogenesis in gonads. The typical male frog gonads are testies in male, while the female gonads are ovaries. The synthesis of both gonads is associated with the process of fertilization. [http://en.wikipedia.org/wiki/Microhylidae]

* The zygote changes into a mature frog through the process of embryology and metamorphosis. Gametogenesis is a in progression which frog gametes are established from germ cells. Initial germ cells are called primordial germ cells, which can be recognised extremely early in the life of frog species.

----

== The Egg & Fertilization ==

[[Image:Fertilized and Unfertilised Eggs.jpg|thumb|left|Fertilized and Unfertilized Eggs:J,Nassif 2009.jpg]]

[[Image:Egg Development.jpg|thumb|left|Egg Development:J,Nassif 2009.jpg]]

- This occurs once the sperm cell has inserted, following the insertion of the sperm cells meiosis II is completed, there is a 30 degree position change of the cytoplasm, gray crescent allows this change to be visible in some amphibians, the gray crescent is able what determines the expect ted outline of how the frog will form. The sperm cell joins with the nuclei of the egg which forms the diploid zygote nucleus. --Sando Rashed 10:09, 24 September 2009 (EST)

- The early phases in the development of the egg is visible, but must be studied in tadpoles throughout maturation. In embryonic tadpoles of about 10 millimetres in length, soon after the opening of the oral cavity, a pair of longitudinal ridge-like thickenings of peritoneum becomes apparent along the posterior surface of the body cavity situated near to the mesentery and along the inner boundaries of the kidneys. Genital ridges are established in all tadpoles of this age, sex is not distinct until a later period. The development of the egg is illustrated in the figure on the left revealing the structure of a developed egg and a mature of egg.

[[Image:Fertilisation life cyle.jpg|thumb|Fertilization of Life cycle:Derived from primary source:[http://en.wikipedia.org/wiki/Frog]]]

== Maturation of the Egg ==

- The eggs have currently accomplished their full size, and develop from the exterior of the ovaries like a small shot, but they still have to pass through the course of maturation before they are prepared to be fertilised. This progression of maturation relates to the nucleus almost completely.

- The nucleus component, containing the nuclear fluid that excludes through the nuclear membrane into the substance of the egg, a great segment of the nuclear reticulum vanishes and becomes degraded into separate globules known as nucleoli, but a extremely small division remains in the midpoint as a slender intricately thread recognised as the nuclear skets.
Relative to the egg getting discharged from the ovary, the follicles shatter allowing the eggs to fall into the abdominal cavity of the frog species, the egg then passes forwards, directly by the contraction of the muscular wall, somewhat by the movement of the cilia of the peritoneum, to the apex of the oviduct, which positioned at the anterior compartment of the body cavity opposite to the roots of the respiratory organs.

- The terminal part of the oviduct establishes a thin-walled pouch capable of great swelling, inside which the eggs gathers in large numbers. In conclusion, the eggs are migrated out through the cloaca into water which the albuminous investments of the eggs rapidly augment to form the gelatinous mass of the frogs spawn.

== Maturation phases ==

'''1. Nuclear skein''', moves from the midpoint of the egg to its outer surface, which it reaches opposite the midpoint of the black pole. The skein, subsequently an unevenly twisted thread, now presumes the specific arrangement of a nuclear spindle, for instance may be visible in the nucleus of an epithelial or additional cell instantly prior to division of the cell occurs.[http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

'''2. The first Polar Body,''' regarding the instance the egg is laid, but prior to its fertilistion, the egg develops a considerably flattened appearance at its upper or black pole, a definite sum of fluid being exuded among the egg and the vitelline membrane. The nuclear spindle currently separate into two identical segments, one of which remains with the egg, and the supplementary is extruded as the first polar body, a small ovoidal white globule, which is situated on the surface of the egg surrounding the exuded peri-vitellline fluid.

'''3. The Second Polar Body''', half of the nuclear spindle that stay behind then splits into two equivalent divisions, one of which remains inside the egg as the female pronucleus, whereas the other segment is extruded as the second polar body, a small white globule extremely related to the first polar body, and like this positioned in the perivitelline fluid on the superior portion of the egg.

'''4. Fertilisation of the egg''', includes the synthesis of the spermatozoon with to egg, specifically, synthesis of the nuclei of these two bodies. The spermatozoa, subsequent to being shed over the seed by the male, distribute vigorously by means of their extended tails, break through the gelatinous investment of the female eggs, bore their way through the vitelline membrane and so go through into the eggs themselves, which they penetrate relative to the superior or black hemispheres.
* Subsequently, an hour following the spermatozoon has entered; a progression may be visible projecting within from the exterior segement of the egg, with a liquid spot in the mid point. This liquid centre is the nucleus of the spermatozoon, and is said to be the male pronucleus, it break through beyond into the female egg, transporting the specialised pigment into it, so that it appears bounded by a pigmented capsule linked with the exterior of the egg by a pigmented stalk.

* By this instance, the second polar body has been established and extruded, and the female pronucleus is merely the only component of the primary egg nucleus still present. Both the male and female pronuceli, which are at initially distance separate to each other, merge and after having enlarged significantly in size then fuse mutually about two and half hours after fertilisation has originated to produce the segmentation nucleus.
* The segmentation nucleus is a huge sphere-shaped vesicle embedded in delicately granular protoplasm, and bounded by a distinct capsule of pigment, its arrangement by the synthesis of the male and female pronuclei completes the action of fertilisation. Specifically female pronucleus may be observe as an imperfect nucleus, and consequently result in the course of fertilisation. The nucleus of the spermatozoon or male pronucleus, replaces the component of the egg- nucleus which has been misplaced as the polar bodies.

'''5. Segmentation of the Egg''', the initial phase of growth consist in constant separation of the egg, whereby it becomes transformed from the unicellular state, which is everlasting only in the lowest species, to muliticelluar state charactertics of all higher species. To these early processes of growth the names segmentation is specified. Shorty subsequent to the competition of fertilisation and arrangement of the segmentation nucleus this later misplaces its sphere-shaped appearance and develops to be spindle-shaped, the yolk granules at the equivalent instance showing a tendency to develop into lines distributing outwards from the distal segment of the spindle.
* The nucleus now split into two halves, which shift away from one another, the yolk granules are likely to combined themselves around the two nuclei, and a slender vertical plate of delicately granular substance is left, dividing the egg.[http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

* Superiorly the eggs depression now becomes visible, initially as a small cavity and then develops as a groove, which almost immediately extends all round, and speedily deepening, splits the egg into two entirely separate halves along a plane equivalent with the vertical plane.

* Shorty after, the two nuclei soon separate again into two, and therefore a second cleft is created in the same state as before, its additionally in the vertical plane, however in a plane at 90 degrees to the initial one, and on its finishing point the egg comprises of four accurately similar segments, each containing a nucleus. The third cleft is horizontal in shape, but not equal, lying closer to the superior than the lower pole, it segregates each of the four cells into, an superior smaller and a inferior larger pole

----

== Cleavage ==

[[Image: Frog Cleavage development.jpg|thumb|left|Cleavage Process details:[http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/F/FrogEmbryology.html].jpg]]

* The egg of the frog is scientifically identified as’ telolecithal’ meaning there is a outsized amount of yolk concentrated at a single pole, in contrast to the concentration of cytoplasm and the site of the nucleus. The cleavage phases are holoblastic, therefore the total and after the second cleavage they are asymmetrical .The initial cleavage stage appears about two and half to three hours after fertilization. It commences as a minor depression in close proximity to the centre of the animal hemisphere. It appears as if some interior force is pushing the surface the egg towards the centre. This small upturned fold steadily continues in the form of a channel until it surrounds the egg. This groove is shallow in the commencement, but develop into deeper eventually separating the fertilized egg into two halves recognised as the blastomeres. [The figure on the left symbolise the development and growth of the frog embryo during cleavage].

* Internally the separation is mitotic, consequently each daughter cell contains a nucleus resulting from the copulation nucleus of the fertilised egg. This cleavage is vertical, the two cells are indistinguishable in respect of cytoplasm, pigment and yolk. The subsequent cleavage appears about an hour after the first. The channel of this cleavage begins at the centre of the animal hemisphere, is at right angles to the first and is vertical. This divides the egg into four blastomeres. The fourth blastomere so produced are not qualitatively equal, since of these only two contain the material from the gray crescent. The cleavage begins about thirty minutes after the second is completed or four hours after fertilisation. the cleavage plane of the third furrow is horizontal and slightly above the equator. Thus the four upper cells are a little smaller than the four lower cells. The smaller blastomeres are called micromeres and the larger blastomeres are called macromeres. The fourth cleavages follow 20 minutes after the third and tend to be vertical. This is usually a double furrow.

* The cleavage rate is accelerated with each of the early divisions and since the blastomeres are of unequal size and have varying amounts of cytoplasm and yolk, synchronous cleavage is lost and there is an obvious overlapping of the division. The upper most cells divide more rapidly than the lowermost cells. From this point onwards perfect symmetry in cleavage and in blastomere is very rare, although the embryo developed perfectly. The fifth cleavage is also doubled, appearing first in the upper hemisphere and then in the lower.

* The cleavage thus far follows the rule that each cleavage plane comes in at right angles to the previous one. The subsequent divisions become so irregular that it is previous one. The subsequent division become so irregular that it is impossible to trace out any plan or procedure. The segmentation continues more rapidly in the pigmented regions, since at that place the protoplasm is most dense, whereas, yolk which is very abundant in the vegetal side delays cell division. The multicelluar embryo at this stage is called morula by some biologists.

----

== Gastrulation ==

[[Image:FROG GASTRULATION .jpg|thumb|left|Frog Gastrulation Image details:[http://www.google.com.au/imgres?imgurl=http://bio1903.nicerweb.com/Locked/media/ch47/47_12FrogGastrulation.jpg&imgrefurl=http://bio1903.nicerweb.com/Locked/media/ch47/gastrulation-frog.html&h=540&w=480&sz=46&tbnid=N78sHjELreGGSM:&tbnh=132&tbnw=117&prev=/images%3Fq%3Dfrog%2B-%2Bgastrulation&hl=en&usg=__4VK9FYLft0W-4lBe6p5EtQAMiaI=&ei=qPy5SurtMJvE6wON8JmdAg&sa=X&oi=image_result&resnum=4&ct=image].jpg]]

''The phase of Blastulation is followed by the unique developmental progression of gastrulation. The process of frog gastrulation involves the following processes.''

'''1. Epiboly Phase'''

The pigmented cellular materials of blastula have the propensity to overgrow the yolk cells within the developing content. This course which is known as epiboly commences gradually in the final blastula and rapidly accelerates with advancing gastrulation development. The cellular matter within the animal pole reproduces and matures on all sides except in area surrounding the dorsal lip of the blastopore has been established.

'''2. Convergence'''

Scientists suggested that the unfolding was thought to result in spreading of the superficial cells over a substrate with suitable absorption properties. Consequently epiboly and convergence are an outcome to this spreading tendency, which is actually increased by a reduction in surface tension of the distributing cells.

'''3. Rotation'''

The epiboly phase is maintained until the region of the dorsal lip has migrated and is a to some extent greater than 90 degrees and the region of the white blastopore is reduced to small circular rings. This section will be positioned away from the developing vegetal pole. Laterally the complete developing gastrula has been rotated to a horizontal axis, allowing it to lie at right angles to the original median plane of the egg. Therefore, the course of rotation is such that the dorsal lip is practically pushed backwards in one direction as rapid or quicker than epiboly moves it forward in the other. The outcome will be that the blastopore produced at roughly the vegetal pole is posterior, and the dorsal and ventral lips are essentially dorsal and ventral. This in addition allows the eggs to form the antero-ventral side of the potential embryo whilst the area marked by the grey crescent is to develop the dorsal segment.

'''4. Invagination'''

Visible is a small fissure- like invagination which is apparent in the middle between the equator and the vegetal segment. The most superior or dorsal border of the cleft produce the dorsal lip of the blastopore. This imput move back and forth on the dorsal plane near the dorsal lip and migrates around the boundaries of the blastocoel in company with the extension of the lateral lips. This adapted invagination is maintained until the blastocoel cavity has been almost abolished; excluding the slender opening separating epiblasts from the hypoblast, the new segment formed is known as the archenteron cavity.

'''5. Involution'''

- Additional to previous course of action a distinct involution also occurs at the blastoporal borders. This is mainly dynamic at the median dorsal lip and gradually more less as it shifts across either side until it reaches the ventral lip where it constant.Throughout this progression, cells positioned beside the superior boundaries of the blastoporal lip migrate over the lip to the interior portion of the lip. These cells are remained within the embryo along the internal edge of the blastopore. This indicates the root of archenteron is composed of involuted cells and beyond this the external layer known as the ectoderm. The base and lateral sides are enclosed mainly of endodermal cellular material, which have been established from larger yolk cells, situated in the vegetal pole of the blastula.

- In the final phases of the gastrula development, the cells contributing to the floor of the archenteron, thin out significantly where they surround the blastocoel.
The hemispherical shaped dorsal lip of blastopore which become visible at the commencement of the gastruation stage carry on to augment, initially becoming semicircular, then transform into a horse shoe shaped and then finally forming into circular band. The band is the accomplished by the blastopore. Various yolk cells of vegetal pole present in the section are crowed into the blastoporal cavity where they form a gathering identified as a yolk plug. Blastopore rapidly reduces in size while the archenteron is still developing and becomes completely formed in the final stage; the yolk plug appears as only a small oval on the gastrula.

==Growth and Modification of Frog Species==

'''1. Changes in habits and habitats:'''

'''a)''' In frogs, metamorphosis is related with to the modifications and adaptations as a frog changes environmental habitats from an aquatic to a terrestrial mode. Metamorphosis has modified the adaption of frogs as this alteration it began during the aquatic adaptations in the surface of water to breathe air. Subsequently, it continues the terrestrial surroundings, therefore the frog species become abundant in vegetation area allowing the frog to transform in to amphibious species.

'''b)''' The transition during metamorphosis is linked with a change in food chain. The tadpoles being the embryonic origin of frogs are herbivorous, feeding on algae and green matter, which they collect by the adapted feature such as their teeth surrounding their mouths. Adult frogs, alternatively, are classified as carnivorous feeding on insects and worms. Occasionally, they also consume larger prey, for instance smaller frogs species and even little birds and rodents which they dominant and ingest.

[[Image:Development of frog from sperm to mature structure.jpg|thumb|left|Development of Frog from sperm to mature structure Image details:J,Nassif 2009.jpg]]

'''2. Changes in Morphology'''

These include the decrease or complete absence of specific organs or structures which are essential during development of early frog embryology, but not critical in the mature frog species. The significant alterations of this nature include the following developmental structures.

'''a)''' The long tail of the tadpole alongside the fin folds is absorbed again during metamorphosis and becomes absent at the final stage of the metamorphosis.

'''b) '''The developing gills are resorted, the gill clefts are congested and the branchial cavities start to become absent. The reabsorbtion of gills also takes place by autolysis.

'''c)''' The teeth of the perioral disc additionally the homey lining of the jaws are shed.

'''d)''' The lateral line sense organs within the skin of tadpoles vanish throughout metamorphosis.

'''e)''' The cloacal tube begins to condensed and reduced.

'''f)''' Various blood vessels, together with parts of the aortic arches, are reduced during mature development.

(The figure on the left represents the transformation from a tadpole to a developing structure.)[http://science.jrank.org/pages/2862/Frogs-Adult-morphology.html]

'''3. Progressive or constructive changes'''

This process comprises of the development of specific organs which mature into functional systems only during metamorphosis.

'''a)''' During development the limbs continue to augment in size and differentiation. The forelimbs, which in the tadpole mature under the opercular membrane, which then break through to the exterior. Simultaneously there is a increase in the length and strength of the hind limbs, joints develop in them and the toes become visible.

'''b)''' The middle ear becomes apparent in relation with the first pharyngeal pouch. The tympanic membrane matures. It is bounded by circular tympanic cartilage which allows the frog to retain air.

'''c)''' The visual organs bulge up on the dorsal surface of the head developing the nictitating membrane.

'''d)''' There is augmentation of the tongue and the formation of thevomerina teeth.

[[Image: Growth model.jpg|thumb|Figure 10 Image details:J,Nassif2009:]]

'''4. Remodelling of some structures'''

Systematic organs which operate both in the early embryonic larva and the mature adult change their differentiation during metamorphosis so as to meet the requirements of the adult mode of life and due to the habitat adaptations. The figure on the right illustrates structures developing from specic germ cell layers.

'''a)''' The skin of the embryonic tadpole is lined with a double-layered epidermis. The number of layers of cells in the epidermis augments throughout metamorphosis. Superficial surface layers become cornified. Multicellular mucous and serous glands originate in the skin. The pigmentation of the skin continuously changes, new patterns and colour start to form.

'''b)''' There is a lengthening of the mouth gap as a result of rotation of the quadrate cartilage and the true jaws become functional.

'''c)''' The tongue rapidly progresses and becomes larger and more muscular.

'''d)''' The eyes become more specialised.

'''e)''' In early tadpoles, the GIT is extremely long and wound up into a spiral folds. The intestine become greatly lengthened in herbivorous species due to the vegetables food chain.[http://en.wikipedia.org/wiki/Frog]

'''5. Development of the reproductive system'''

(The figure below represents the reproductive and development cycle of a frog as it transform from egg to frog specie.)

In tadpoles, right after the mouth is being formed, two indentation like thickenings of peritoneum begin to appear near the body cavity (dorsal surface), which is nearest to the mesentery which is near the developing kidneys. These appear in all tadpoles.

These indentations appear here because of a change in the endothelial cells, everywhere else they are usually flat looking cells but they undergo a change and in this particular area become somewhat cuboidal/columnar.

Later on the indentations become more obvious due to the epithelial cells replicating numerously to form a thick layer. The posterior two thirds of the indentation for the female is the ovary and for the male it is the testis. The third that is left differentiates and becomes fat for the body.

[[Image: Mature frog life cyle.jpg|thumb|200px|left|Mature from life cycle Image details:Derived from primary source:http://www.scienceclarified.com/images/uesc_01_img0038.jpg]]

[[Image: Developing frog.jpg|thumb|Developing Frog Image details:
[[Image: Mature develop frog.jpg|thumb|Image details: Wikipedia (2009) TYPICAL FROG Primary source:[http://en.wikipedia.org/wiki/File:Red-eyed_Tree_Frog_-_Litoria_chloris_edit1.jpg]].jpg]]

===Delamination===

Delamination indicates a mass separating a group of cellular matter from other cellular groups. It has been illustrated that the division of notochord, mesoderm and endoderm tissues from each other to form distinct cellular masses is completed by the progression of delamination, subsequent to these materials moving to the inside throughout gastrulation. During the developing gastrula, the germ layers are all recognized. These distinct segments of the embryo develop from these germ tissue layers.

===Polarity and Rotation===

Throughout fertilisation to the beginning of gastrulation, the frog’s egg continues in the original location in relation to its polarity. Subsequent to gastrulation its polarity begins to differentiate. This progression is linked with migration of materials within the gastrula and can be responsible for the alterations of the centre of gravity.

===Closing of Blastopore===

Subsequent to the formation of the gastrula, the blastopore is visible as a tiny round circular filled cavity containing the yolk plug. As it continues to reduce in dimension, it represented as a pear-shaped outline through the mutual approach of its lateral lips. Through it final progression these fuse entirely to produce a longitudinal groove, the streak which continue dorsally and ventrally in a small aperture. The inferior aperture closes, resulting in a depression called the anal pit. The superior region remains open for some period and begins to as the neural groove is laid down.

===Post Gastrulation or Organogenesis===

Throughout the duration of pre-gastrulation, all tissues for different organs vanish from the surface of blastula and migrate inside to take their final arrangement in the embryo structure where organs are developed from their potential regions. Consequently organogenesis transfers an embryo into free larva structure.

----

==Germ-layer origin of various body tissues==
[[Image: Development Models of Frog.jpg|thumb|right|Figure 13 Image details:Vertebrate Structure and Development.jpg]]

Ectoderm will give raise to structures such as skin, brain, spinal cord, neurons and sense receptors.
Mesoderm will give raise to structrues such as notochord, muscles, blood, bone and sex organs.
Endoderm will give raise to sturctures such as inner lining of gut, liver, pancreas, lungs and bladder, thyroid and parathyroid glands and thymus.

== Structures derived from Germ-layers of frog species ==

[[Image:Development of Frog Layers.jpg|thumb|left|Figure 14 Primary source[http://www.bio.miami.edu/~cmallery/150/physiol/sf19x11b.jpg]Image details:J,Nassif 2009.jpg]]

[[Image:Development of frog layers.jpg|thumb|left|Figure 15 Primary source [http://www.bio.miami.edu/~cmallery/150/physiol/sf19x11b.jpg]Image details:J,Nassif 2009.jpg]]

'''Ectoderm '''

''Establishes the epidermal segments and its derivatives, to the frog’s nervous system. The ectoderm also contributes to :''

1. The olfactory and auditory epithelium.

2. The retina and lens of the eye.

3. Sensory organs.

4. The epithelial lining of the oral cavity and the anus.

5. The pineal and pituitary body.

'''Mesoderm'''

''Mesoderm originates:''

1. Connective tissue.

2. Muscles, except the notochord.

3. Blood vessels.

4. Lymphatics.

5. The peritoneum and the urinary and reproductive system.

6. The dermis, parts of the eye excluding lens, cornea, and conjunctiva.

'''Endoderm'''

''From the endoderm arises:''

1. The epithelial lining to the gut and oesophagus, stomach, intestine, bile duct.

2. The hepatic cells of the liver, respiratory tract, larynx, trachea and lungs.

3. The lining of the urinary bladder, pancreas thyroid and thymus.

[The two figures reveal the development of structures deriving from the celluar components of the embryology of the frog].[Structures derived from Germ-layers of frog species ]

==Life cycle of a frog==

'''Fertilization-egg''':

The female lays eggs in the spring. A group of fertilized eggs is called spawn;

'''7-10 days''':

Fertilized egg feed on remaining yolk which is in its gut. Their gills, mouth and tail have poorly developed. Begin to swim and feed on algae;

'''10-30 days(4 weeks):'''

A layer of skin grows over gills. Teeth begin to appear. A coiled gut start to develop. This is aid in digestion;

'''30-60 days(6-9 weeks):'''

Legs being to grow and head is more distinct. Start to eat insects. Arms begin to grow;

'''60-80 days(12 weeks):'''

Resemble a frog. Still have remaining tail;

'''80-140 days(20 weeks):'''

Fully developed, spend most of time out of water. Majority of frog live between 4-15 years.

==Timeline of frog development==

Development of egg and embryo at temperature 18 degree celsius.

'''0 hours''' - fertilization of the egg

'''1 hours''' - formation of the gray crescent due to pigment migration

'''3.5 hours''' - early cleavage

'''4.5 hours''' - blastula stage(coeloblastula with eccentric blastocoel

'''26 hours''' - gastrulation

'''26 hours''' -'' early'' - crescent shaped dorsal lip

'''34 hours''' - ''middle''- semicircular blastoporal lip

'''42 hours''' - ''late'' - circular blastoporal lip

'''50 hours''' - neurulation

'''50 hours''' - ''early'' - medullary plate

'''62 hours''' -'' middle''- neural folds converging

'''67 hours''' - ''late'' - neural tube formed and ciliation of embryo

'''84 hours''' - tail bud stage(early organogeny)

'''96 hours''' - muscular response to tactile stimulation

'''118 hours''' - early heart beat, development of gill buds

'''140 hours''' - hatching and gill circulation

'''162 hours''' - mouth opens and cornea becomes transparent

'''192 hours''' - tail fin circulation established

'''216 hours''' - degeneration of external gills, formation of operculum, development of embryonic teeth

'''240 hours''' - opercular fold over brachial chamber except for spiracle and internal gills

'''255 hours''' - prolonged larval stage with refinement of organs

'''270 hours''' - development of hindlimbs, internal development of forelimbs in opercular cavity

'''275 hours''' - projection of forelimbs through operculum, left side first

'''280 hours''' - absorption of the tail and reduction in size of the gut

'''284 hours''' - metamorphosis complete, emergence from water as miniature, air breathing frog

==Stages of frog embryology==
--[[User:S8600021|Mark Hill]] 08:40, 9 October 2009 (EST) [[Talk:2009_Group_Project_5#Constructive_Criticism_of_Coordinator|see my comment on images]]

The rate of development of the egg and embryo will depend upon the temperature at which they are kept. The approximate schedule of development at 23 degree celsius is provided below.

{| border='1px'
|+ Table 1: Stages of frog development
!Stage !!Time since fertilisation (hours)!!Stage Characteristic !!Embryo characteristic !!Image of frog stage
|-
|1
|0.00-1.30
|fertilization of the egg, post fertilization
|animal hemisphere, gray crescent and vegetal hemisphere are present
|[[File:Stage01ventral.jpg|100px]]
|-
|2
|1.30-2.00
|splits into two cells
|appearance of first cleavage furrow
|[[File:Stage02ventral.jpg|100px]]
|-
|3
|2.00-2.15
|becomes four cells
|appearance of second cleavage furrow
|[[File:Stage03dorsolat.jpg|100px]]
|-
|4
|2.15-2.45
|becomes eight cells
|appearance of third cleavage furrow
|[[File:Stage04dorsolat.jpg|100px]]
|-
|5
|2.45-3.00
|becomes sixteen cells
|appearance of fourth cleavage furrow
|[[File:Stage05dorsal.jpg|100px]]
|-
|6
|3.00-3.30
|becomes thirty-two cells
|appearance of fifth cleavage furrow
|[[File:Stage06animal.jpg|100px]]
|-
|6.5
|3.30-4.00
|blastula stage
|Three dorsal folds become visible as a result of endoderm invagination. Pole cells no longer visible on surface
|[[File:Stage065dorsal.jpg|100px]]
|-
|7
|4.00-5.00
|Gastrulation stage
|two primary germ layers. epiblast and endoderm
|[[File:Stage07ventral.jpg|100px]]
|-
|8
|5.00-7.00
|neurulation
|medullary plate, neural folds and neural tube
|[[File:Stage08animal.jpg|100px]]
|-
|9
|7.00-9.00
|germ layer
|complete lip involution encircling yolk
|[[File:Stage09veg.jpg|100px]]
|-
|10
|9.00-11.00
|early gastrula
|two primary germ layers
|[[File:Stage10veg.jpg|100px]]
|-
|10.5
|11.00-11.45
|gastrula
|two germ layers
|[[File:Stage105vegb.jpg|100px]]
|-
|11
|11.45-12.30
|medulla plate
|Yolk sac protrudes dorsally, labium moves to midline on ventral side
|[[File:Stage11veg.jpg|100px]]
|-
|11.5
|12.30-13.15
|continuation of medulla plate
|start closing the plate
|[[File:Stage115veg.jpg|100px]]
|-
|12
|13.15-14.15
|early neurula
|thickened ectoderm give rise to CNS
|[[File:Stage12veg.jpg|100px]]
|-
|12.5
|14.15-14.45
|neural folds
|expansion of cavity
|[[File:Stage125postdors.jpg|100px]]
|-
|13
|14.45-16.15
|neural folds
|continue expanding cavity
|[[File:Stage13postdors.jpg|100px]]
|-
|14
|16.15-17.30
|neural folds
|continuation of cavity
|[[File:Stage14postdors.jpg|100px]]
|-
|15
|17.30-18.15
|tail bud stage
|early organogeny
|[[File:Stage15postdors.jpg|100px]]
|-
|16
|18.15-18.45
|tail bud stage
|posterior ventral view
|[[File:Stage16ant.jpg|100px]]
|-
|17
|18.45-19.45
|tail bud stage
|anterior view
|[[File:Stage17ant.jpg|100px]]
|-
|19
|20.45-21.45
|neural fold close complete
|dorsal view
|[[File:Stage19dorsal.jpg|100px]]
|-
|20
|21.45-22.30
|early tail bud
|anterior view
|[[File:Stage20dorsal.jpg|100px]]
|-
|21
|22.30-24.00
|termination of neural crest
|progress to next stage
|[[File:Stage21ant.jpg|100px]]
|-
|22
|24.00-24.45
|prolonged development
|elongation
|[[File:Stage22lat.jpg|100px]]
|-
|23
|24.45-26.15
|elongation of embryo
|later view
|[[File:Stage23lat.jpg|100px]]
|-
|24
|26.15-27.30
|continuation of elongation of embryo
|dorsal view
|[[File:Stage24latsmall.jpg|50px]]
|-
|25
|27.30-29.30
|organs development
|embryo elongates and develops dorsal thickening
|[[File:Stage25dorsal.jpg|50px]]
|-
|26
|29.30-31.15
|elongation
|dorsally forms neural and brain cavity
|[[File:Stage26lat.jpg|50px]]
|-
|27
|31.15-32.30
|elongation of embryo
|dorsal view
|[[File:Stage27lat.jpg|50px]]
|-
|28
|32.30-35.00
|further development
|lateral view
|[[File:Stage28lat.jpg|50px]]
|-
|29-30
|35.00-37.30
|tail bud
|growth
|[[File:Stage29-30lat.jpg|50px]]
|-
|31
|37.30-40.00
|prolonged development
|bud development
|[[File:Stage31lat.jpg|50px]]
|-
|32
|40.00-44.30
|early muscular development
|elongation
|[[File:Stage32lat.jpg|50px]]
|-
|33-34
|44.30-50.00
|muscular movement
|apparatus for locomotion
|[[File:Stage33-34lat.jpg|50px]]
|-
|35-36
|50.00-53.30
|muscular movement
|apparatus for locomotion
|[[File:Stage35-36lat.jpg|50px]]
|-
|37-38
|53.30-56.30
|heart beat
|develops apparatus
|[[File:Stage37-38lat.jpg|50px]]
|-
|39
|56.30-66.00
|mouth opens
|cornea transparent
|[[File:Stage39latsmall.jpg|50px]]
|-
|40
|66.00-76.00
|gill circulation
|hatching
|[[File:Stage40lat.jpg|50px]]
|-
|41
|76.00-80.00
|tail, fin circulation
|circulation
|[[File:Stage41lat.jpg|50px]]
|-
|42
|80.00-86.00
|internal gills, operculum
|opercular fold, teeth
|[[File:Stage42lat.jpg|50px]]
|-
|43
|86.00-98.00
|operculum complete
|operculum closed on right
|[[File:Stage43lat.jpg|50px]]
|-
|46
|98.00-106.00
|metamorphosis
|emergence from water as miniature, operculum complete|
|[[File:Stage46lat.jpg|50px]]
|-
|}

==Abnormalities of frog==

Abnormalities of frog could be caused by multiple factors. These include change in climate, predators, parasites, bacteria, fungi, viruses or pollution and contaminants such as pesticides, metals and fertilizer.[http://www.fws.gov/contaminants/documents/frogsrefup_septoct_2006.pdf]

The Abnormalities are further classified into different categories. These categories are:

===1. Infectious Diseases:===

'''Perkinsus Symptoms-''' caused by perkinsus-like protozoan organism. Symptoms include swollen viscera that leads to a bloated body and and infected swollen heart

'''Ichthyophonus symptoms-''' cause by parasitic genus, where symptoms include a swollen tail resorption site that matches the surrounding skin in color and translucency.

[[Image:Abnormalities of Frog species.jpg|thumb|left|Figure A Image details[waterwatchadelaide.net.au].jpg]]

===2. Surficial Abnormalities:===

Surficial abnormalities as the one that are visible on the surface of the skin. This includes abnormal pigmentation, , subcutaneous hemorrhaging, wounds due to trauma or from a predator
Edema is a fluid-filled swelling under skin whihc is also a surficial abnormality.

===3. Skeletal Abnormalities:===

This is further classified into three more categories:

'''a. Skeletal Malformations-'''

* Microcephaly (small head or blunt snout)
*Scoliosis (Curved spine in lateral direction)
*Shrunken Limb (Micromelia)
*Amelia (Completely missing limb with no stump)

'''b. Skeletal Abnormalities of Unclear Etiology-'''

This condition arises when a frog has ectromelia (missing limb), brachydactyly (missing digits) or other such condition with no visible trauma or external damage, then this will be classified as the Skeletal abnormality of unclear etiology.

'''c. Skeletal Injuries-'''

Any limb missing or broken due to trauma or other related reason which shows clear evidence of it is classified as skeletal injury

===4. Eye Abnormalities:===

Most common includes-

'''i. Anophthalmia:''' Skin covers the eye socket as there is no eye

'''ii. Abnormal Iris Coloration:''' Reduced pigment in either one eye or both resulting in two different colours of the iris at times

'''iii. Abnormal size or shape:''' Both eyes either deviating from each other or size of pupil or iris is different than the other eye

[http://www.fws.gov/contaminants/Amphibian/pdfs/AbnormalitySOP_woutpics_Jan08.pdf ]

==Genetics==

There are a wide variety of species that differ from each other when it comes to genetics and their functioning.

'''TAXONOMY:''' '''Phylum''' ''Chordata'' / '''Sub Phylum''' ''Vertebrata'' / '''Class''' ''Amphibia'' / '''Order''' ''Anura''

Their are more than two dozen different families of frogs, where suborders are:

'''1. ARCHAEBATRACHIA-''' most primitive frogs

'''2. MESOBATRACHIA-''' linked between the Archaebatrachia and Neobatrachia

'''3. NEOBATRACHIA-''' most modern frogs

{| border='4px'
|+ '''General Info:'''
! !!
|-
| '''Number of frogs' species'''
| 5280
|-
| '''Smallest frog genome size:'''
| 0.95pg, Ornate burrowing frog
|-
| '''Largest frog genome size:'''
| 13.40pg, Ornate horned frog
|-
| '''Mean of frogs' genome'''
| 4.68pg ± 0.13
|-
|}

[http://www.genomesize.com]

*Majority of frogs have only 22 to 26 chromosomes and polyploid is very common where they are almost bisexual.

*Polyploid Amphibians reduce their total cell number such that they acheive the same body size as diploids. One of the most unsual forms of polypoidy in amphibians is the water frog ''Rana esculenta'' from Europe and Western Asia.

* The species with larger genomes have more genes for e.g. the frog genus ''Xenopus'' includes 16 species, with genome sizes ranging from 3.5 x 10^9 bp to 1.6 x 10^10 bp. These differences have arisen by numerous events of polyploidization within the past 40 million years or so. The ancestral chromosome number for the genus seems to have been 18, but there are species with 36, 72 and 105 chromosomes [http://www.xenbase.org/common/]

{| border='4px'
|+ '''Difference within two families'''
! '''SPECIES''' !! ''X.LAEVIS'' !! ''X.TROPICALIS''
|-
| '''PLOIDY'''
| Allotetraploid
| Diploid
|-
| '''NO. OF CHROMOSOMES'''
| 36 chromosomes
| 20 chromosomes
|-
| '''GENOME SIZE'''
| 3.1 x 10^9 bp
| 1.7 x 10^9 bp
|-
| '''EGG SIZE'''
| 1-1.3 mm
| 0.7-0.8 mm
|-
| '''GENERATION TIME'''
| 1-2 years
| 4 months
|-
|}
[http://www.xenbase.org/common/]

===Genome Sequencing===

Since Frog has a huge family with many different species, only few main species that are used widely for the purposes of experiments have their genome sequenced.

''Xenopus tropicalis'' has one of the smallest genomes among amphibians and has the shortest generation time- four to six months and the only diploid genome among the 14 Xenopus species. This means it has no more than two copies of most genes, whereas the other species of Xenopus have four copies of most genes (pseudotetraploid). US Department of Energy's Joint Genome Institute (JGI) in Walnut Creek, California, initiated the X. tropicalis Genome Project, finding 1,700 million base pairs.
[http://www.genome.gov/Pages/Research/Sequencing/BACLibrary/xenopusTropicalis.pdf]

===Xenopus oocytes===

* The oocytes provide an important expression system for molecular biology.

* By injecting DNA or mRNA into the oocyte or developing embryo, scientists can study the protein products in a controlled system. This allows rapid functional expression of manipulated DNAs (or mRNA). This is particularly useful in electrophysiology, where the ease of recording from the oocyte makes expression of membrane channels attractive.

* One challenge of oocyte work is eliminating native proteins that might confound results, such as membrane channels native to the oocyte.

* Translation of proteins can be blocked or splicing of pre-mRNA can be modified by injection of Morpholino antisense oligos into the oocyte (for distribution throughout the embryo) or early embryo (for distribution only into daughter cells of the injected cell).
[http://www.staff.unibe.ch/sigel/xenopus.html]

===Xenopus Laevis===

* ''Xenopus Laevis'' is an important model organism in developmental biology. X. laevis is tetraploid and reaches sexual maturity in 1 to 2 years. What makes it important in developmental biology is its large and easily manipulable embryo.

* Extracts from the eggs of X. laevis frogs are also commonly used for biochemical studies of DNA replication and repair, as these extracts fully support DNA replication and other related processes in a cell-free environment which allows easier manipulation.

* The Human chorionic gonadotropin hormone (hCG) is present in the urine of the pregnant women in large quantities only. This hormone in the urine induces X.laevis oocyte production which formed the basis of first well-documented method of pregnancy testing X. laevis is also notable for its use as the first well-documented method of pregnancy testing when it was discovered. Today, commercially available HCG is injected into Xenopus males and females to induce mating behavior and breed these frogs in captivity at any time of the year.

===Gene cluster===

* The alpha and beta globin genes are closely linked in small cluster of frogs compared to human and chicken

* The similarity of architecture of two clusters found in X.laevis supports the tetraploid origin

* The two loci encoding the muscle specific creatine kinase isoenzymes and have large differences in developmental profile, therefore suggesting that duplicate loci that have not undergone silencing are not simply redundant copies but have acquired specialization.

* Contains twice number of genes for proteins i.e. haemoglobin and sarcomeric actin serum albumin compared with other species

----

==Current Embrology Research==

Currently, a number of fields have benefited from the development of frog embrology. These include cloning, verification of messenger RNA, and Cell cycle.

===Cloning===
[[Image:Robert Briggs.jpg|thumb|left|Figure 16 Image details:Robert Briggs.jpg]]

In 1952, Robert Briggs and Thomas J King cloned northern leopard frogs using a method of nuclear transfer. Briggs and King's experiment was similar to that envisioned - and piloted using salamanders - by Hans Spemann in his 1938 proposal for a 'fantastical experiment'. Later, John Gurdon extended this work and showed that nuclei from differentiated cells could support development, although less well than those from early embryos. [http://genome.wellcome.ac.uk/doc_WTD020799.html]

Lemaitre et a. (2005) from MRC Cancer Cell Unit, Cambridge, U.K. worked on experiments that demonstrated that importance of serial nuclear transplantation for the sucessful cloning of frogs. He demonstrated that exposure of somatic-cell nuclei (erythrocyte nuclei) and sperm nuclei to an extract of mitotic cell extract reorganizes the chromatin into shorter loops and allows replication at much shorter intervals along the DNA. This increases the efficiency of DNA replication in mammalian cell-free systems.

===Transgenesis techniques for functional genomics in Xenopus===

Transgenesis in Xenopus is made possible due to large embryos, a reliable fate map, ease of microinjection, ease of dissection/micromanipulation and existence of the neuroendocrine reflex of background adaptation as a model for activation/inact.

Recently, Hajime Ogino and Haruki Ochi from Nura Institute of Science and Technology in Japan focused on the genomic resources and principles of the transgenesis techniques in Xenopus, and discusses their applications to genome wide network analysis, with emphasis on the use of bioinformatics tools. This is will to understand the gene regulatory networks that control vertebrate development. [http://www.ingentaconnect.com/content/bsc/dgd/2009/00000051/00000004/art00001%3Bjsessionid=4ah96rms73gcu.alexandra]

Xenopus used to be a problem in earlier days when it came to transgenesis. Current methods involves isolated sperm nuclei from Xenopus testis that are microinjected into unfertilized eggs. The generated transgenic tadpoles contain 5-35 copies of the integrated plasmid that are expressed in all cells. If desired, expression of the transgene can be directed to the appropriate tissue and at the appropriate time by using specific promoters, mostly the Xenopus POMC gene promoter (isolated from a Xenopus genomic DNA library) to specifically direct expression of green fluorescent protein (GFP) at high levels to the intermediate pituitary cells, which can either be over expressed or inhibited.[http://molanphys.ruhosting.nl/transgenesis.htm]

[[File:Transgenesis.JPG]]

===Verification of messenger RNA===

While the existence and role of messenger RNA (mRNA) was known in bacteria, in the 1960s it was still debated whether it also existed in vertebrates. Taking haemoglobin mRNA from immature red blood cells and injecting it into a Xenopus oocyte, John Gurdon showed that the haemoglobin protein was indeed produced. Producing proteins in Xenopus oocytes has proved to be extremely useful in cell biology, in particular for the study of receptor proteins.[http://genome.wellcome.ac.uk/doc_WTD020799.html]

===Cell Cycle===

As they develop outside the mother, frog eggs are well stocked with the proteins needed to drive the development of the embryo. Studies of these processes has shed considerable light on the processes involved in cell division - termed the cell cycle. [http://genome.wellcome.ac.uk/doc_WTD020799.html]

===Limb development in Xenopus Laevis===

[[Image: Frog Limb development.jpg|thumb|right|Image details:Primary source:[http://images.google.com.au/imgres?imgurl=http://www.sciencedaily.com/images/2006/06/060616130718.jpg&imgrefurl=http://www.sciencedaily.com/releases/2006/06/060616130718.htm&usg=__xliPsPAvheUBME_kjv_q7auiFbo=&h=333&w=300&sz=11&hl=en&start=2&um=1&tbnid=y_ntJtmkRSK7WM:&tbnh=119&tbnw=107&prev=/images%3Fq%3DLimb%2Bdevelopment%2Bin%2BXenopus%2BLaevis%26ndsp%3D18%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

Donald D. Brown (2005),Department of Embryology, Carnegie Institution of Washington demonstrated factors related to limb development of Xenopus Laevis. Thyroid hormone (TH) is found to be required for limb development in this frog. Specific cell types in the growing limb were targeted for expression of a dominant negative form of the TH receptor by sperm-mediated transgenesis. Limb muscle development, the innervation of muscle from the spinal cord, and cartilage growth can be inhibited without affecting patterning of the limb or differentiation of other cell types. Remodeling of the skin occurs late in metamorphosis after the limb has formed. The coordination of these independent programs is affected in part by the control that TH exerts over DNA replication in all cell types of the limb. [http://www.pnas.org/content/102/35/12455.full]

----

== Glossary ==

[[Image: Frog species.jpg|thumb|left|Image details:Primary source:www.olympus.co.jp/.../080925/large/p02L.jpg].jpg]]

*'''Amphibian:'''

''Relating to or characteristic of animals of the class amphibia.Amphibians are found in the taxonomic class of amphibia, amphibians are capable of both occupying and successfully living in both land and aquatic communities.amphibian''

*'''Augmentation:'''

''Enlargement/Increase in cellular size.''

*'''Autolysis:'''

''breakdown of a part or whole cell or tissue by self-produced enzymes''

*'''Blastomeres:'''

''The undifferentiated cells formed by cleavage of the fertilised ovum. This includes cells in the cleavage, morula, and blastula stages of the embryo''

*'''Carnivorous:'''
''
Flesh-eating; subsisting on animals as food.''

*'''Cleavage:'''

''he repeated division of a fertilised ovum ''

* '''Cleft:'''

''an opening, fissure, or V-shaped indentation made by or as if by splitting''

*'''Chordate:'''

''Members of a diverse phylum of animals that, as embryos, possess a (1) notochord; (2) a dorsal, hollow nerve cord, (3) pharyngeal gill slits; and (4) a post-anal tail''

''The act or state of splitting or dividing of a cell, particularly during the telophase of (animal) cell division.''

*'''Cytoplasm:'''

''The cytoplasm (of both eukaryotes and prokaryotes) is where the functions for cell expansion, growth, metabolism, and replication are carried out''

* '''Epiboly:'''
''The expansion of one cell sheet over other cells, as takes place during gastrulation''

*'''Fertilization:'''

''A process in sexual reproduction that involves the union of male (sperm) and female (ovum) gametes (each with a single, haploid set of chromosomes) to produce a diploid zygote.''

*'''Gamete:'''
''A reproductive cell (male (sperm) or female (egg)) that has only half the usual number of chromosomes''

*'''Gametogenesis:'''

''process leading to the production of gametes. The development and maturation of sex cells through meiosis.Another name for meiosis where a diploid cell is divided into two haploid cells with half the chromosome content of the diploid parent cell.''

*'''Herbivorous:'''

''eating plants; of or pertaining to the herbivora.''

*'''Holoblastic:'''

''The complete division of an isolecithal or microlecithal egg into blastomeres''

*'''Invagination:'''

''One of the methods by which the various germinal layers of the ovum are differentiated.''

*'''Isoenzymes:'''

''Isozymes (also known as isoenzymes) are enzymes that differ in amino acid sequence but catalyze the same chemical reaction.''

*'''Mesentery:'''

'' membranous fold attaching various organs to the body wall.''

*'''Metamorphosis:'''

''A change in the form and often habits of an animal after the embryonic stage during normal development.''

*'''Neuroendocrine:'''

''Neuroendocrine [IPA nʊəroʊˈɛndəkrɪn] cells are cells that release a hormone into the circulating blood in response to a neural stimulus.''

*'''Organogenesis:'''

''The part of embryonic development where the body's main organs develop.''

*'''Peritoneum:'''

''The smooth serous membrane which lines the cavity of the abdomen, or the whole body cavity when there is no diaphragm, and, turning back, surrounds the viscera, forming a closed, or nearly closed, sac.''

*'''Perivitelline space:'''

''The perivitelline space is the space between the zona pellucida and the plasma membrane (sometimes called the vitelline membrane) in a fertilized ovum.''

*'''Polyploidy:'''

''Cells with three or more sets of chromosomes.''

*'''Pronucleus:'''

''the nucleus of the ovum or sperm after fertilization but before they fuse to form the nucleus of the zygote ''

*'''Protoplasm:'''

''The fluid living content of the cell that consists of two major divisions, the cytoplasm and the nucleoplasm (cell nucleus). It is composed mainly of nucleic acids, proteins, lipids, carbohydrates, and inorganic salts''

*'''Segmentation:'''

''division of some metazoan bodies (such as annelida and Arthropoda) into repeated parts, segments. Segmentation can be homomeric (more or less the same) or heteromeric(different from each other).''

*'''Terrestrial:'''

''Of or on the ground, of the habitat of a plant, on land as opposed to in water, or on the ground as opposed to on another plant.''

*'''Transgenesis:'''

''Transgenesis is the process of introducing an exogenous gene - called a transgene - into a living organism so that the organism will exhibit a new property and transmit that property to its offspring.''

*'''Yolk:'''

''nutritive material of an ovum stored for the nutrition of an embryo''

*'''Zygote:'''

''The cell from which an organism develops, that results from the fertilization of the egg by the sperm.''

''Primary Resource "Biology- Online Dictionary''[http://www.biology-online.org/dictionary/Main_Page]

== References - Frog Embryology: ==

[[Image:Frog Research.jpg|thumb|left|Image details:[http://images.google.com.au/imgres?imgurl=http://www.odt.co.nz/files/story/2008/09/university_of_otago_zoology_senior_lecturer_phil_b_3343259744.jpg&imgrefurl=http://www.odt.co.nz/on-campus/university-otago/21670/dunedin-frog-man-wins-zoo-award&usg=__JvJJU5QfOnIwY2bk4xo64UXuJRs=&h=600&w=404&sz=22&hl=en&start=14&um=1&tbnid=AbsP89yWcUiilM:&tbnh=135&tbnw=91&prev=/images%3Fq%3Dfrog%2Bresearch%26hl%3Den%26um%3D1].jpg]]

1. Savage, J. M. (2002). The Amphibians and Reptiles of Costa Rica. University of Chicago Press, Chicago [http://www.springerlink.com/content/vv015277w1746llw/]

2. Ford, L.S.; D.C. Cannatella (1993). "The major clades of frogs". Herpetological Monographs 7: 94–117 [http://digimorph.org/specimens/Xenopus_laevis/]

3. Tyler, M. J. (1994). Australian Frogs A Natural History. Reed Books [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.gracilenta.html]

4. Cogger, H.G.; R.G. Zweifel, and D. Kirschner (2004). Encyclopedia of Reptiles & Amphibians Second Edition. Fog City Press [http://en.wikipedia.org/wiki/Microhylidae]

5. Beltz, Ellin (2005). Frogs: Inside their Remarkable World. Firefly Books [http://unjobs.org/authors/ellin-beltz]

6. Tyler, M. J. (1994). Australian Frogs A Natural History. Reed Books [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

7. Moury JD, Hanken J (1995) Early cranial neural crest migration in the direct-developing frog, Eleutherodactylus coqui. Acta
Anatomica (Basel) 153, 243-253.

8.Raynaud A (1985) Development of limbs and embryonic limb reduction. In Biology of the Reptilia (ed. Gans C, Billett F), pp.
59-148. New York: John Wiley.[http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=9309]

9. Hanken J (1986) Developmental evidence for amphibian origins. In Evolutionary Biology (ed. Hecht MK, Wallace B, Prance GT), 20, pp. 389-417. New York: Plenum Press. [Hanken J (1986) Developmental evidence for amphibian origins. In Evolutionary Biology (ed. Hecht MK, Wallace B, Prance GT), 20, pp. 389-417. New York: Plenum Press.]

10. Elinson RP (1990) Direct development in frogs : wiping the recapitulationist slate clean. Seminars in Developmental Biology
1, 263-270.

11. Beebee, T. J. C. 1996. Ecology and Conservation of Amphibians. Chapman and Hall. London. [http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V5X-3SVHMKH-1X&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=1021245355&_rerunOrigin=google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=825868e10cd178d16a8a0e5ad14dc5ef]

12. Lehtinen, R. M. 2002. The use of screw pines (Pandanus spp.) by amphibians and reptiles in Madagascar. Herpetological Bulletin 2002:20–25.

13. Parris, K. M. and M. A. McCarthy. 1999. What influences the structure of frog assemblages at forest streams. Australian Journal of Ecology 24:495–502. CrossRef

14. Zug, G. R. 1993. Herpetology: An Introductory Biology of Amphibians and Reptiles. Academic Press. San Diego, CA.

15. Slack,J.M.W., Darlington,B.G., Heath,J.K. and Godsave,S.F. (1987)Mesoderm induction in early Xenopus embryos by heparin-binding growth factors. Nature, 326, 197-200.

16. Melton,D.A. (1990) Activins are expressed early in Xenopus embryogenesis and can induce axial mesoderm and anterior structures. Cell, 63, 485-493.

17. Harland,R.M. and Misher,L. (1988) Stability of RNA in developing Xenopus embryos and identification of a destabilizing sequence in TFIIIA RNA. Development, 102, 837-852.

18. Cunliffe,V. and Smith,J.C. (1992) Ectopic mesoderm formation in Xenopus embryos caused by widespread expression of a Brachyury homologue. Nature, 358, 427-430.

19. Kinoshita,K., Bessho,T. and Asashima,M. (1993) Competence prepattern in the animal hemisphere of the 8-cell-stage Xenopus embryo. Devel. Biol., 160, 276-284.

20. LaBonne,C., Burke,B. and Whitman,M. (1995) Role of MAP kinase in mesoderm induction and axial patterning in Xenopus development. Development, 121, 1475-1486.

21. Green,J.B.A., New,H.V. and Smith,J.C. (1992) Responses of embryonic Xenopus cells to activin and FGF are separated by multiple dose thresholds and correspond to distinct axes of the mesoderm. Cell, 71, 731-739.

22. Grainger R., Blumberg B., Harland R., Amemiya C., Importance of Xenopus Tropicalis to biomedical and biological research, Benaroya Research Institute, Virginia Mason Research Center [http://www.genome.gov/Pages/Research/Sequencing/BACLibrary/xenopusTropicalis.pdf ]

23. Gregory, T.R. (2005). Animal Genome Size Database. [http://www.genomesize.com]

24. U.S Fish and Wildlife Services, ABNORMALITY CLASSIFICATION SOP, [http://www.fws.gov/contaminants/Amphibian/pdfs/AbnormalitySOP_woutpics_Jan08.pdf ]

25. Donald D. Brown*, Liquan Cai*, Biswajit Das*, Nicholas Marsh-Armstrong‡, Alexander M. Schreiber*, and Rejeanne Juste*(2005), Thyroid hormone controls multiple independent programs required for limb development in Xenopus laevis metamorphosis [http://www.pnas.org/content/102/35/12455.full]

26. Ogino, Hajime; Ochi, Haruki, Resources and transgenesis techniques for functional genomics in Xenopus, Development Growth & Differentiation, Volume 51, Number 4, May 2009 , pp. 387-401(15) [http://www.ingentaconnect.com/content/bsc/dgd/2009/00000051/00000004/art00001%3Bjsessionid=4ah96rms73gcu.alexandra]

27. Giles Newton (2004) Why the frog? The Human Genome, [http://genome.wellcome.ac.uk/doc_WTD020799.html]

28. Xenbase, [http://www.xenbase.org/common/]

29. Donders Center for Neuroscience & Nijmegen Center for Molecular Life Sciences (NCMLS), Beyond the genome (Xenopus transgenesis for functional genomics),Faculty of Science, Radboud University [http://molanphys.ruhosting.nl/transgenesis.htm]

== External Links ==
[[Image:Frog links.jpg|thumb|left|Image details:[http://images.google.com.au/imgres?imgurl=http://2.bp.blogspot.com/_o93AaY0GzH4/SjY_ZYv0PII/AAAAAAAAAgk/skruNc2yN78/s400/computer%2Bfrog.jpg&imgrefurl=http://hellaheaven-ana.blogspot.com/2009/06/talking-frog-contemporary-fairy-tale.html&usg=__oxji1TGLV2Fi7xe0dnlmuYk8gDo=&h=288&w=288&sz=16&hl=en&start=2&um=1&tbnid=ywZd4zpdxC5plM:&tbnh=115&tbnw=115&prev=/images%3Fq%3Dfrog%2Bon%2Bcomputer%26hl%3Den%26um%3D1].jpg]]

1. Frog embryology [http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/F/FrogEmbryology.html Frog Embryology]

2. Frog cellular materials [http://www.xenbase.org/xenbase/original/cell/cell.html xenbase]

3. The zoology of frog species [http://worms.zoology.wisc.edu/frogs/mainmenu.html zoology frogs]

4. Frog cycle [http://www.bioethics.gov/images/sc_images/frog_dev.gif bioethics frog] Just a little cycle of FROG'S life cycle

5. Frog Embryology [http://embryology.med.unsw.edu.au/OtherEmb/Frog.htm UNSW Embryology]

6. Frog Research [http://apps.carleton.edu/campus/library/now/exhibits/wallcharts/frog/ carleton library exhibit]

{{Template:Projects09}}
[[Category:Frog]]

2009 Group Project 5

2009-10-14T22:40:17Z

Z3258567: /* Growth and Modification of Frog Species */

== The Embryology of Frogs ==

== The Frog ==

[[Image: Frog species .jpg|thumb|left|Image details: Wikipedia (2009) Frog species[http://en.wikipedia.org/wiki/Frog#Uses_in_agriculture_and_research].jpg]]

Frogs are scientifically identified by the structure of their long posterior limbs, a petite framework, webbed fingers and feet, budged eyes and the lack of a tail. The majority of frog species are extensively recognized as outstanding jumpers, due to their long, dominant legs, which are adaptations to progress jumping performance during activities. The Frog is one of the most frequently studied species in experimental embryology and most anatomical sciences. ''The Frog is a practically effective model for human embryological development given that the Frog:''

- Comprises of genes which can be effectively manipulated.

- Comprises of similar homogeny with humans species.

- Reproduces a large quantity of offspring in a short period of time.

- Are small species which can be simply sustained.

- Are not extremely luxurious and expensive.

== The History of the uses in agriculture and research ==

[[Image: Frog experiments .jpg|thumb|right|Image details: Scans of chemically cleared and dyed preserved deformed frogs and toads [http://www.sat.qc.ca/upload/residence/frog-04.jpg].jpg]]

There are numerous types of frog species that have been manipulated in many developmental experiments. The frog was traditionally used by countless of the early embryology investigators and presently there are several diverse molecular mechanisms regarding progression of the frog. Theses include:

'''1.''' Food source; frog legs are a delicacy and are eaten in European countries and in many parts of South American regions.

'''2.''' Frogs have the finest biochemical dissection of phenomena that take place in the egg and oocyte. Frogs are the evolutionarily closest to mammals, commonly used as a vertebrate model.

'''3.''' Frogs lay thousands of outsized eggs, from which cell extracts can be readily prepared that is capable of recapitulating most molecular phenomena in a test tube.

'''4.''' Frogs have been commonly used as a laboratory system for a very long period, and have an extensive history of producing crucial observations in countless fields of biology.

'''5.''' Frogs have a important historical connection to the study of epigenetics (John Gurdon-vertebrate cloning and reprogramming) which has been mostly performed on frog species.

'''6.''' Frogs also have very strong evidence of pattern formation and early development, as the embryos are large in size and experimentally manipulative.

'''7.''' Recent research into the biochemistry of chromatin and epigenetics has been performed with frog species and mammalian cultured cells.

'''8.''' The biggest weakness of the Frog model system is the difficulty of performing genetic experiments and analysis, as frogs are allotetraploid, meaning they take approximately a year to fully develop to sexual maturity, and the genome has not been completely sequenced. Nevertheless, biochemical manipulations of cell extracts, such as immunodepletions and application of heterologous DNAs and nuclei can avoid the need for genetic exploitation.

----

== Growth and development of the Frog ==

[[Image: Mature develop frog.jpg|thumb|Image details: Wikipedia (2009) Red Eyed Tree Frog Figure 1 Primary source:[http://en.wikipedia.org/wiki/File:Red-eyed_Tree_Frog_-_Litoria_chloris_edit1].jpg]]

* The frog is a well recognised species, abundant predominantly in ponds, swamps, though various species may also exist in damp or shady environments distant from moist habitats.

* Eggs of specific frogs are easily obtained and may be examined in from the beginning of fertilization onwards. The phases of embryonic development differs in various chordates, yet the typical phases are basically apparent in all frog species. The differences are associated principally to the amount of yolk particles present in an egg.

* The yolk particles offer nourishment of the developing embryo. The process of frog development will be discussed from the phases of gametogenesis to the adult stage.

----

== The Egg ==
[[Image:Development of Poles in frog Fertilization.jpg|thumb|left|Development of Poles in Frog Fertilisation:J,Nassif 2009.jpg]]

- The embryology of a frog egg is a vast cell; its dimensions are approximately 1.4-1.6 million times larger than a typical aquatic species egg cell. Throughout the frog’s embryonic maturation period, the egg will be transformed into a tadpole encompassing millions of cells but still remains with its constant volume of genetic material, the vast prodction of cell have been illusttrated in the figure on the right revealing the production of eggs from female frogs. [http://en.wikipedia.org/wiki/Microhylidae]

- The early embryonic frog structure consists of three main segments the superior hemisphere known as the animal pole which is usually visible as a grey coloured area. The innermost layer appears to be between the outer two sections known as the gray crescent represented in black. Inferiorly, represents the vegetal pole typically lighter than the superior compartment illustrated in gold.

VIDEO RESOURCE: [http://www.youtube.com/watch?v=GO5YN_t1fqw&feature=related]

[[Image:Early Development of Frogs.jpg|thumb|left|Early Development of Frog:J,Nassif 2009.jpg]]

==History of frog embryology use ==

*'''1851''' - ''Henby Nelson''(MD): He identified a remarkable fact through the frog embryo. Henby observed the first cleavage of the yolk, in the egg of the frog. And cleaved structure corresponds in line of direction to the longitudinal axis of the body of the embryo of the frog species.

[[Image:Wilhelm Roux.jpg|thumb|right|Wilhelm Roux[http://images.google.com.au/imgres?imgurl=http://www.todayinsci.com/R/Roux_Wilhelm/RouxWilhelmThm.jpg&imgrefurl=http://www.todayinsci.com/6/6_09.htm&usg=__qRLTEMTHdZpAHxiNX12hWjcm9tA=&h=125&w=100&sz=4&hl=en&start=2&um=1&tbnid=LIKIwZTqCpk7MM:&tbnh=90&tbnw=72&prev=/images%3Fq%3DWilhelm%2BRoux%26gbv%3D2%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

*'''1888''' - ''Wilhelm Roux'': Wilhelm Roux attempted to solve the above observation by damaging one cell of a two-cell frog embryo with a hot needle. The cell stayed in place. However, it did not develop further. Its partner developed into a left or right half-embryo;

*'''1907''' - ''John Hopkins'' hospital: In order to identify the cellular source of neuronal fibres. Scientist placed small portions of frog embryo spinal cords in lymph on a microscope slide and was able to observe clear cut neuronal sprouting.

*'''1951''' - ''Robert Briggs'': Robert Briggs was able to clone a frog embryo by substituting the nucleus of an unfertilized frog egg cell with the nucleus of a frog embryo cell. This process is known as nuclear transplant, has formed the basis for all cloning.

*'''1952''' - ''Robert Briggs and T.J. King'': Robert Briggs and T.J. King used frog for test experiment. Because the size of the eggs in the frogs are enormous compared with those of mammals, which make them easier to manipulate.

*'''1976'''- Using the technique that had been successful in cloning frog embryos, the doctor transferred the nucleus of one cells into a donated egg cell. As an embryo began to develop, it was implanted into the uterus of a young woman.

*'''1997''' - ''Wilmut and Campbell'': Utilizing the cloning technique from frog embryo, Drs. Wilmut and Campbell tried the starvation technique on embryo cells to produce Megan and Morag, the world's first cloned sheep and, until now, the most famous sheep in history.

*'''2000''' - ''Tokyo University'': Scientists at Tokyo University have grown artificial eyeballs. Scientists formed them in tadpoles by using frog embryo cells.

*'''2001''' - ''Advanced Cell Technology'': Scientists from Advanced Cell Technology announced production of a human embryo clone. This is significant as its parthenogenesis has been artificially induced in frogs.

[[Image:John Gurdon .jpg|thumb|right|John Gurdon [http://images.google.com.au/imgres?imgurl=http://www.pnas.org/site/misc/images/gurdon.jpg&imgrefurl=http://www.pnas.org/site/misc/classics4.shtml&usg=__1p-GA1PdOYsxKL-cznMb3RHCm98=&h=526&w=400&sz=223&hl=en&start=1&um=1&tbnid=9k4lhuLssiWCAM:&tbnh=132&tbnw=100&prev=/images%3Fq%3DJohn%2BGurdon%26gbv%3D2%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

*'''2002''' - ''John Gurdon'': John Gurdon from Wellcome Cancer Research Institute in Cambridge experimented on cloned frog embryo.

== Gametogenesis ==

* The sexual reproduction occurs through the fusion of either mature reproductive cells or germ cells known as gametes, which include the sperm from the male frog and ova from female frog species so as to form a single cell, the fertilized zygote. The gametes are typically developed in parents of different sexes . [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

* Males gametes is a spermatozoon , the female frog gamete is an ovum. Each gamete is formed by a process, recognised as maturation or gametogenesis in gonads. The typical male frog gonads are testies in male, while the female gonads are ovaries. The synthesis of both gonads is associated with the process of fertilization. [http://en.wikipedia.org/wiki/Microhylidae]

* The zygote changes into a mature frog through the process of embryology and metamorphosis. Gametogenesis is a in progression which frog gametes are established from germ cells. Initial germ cells are called primordial germ cells, which can be recognised extremely early in the life of frog species.

----

== The Egg & Fertilization ==

[[Image:Fertilized and Unfertilised Eggs.jpg|thumb|left|Fertilized and Unfertilized Eggs:J,Nassif 2009.jpg]]

[[Image:Egg Development.jpg|thumb|left|Egg Development:J,Nassif 2009.jpg]]

- This occurs once the sperm cell has inserted, following the insertion of the sperm cells meiosis II is completed, there is a 30 degree position change of the cytoplasm, gray crescent allows this change to be visible in some amphibians, the gray crescent is able what determines the expect ted outline of how the frog will form. The sperm cell joins with the nuclei of the egg which forms the diploid zygote nucleus. --Sando Rashed 10:09, 24 September 2009 (EST)

- The early phases in the development of the egg is visible, but must be studied in tadpoles throughout maturation. In embryonic tadpoles of about 10 millimetres in length, soon after the opening of the oral cavity, a pair of longitudinal ridge-like thickenings of peritoneum becomes apparent along the posterior surface of the body cavity situated near to the mesentery and along the inner boundaries of the kidneys. Genital ridges are established in all tadpoles of this age, sex is not distinct until a later period. The development of the egg is illustrated in the figure on the left revealing the structure of a developed egg and a mature of egg.

[[Image:Fertilisation life cyle.jpg|thumb|Fertilization of Life cycle:Derived from primary source:[http://en.wikipedia.org/wiki/Frog]]]

== Maturation of the Egg ==

- The eggs have currently accomplished their full size, and develop from the exterior of the ovaries like a small shot, but they still have to pass through the course of maturation before they are prepared to be fertilised. This progression of maturation relates to the nucleus almost completely.

- The nucleus component, containing the nuclear fluid that excludes through the nuclear membrane into the substance of the egg, a great segment of the nuclear reticulum vanishes and becomes degraded into separate globules known as nucleoli, but a extremely small division remains in the midpoint as a slender intricately thread recognised as the nuclear skets.
Relative to the egg getting discharged from the ovary, the follicles shatter allowing the eggs to fall into the abdominal cavity of the frog species, the egg then passes forwards, directly by the contraction of the muscular wall, somewhat by the movement of the cilia of the peritoneum, to the apex of the oviduct, which positioned at the anterior compartment of the body cavity opposite to the roots of the respiratory organs.

- The terminal part of the oviduct establishes a thin-walled pouch capable of great swelling, inside which the eggs gathers in large numbers. In conclusion, the eggs are migrated out through the cloaca into water which the albuminous investments of the eggs rapidly augment to form the gelatinous mass of the frogs spawn.

== Maturation phases ==

'''1. Nuclear skein''', moves from the midpoint of the egg to its outer surface, which it reaches opposite the midpoint of the black pole. The skein, subsequently an unevenly twisted thread, now presumes the specific arrangement of a nuclear spindle, for instance may be visible in the nucleus of an epithelial or additional cell instantly prior to division of the cell occurs.[http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

'''2. The first Polar Body,''' regarding the instance the egg is laid, but prior to its fertilistion, the egg develops a considerably flattened appearance at its upper or black pole, a definite sum of fluid being exuded among the egg and the vitelline membrane. The nuclear spindle currently separate into two identical segments, one of which remains with the egg, and the supplementary is extruded as the first polar body, a small ovoidal white globule, which is situated on the surface of the egg surrounding the exuded peri-vitellline fluid.

'''3. The Second Polar Body''', half of the nuclear spindle that stay behind then splits into two equivalent divisions, one of which remains inside the egg as the female pronucleus, whereas the other segment is extruded as the second polar body, a small white globule extremely related to the first polar body, and like this positioned in the perivitelline fluid on the superior portion of the egg.

'''4. Fertilisation of the egg''', includes the synthesis of the spermatozoon with to egg, specifically, synthesis of the nuclei of these two bodies. The spermatozoa, subsequent to being shed over the seed by the male, distribute vigorously by means of their extended tails, break through the gelatinous investment of the female eggs, bore their way through the vitelline membrane and so go through into the eggs themselves, which they penetrate relative to the superior or black hemispheres.
* Subsequently, an hour following the spermatozoon has entered; a progression may be visible projecting within from the exterior segement of the egg, with a liquid spot in the mid point. This liquid centre is the nucleus of the spermatozoon, and is said to be the male pronucleus, it break through beyond into the female egg, transporting the specialised pigment into it, so that it appears bounded by a pigmented capsule linked with the exterior of the egg by a pigmented stalk.

* By this instance, the second polar body has been established and extruded, and the female pronucleus is merely the only component of the primary egg nucleus still present. Both the male and female pronuceli, which are at initially distance separate to each other, merge and after having enlarged significantly in size then fuse mutually about two and half hours after fertilisation has originated to produce the segmentation nucleus.
* The segmentation nucleus is a huge sphere-shaped vesicle embedded in delicately granular protoplasm, and bounded by a distinct capsule of pigment, its arrangement by the synthesis of the male and female pronuclei completes the action of fertilisation. Specifically female pronucleus may be observe as an imperfect nucleus, and consequently result in the course of fertilisation. The nucleus of the spermatozoon or male pronucleus, replaces the component of the egg- nucleus which has been misplaced as the polar bodies.

'''5. Segmentation of the Egg''', the initial phase of growth consist in constant separation of the egg, whereby it becomes transformed from the unicellular state, which is everlasting only in the lowest species, to muliticelluar state charactertics of all higher species. To these early processes of growth the names segmentation is specified. Shorty subsequent to the competition of fertilisation and arrangement of the segmentation nucleus this later misplaces its sphere-shaped appearance and develops to be spindle-shaped, the yolk granules at the equivalent instance showing a tendency to develop into lines distributing outwards from the distal segment of the spindle.
* The nucleus now split into two halves, which shift away from one another, the yolk granules are likely to combined themselves around the two nuclei, and a slender vertical plate of delicately granular substance is left, dividing the egg.[http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

* Superiorly the eggs depression now becomes visible, initially as a small cavity and then develops as a groove, which almost immediately extends all round, and speedily deepening, splits the egg into two entirely separate halves along a plane equivalent with the vertical plane.

* Shorty after, the two nuclei soon separate again into two, and therefore a second cleft is created in the same state as before, its additionally in the vertical plane, however in a plane at 90 degrees to the initial one, and on its finishing point the egg comprises of four accurately similar segments, each containing a nucleus. The third cleft is horizontal in shape, but not equal, lying closer to the superior than the lower pole, it segregates each of the four cells into, an superior smaller and a inferior larger pole

----

== Cleavage ==

[[Image: Frog Cleavage development.jpg|thumb|left|Cleavage Process details:[http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/F/FrogEmbryology.html].jpg]]

* The egg of the frog is scientifically identified as’ telolecithal’ meaning there is a outsized amount of yolk concentrated at a single pole, in contrast to the concentration of cytoplasm and the site of the nucleus. The cleavage phases are holoblastic, therefore the total and after the second cleavage they are asymmetrical .The initial cleavage stage appears about two and half to three hours after fertilization. It commences as a minor depression in close proximity to the centre of the animal hemisphere. It appears as if some interior force is pushing the surface the egg towards the centre. This small upturned fold steadily continues in the form of a channel until it surrounds the egg. This groove is shallow in the commencement, but develop into deeper eventually separating the fertilized egg into two halves recognised as the blastomeres. [The figure on the left symbolise the development and growth of the frog embryo during cleavage].

* Internally the separation is mitotic, consequently each daughter cell contains a nucleus resulting from the copulation nucleus of the fertilised egg. This cleavage is vertical, the two cells are indistinguishable in respect of cytoplasm, pigment and yolk. The subsequent cleavage appears about an hour after the first. The channel of this cleavage begins at the centre of the animal hemisphere, is at right angles to the first and is vertical. This divides the egg into four blastomeres. The fourth blastomere so produced are not qualitatively equal, since of these only two contain the material from the gray crescent. The cleavage begins about thirty minutes after the second is completed or four hours after fertilisation. the cleavage plane of the third furrow is horizontal and slightly above the equator. Thus the four upper cells are a little smaller than the four lower cells. The smaller blastomeres are called micromeres and the larger blastomeres are called macromeres. The fourth cleavages follow 20 minutes after the third and tend to be vertical. This is usually a double furrow.

* The cleavage rate is accelerated with each of the early divisions and since the blastomeres are of unequal size and have varying amounts of cytoplasm and yolk, synchronous cleavage is lost and there is an obvious overlapping of the division. The upper most cells divide more rapidly than the lowermost cells. From this point onwards perfect symmetry in cleavage and in blastomere is very rare, although the embryo developed perfectly. The fifth cleavage is also doubled, appearing first in the upper hemisphere and then in the lower.

* The cleavage thus far follows the rule that each cleavage plane comes in at right angles to the previous one. The subsequent divisions become so irregular that it is previous one. The subsequent division become so irregular that it is impossible to trace out any plan or procedure. The segmentation continues more rapidly in the pigmented regions, since at that place the protoplasm is most dense, whereas, yolk which is very abundant in the vegetal side delays cell division. The multicelluar embryo at this stage is called morula by some biologists.

----

== Gastrulation ==

[[Image:FROG GASTRULATION .jpg|thumb|left|Frog Gastrulation Image details:[http://www.google.com.au/imgres?imgurl=http://bio1903.nicerweb.com/Locked/media/ch47/47_12FrogGastrulation.jpg&imgrefurl=http://bio1903.nicerweb.com/Locked/media/ch47/gastrulation-frog.html&h=540&w=480&sz=46&tbnid=N78sHjELreGGSM:&tbnh=132&tbnw=117&prev=/images%3Fq%3Dfrog%2B-%2Bgastrulation&hl=en&usg=__4VK9FYLft0W-4lBe6p5EtQAMiaI=&ei=qPy5SurtMJvE6wON8JmdAg&sa=X&oi=image_result&resnum=4&ct=image].jpg]]

''The phase of Blastulation is followed by the unique developmental progression of gastrulation. The process of frog gastrulation involves the following processes.''

'''1. Epiboly Phase'''

The pigmented cellular materials of blastula have the propensity to overgrow the yolk cells within the developing content. This course which is known as epiboly commences gradually in the final blastula and rapidly accelerates with advancing gastrulation development. The cellular matter within the animal pole reproduces and matures on all sides except in area surrounding the dorsal lip of the blastopore has been established.

'''2. Convergence'''

Scientists suggested that the unfolding was thought to result in spreading of the superficial cells over a substrate with suitable absorption properties. Consequently epiboly and convergence are an outcome to this spreading tendency, which is actually increased by a reduction in surface tension of the distributing cells.

'''3. Rotation'''

The epiboly phase is maintained until the region of the dorsal lip has migrated and is a to some extent greater than 90 degrees and the region of the white blastopore is reduced to small circular rings. This section will be positioned away from the developing vegetal pole. Laterally the complete developing gastrula has been rotated to a horizontal axis, allowing it to lie at right angles to the original median plane of the egg. Therefore, the course of rotation is such that the dorsal lip is practically pushed backwards in one direction as rapid or quicker than epiboly moves it forward in the other. The outcome will be that the blastopore produced at roughly the vegetal pole is posterior, and the dorsal and ventral lips are essentially dorsal and ventral. This in addition allows the eggs to form the antero-ventral side of the potential embryo whilst the area marked by the grey crescent is to develop the dorsal segment.

'''4. Invagination'''

Visible is a small fissure- like invagination which is apparent in the middle between the equator and the vegetal segment. The most superior or dorsal border of the cleft produce the dorsal lip of the blastopore. This imput move back and forth on the dorsal plane near the dorsal lip and migrates around the boundaries of the blastocoel in company with the extension of the lateral lips. This adapted invagination is maintained until the blastocoel cavity has been almost abolished; excluding the slender opening separating epiblasts from the hypoblast, the new segment formed is known as the archenteron cavity.

'''5. Involution'''

- Additional to previous course of action a distinct involution also occurs at the blastoporal borders. This is mainly dynamic at the median dorsal lip and gradually more less as it shifts across either side until it reaches the ventral lip where it constant.Throughout this progression, cells positioned beside the superior boundaries of the blastoporal lip migrate over the lip to the interior portion of the lip. These cells are remained within the embryo along the internal edge of the blastopore. This indicates the root of archenteron is composed of involuted cells and beyond this the external layer known as the ectoderm. The base and lateral sides are enclosed mainly of endodermal cellular material, which have been established from larger yolk cells, situated in the vegetal pole of the blastula.

- In the final phases of the gastrula development, the cells contributing to the floor of the archenteron, thin out significantly where they surround the blastocoel.
The hemispherical shaped dorsal lip of blastopore which become visible at the commencement of the gastruation stage carry on to augment, initially becoming semicircular, then transform into a horse shoe shaped and then finally forming into circular band. The band is the accomplished by the blastopore. Various yolk cells of vegetal pole present in the section are crowed into the blastoporal cavity where they form a gathering identified as a yolk plug. Blastopore rapidly reduces in size while the archenteron is still developing and becomes completely formed in the final stage; the yolk plug appears as only a small oval on the gastrula.

==Growth and Modification of Frog Species==

'''1. Changes in habits and habitats:'''

'''a)''' In frogs, metamorphosis is related with to the modifications and adaptations as a frog changes environmental habitats from an aquatic to a terrestrial mode. Metamorphosis has modified the adaption of frogs as this alteration it began during the aquatic adaptations in the surface of water to breathe air. Subsequently, it continues the terrestrial surroundings, therefore the frog species become abundant in vegetation area allowing the frog to transform in to amphibious species.

'''b)''' The transition during metamorphosis is linked with a change in food chain. The tadpoles being the embryonic origin of frogs are herbivorous, feeding on algae and green matter, which they collect by the adapted feature such as their teeth surrounding their mouths. Adult frogs, alternatively, are classified as carnivorous feeding on insects and worms. Occasionally, they also consume larger prey, for instance smaller frogs species and even little birds and rodents which they dominant and ingest.

[[Image:Development of frog from sperm to mature structure.jpg|thumb|left|Development of Frog from sperm to mature structure Image details:J,Nassif 2009.jpg]]

'''2. Changes in Morphology'''

These include the decrease or complete absence of specific organs or structures which are essential during development of early frog embryology, but not critical in the mature frog species. The significant alterations of this nature include the following developmental structures.

'''a)''' The long tail of the tadpole alongside the fin folds is absorbed again during metamorphosis and becomes absent at the final stage of the metamorphosis.

'''b) '''The developing gills are resorted, the gill clefts are congested and the branchial cavities start to become absent. The reabsorbtion of gills also takes place by autolysis.

'''c)''' The teeth of the perioral disc additionally the homey lining of the jaws are shed.

'''d)''' The lateral line sense organs within the skin of tadpoles vanish throughout metamorphosis.

'''e)''' The cloacal tube begins to condensed and reduced.

'''f)''' Various blood vessels, together with parts of the aortic arches, are reduced during mature development.

(The figure on the left represents the transformation from a tadpole to a developing structure.)[http://science.jrank.org/pages/2862/Frogs-Adult-morphology.html]

'''3. Progressive or constructive changes'''

This process comprises of the development of specific organs which mature into functional systems only during metamorphosis.

'''a)''' During development the limbs continue to augment in size and differentiation. The forelimbs, which in the tadpole mature under the opercular membrane, which then break through to the exterior. Simultaneously there is a increase in the length and strength of the hind limbs, joints develop in them and the toes become visible.

'''b)''' The middle ear becomes apparent in relation with the first pharyngeal pouch. The tympanic membrane matures. It is bounded by circular tympanic cartilage which allows the frog to retain air.

'''c)''' The visual organs bulge up on the dorsal surface of the head developing the nictitating membrane.

'''d)''' There is augmentation of the tongue and the formation of thevomerina teeth.

[[Image: Growth model.jpg|thumb|Figure 10 Image details:J,Nassif2009:]]

'''4. Remodelling of some structures'''

Systematic organs which operate both in the early embryonic larva and the mature adult change their differentiation during metamorphosis so as to meet the requirements of the adult mode of life and due to the habitat adaptations. The figure on the right illustrates structures developing from specic germ cell layers.

'''a)''' The skin of the embryonic tadpole is lined with a double-layered epidermis. The number of layers of cells in the epidermis augments throughout metamorphosis. Superficial surface layers become cornified. Multicellular mucous and serous glands originate in the skin. The pigmentation of the skin continuously changes, new patterns and colour start to form.

'''b)''' There is a lengthening of the mouth gap as a result of rotation of the quadrate cartilage and the true jaws become functional.

'''c)''' The tongue rapidly progresses and becomes larger and more muscular.

'''d)''' The eyes become more specialised.

'''e)''' In early tadpoles, the GIT is extremely long and wound up into a spiral folds. The intestine become greatly lengthened in herbivorous species due to the vegetables food chain.[http://en.wikipedia.org/wiki/Frog]

'''5. Development of the reproductive system'''

(The figure below represents the reproductive and development cycle of a frog as it transform from egg to frog specie.)

In tadpoles, right after the mouth is being formed, two indentation like thickenings of peritoneum begin to appear near the body cavity (dorsal surface), which is nearest to the mesentery which is near the developing kidneys. These appear in all tadpoles.

These indentations appear here because of a change in the endothelial cells, everywhere else they are usually flat looking cells but they undergo a change and in this particular area become somewhat cuboidal/columnar.

Later on the indentations become more obvious due to the epithelial cells replicating numerously to form a thick layer. The posterior two thirds of the indentation for the female is the ovary and for the male it is the testis. The third that is left differentiates and becomes fat for the body.

[[Image: Mature frog life cyle.jpg|thumb|200px|left|Figure 11 Image details:Derived from primary source:http://www.scienceclarified.com/images/uesc_01_img0038.jpg]]

[[Image: Developing frog.jpg|thumb|Figure 12 Image details:
[[Image: Mature develop frog.jpg|thumb|Image details: Wikipedia (2009) TYPICAL FROG Primary source:[http://en.wikipedia.org/wiki/File:Red-eyed_Tree_Frog_-_Litoria_chloris_edit1.jpg]].jpg]]

===Delamination===

Delamination indicates a mass separating a group of cellular matter from other cellular groups. It has been illustrated that the division of notochord, mesoderm and endoderm tissues from each other to form distinct cellular masses is completed by the progression of delamination, subsequent to these materials moving to the inside throughout gastrulation. During the developing gastrula, the germ layers are all recognized. These distinct segments of the embryo develop from these germ tissue layers.

===Polarity and Rotation===

Throughout fertilisation to the beginning of gastrulation, the frog’s egg continues in the original location in relation to its polarity. Subsequent to gastrulation its polarity begins to differentiate. This progression is linked with migration of materials within the gastrula and can be responsible for the alterations of the centre of gravity.

===Closing of Blastopore===

Subsequent to the formation of the gastrula, the blastopore is visible as a tiny round circular filled cavity containing the yolk plug. As it continues to reduce in dimension, it represented as a pear-shaped outline through the mutual approach of its lateral lips. Through it final progression these fuse entirely to produce a longitudinal groove, the streak which continue dorsally and ventrally in a small aperture. The inferior aperture closes, resulting in a depression called the anal pit. The superior region remains open for some period and begins to as the neural groove is laid down.

===Post Gastrulation or Organogenesis===

Throughout the duration of pre-gastrulation, all tissues for different organs vanish from the surface of blastula and migrate inside to take their final arrangement in the embryo structure where organs are developed from their potential regions. Consequently organogenesis transfers an embryo into free larva structure.

----

==Germ-layer origin of various body tissues==
[[Image: Development Models of Frog.jpg|thumb|right|Figure 13 Image details:Vertebrate Structure and Development.jpg]]

Ectoderm will give raise to structures such as skin, brain, spinal cord, neurons and sense receptors.
Mesoderm will give raise to structrues such as notochord, muscles, blood, bone and sex organs.
Endoderm will give raise to sturctures such as inner lining of gut, liver, pancreas, lungs and bladder, thyroid and parathyroid glands and thymus.

== Structures derived from Germ-layers of frog species ==

[[Image:Development of Frog Layers.jpg|thumb|left|Figure 14 Primary source[http://www.bio.miami.edu/~cmallery/150/physiol/sf19x11b.jpg]Image details:J,Nassif 2009.jpg]]

[[Image:Development of frog layers.jpg|thumb|left|Figure 15 Primary source [http://www.bio.miami.edu/~cmallery/150/physiol/sf19x11b.jpg]Image details:J,Nassif 2009.jpg]]

'''Ectoderm '''

''Establishes the epidermal segments and its derivatives, to the frog’s nervous system. The ectoderm also contributes to :''

1. The olfactory and auditory epithelium.

2. The retina and lens of the eye.

3. Sensory organs.

4. The epithelial lining of the oral cavity and the anus.

5. The pineal and pituitary body.

'''Mesoderm'''

''Mesoderm originates:''

1. Connective tissue.

2. Muscles, except the notochord.

3. Blood vessels.

4. Lymphatics.

5. The peritoneum and the urinary and reproductive system.

6. The dermis, parts of the eye excluding lens, cornea, and conjunctiva.

'''Endoderm'''

''From the endoderm arises:''

1. The epithelial lining to the gut and oesophagus, stomach, intestine, bile duct.

2. The hepatic cells of the liver, respiratory tract, larynx, trachea and lungs.

3. The lining of the urinary bladder, pancreas thyroid and thymus.

[The two figures reveal the development of structures deriving from the celluar components of the embryology of the frog].[Structures derived from Germ-layers of frog species ]

==Life cycle of a frog==

'''Fertilization-egg''':

The female lays eggs in the spring. A group of fertilized eggs is called spawn;

'''7-10 days''':

Fertilized egg feed on remaining yolk which is in its gut. Their gills, mouth and tail have poorly developed. Begin to swim and feed on algae;

'''10-30 days(4 weeks):'''

A layer of skin grows over gills. Teeth begin to appear. A coiled gut start to develop. This is aid in digestion;

'''30-60 days(6-9 weeks):'''

Legs being to grow and head is more distinct. Start to eat insects. Arms begin to grow;

'''60-80 days(12 weeks):'''

Resemble a frog. Still have remaining tail;

'''80-140 days(20 weeks):'''

Fully developed, spend most of time out of water. Majority of frog live between 4-15 years.

==Timeline of frog development==

Development of egg and embryo at temperature 18 degree celsius.

'''0 hours''' - fertilization of the egg

'''1 hours''' - formation of the gray crescent due to pigment migration

'''3.5 hours''' - early cleavage

'''4.5 hours''' - blastula stage(coeloblastula with eccentric blastocoel

'''26 hours''' - gastrulation

'''26 hours''' -'' early'' - crescent shaped dorsal lip

'''34 hours''' - ''middle''- semicircular blastoporal lip

'''42 hours''' - ''late'' - circular blastoporal lip

'''50 hours''' - neurulation

'''50 hours''' - ''early'' - medullary plate

'''62 hours''' -'' middle''- neural folds converging

'''67 hours''' - ''late'' - neural tube formed and ciliation of embryo

'''84 hours''' - tail bud stage(early organogeny)

'''96 hours''' - muscular response to tactile stimulation

'''118 hours''' - early heart beat, development of gill buds

'''140 hours''' - hatching and gill circulation

'''162 hours''' - mouth opens and cornea becomes transparent

'''192 hours''' - tail fin circulation established

'''216 hours''' - degeneration of external gills, formation of operculum, development of embryonic teeth

'''240 hours''' - opercular fold over brachial chamber except for spiracle and internal gills

'''255 hours''' - prolonged larval stage with refinement of organs

'''270 hours''' - development of hindlimbs, internal development of forelimbs in opercular cavity

'''275 hours''' - projection of forelimbs through operculum, left side first

'''280 hours''' - absorption of the tail and reduction in size of the gut

'''284 hours''' - metamorphosis complete, emergence from water as miniature, air breathing frog

==Stages of frog embryology==
--[[User:S8600021|Mark Hill]] 08:40, 9 October 2009 (EST) [[Talk:2009_Group_Project_5#Constructive_Criticism_of_Coordinator|see my comment on images]]

The rate of development of the egg and embryo will depend upon the temperature at which they are kept. The approximate schedule of development at 23 degree celsius is provided below.

{| border='1px'
|+ Table 1: Stages of frog development
!Stage !!Time since fertilisation (hours)!!Stage Characteristic !!Embryo characteristic !!Image of frog stage
|-
|1
|0.00-1.30
|fertilization of the egg, post fertilization
|animal hemisphere, gray crescent and vegetal hemisphere are present
|[[File:Stage01ventral.jpg|100px]]
|-
|2
|1.30-2.00
|splits into two cells
|appearance of first cleavage furrow
|[[File:Stage02ventral.jpg|100px]]
|-
|3
|2.00-2.15
|becomes four cells
|appearance of second cleavage furrow
|[[File:Stage03dorsolat.jpg|100px]]
|-
|4
|2.15-2.45
|becomes eight cells
|appearance of third cleavage furrow
|[[File:Stage04dorsolat.jpg|100px]]
|-
|5
|2.45-3.00
|becomes sixteen cells
|appearance of fourth cleavage furrow
|[[File:Stage05dorsal.jpg|100px]]
|-
|6
|3.00-3.30
|becomes thirty-two cells
|appearance of fifth cleavage furrow
|[[File:Stage06animal.jpg|100px]]
|-
|6.5
|3.30-4.00
|blastula stage
|Three dorsal folds become visible as a result of endoderm invagination. Pole cells no longer visible on surface
|[[File:Stage065dorsal.jpg|100px]]
|-
|7
|4.00-5.00
|Gastrulation stage
|two primary germ layers. epiblast and endoderm
|[[File:Stage07ventral.jpg|100px]]
|-
|8
|5.00-7.00
|neurulation
|medullary plate, neural folds and neural tube
|[[File:Stage08animal.jpg|100px]]
|-
|9
|7.00-9.00
|germ layer
|complete lip involution encircling yolk
|[[File:Stage09veg.jpg|100px]]
|-
|10
|9.00-11.00
|early gastrula
|two primary germ layers
|[[File:Stage10veg.jpg|100px]]
|-
|10.5
|11.00-11.45
|gastrula
|two germ layers
|[[File:Stage105vegb.jpg|100px]]
|-
|11
|11.45-12.30
|medulla plate
|Yolk sac protrudes dorsally, labium moves to midline on ventral side
|[[File:Stage11veg.jpg|100px]]
|-
|11.5
|12.30-13.15
|continuation of medulla plate
|start closing the plate
|[[File:Stage115veg.jpg|100px]]
|-
|12
|13.15-14.15
|early neurula
|thickened ectoderm give rise to CNS
|[[File:Stage12veg.jpg|100px]]
|-
|12.5
|14.15-14.45
|neural folds
|expansion of cavity
|[[File:Stage125postdors.jpg|100px]]
|-
|13
|14.45-16.15
|neural folds
|continue expanding cavity
|[[File:Stage13postdors.jpg|100px]]
|-
|14
|16.15-17.30
|neural folds
|continuation of cavity
|[[File:Stage14postdors.jpg|100px]]
|-
|15
|17.30-18.15
|tail bud stage
|early organogeny
|[[File:Stage15postdors.jpg|100px]]
|-
|16
|18.15-18.45
|tail bud stage
|posterior ventral view
|[[File:Stage16ant.jpg|100px]]
|-
|17
|18.45-19.45
|tail bud stage
|anterior view
|[[File:Stage17ant.jpg|100px]]
|-
|19
|20.45-21.45
|neural fold close complete
|dorsal view
|[[File:Stage19dorsal.jpg|100px]]
|-
|20
|21.45-22.30
|early tail bud
|anterior view
|[[File:Stage20dorsal.jpg|100px]]
|-
|21
|22.30-24.00
|termination of neural crest
|progress to next stage
|[[File:Stage21ant.jpg|100px]]
|-
|22
|24.00-24.45
|prolonged development
|elongation
|[[File:Stage22lat.jpg|100px]]
|-
|23
|24.45-26.15
|elongation of embryo
|later view
|[[File:Stage23lat.jpg|100px]]
|-
|24
|26.15-27.30
|continuation of elongation of embryo
|dorsal view
|[[File:Stage24latsmall.jpg|50px]]
|-
|25
|27.30-29.30
|organs development
|embryo elongates and develops dorsal thickening
|[[File:Stage25dorsal.jpg|50px]]
|-
|26
|29.30-31.15
|elongation
|dorsally forms neural and brain cavity
|[[File:Stage26lat.jpg|50px]]
|-
|27
|31.15-32.30
|elongation of embryo
|dorsal view
|[[File:Stage27lat.jpg|50px]]
|-
|28
|32.30-35.00
|further development
|lateral view
|[[File:Stage28lat.jpg|50px]]
|-
|29-30
|35.00-37.30
|tail bud
|growth
|[[File:Stage29-30lat.jpg|50px]]
|-
|31
|37.30-40.00
|prolonged development
|bud development
|[[File:Stage31lat.jpg|50px]]
|-
|32
|40.00-44.30
|early muscular development
|elongation
|[[File:Stage32lat.jpg|50px]]
|-
|33-34
|44.30-50.00
|muscular movement
|apparatus for locomotion
|[[File:Stage33-34lat.jpg|50px]]
|-
|35-36
|50.00-53.30
|muscular movement
|apparatus for locomotion
|[[File:Stage35-36lat.jpg|50px]]
|-
|37-38
|53.30-56.30
|heart beat
|develops apparatus
|[[File:Stage37-38lat.jpg|50px]]
|-
|39
|56.30-66.00
|mouth opens
|cornea transparent
|[[File:Stage39latsmall.jpg|50px]]
|-
|40
|66.00-76.00
|gill circulation
|hatching
|[[File:Stage40lat.jpg|50px]]
|-
|41
|76.00-80.00
|tail, fin circulation
|circulation
|[[File:Stage41lat.jpg|50px]]
|-
|42
|80.00-86.00
|internal gills, operculum
|opercular fold, teeth
|[[File:Stage42lat.jpg|50px]]
|-
|43
|86.00-98.00
|operculum complete
|operculum closed on right
|[[File:Stage43lat.jpg|50px]]
|-
|46
|98.00-106.00
|metamorphosis
|emergence from water as miniature, operculum complete|
|[[File:Stage46lat.jpg|50px]]
|-
|}

==Abnormalities of frog==

Abnormalities of frog could be caused by multiple factors. These include change in climate, predators, parasites, bacteria, fungi, viruses or pollution and contaminants such as pesticides, metals and fertilizer.[http://www.fws.gov/contaminants/documents/frogsrefup_septoct_2006.pdf]

The Abnormalities are further classified into different categories. These categories are:

===1. Infectious Diseases:===

'''Perkinsus Symptoms-''' caused by perkinsus-like protozoan organism. Symptoms include swollen viscera that leads to a bloated body and and infected swollen heart

'''Ichthyophonus symptoms-''' cause by parasitic genus, where symptoms include a swollen tail resorption site that matches the surrounding skin in color and translucency.

[[Image:Abnormalities of Frog species.jpg|thumb|left|Figure A Image details[waterwatchadelaide.net.au].jpg]]

===2. Surficial Abnormalities:===

Surficial abnormalities as the one that are visible on the surface of the skin. This includes abnormal pigmentation, , subcutaneous hemorrhaging, wounds due to trauma or from a predator
Edema is a fluid-filled swelling under skin whihc is also a surficial abnormality.

===3. Skeletal Abnormalities:===

This is further classified into three more categories:

'''a. Skeletal Malformations-'''

* Microcephaly (small head or blunt snout)
*Scoliosis (Curved spine in lateral direction)
*Shrunken Limb (Micromelia)
*Amelia (Completely missing limb with no stump)

'''b. Skeletal Abnormalities of Unclear Etiology-'''

This condition arises when a frog has ectromelia (missing limb), brachydactyly (missing digits) or other such condition with no visible trauma or external damage, then this will be classified as the Skeletal abnormality of unclear etiology.

'''c. Skeletal Injuries-'''

Any limb missing or broken due to trauma or other related reason which shows clear evidence of it is classified as skeletal injury

===4. Eye Abnormalities:===

Most common includes-

'''i. Anophthalmia:''' Skin covers the eye socket as there is no eye

'''ii. Abnormal Iris Coloration:''' Reduced pigment in either one eye or both resulting in two different colours of the iris at times

'''iii. Abnormal size or shape:''' Both eyes either deviating from each other or size of pupil or iris is different than the other eye

[http://www.fws.gov/contaminants/Amphibian/pdfs/AbnormalitySOP_woutpics_Jan08.pdf ]

==Genetics==

There are a wide variety of species that differ from each other when it comes to genetics and their functioning.

'''TAXONOMY:''' '''Phylum''' ''Chordata'' / '''Sub Phylum''' ''Vertebrata'' / '''Class''' ''Amphibia'' / '''Order''' ''Anura''

Their are more than two dozen different families of frogs, where suborders are:

'''1. ARCHAEBATRACHIA-''' most primitive frogs

'''2. MESOBATRACHIA-''' linked between the Archaebatrachia and Neobatrachia

'''3. NEOBATRACHIA-''' most modern frogs

{| border='4px'
|+ '''General Info:'''
! !!
|-
| '''Number of frogs' species'''
| 5280
|-
| '''Smallest frog genome size:'''
| 0.95pg, Ornate burrowing frog
|-
| '''Largest frog genome size:'''
| 13.40pg, Ornate horned frog
|-
| '''Mean of frogs' genome'''
| 4.68pg ± 0.13
|-
|}

[http://www.genomesize.com]

*Majority of frogs have only 22 to 26 chromosomes and polyploid is very common where they are almost bisexual.

*Polyploid Amphibians reduce their total cell number such that they acheive the same body size as diploids. One of the most unsual forms of polypoidy in amphibians is the water frog ''Rana esculenta'' from Europe and Western Asia.

* The species with larger genomes have more genes for e.g. the frog genus ''Xenopus'' includes 16 species, with genome sizes ranging from 3.5 x 10^9 bp to 1.6 x 10^10 bp. These differences have arisen by numerous events of polyploidization within the past 40 million years or so. The ancestral chromosome number for the genus seems to have been 18, but there are species with 36, 72 and 105 chromosomes [http://www.xenbase.org/common/]

{| border='4px'
|+ '''Difference within two families'''
! '''SPECIES''' !! ''X.LAEVIS'' !! ''X.TROPICALIS''
|-
| '''PLOIDY'''
| Allotetraploid
| Diploid
|-
| '''NO. OF CHROMOSOMES'''
| 36 chromosomes
| 20 chromosomes
|-
| '''GENOME SIZE'''
| 3.1 x 10^9 bp
| 1.7 x 10^9 bp
|-
| '''EGG SIZE'''
| 1-1.3 mm
| 0.7-0.8 mm
|-
| '''GENERATION TIME'''
| 1-2 years
| 4 months
|-
|}
[http://www.xenbase.org/common/]

===Genome Sequencing===

Since Frog has a huge family with many different species, only few main species that are used widely for the purposes of experiments have their genome sequenced.

''Xenopus tropicalis'' has one of the smallest genomes among amphibians and has the shortest generation time- four to six months and the only diploid genome among the 14 Xenopus species. This means it has no more than two copies of most genes, whereas the other species of Xenopus have four copies of most genes (pseudotetraploid). US Department of Energy's Joint Genome Institute (JGI) in Walnut Creek, California, initiated the X. tropicalis Genome Project, finding 1,700 million base pairs.
[http://www.genome.gov/Pages/Research/Sequencing/BACLibrary/xenopusTropicalis.pdf]

===Xenopus oocytes===

* The oocytes provide an important expression system for molecular biology.

* By injecting DNA or mRNA into the oocyte or developing embryo, scientists can study the protein products in a controlled system. This allows rapid functional expression of manipulated DNAs (or mRNA). This is particularly useful in electrophysiology, where the ease of recording from the oocyte makes expression of membrane channels attractive.

* One challenge of oocyte work is eliminating native proteins that might confound results, such as membrane channels native to the oocyte.

* Translation of proteins can be blocked or splicing of pre-mRNA can be modified by injection of Morpholino antisense oligos into the oocyte (for distribution throughout the embryo) or early embryo (for distribution only into daughter cells of the injected cell).
[http://www.staff.unibe.ch/sigel/xenopus.html]

===Xenopus Laevis===

* ''Xenopus Laevis'' is an important model organism in developmental biology. X. laevis is tetraploid and reaches sexual maturity in 1 to 2 years. What makes it important in developmental biology is its large and easily manipulable embryo.

* Extracts from the eggs of X. laevis frogs are also commonly used for biochemical studies of DNA replication and repair, as these extracts fully support DNA replication and other related processes in a cell-free environment which allows easier manipulation.

* The Human chorionic gonadotropin hormone (hCG) is present in the urine of the pregnant women in large quantities only. This hormone in the urine induces X.laevis oocyte production which formed the basis of first well-documented method of pregnancy testing X. laevis is also notable for its use as the first well-documented method of pregnancy testing when it was discovered. Today, commercially available HCG is injected into Xenopus males and females to induce mating behavior and breed these frogs in captivity at any time of the year.

===Gene cluster===

* The alpha and beta globin genes are closely linked in small cluster of frogs compared to human and chicken

* The similarity of architecture of two clusters found in X.laevis supports the tetraploid origin

* The two loci encoding the muscle specific creatine kinase isoenzymes and have large differences in developmental profile, therefore suggesting that duplicate loci that have not undergone silencing are not simply redundant copies but have acquired specialization.

* Contains twice number of genes for proteins i.e. haemoglobin and sarcomeric actin serum albumin compared with other species

----

==Current Embrology Research==

Currently, a number of fields have benefited from the development of frog embrology. These include cloning, verification of messenger RNA, and Cell cycle.

===Cloning===
[[Image:Robert Briggs.jpg|thumb|left|Figure 16 Image details:Robert Briggs.jpg]]

In 1952, Robert Briggs and Thomas J King cloned northern leopard frogs using a method of nuclear transfer. Briggs and King's experiment was similar to that envisioned - and piloted using salamanders - by Hans Spemann in his 1938 proposal for a 'fantastical experiment'. Later, John Gurdon extended this work and showed that nuclei from differentiated cells could support development, although less well than those from early embryos. [http://genome.wellcome.ac.uk/doc_WTD020799.html]

Lemaitre et a. (2005) from MRC Cancer Cell Unit, Cambridge, U.K. worked on experiments that demonstrated that importance of serial nuclear transplantation for the sucessful cloning of frogs. He demonstrated that exposure of somatic-cell nuclei (erythrocyte nuclei) and sperm nuclei to an extract of mitotic cell extract reorganizes the chromatin into shorter loops and allows replication at much shorter intervals along the DNA. This increases the efficiency of DNA replication in mammalian cell-free systems.

===Transgenesis techniques for functional genomics in Xenopus===

Transgenesis in Xenopus is made possible due to large embryos, a reliable fate map, ease of microinjection, ease of dissection/micromanipulation and existence of the neuroendocrine reflex of background adaptation as a model for activation/inact.

Recently, Hajime Ogino and Haruki Ochi from Nura Institute of Science and Technology in Japan focused on the genomic resources and principles of the transgenesis techniques in Xenopus, and discusses their applications to genome wide network analysis, with emphasis on the use of bioinformatics tools. This is will to understand the gene regulatory networks that control vertebrate development. [http://www.ingentaconnect.com/content/bsc/dgd/2009/00000051/00000004/art00001%3Bjsessionid=4ah96rms73gcu.alexandra]

Xenopus used to be a problem in earlier days when it came to transgenesis. Current methods involves isolated sperm nuclei from Xenopus testis that are microinjected into unfertilized eggs. The generated transgenic tadpoles contain 5-35 copies of the integrated plasmid that are expressed in all cells. If desired, expression of the transgene can be directed to the appropriate tissue and at the appropriate time by using specific promoters, mostly the Xenopus POMC gene promoter (isolated from a Xenopus genomic DNA library) to specifically direct expression of green fluorescent protein (GFP) at high levels to the intermediate pituitary cells, which can either be over expressed or inhibited.[http://molanphys.ruhosting.nl/transgenesis.htm]

[[File:Transgenesis.JPG]]

===Verification of messenger RNA===

While the existence and role of messenger RNA (mRNA) was known in bacteria, in the 1960s it was still debated whether it also existed in vertebrates. Taking haemoglobin mRNA from immature red blood cells and injecting it into a Xenopus oocyte, John Gurdon showed that the haemoglobin protein was indeed produced. Producing proteins in Xenopus oocytes has proved to be extremely useful in cell biology, in particular for the study of receptor proteins.[http://genome.wellcome.ac.uk/doc_WTD020799.html]

===Cell Cycle===

As they develop outside the mother, frog eggs are well stocked with the proteins needed to drive the development of the embryo. Studies of these processes has shed considerable light on the processes involved in cell division - termed the cell cycle. [http://genome.wellcome.ac.uk/doc_WTD020799.html]

===Limb development in Xenopus Laevis===

[[Image: Frog Limb development.jpg|thumb|right|Image details:Primary source:[http://images.google.com.au/imgres?imgurl=http://www.sciencedaily.com/images/2006/06/060616130718.jpg&imgrefurl=http://www.sciencedaily.com/releases/2006/06/060616130718.htm&usg=__xliPsPAvheUBME_kjv_q7auiFbo=&h=333&w=300&sz=11&hl=en&start=2&um=1&tbnid=y_ntJtmkRSK7WM:&tbnh=119&tbnw=107&prev=/images%3Fq%3DLimb%2Bdevelopment%2Bin%2BXenopus%2BLaevis%26ndsp%3D18%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

Donald D. Brown (2005),Department of Embryology, Carnegie Institution of Washington demonstrated factors related to limb development of Xenopus Laevis. Thyroid hormone (TH) is found to be required for limb development in this frog. Specific cell types in the growing limb were targeted for expression of a dominant negative form of the TH receptor by sperm-mediated transgenesis. Limb muscle development, the innervation of muscle from the spinal cord, and cartilage growth can be inhibited without affecting patterning of the limb or differentiation of other cell types. Remodeling of the skin occurs late in metamorphosis after the limb has formed. The coordination of these independent programs is affected in part by the control that TH exerts over DNA replication in all cell types of the limb. [http://www.pnas.org/content/102/35/12455.full]

----

== Glossary ==

[[Image: Frog species.jpg|thumb|left|Image details:Primary source:www.olympus.co.jp/.../080925/large/p02L.jpg].jpg]]

*'''Amphibian:'''

''Relating to or characteristic of animals of the class amphibia.Amphibians are found in the taxonomic class of amphibia, amphibians are capable of both occupying and successfully living in both land and aquatic communities.amphibian''

*'''Augmentation:'''

''Enlargement/Increase in cellular size.''

*'''Autolysis:'''

''breakdown of a part or whole cell or tissue by self-produced enzymes''

*'''Blastomeres:'''

''The undifferentiated cells formed by cleavage of the fertilised ovum. This includes cells in the cleavage, morula, and blastula stages of the embryo''

*'''Carnivorous:'''
''
Flesh-eating; subsisting on animals as food.''

*'''Cleavage:'''

''he repeated division of a fertilised ovum ''

* '''Cleft:'''

''an opening, fissure, or V-shaped indentation made by or as if by splitting''

*'''Chordate:'''

''Members of a diverse phylum of animals that, as embryos, possess a (1) notochord; (2) a dorsal, hollow nerve cord, (3) pharyngeal gill slits; and (4) a post-anal tail''

''The act or state of splitting or dividing of a cell, particularly during the telophase of (animal) cell division.''

*'''Cytoplasm:'''

''The cytoplasm (of both eukaryotes and prokaryotes) is where the functions for cell expansion, growth, metabolism, and replication are carried out''

* '''Epiboly:'''
''The expansion of one cell sheet over other cells, as takes place during gastrulation''

*'''Fertilization:'''

''A process in sexual reproduction that involves the union of male (sperm) and female (ovum) gametes (each with a single, haploid set of chromosomes) to produce a diploid zygote.''

*'''Gamete:'''
''A reproductive cell (male (sperm) or female (egg)) that has only half the usual number of chromosomes''

*'''Gametogenesis:'''

''process leading to the production of gametes. The development and maturation of sex cells through meiosis.Another name for meiosis where a diploid cell is divided into two haploid cells with half the chromosome content of the diploid parent cell.''

*'''Herbivorous:'''

''eating plants; of or pertaining to the herbivora.''

*'''Holoblastic:'''

''The complete division of an isolecithal or microlecithal egg into blastomeres''

*'''Invagination:'''

''One of the methods by which the various germinal layers of the ovum are differentiated.''

*'''Isoenzymes:'''

''Isozymes (also known as isoenzymes) are enzymes that differ in amino acid sequence but catalyze the same chemical reaction.''

*'''Mesentery:'''

'' membranous fold attaching various organs to the body wall.''

*'''Metamorphosis:'''

''A change in the form and often habits of an animal after the embryonic stage during normal development.''

*'''Neuroendocrine:'''

''Neuroendocrine [IPA nʊəroʊˈɛndəkrɪn] cells are cells that release a hormone into the circulating blood in response to a neural stimulus.''

*'''Organogenesis:'''

''The part of embryonic development where the body's main organs develop.''

*'''Peritoneum:'''

''The smooth serous membrane which lines the cavity of the abdomen, or the whole body cavity when there is no diaphragm, and, turning back, surrounds the viscera, forming a closed, or nearly closed, sac.''

*'''Perivitelline space:'''

''The perivitelline space is the space between the zona pellucida and the plasma membrane (sometimes called the vitelline membrane) in a fertilized ovum.''

*'''Polyploidy:'''

''Cells with three or more sets of chromosomes.''

*'''Pronucleus:'''

''the nucleus of the ovum or sperm after fertilization but before they fuse to form the nucleus of the zygote ''

*'''Protoplasm:'''

''The fluid living content of the cell that consists of two major divisions, the cytoplasm and the nucleoplasm (cell nucleus). It is composed mainly of nucleic acids, proteins, lipids, carbohydrates, and inorganic salts''

*'''Segmentation:'''

''division of some metazoan bodies (such as annelida and Arthropoda) into repeated parts, segments. Segmentation can be homomeric (more or less the same) or heteromeric(different from each other).''

*'''Terrestrial:'''

''Of or on the ground, of the habitat of a plant, on land as opposed to in water, or on the ground as opposed to on another plant.''

*'''Transgenesis:'''

''Transgenesis is the process of introducing an exogenous gene - called a transgene - into a living organism so that the organism will exhibit a new property and transmit that property to its offspring.''

*'''Yolk:'''

''nutritive material of an ovum stored for the nutrition of an embryo''

*'''Zygote:'''

''The cell from which an organism develops, that results from the fertilization of the egg by the sperm.''

''Primary Resource "Biology- Online Dictionary''[http://www.biology-online.org/dictionary/Main_Page]

== References - Frog Embryology: ==

[[Image:Frog Research.jpg|thumb|left|Image details:[http://images.google.com.au/imgres?imgurl=http://www.odt.co.nz/files/story/2008/09/university_of_otago_zoology_senior_lecturer_phil_b_3343259744.jpg&imgrefurl=http://www.odt.co.nz/on-campus/university-otago/21670/dunedin-frog-man-wins-zoo-award&usg=__JvJJU5QfOnIwY2bk4xo64UXuJRs=&h=600&w=404&sz=22&hl=en&start=14&um=1&tbnid=AbsP89yWcUiilM:&tbnh=135&tbnw=91&prev=/images%3Fq%3Dfrog%2Bresearch%26hl%3Den%26um%3D1].jpg]]

1. Savage, J. M. (2002). The Amphibians and Reptiles of Costa Rica. University of Chicago Press, Chicago [http://www.springerlink.com/content/vv015277w1746llw/]

2. Ford, L.S.; D.C. Cannatella (1993). "The major clades of frogs". Herpetological Monographs 7: 94–117 [http://digimorph.org/specimens/Xenopus_laevis/]

3. Tyler, M. J. (1994). Australian Frogs A Natural History. Reed Books [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.gracilenta.html]

4. Cogger, H.G.; R.G. Zweifel, and D. Kirschner (2004). Encyclopedia of Reptiles & Amphibians Second Edition. Fog City Press [http://en.wikipedia.org/wiki/Microhylidae]

5. Beltz, Ellin (2005). Frogs: Inside their Remarkable World. Firefly Books [http://unjobs.org/authors/ellin-beltz]

6. Tyler, M. J. (1994). Australian Frogs A Natural History. Reed Books [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

7. Moury JD, Hanken J (1995) Early cranial neural crest migration in the direct-developing frog, Eleutherodactylus coqui. Acta
Anatomica (Basel) 153, 243-253.

8.Raynaud A (1985) Development of limbs and embryonic limb reduction. In Biology of the Reptilia (ed. Gans C, Billett F), pp.
59-148. New York: John Wiley.[http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=9309]

9. Hanken J (1986) Developmental evidence for amphibian origins. In Evolutionary Biology (ed. Hecht MK, Wallace B, Prance GT), 20, pp. 389-417. New York: Plenum Press. [Hanken J (1986) Developmental evidence for amphibian origins. In Evolutionary Biology (ed. Hecht MK, Wallace B, Prance GT), 20, pp. 389-417. New York: Plenum Press.]

10. Elinson RP (1990) Direct development in frogs : wiping the recapitulationist slate clean. Seminars in Developmental Biology
1, 263-270.

11. Beebee, T. J. C. 1996. Ecology and Conservation of Amphibians. Chapman and Hall. London. [http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V5X-3SVHMKH-1X&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=1021245355&_rerunOrigin=google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=825868e10cd178d16a8a0e5ad14dc5ef]

12. Lehtinen, R. M. 2002. The use of screw pines (Pandanus spp.) by amphibians and reptiles in Madagascar. Herpetological Bulletin 2002:20–25.

13. Parris, K. M. and M. A. McCarthy. 1999. What influences the structure of frog assemblages at forest streams. Australian Journal of Ecology 24:495–502. CrossRef

14. Zug, G. R. 1993. Herpetology: An Introductory Biology of Amphibians and Reptiles. Academic Press. San Diego, CA.

15. Slack,J.M.W., Darlington,B.G., Heath,J.K. and Godsave,S.F. (1987)Mesoderm induction in early Xenopus embryos by heparin-binding growth factors. Nature, 326, 197-200.

16. Melton,D.A. (1990) Activins are expressed early in Xenopus embryogenesis and can induce axial mesoderm and anterior structures. Cell, 63, 485-493.

17. Harland,R.M. and Misher,L. (1988) Stability of RNA in developing Xenopus embryos and identification of a destabilizing sequence in TFIIIA RNA. Development, 102, 837-852.

18. Cunliffe,V. and Smith,J.C. (1992) Ectopic mesoderm formation in Xenopus embryos caused by widespread expression of a Brachyury homologue. Nature, 358, 427-430.

19. Kinoshita,K., Bessho,T. and Asashima,M. (1993) Competence prepattern in the animal hemisphere of the 8-cell-stage Xenopus embryo. Devel. Biol., 160, 276-284.

20. LaBonne,C., Burke,B. and Whitman,M. (1995) Role of MAP kinase in mesoderm induction and axial patterning in Xenopus development. Development, 121, 1475-1486.

21. Green,J.B.A., New,H.V. and Smith,J.C. (1992) Responses of embryonic Xenopus cells to activin and FGF are separated by multiple dose thresholds and correspond to distinct axes of the mesoderm. Cell, 71, 731-739.

22. Grainger R., Blumberg B., Harland R., Amemiya C., Importance of Xenopus Tropicalis to biomedical and biological research, Benaroya Research Institute, Virginia Mason Research Center [http://www.genome.gov/Pages/Research/Sequencing/BACLibrary/xenopusTropicalis.pdf ]

23. Gregory, T.R. (2005). Animal Genome Size Database. [http://www.genomesize.com]

24. U.S Fish and Wildlife Services, ABNORMALITY CLASSIFICATION SOP, [http://www.fws.gov/contaminants/Amphibian/pdfs/AbnormalitySOP_woutpics_Jan08.pdf ]

25. Donald D. Brown*, Liquan Cai*, Biswajit Das*, Nicholas Marsh-Armstrong‡, Alexander M. Schreiber*, and Rejeanne Juste*(2005), Thyroid hormone controls multiple independent programs required for limb development in Xenopus laevis metamorphosis [http://www.pnas.org/content/102/35/12455.full]

26. Ogino, Hajime; Ochi, Haruki, Resources and transgenesis techniques for functional genomics in Xenopus, Development Growth & Differentiation, Volume 51, Number 4, May 2009 , pp. 387-401(15) [http://www.ingentaconnect.com/content/bsc/dgd/2009/00000051/00000004/art00001%3Bjsessionid=4ah96rms73gcu.alexandra]

27. Giles Newton (2004) Why the frog? The Human Genome, [http://genome.wellcome.ac.uk/doc_WTD020799.html]

28. Xenbase, [http://www.xenbase.org/common/]

29. Donders Center for Neuroscience & Nijmegen Center for Molecular Life Sciences (NCMLS), Beyond the genome (Xenopus transgenesis for functional genomics),Faculty of Science, Radboud University [http://molanphys.ruhosting.nl/transgenesis.htm]

== External Links ==
[[Image:Frog links.jpg|thumb|left|Image details:[http://images.google.com.au/imgres?imgurl=http://2.bp.blogspot.com/_o93AaY0GzH4/SjY_ZYv0PII/AAAAAAAAAgk/skruNc2yN78/s400/computer%2Bfrog.jpg&imgrefurl=http://hellaheaven-ana.blogspot.com/2009/06/talking-frog-contemporary-fairy-tale.html&usg=__oxji1TGLV2Fi7xe0dnlmuYk8gDo=&h=288&w=288&sz=16&hl=en&start=2&um=1&tbnid=ywZd4zpdxC5plM:&tbnh=115&tbnw=115&prev=/images%3Fq%3Dfrog%2Bon%2Bcomputer%26hl%3Den%26um%3D1].jpg]]

1. Frog embryology [http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/F/FrogEmbryology.html Frog Embryology]

2. Frog cellular materials [http://www.xenbase.org/xenbase/original/cell/cell.html xenbase]

3. The zoology of frog species [http://worms.zoology.wisc.edu/frogs/mainmenu.html zoology frogs]

4. Frog cycle [http://www.bioethics.gov/images/sc_images/frog_dev.gif bioethics frog] Just a little cycle of FROG'S life cycle

5. Frog Embryology [http://embryology.med.unsw.edu.au/OtherEmb/Frog.htm UNSW Embryology]

6. Frog Research [http://apps.carleton.edu/campus/library/now/exhibits/wallcharts/frog/ carleton library exhibit]

{{Template:Projects09}}
[[Category:Frog]]

2009 Group Project 5

2009-10-14T22:39:41Z

Z3258567: /* Gastrulation */

== The Embryology of Frogs ==

== The Frog ==

[[Image: Frog species .jpg|thumb|left|Image details: Wikipedia (2009) Frog species[http://en.wikipedia.org/wiki/Frog#Uses_in_agriculture_and_research].jpg]]

Frogs are scientifically identified by the structure of their long posterior limbs, a petite framework, webbed fingers and feet, budged eyes and the lack of a tail. The majority of frog species are extensively recognized as outstanding jumpers, due to their long, dominant legs, which are adaptations to progress jumping performance during activities. The Frog is one of the most frequently studied species in experimental embryology and most anatomical sciences. ''The Frog is a practically effective model for human embryological development given that the Frog:''

- Comprises of genes which can be effectively manipulated.

- Comprises of similar homogeny with humans species.

- Reproduces a large quantity of offspring in a short period of time.

- Are small species which can be simply sustained.

- Are not extremely luxurious and expensive.

== The History of the uses in agriculture and research ==

[[Image: Frog experiments .jpg|thumb|right|Image details: Scans of chemically cleared and dyed preserved deformed frogs and toads [http://www.sat.qc.ca/upload/residence/frog-04.jpg].jpg]]

There are numerous types of frog species that have been manipulated in many developmental experiments. The frog was traditionally used by countless of the early embryology investigators and presently there are several diverse molecular mechanisms regarding progression of the frog. Theses include:

'''1.''' Food source; frog legs are a delicacy and are eaten in European countries and in many parts of South American regions.

'''2.''' Frogs have the finest biochemical dissection of phenomena that take place in the egg and oocyte. Frogs are the evolutionarily closest to mammals, commonly used as a vertebrate model.

'''3.''' Frogs lay thousands of outsized eggs, from which cell extracts can be readily prepared that is capable of recapitulating most molecular phenomena in a test tube.

'''4.''' Frogs have been commonly used as a laboratory system for a very long period, and have an extensive history of producing crucial observations in countless fields of biology.

'''5.''' Frogs have a important historical connection to the study of epigenetics (John Gurdon-vertebrate cloning and reprogramming) which has been mostly performed on frog species.

'''6.''' Frogs also have very strong evidence of pattern formation and early development, as the embryos are large in size and experimentally manipulative.

'''7.''' Recent research into the biochemistry of chromatin and epigenetics has been performed with frog species and mammalian cultured cells.

'''8.''' The biggest weakness of the Frog model system is the difficulty of performing genetic experiments and analysis, as frogs are allotetraploid, meaning they take approximately a year to fully develop to sexual maturity, and the genome has not been completely sequenced. Nevertheless, biochemical manipulations of cell extracts, such as immunodepletions and application of heterologous DNAs and nuclei can avoid the need for genetic exploitation.

----

== Growth and development of the Frog ==

[[Image: Mature develop frog.jpg|thumb|Image details: Wikipedia (2009) Red Eyed Tree Frog Figure 1 Primary source:[http://en.wikipedia.org/wiki/File:Red-eyed_Tree_Frog_-_Litoria_chloris_edit1].jpg]]

* The frog is a well recognised species, abundant predominantly in ponds, swamps, though various species may also exist in damp or shady environments distant from moist habitats.

* Eggs of specific frogs are easily obtained and may be examined in from the beginning of fertilization onwards. The phases of embryonic development differs in various chordates, yet the typical phases are basically apparent in all frog species. The differences are associated principally to the amount of yolk particles present in an egg.

* The yolk particles offer nourishment of the developing embryo. The process of frog development will be discussed from the phases of gametogenesis to the adult stage.

----

== The Egg ==
[[Image:Development of Poles in frog Fertilization.jpg|thumb|left|Development of Poles in Frog Fertilisation:J,Nassif 2009.jpg]]

- The embryology of a frog egg is a vast cell; its dimensions are approximately 1.4-1.6 million times larger than a typical aquatic species egg cell. Throughout the frog’s embryonic maturation period, the egg will be transformed into a tadpole encompassing millions of cells but still remains with its constant volume of genetic material, the vast prodction of cell have been illusttrated in the figure on the right revealing the production of eggs from female frogs. [http://en.wikipedia.org/wiki/Microhylidae]

- The early embryonic frog structure consists of three main segments the superior hemisphere known as the animal pole which is usually visible as a grey coloured area. The innermost layer appears to be between the outer two sections known as the gray crescent represented in black. Inferiorly, represents the vegetal pole typically lighter than the superior compartment illustrated in gold.

VIDEO RESOURCE: [http://www.youtube.com/watch?v=GO5YN_t1fqw&feature=related]

[[Image:Early Development of Frogs.jpg|thumb|left|Early Development of Frog:J,Nassif 2009.jpg]]

==History of frog embryology use ==

*'''1851''' - ''Henby Nelson''(MD): He identified a remarkable fact through the frog embryo. Henby observed the first cleavage of the yolk, in the egg of the frog. And cleaved structure corresponds in line of direction to the longitudinal axis of the body of the embryo of the frog species.

[[Image:Wilhelm Roux.jpg|thumb|right|Wilhelm Roux[http://images.google.com.au/imgres?imgurl=http://www.todayinsci.com/R/Roux_Wilhelm/RouxWilhelmThm.jpg&imgrefurl=http://www.todayinsci.com/6/6_09.htm&usg=__qRLTEMTHdZpAHxiNX12hWjcm9tA=&h=125&w=100&sz=4&hl=en&start=2&um=1&tbnid=LIKIwZTqCpk7MM:&tbnh=90&tbnw=72&prev=/images%3Fq%3DWilhelm%2BRoux%26gbv%3D2%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

*'''1888''' - ''Wilhelm Roux'': Wilhelm Roux attempted to solve the above observation by damaging one cell of a two-cell frog embryo with a hot needle. The cell stayed in place. However, it did not develop further. Its partner developed into a left or right half-embryo;

*'''1907''' - ''John Hopkins'' hospital: In order to identify the cellular source of neuronal fibres. Scientist placed small portions of frog embryo spinal cords in lymph on a microscope slide and was able to observe clear cut neuronal sprouting.

*'''1951''' - ''Robert Briggs'': Robert Briggs was able to clone a frog embryo by substituting the nucleus of an unfertilized frog egg cell with the nucleus of a frog embryo cell. This process is known as nuclear transplant, has formed the basis for all cloning.

*'''1952''' - ''Robert Briggs and T.J. King'': Robert Briggs and T.J. King used frog for test experiment. Because the size of the eggs in the frogs are enormous compared with those of mammals, which make them easier to manipulate.

*'''1976'''- Using the technique that had been successful in cloning frog embryos, the doctor transferred the nucleus of one cells into a donated egg cell. As an embryo began to develop, it was implanted into the uterus of a young woman.

*'''1997''' - ''Wilmut and Campbell'': Utilizing the cloning technique from frog embryo, Drs. Wilmut and Campbell tried the starvation technique on embryo cells to produce Megan and Morag, the world's first cloned sheep and, until now, the most famous sheep in history.

*'''2000''' - ''Tokyo University'': Scientists at Tokyo University have grown artificial eyeballs. Scientists formed them in tadpoles by using frog embryo cells.

*'''2001''' - ''Advanced Cell Technology'': Scientists from Advanced Cell Technology announced production of a human embryo clone. This is significant as its parthenogenesis has been artificially induced in frogs.

[[Image:John Gurdon .jpg|thumb|right|John Gurdon [http://images.google.com.au/imgres?imgurl=http://www.pnas.org/site/misc/images/gurdon.jpg&imgrefurl=http://www.pnas.org/site/misc/classics4.shtml&usg=__1p-GA1PdOYsxKL-cznMb3RHCm98=&h=526&w=400&sz=223&hl=en&start=1&um=1&tbnid=9k4lhuLssiWCAM:&tbnh=132&tbnw=100&prev=/images%3Fq%3DJohn%2BGurdon%26gbv%3D2%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

*'''2002''' - ''John Gurdon'': John Gurdon from Wellcome Cancer Research Institute in Cambridge experimented on cloned frog embryo.

== Gametogenesis ==

* The sexual reproduction occurs through the fusion of either mature reproductive cells or germ cells known as gametes, which include the sperm from the male frog and ova from female frog species so as to form a single cell, the fertilized zygote. The gametes are typically developed in parents of different sexes . [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

* Males gametes is a spermatozoon , the female frog gamete is an ovum. Each gamete is formed by a process, recognised as maturation or gametogenesis in gonads. The typical male frog gonads are testies in male, while the female gonads are ovaries. The synthesis of both gonads is associated with the process of fertilization. [http://en.wikipedia.org/wiki/Microhylidae]

* The zygote changes into a mature frog through the process of embryology and metamorphosis. Gametogenesis is a in progression which frog gametes are established from germ cells. Initial germ cells are called primordial germ cells, which can be recognised extremely early in the life of frog species.

----

== The Egg & Fertilization ==

[[Image:Fertilized and Unfertilised Eggs.jpg|thumb|left|Fertilized and Unfertilized Eggs:J,Nassif 2009.jpg]]

[[Image:Egg Development.jpg|thumb|left|Egg Development:J,Nassif 2009.jpg]]

- This occurs once the sperm cell has inserted, following the insertion of the sperm cells meiosis II is completed, there is a 30 degree position change of the cytoplasm, gray crescent allows this change to be visible in some amphibians, the gray crescent is able what determines the expect ted outline of how the frog will form. The sperm cell joins with the nuclei of the egg which forms the diploid zygote nucleus. --Sando Rashed 10:09, 24 September 2009 (EST)

- The early phases in the development of the egg is visible, but must be studied in tadpoles throughout maturation. In embryonic tadpoles of about 10 millimetres in length, soon after the opening of the oral cavity, a pair of longitudinal ridge-like thickenings of peritoneum becomes apparent along the posterior surface of the body cavity situated near to the mesentery and along the inner boundaries of the kidneys. Genital ridges are established in all tadpoles of this age, sex is not distinct until a later period. The development of the egg is illustrated in the figure on the left revealing the structure of a developed egg and a mature of egg.

[[Image:Fertilisation life cyle.jpg|thumb|Fertilization of Life cycle:Derived from primary source:[http://en.wikipedia.org/wiki/Frog]]]

== Maturation of the Egg ==

- The eggs have currently accomplished their full size, and develop from the exterior of the ovaries like a small shot, but they still have to pass through the course of maturation before they are prepared to be fertilised. This progression of maturation relates to the nucleus almost completely.

- The nucleus component, containing the nuclear fluid that excludes through the nuclear membrane into the substance of the egg, a great segment of the nuclear reticulum vanishes and becomes degraded into separate globules known as nucleoli, but a extremely small division remains in the midpoint as a slender intricately thread recognised as the nuclear skets.
Relative to the egg getting discharged from the ovary, the follicles shatter allowing the eggs to fall into the abdominal cavity of the frog species, the egg then passes forwards, directly by the contraction of the muscular wall, somewhat by the movement of the cilia of the peritoneum, to the apex of the oviduct, which positioned at the anterior compartment of the body cavity opposite to the roots of the respiratory organs.

- The terminal part of the oviduct establishes a thin-walled pouch capable of great swelling, inside which the eggs gathers in large numbers. In conclusion, the eggs are migrated out through the cloaca into water which the albuminous investments of the eggs rapidly augment to form the gelatinous mass of the frogs spawn.

== Maturation phases ==

'''1. Nuclear skein''', moves from the midpoint of the egg to its outer surface, which it reaches opposite the midpoint of the black pole. The skein, subsequently an unevenly twisted thread, now presumes the specific arrangement of a nuclear spindle, for instance may be visible in the nucleus of an epithelial or additional cell instantly prior to division of the cell occurs.[http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

'''2. The first Polar Body,''' regarding the instance the egg is laid, but prior to its fertilistion, the egg develops a considerably flattened appearance at its upper or black pole, a definite sum of fluid being exuded among the egg and the vitelline membrane. The nuclear spindle currently separate into two identical segments, one of which remains with the egg, and the supplementary is extruded as the first polar body, a small ovoidal white globule, which is situated on the surface of the egg surrounding the exuded peri-vitellline fluid.

'''3. The Second Polar Body''', half of the nuclear spindle that stay behind then splits into two equivalent divisions, one of which remains inside the egg as the female pronucleus, whereas the other segment is extruded as the second polar body, a small white globule extremely related to the first polar body, and like this positioned in the perivitelline fluid on the superior portion of the egg.

'''4. Fertilisation of the egg''', includes the synthesis of the spermatozoon with to egg, specifically, synthesis of the nuclei of these two bodies. The spermatozoa, subsequent to being shed over the seed by the male, distribute vigorously by means of their extended tails, break through the gelatinous investment of the female eggs, bore their way through the vitelline membrane and so go through into the eggs themselves, which they penetrate relative to the superior or black hemispheres.
* Subsequently, an hour following the spermatozoon has entered; a progression may be visible projecting within from the exterior segement of the egg, with a liquid spot in the mid point. This liquid centre is the nucleus of the spermatozoon, and is said to be the male pronucleus, it break through beyond into the female egg, transporting the specialised pigment into it, so that it appears bounded by a pigmented capsule linked with the exterior of the egg by a pigmented stalk.

* By this instance, the second polar body has been established and extruded, and the female pronucleus is merely the only component of the primary egg nucleus still present. Both the male and female pronuceli, which are at initially distance separate to each other, merge and after having enlarged significantly in size then fuse mutually about two and half hours after fertilisation has originated to produce the segmentation nucleus.
* The segmentation nucleus is a huge sphere-shaped vesicle embedded in delicately granular protoplasm, and bounded by a distinct capsule of pigment, its arrangement by the synthesis of the male and female pronuclei completes the action of fertilisation. Specifically female pronucleus may be observe as an imperfect nucleus, and consequently result in the course of fertilisation. The nucleus of the spermatozoon or male pronucleus, replaces the component of the egg- nucleus which has been misplaced as the polar bodies.

'''5. Segmentation of the Egg''', the initial phase of growth consist in constant separation of the egg, whereby it becomes transformed from the unicellular state, which is everlasting only in the lowest species, to muliticelluar state charactertics of all higher species. To these early processes of growth the names segmentation is specified. Shorty subsequent to the competition of fertilisation and arrangement of the segmentation nucleus this later misplaces its sphere-shaped appearance and develops to be spindle-shaped, the yolk granules at the equivalent instance showing a tendency to develop into lines distributing outwards from the distal segment of the spindle.
* The nucleus now split into two halves, which shift away from one another, the yolk granules are likely to combined themselves around the two nuclei, and a slender vertical plate of delicately granular substance is left, dividing the egg.[http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

* Superiorly the eggs depression now becomes visible, initially as a small cavity and then develops as a groove, which almost immediately extends all round, and speedily deepening, splits the egg into two entirely separate halves along a plane equivalent with the vertical plane.

* Shorty after, the two nuclei soon separate again into two, and therefore a second cleft is created in the same state as before, its additionally in the vertical plane, however in a plane at 90 degrees to the initial one, and on its finishing point the egg comprises of four accurately similar segments, each containing a nucleus. The third cleft is horizontal in shape, but not equal, lying closer to the superior than the lower pole, it segregates each of the four cells into, an superior smaller and a inferior larger pole

----

== Cleavage ==

[[Image: Frog Cleavage development.jpg|thumb|left|Cleavage Process details:[http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/F/FrogEmbryology.html].jpg]]

* The egg of the frog is scientifically identified as’ telolecithal’ meaning there is a outsized amount of yolk concentrated at a single pole, in contrast to the concentration of cytoplasm and the site of the nucleus. The cleavage phases are holoblastic, therefore the total and after the second cleavage they are asymmetrical .The initial cleavage stage appears about two and half to three hours after fertilization. It commences as a minor depression in close proximity to the centre of the animal hemisphere. It appears as if some interior force is pushing the surface the egg towards the centre. This small upturned fold steadily continues in the form of a channel until it surrounds the egg. This groove is shallow in the commencement, but develop into deeper eventually separating the fertilized egg into two halves recognised as the blastomeres. [The figure on the left symbolise the development and growth of the frog embryo during cleavage].

* Internally the separation is mitotic, consequently each daughter cell contains a nucleus resulting from the copulation nucleus of the fertilised egg. This cleavage is vertical, the two cells are indistinguishable in respect of cytoplasm, pigment and yolk. The subsequent cleavage appears about an hour after the first. The channel of this cleavage begins at the centre of the animal hemisphere, is at right angles to the first and is vertical. This divides the egg into four blastomeres. The fourth blastomere so produced are not qualitatively equal, since of these only two contain the material from the gray crescent. The cleavage begins about thirty minutes after the second is completed or four hours after fertilisation. the cleavage plane of the third furrow is horizontal and slightly above the equator. Thus the four upper cells are a little smaller than the four lower cells. The smaller blastomeres are called micromeres and the larger blastomeres are called macromeres. The fourth cleavages follow 20 minutes after the third and tend to be vertical. This is usually a double furrow.

* The cleavage rate is accelerated with each of the early divisions and since the blastomeres are of unequal size and have varying amounts of cytoplasm and yolk, synchronous cleavage is lost and there is an obvious overlapping of the division. The upper most cells divide more rapidly than the lowermost cells. From this point onwards perfect symmetry in cleavage and in blastomere is very rare, although the embryo developed perfectly. The fifth cleavage is also doubled, appearing first in the upper hemisphere and then in the lower.

* The cleavage thus far follows the rule that each cleavage plane comes in at right angles to the previous one. The subsequent divisions become so irregular that it is previous one. The subsequent division become so irregular that it is impossible to trace out any plan or procedure. The segmentation continues more rapidly in the pigmented regions, since at that place the protoplasm is most dense, whereas, yolk which is very abundant in the vegetal side delays cell division. The multicelluar embryo at this stage is called morula by some biologists.

----

== Gastrulation ==

[[Image:FROG GASTRULATION .jpg|thumb|left|Frog Gastrulation Image details:[http://www.google.com.au/imgres?imgurl=http://bio1903.nicerweb.com/Locked/media/ch47/47_12FrogGastrulation.jpg&imgrefurl=http://bio1903.nicerweb.com/Locked/media/ch47/gastrulation-frog.html&h=540&w=480&sz=46&tbnid=N78sHjELreGGSM:&tbnh=132&tbnw=117&prev=/images%3Fq%3Dfrog%2B-%2Bgastrulation&hl=en&usg=__4VK9FYLft0W-4lBe6p5EtQAMiaI=&ei=qPy5SurtMJvE6wON8JmdAg&sa=X&oi=image_result&resnum=4&ct=image].jpg]]

''The phase of Blastulation is followed by the unique developmental progression of gastrulation. The process of frog gastrulation involves the following processes.''

'''1. Epiboly Phase'''

The pigmented cellular materials of blastula have the propensity to overgrow the yolk cells within the developing content. This course which is known as epiboly commences gradually in the final blastula and rapidly accelerates with advancing gastrulation development. The cellular matter within the animal pole reproduces and matures on all sides except in area surrounding the dorsal lip of the blastopore has been established.

'''2. Convergence'''

Scientists suggested that the unfolding was thought to result in spreading of the superficial cells over a substrate with suitable absorption properties. Consequently epiboly and convergence are an outcome to this spreading tendency, which is actually increased by a reduction in surface tension of the distributing cells.

'''3. Rotation'''

The epiboly phase is maintained until the region of the dorsal lip has migrated and is a to some extent greater than 90 degrees and the region of the white blastopore is reduced to small circular rings. This section will be positioned away from the developing vegetal pole. Laterally the complete developing gastrula has been rotated to a horizontal axis, allowing it to lie at right angles to the original median plane of the egg. Therefore, the course of rotation is such that the dorsal lip is practically pushed backwards in one direction as rapid or quicker than epiboly moves it forward in the other. The outcome will be that the blastopore produced at roughly the vegetal pole is posterior, and the dorsal and ventral lips are essentially dorsal and ventral. This in addition allows the eggs to form the antero-ventral side of the potential embryo whilst the area marked by the grey crescent is to develop the dorsal segment.

'''4. Invagination'''

Visible is a small fissure- like invagination which is apparent in the middle between the equator and the vegetal segment. The most superior or dorsal border of the cleft produce the dorsal lip of the blastopore. This imput move back and forth on the dorsal plane near the dorsal lip and migrates around the boundaries of the blastocoel in company with the extension of the lateral lips. This adapted invagination is maintained until the blastocoel cavity has been almost abolished; excluding the slender opening separating epiblasts from the hypoblast, the new segment formed is known as the archenteron cavity.

'''5. Involution'''

- Additional to previous course of action a distinct involution also occurs at the blastoporal borders. This is mainly dynamic at the median dorsal lip and gradually more less as it shifts across either side until it reaches the ventral lip where it constant.Throughout this progression, cells positioned beside the superior boundaries of the blastoporal lip migrate over the lip to the interior portion of the lip. These cells are remained within the embryo along the internal edge of the blastopore. This indicates the root of archenteron is composed of involuted cells and beyond this the external layer known as the ectoderm. The base and lateral sides are enclosed mainly of endodermal cellular material, which have been established from larger yolk cells, situated in the vegetal pole of the blastula.

- In the final phases of the gastrula development, the cells contributing to the floor of the archenteron, thin out significantly where they surround the blastocoel.
The hemispherical shaped dorsal lip of blastopore which become visible at the commencement of the gastruation stage carry on to augment, initially becoming semicircular, then transform into a horse shoe shaped and then finally forming into circular band. The band is the accomplished by the blastopore. Various yolk cells of vegetal pole present in the section are crowed into the blastoporal cavity where they form a gathering identified as a yolk plug. Blastopore rapidly reduces in size while the archenteron is still developing and becomes completely formed in the final stage; the yolk plug appears as only a small oval on the gastrula.

==Growth and Modification of Frog Species==

'''1. Changes in habits and habitats:'''

'''a)''' In frogs, metamorphosis is related with to the modifications and adaptations as a frog changes environmental habitats from an aquatic to a terrestrial mode. Metamorphosis has modified the adaption of frogs as this alteration it began during the aquatic adaptations in the surface of water to breathe air. Subsequently, it continues the terrestrial surroundings, therefore the frog species become abundant in vegetation area allowing the frog to transform in to amphibious species.

'''b)''' The transition during metamorphosis is linked with a change in food chain. The tadpoles being the embryonic origin of frogs are herbivorous, feeding on algae and green matter, which they collect by the adapted feature such as their teeth surrounding their mouths. Adult frogs, alternatively, are classified as carnivorous feeding on insects and worms. Occasionally, they also consume larger prey, for instance smaller frogs species and even little birds and rodents which they dominant and ingest.

[[Image:Development of frog from sperm to mature structure.jpg|thumb|left|Figure 9 Image details:J,Nassif 2009.jpg]]

'''2. Changes in Morphology'''

These include the decrease or complete absence of specific organs or structures which are essential during development of early frog embryology, but not critical in the mature frog species. The significant alterations of this nature include the following developmental structures.

'''a)''' The long tail of the tadpole alongside the fin folds is absorbed again during metamorphosis and becomes absent at the final stage of the metamorphosis.

'''b) '''The developing gills are resorted, the gill clefts are congested and the branchial cavities start to become absent. The reabsorbtion of gills also takes place by autolysis.

'''c)''' The teeth of the perioral disc additionally the homey lining of the jaws are shed.

'''d)''' The lateral line sense organs within the skin of tadpoles vanish throughout metamorphosis.

'''e)''' The cloacal tube begins to condensed and reduced.

'''f)''' Various blood vessels, together with parts of the aortic arches, are reduced during mature development.

(The figure on the left represents the transformation from a tadpole to a developing structure.)[http://science.jrank.org/pages/2862/Frogs-Adult-morphology.html]

'''3. Progressive or constructive changes'''

This process comprises of the development of specific organs which mature into functional systems only during metamorphosis.

'''a)''' During development the limbs continue to augment in size and differentiation. The forelimbs, which in the tadpole mature under the opercular membrane, which then break through to the exterior. Simultaneously there is a increase in the length and strength of the hind limbs, joints develop in them and the toes become visible.

'''b)''' The middle ear becomes apparent in relation with the first pharyngeal pouch. The tympanic membrane matures. It is bounded by circular tympanic cartilage which allows the frog to retain air.

'''c)''' The visual organs bulge up on the dorsal surface of the head developing the nictitating membrane.

'''d)''' There is augmentation of the tongue and the formation of thevomerina teeth.

[[Image: Growth model.jpg|thumb|Figure 10 Image details:J,Nassif2009:]]

'''4. Remodelling of some structures'''

Systematic organs which operate both in the early embryonic larva and the mature adult change their differentiation during metamorphosis so as to meet the requirements of the adult mode of life and due to the habitat adaptations. The figure on the right illustrates structures developing from specic germ cell layers.

'''a)''' The skin of the embryonic tadpole is lined with a double-layered epidermis. The number of layers of cells in the epidermis augments throughout metamorphosis. Superficial surface layers become cornified. Multicellular mucous and serous glands originate in the skin. The pigmentation of the skin continuously changes, new patterns and colour start to form.

'''b)''' There is a lengthening of the mouth gap as a result of rotation of the quadrate cartilage and the true jaws become functional.

'''c)''' The tongue rapidly progresses and becomes larger and more muscular.

'''d)''' The eyes become more specialised.

'''e)''' In early tadpoles, the GIT is extremely long and wound up into a spiral folds. The intestine become greatly lengthened in herbivorous species due to the vegetables food chain.[http://en.wikipedia.org/wiki/Frog]

'''5. Development of the reproductive system'''

(The figure below represents the reproductive and development cycle of a frog as it transform from egg to frog specie.)

In tadpoles, right after the mouth is being formed, two indentation like thickenings of peritoneum begin to appear near the body cavity (dorsal surface), which is nearest to the mesentery which is near the developing kidneys. These appear in all tadpoles.

These indentations appear here because of a change in the endothelial cells, everywhere else they are usually flat looking cells but they undergo a change and in this particular area become somewhat cuboidal/columnar.

Later on the indentations become more obvious due to the epithelial cells replicating numerously to form a thick layer. The posterior two thirds of the indentation for the female is the ovary and for the male it is the testis. The third that is left differentiates and becomes fat for the body.

[[Image: Mature frog life cyle.jpg|thumb|200px|left|Figure 11 Image details:Derived from primary source:http://www.scienceclarified.com/images/uesc_01_img0038.jpg]]

[[Image: Developing frog.jpg|thumb|Figure 12 Image details:
[[Image: Mature develop frog.jpg|thumb|Image details: Wikipedia (2009) TYPICAL FROG Primary source:[http://en.wikipedia.org/wiki/File:Red-eyed_Tree_Frog_-_Litoria_chloris_edit1.jpg]].jpg]]

===Delamination===

Delamination indicates a mass separating a group of cellular matter from other cellular groups. It has been illustrated that the division of notochord, mesoderm and endoderm tissues from each other to form distinct cellular masses is completed by the progression of delamination, subsequent to these materials moving to the inside throughout gastrulation. During the developing gastrula, the germ layers are all recognized. These distinct segments of the embryo develop from these germ tissue layers.

===Polarity and Rotation===

Throughout fertilisation to the beginning of gastrulation, the frog’s egg continues in the original location in relation to its polarity. Subsequent to gastrulation its polarity begins to differentiate. This progression is linked with migration of materials within the gastrula and can be responsible for the alterations of the centre of gravity.

===Closing of Blastopore===

Subsequent to the formation of the gastrula, the blastopore is visible as a tiny round circular filled cavity containing the yolk plug. As it continues to reduce in dimension, it represented as a pear-shaped outline through the mutual approach of its lateral lips. Through it final progression these fuse entirely to produce a longitudinal groove, the streak which continue dorsally and ventrally in a small aperture. The inferior aperture closes, resulting in a depression called the anal pit. The superior region remains open for some period and begins to as the neural groove is laid down.

===Post Gastrulation or Organogenesis===

Throughout the duration of pre-gastrulation, all tissues for different organs vanish from the surface of blastula and migrate inside to take their final arrangement in the embryo structure where organs are developed from their potential regions. Consequently organogenesis transfers an embryo into free larva structure.

----

==Germ-layer origin of various body tissues==
[[Image: Development Models of Frog.jpg|thumb|right|Figure 13 Image details:Vertebrate Structure and Development.jpg]]

Ectoderm will give raise to structures such as skin, brain, spinal cord, neurons and sense receptors.
Mesoderm will give raise to structrues such as notochord, muscles, blood, bone and sex organs.
Endoderm will give raise to sturctures such as inner lining of gut, liver, pancreas, lungs and bladder, thyroid and parathyroid glands and thymus.

== Structures derived from Germ-layers of frog species ==

[[Image:Development of Frog Layers.jpg|thumb|left|Figure 14 Primary source[http://www.bio.miami.edu/~cmallery/150/physiol/sf19x11b.jpg]Image details:J,Nassif 2009.jpg]]

[[Image:Development of frog layers.jpg|thumb|left|Figure 15 Primary source [http://www.bio.miami.edu/~cmallery/150/physiol/sf19x11b.jpg]Image details:J,Nassif 2009.jpg]]

'''Ectoderm '''

''Establishes the epidermal segments and its derivatives, to the frog’s nervous system. The ectoderm also contributes to :''

1. The olfactory and auditory epithelium.

2. The retina and lens of the eye.

3. Sensory organs.

4. The epithelial lining of the oral cavity and the anus.

5. The pineal and pituitary body.

'''Mesoderm'''

''Mesoderm originates:''

1. Connective tissue.

2. Muscles, except the notochord.

3. Blood vessels.

4. Lymphatics.

5. The peritoneum and the urinary and reproductive system.

6. The dermis, parts of the eye excluding lens, cornea, and conjunctiva.

'''Endoderm'''

''From the endoderm arises:''

1. The epithelial lining to the gut and oesophagus, stomach, intestine, bile duct.

2. The hepatic cells of the liver, respiratory tract, larynx, trachea and lungs.

3. The lining of the urinary bladder, pancreas thyroid and thymus.

[The two figures reveal the development of structures deriving from the celluar components of the embryology of the frog].[Structures derived from Germ-layers of frog species ]

==Life cycle of a frog==

'''Fertilization-egg''':

The female lays eggs in the spring. A group of fertilized eggs is called spawn;

'''7-10 days''':

Fertilized egg feed on remaining yolk which is in its gut. Their gills, mouth and tail have poorly developed. Begin to swim and feed on algae;

'''10-30 days(4 weeks):'''

A layer of skin grows over gills. Teeth begin to appear. A coiled gut start to develop. This is aid in digestion;

'''30-60 days(6-9 weeks):'''

Legs being to grow and head is more distinct. Start to eat insects. Arms begin to grow;

'''60-80 days(12 weeks):'''

Resemble a frog. Still have remaining tail;

'''80-140 days(20 weeks):'''

Fully developed, spend most of time out of water. Majority of frog live between 4-15 years.

==Timeline of frog development==

Development of egg and embryo at temperature 18 degree celsius.

'''0 hours''' - fertilization of the egg

'''1 hours''' - formation of the gray crescent due to pigment migration

'''3.5 hours''' - early cleavage

'''4.5 hours''' - blastula stage(coeloblastula with eccentric blastocoel

'''26 hours''' - gastrulation

'''26 hours''' -'' early'' - crescent shaped dorsal lip

'''34 hours''' - ''middle''- semicircular blastoporal lip

'''42 hours''' - ''late'' - circular blastoporal lip

'''50 hours''' - neurulation

'''50 hours''' - ''early'' - medullary plate

'''62 hours''' -'' middle''- neural folds converging

'''67 hours''' - ''late'' - neural tube formed and ciliation of embryo

'''84 hours''' - tail bud stage(early organogeny)

'''96 hours''' - muscular response to tactile stimulation

'''118 hours''' - early heart beat, development of gill buds

'''140 hours''' - hatching and gill circulation

'''162 hours''' - mouth opens and cornea becomes transparent

'''192 hours''' - tail fin circulation established

'''216 hours''' - degeneration of external gills, formation of operculum, development of embryonic teeth

'''240 hours''' - opercular fold over brachial chamber except for spiracle and internal gills

'''255 hours''' - prolonged larval stage with refinement of organs

'''270 hours''' - development of hindlimbs, internal development of forelimbs in opercular cavity

'''275 hours''' - projection of forelimbs through operculum, left side first

'''280 hours''' - absorption of the tail and reduction in size of the gut

'''284 hours''' - metamorphosis complete, emergence from water as miniature, air breathing frog

==Stages of frog embryology==
--[[User:S8600021|Mark Hill]] 08:40, 9 October 2009 (EST) [[Talk:2009_Group_Project_5#Constructive_Criticism_of_Coordinator|see my comment on images]]

The rate of development of the egg and embryo will depend upon the temperature at which they are kept. The approximate schedule of development at 23 degree celsius is provided below.

{| border='1px'
|+ Table 1: Stages of frog development
!Stage !!Time since fertilisation (hours)!!Stage Characteristic !!Embryo characteristic !!Image of frog stage
|-
|1
|0.00-1.30
|fertilization of the egg, post fertilization
|animal hemisphere, gray crescent and vegetal hemisphere are present
|[[File:Stage01ventral.jpg|100px]]
|-
|2
|1.30-2.00
|splits into two cells
|appearance of first cleavage furrow
|[[File:Stage02ventral.jpg|100px]]
|-
|3
|2.00-2.15
|becomes four cells
|appearance of second cleavage furrow
|[[File:Stage03dorsolat.jpg|100px]]
|-
|4
|2.15-2.45
|becomes eight cells
|appearance of third cleavage furrow
|[[File:Stage04dorsolat.jpg|100px]]
|-
|5
|2.45-3.00
|becomes sixteen cells
|appearance of fourth cleavage furrow
|[[File:Stage05dorsal.jpg|100px]]
|-
|6
|3.00-3.30
|becomes thirty-two cells
|appearance of fifth cleavage furrow
|[[File:Stage06animal.jpg|100px]]
|-
|6.5
|3.30-4.00
|blastula stage
|Three dorsal folds become visible as a result of endoderm invagination. Pole cells no longer visible on surface
|[[File:Stage065dorsal.jpg|100px]]
|-
|7
|4.00-5.00
|Gastrulation stage
|two primary germ layers. epiblast and endoderm
|[[File:Stage07ventral.jpg|100px]]
|-
|8
|5.00-7.00
|neurulation
|medullary plate, neural folds and neural tube
|[[File:Stage08animal.jpg|100px]]
|-
|9
|7.00-9.00
|germ layer
|complete lip involution encircling yolk
|[[File:Stage09veg.jpg|100px]]
|-
|10
|9.00-11.00
|early gastrula
|two primary germ layers
|[[File:Stage10veg.jpg|100px]]
|-
|10.5
|11.00-11.45
|gastrula
|two germ layers
|[[File:Stage105vegb.jpg|100px]]
|-
|11
|11.45-12.30
|medulla plate
|Yolk sac protrudes dorsally, labium moves to midline on ventral side
|[[File:Stage11veg.jpg|100px]]
|-
|11.5
|12.30-13.15
|continuation of medulla plate
|start closing the plate
|[[File:Stage115veg.jpg|100px]]
|-
|12
|13.15-14.15
|early neurula
|thickened ectoderm give rise to CNS
|[[File:Stage12veg.jpg|100px]]
|-
|12.5
|14.15-14.45
|neural folds
|expansion of cavity
|[[File:Stage125postdors.jpg|100px]]
|-
|13
|14.45-16.15
|neural folds
|continue expanding cavity
|[[File:Stage13postdors.jpg|100px]]
|-
|14
|16.15-17.30
|neural folds
|continuation of cavity
|[[File:Stage14postdors.jpg|100px]]
|-
|15
|17.30-18.15
|tail bud stage
|early organogeny
|[[File:Stage15postdors.jpg|100px]]
|-
|16
|18.15-18.45
|tail bud stage
|posterior ventral view
|[[File:Stage16ant.jpg|100px]]
|-
|17
|18.45-19.45
|tail bud stage
|anterior view
|[[File:Stage17ant.jpg|100px]]
|-
|19
|20.45-21.45
|neural fold close complete
|dorsal view
|[[File:Stage19dorsal.jpg|100px]]
|-
|20
|21.45-22.30
|early tail bud
|anterior view
|[[File:Stage20dorsal.jpg|100px]]
|-
|21
|22.30-24.00
|termination of neural crest
|progress to next stage
|[[File:Stage21ant.jpg|100px]]
|-
|22
|24.00-24.45
|prolonged development
|elongation
|[[File:Stage22lat.jpg|100px]]
|-
|23
|24.45-26.15
|elongation of embryo
|later view
|[[File:Stage23lat.jpg|100px]]
|-
|24
|26.15-27.30
|continuation of elongation of embryo
|dorsal view
|[[File:Stage24latsmall.jpg|50px]]
|-
|25
|27.30-29.30
|organs development
|embryo elongates and develops dorsal thickening
|[[File:Stage25dorsal.jpg|50px]]
|-
|26
|29.30-31.15
|elongation
|dorsally forms neural and brain cavity
|[[File:Stage26lat.jpg|50px]]
|-
|27
|31.15-32.30
|elongation of embryo
|dorsal view
|[[File:Stage27lat.jpg|50px]]
|-
|28
|32.30-35.00
|further development
|lateral view
|[[File:Stage28lat.jpg|50px]]
|-
|29-30
|35.00-37.30
|tail bud
|growth
|[[File:Stage29-30lat.jpg|50px]]
|-
|31
|37.30-40.00
|prolonged development
|bud development
|[[File:Stage31lat.jpg|50px]]
|-
|32
|40.00-44.30
|early muscular development
|elongation
|[[File:Stage32lat.jpg|50px]]
|-
|33-34
|44.30-50.00
|muscular movement
|apparatus for locomotion
|[[File:Stage33-34lat.jpg|50px]]
|-
|35-36
|50.00-53.30
|muscular movement
|apparatus for locomotion
|[[File:Stage35-36lat.jpg|50px]]
|-
|37-38
|53.30-56.30
|heart beat
|develops apparatus
|[[File:Stage37-38lat.jpg|50px]]
|-
|39
|56.30-66.00
|mouth opens
|cornea transparent
|[[File:Stage39latsmall.jpg|50px]]
|-
|40
|66.00-76.00
|gill circulation
|hatching
|[[File:Stage40lat.jpg|50px]]
|-
|41
|76.00-80.00
|tail, fin circulation
|circulation
|[[File:Stage41lat.jpg|50px]]
|-
|42
|80.00-86.00
|internal gills, operculum
|opercular fold, teeth
|[[File:Stage42lat.jpg|50px]]
|-
|43
|86.00-98.00
|operculum complete
|operculum closed on right
|[[File:Stage43lat.jpg|50px]]
|-
|46
|98.00-106.00
|metamorphosis
|emergence from water as miniature, operculum complete|
|[[File:Stage46lat.jpg|50px]]
|-
|}

==Abnormalities of frog==

Abnormalities of frog could be caused by multiple factors. These include change in climate, predators, parasites, bacteria, fungi, viruses or pollution and contaminants such as pesticides, metals and fertilizer.[http://www.fws.gov/contaminants/documents/frogsrefup_septoct_2006.pdf]

The Abnormalities are further classified into different categories. These categories are:

===1. Infectious Diseases:===

'''Perkinsus Symptoms-''' caused by perkinsus-like protozoan organism. Symptoms include swollen viscera that leads to a bloated body and and infected swollen heart

'''Ichthyophonus symptoms-''' cause by parasitic genus, where symptoms include a swollen tail resorption site that matches the surrounding skin in color and translucency.

[[Image:Abnormalities of Frog species.jpg|thumb|left|Figure A Image details[waterwatchadelaide.net.au].jpg]]

===2. Surficial Abnormalities:===

Surficial abnormalities as the one that are visible on the surface of the skin. This includes abnormal pigmentation, , subcutaneous hemorrhaging, wounds due to trauma or from a predator
Edema is a fluid-filled swelling under skin whihc is also a surficial abnormality.

===3. Skeletal Abnormalities:===

This is further classified into three more categories:

'''a. Skeletal Malformations-'''

* Microcephaly (small head or blunt snout)
*Scoliosis (Curved spine in lateral direction)
*Shrunken Limb (Micromelia)
*Amelia (Completely missing limb with no stump)

'''b. Skeletal Abnormalities of Unclear Etiology-'''

This condition arises when a frog has ectromelia (missing limb), brachydactyly (missing digits) or other such condition with no visible trauma or external damage, then this will be classified as the Skeletal abnormality of unclear etiology.

'''c. Skeletal Injuries-'''

Any limb missing or broken due to trauma or other related reason which shows clear evidence of it is classified as skeletal injury

===4. Eye Abnormalities:===

Most common includes-

'''i. Anophthalmia:''' Skin covers the eye socket as there is no eye

'''ii. Abnormal Iris Coloration:''' Reduced pigment in either one eye or both resulting in two different colours of the iris at times

'''iii. Abnormal size or shape:''' Both eyes either deviating from each other or size of pupil or iris is different than the other eye

[http://www.fws.gov/contaminants/Amphibian/pdfs/AbnormalitySOP_woutpics_Jan08.pdf ]

==Genetics==

There are a wide variety of species that differ from each other when it comes to genetics and their functioning.

'''TAXONOMY:''' '''Phylum''' ''Chordata'' / '''Sub Phylum''' ''Vertebrata'' / '''Class''' ''Amphibia'' / '''Order''' ''Anura''

Their are more than two dozen different families of frogs, where suborders are:

'''1. ARCHAEBATRACHIA-''' most primitive frogs

'''2. MESOBATRACHIA-''' linked between the Archaebatrachia and Neobatrachia

'''3. NEOBATRACHIA-''' most modern frogs

{| border='4px'
|+ '''General Info:'''
! !!
|-
| '''Number of frogs' species'''
| 5280
|-
| '''Smallest frog genome size:'''
| 0.95pg, Ornate burrowing frog
|-
| '''Largest frog genome size:'''
| 13.40pg, Ornate horned frog
|-
| '''Mean of frogs' genome'''
| 4.68pg ± 0.13
|-
|}

[http://www.genomesize.com]

*Majority of frogs have only 22 to 26 chromosomes and polyploid is very common where they are almost bisexual.

*Polyploid Amphibians reduce their total cell number such that they acheive the same body size as diploids. One of the most unsual forms of polypoidy in amphibians is the water frog ''Rana esculenta'' from Europe and Western Asia.

* The species with larger genomes have more genes for e.g. the frog genus ''Xenopus'' includes 16 species, with genome sizes ranging from 3.5 x 10^9 bp to 1.6 x 10^10 bp. These differences have arisen by numerous events of polyploidization within the past 40 million years or so. The ancestral chromosome number for the genus seems to have been 18, but there are species with 36, 72 and 105 chromosomes [http://www.xenbase.org/common/]

{| border='4px'
|+ '''Difference within two families'''
! '''SPECIES''' !! ''X.LAEVIS'' !! ''X.TROPICALIS''
|-
| '''PLOIDY'''
| Allotetraploid
| Diploid
|-
| '''NO. OF CHROMOSOMES'''
| 36 chromosomes
| 20 chromosomes
|-
| '''GENOME SIZE'''
| 3.1 x 10^9 bp
| 1.7 x 10^9 bp
|-
| '''EGG SIZE'''
| 1-1.3 mm
| 0.7-0.8 mm
|-
| '''GENERATION TIME'''
| 1-2 years
| 4 months
|-
|}
[http://www.xenbase.org/common/]

===Genome Sequencing===

Since Frog has a huge family with many different species, only few main species that are used widely for the purposes of experiments have their genome sequenced.

''Xenopus tropicalis'' has one of the smallest genomes among amphibians and has the shortest generation time- four to six months and the only diploid genome among the 14 Xenopus species. This means it has no more than two copies of most genes, whereas the other species of Xenopus have four copies of most genes (pseudotetraploid). US Department of Energy's Joint Genome Institute (JGI) in Walnut Creek, California, initiated the X. tropicalis Genome Project, finding 1,700 million base pairs.
[http://www.genome.gov/Pages/Research/Sequencing/BACLibrary/xenopusTropicalis.pdf]

===Xenopus oocytes===

* The oocytes provide an important expression system for molecular biology.

* By injecting DNA or mRNA into the oocyte or developing embryo, scientists can study the protein products in a controlled system. This allows rapid functional expression of manipulated DNAs (or mRNA). This is particularly useful in electrophysiology, where the ease of recording from the oocyte makes expression of membrane channels attractive.

* One challenge of oocyte work is eliminating native proteins that might confound results, such as membrane channels native to the oocyte.

* Translation of proteins can be blocked or splicing of pre-mRNA can be modified by injection of Morpholino antisense oligos into the oocyte (for distribution throughout the embryo) or early embryo (for distribution only into daughter cells of the injected cell).
[http://www.staff.unibe.ch/sigel/xenopus.html]

===Xenopus Laevis===

* ''Xenopus Laevis'' is an important model organism in developmental biology. X. laevis is tetraploid and reaches sexual maturity in 1 to 2 years. What makes it important in developmental biology is its large and easily manipulable embryo.

* Extracts from the eggs of X. laevis frogs are also commonly used for biochemical studies of DNA replication and repair, as these extracts fully support DNA replication and other related processes in a cell-free environment which allows easier manipulation.

* The Human chorionic gonadotropin hormone (hCG) is present in the urine of the pregnant women in large quantities only. This hormone in the urine induces X.laevis oocyte production which formed the basis of first well-documented method of pregnancy testing X. laevis is also notable for its use as the first well-documented method of pregnancy testing when it was discovered. Today, commercially available HCG is injected into Xenopus males and females to induce mating behavior and breed these frogs in captivity at any time of the year.

===Gene cluster===

* The alpha and beta globin genes are closely linked in small cluster of frogs compared to human and chicken

* The similarity of architecture of two clusters found in X.laevis supports the tetraploid origin

* The two loci encoding the muscle specific creatine kinase isoenzymes and have large differences in developmental profile, therefore suggesting that duplicate loci that have not undergone silencing are not simply redundant copies but have acquired specialization.

* Contains twice number of genes for proteins i.e. haemoglobin and sarcomeric actin serum albumin compared with other species

----

==Current Embrology Research==

Currently, a number of fields have benefited from the development of frog embrology. These include cloning, verification of messenger RNA, and Cell cycle.

===Cloning===
[[Image:Robert Briggs.jpg|thumb|left|Figure 16 Image details:Robert Briggs.jpg]]

In 1952, Robert Briggs and Thomas J King cloned northern leopard frogs using a method of nuclear transfer. Briggs and King's experiment was similar to that envisioned - and piloted using salamanders - by Hans Spemann in his 1938 proposal for a 'fantastical experiment'. Later, John Gurdon extended this work and showed that nuclei from differentiated cells could support development, although less well than those from early embryos. [http://genome.wellcome.ac.uk/doc_WTD020799.html]

Lemaitre et a. (2005) from MRC Cancer Cell Unit, Cambridge, U.K. worked on experiments that demonstrated that importance of serial nuclear transplantation for the sucessful cloning of frogs. He demonstrated that exposure of somatic-cell nuclei (erythrocyte nuclei) and sperm nuclei to an extract of mitotic cell extract reorganizes the chromatin into shorter loops and allows replication at much shorter intervals along the DNA. This increases the efficiency of DNA replication in mammalian cell-free systems.

===Transgenesis techniques for functional genomics in Xenopus===

Transgenesis in Xenopus is made possible due to large embryos, a reliable fate map, ease of microinjection, ease of dissection/micromanipulation and existence of the neuroendocrine reflex of background adaptation as a model for activation/inact.

Recently, Hajime Ogino and Haruki Ochi from Nura Institute of Science and Technology in Japan focused on the genomic resources and principles of the transgenesis techniques in Xenopus, and discusses their applications to genome wide network analysis, with emphasis on the use of bioinformatics tools. This is will to understand the gene regulatory networks that control vertebrate development. [http://www.ingentaconnect.com/content/bsc/dgd/2009/00000051/00000004/art00001%3Bjsessionid=4ah96rms73gcu.alexandra]

Xenopus used to be a problem in earlier days when it came to transgenesis. Current methods involves isolated sperm nuclei from Xenopus testis that are microinjected into unfertilized eggs. The generated transgenic tadpoles contain 5-35 copies of the integrated plasmid that are expressed in all cells. If desired, expression of the transgene can be directed to the appropriate tissue and at the appropriate time by using specific promoters, mostly the Xenopus POMC gene promoter (isolated from a Xenopus genomic DNA library) to specifically direct expression of green fluorescent protein (GFP) at high levels to the intermediate pituitary cells, which can either be over expressed or inhibited.[http://molanphys.ruhosting.nl/transgenesis.htm]

[[File:Transgenesis.JPG]]

===Verification of messenger RNA===

While the existence and role of messenger RNA (mRNA) was known in bacteria, in the 1960s it was still debated whether it also existed in vertebrates. Taking haemoglobin mRNA from immature red blood cells and injecting it into a Xenopus oocyte, John Gurdon showed that the haemoglobin protein was indeed produced. Producing proteins in Xenopus oocytes has proved to be extremely useful in cell biology, in particular for the study of receptor proteins.[http://genome.wellcome.ac.uk/doc_WTD020799.html]

===Cell Cycle===

As they develop outside the mother, frog eggs are well stocked with the proteins needed to drive the development of the embryo. Studies of these processes has shed considerable light on the processes involved in cell division - termed the cell cycle. [http://genome.wellcome.ac.uk/doc_WTD020799.html]

===Limb development in Xenopus Laevis===

[[Image: Frog Limb development.jpg|thumb|right|Image details:Primary source:[http://images.google.com.au/imgres?imgurl=http://www.sciencedaily.com/images/2006/06/060616130718.jpg&imgrefurl=http://www.sciencedaily.com/releases/2006/06/060616130718.htm&usg=__xliPsPAvheUBME_kjv_q7auiFbo=&h=333&w=300&sz=11&hl=en&start=2&um=1&tbnid=y_ntJtmkRSK7WM:&tbnh=119&tbnw=107&prev=/images%3Fq%3DLimb%2Bdevelopment%2Bin%2BXenopus%2BLaevis%26ndsp%3D18%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

Donald D. Brown (2005),Department of Embryology, Carnegie Institution of Washington demonstrated factors related to limb development of Xenopus Laevis. Thyroid hormone (TH) is found to be required for limb development in this frog. Specific cell types in the growing limb were targeted for expression of a dominant negative form of the TH receptor by sperm-mediated transgenesis. Limb muscle development, the innervation of muscle from the spinal cord, and cartilage growth can be inhibited without affecting patterning of the limb or differentiation of other cell types. Remodeling of the skin occurs late in metamorphosis after the limb has formed. The coordination of these independent programs is affected in part by the control that TH exerts over DNA replication in all cell types of the limb. [http://www.pnas.org/content/102/35/12455.full]

----

== Glossary ==

[[Image: Frog species.jpg|thumb|left|Image details:Primary source:www.olympus.co.jp/.../080925/large/p02L.jpg].jpg]]

*'''Amphibian:'''

''Relating to or characteristic of animals of the class amphibia.Amphibians are found in the taxonomic class of amphibia, amphibians are capable of both occupying and successfully living in both land and aquatic communities.amphibian''

*'''Augmentation:'''

''Enlargement/Increase in cellular size.''

*'''Autolysis:'''

''breakdown of a part or whole cell or tissue by self-produced enzymes''

*'''Blastomeres:'''

''The undifferentiated cells formed by cleavage of the fertilised ovum. This includes cells in the cleavage, morula, and blastula stages of the embryo''

*'''Carnivorous:'''
''
Flesh-eating; subsisting on animals as food.''

*'''Cleavage:'''

''he repeated division of a fertilised ovum ''

* '''Cleft:'''

''an opening, fissure, or V-shaped indentation made by or as if by splitting''

*'''Chordate:'''

''Members of a diverse phylum of animals that, as embryos, possess a (1) notochord; (2) a dorsal, hollow nerve cord, (3) pharyngeal gill slits; and (4) a post-anal tail''

''The act or state of splitting or dividing of a cell, particularly during the telophase of (animal) cell division.''

*'''Cytoplasm:'''

''The cytoplasm (of both eukaryotes and prokaryotes) is where the functions for cell expansion, growth, metabolism, and replication are carried out''

* '''Epiboly:'''
''The expansion of one cell sheet over other cells, as takes place during gastrulation''

*'''Fertilization:'''

''A process in sexual reproduction that involves the union of male (sperm) and female (ovum) gametes (each with a single, haploid set of chromosomes) to produce a diploid zygote.''

*'''Gamete:'''
''A reproductive cell (male (sperm) or female (egg)) that has only half the usual number of chromosomes''

*'''Gametogenesis:'''

''process leading to the production of gametes. The development and maturation of sex cells through meiosis.Another name for meiosis where a diploid cell is divided into two haploid cells with half the chromosome content of the diploid parent cell.''

*'''Herbivorous:'''

''eating plants; of or pertaining to the herbivora.''

*'''Holoblastic:'''

''The complete division of an isolecithal or microlecithal egg into blastomeres''

*'''Invagination:'''

''One of the methods by which the various germinal layers of the ovum are differentiated.''

*'''Isoenzymes:'''

''Isozymes (also known as isoenzymes) are enzymes that differ in amino acid sequence but catalyze the same chemical reaction.''

*'''Mesentery:'''

'' membranous fold attaching various organs to the body wall.''

*'''Metamorphosis:'''

''A change in the form and often habits of an animal after the embryonic stage during normal development.''

*'''Neuroendocrine:'''

''Neuroendocrine [IPA nʊəroʊˈɛndəkrɪn] cells are cells that release a hormone into the circulating blood in response to a neural stimulus.''

*'''Organogenesis:'''

''The part of embryonic development where the body's main organs develop.''

*'''Peritoneum:'''

''The smooth serous membrane which lines the cavity of the abdomen, or the whole body cavity when there is no diaphragm, and, turning back, surrounds the viscera, forming a closed, or nearly closed, sac.''

*'''Perivitelline space:'''

''The perivitelline space is the space between the zona pellucida and the plasma membrane (sometimes called the vitelline membrane) in a fertilized ovum.''

*'''Polyploidy:'''

''Cells with three or more sets of chromosomes.''

*'''Pronucleus:'''

''the nucleus of the ovum or sperm after fertilization but before they fuse to form the nucleus of the zygote ''

*'''Protoplasm:'''

''The fluid living content of the cell that consists of two major divisions, the cytoplasm and the nucleoplasm (cell nucleus). It is composed mainly of nucleic acids, proteins, lipids, carbohydrates, and inorganic salts''

*'''Segmentation:'''

''division of some metazoan bodies (such as annelida and Arthropoda) into repeated parts, segments. Segmentation can be homomeric (more or less the same) or heteromeric(different from each other).''

*'''Terrestrial:'''

''Of or on the ground, of the habitat of a plant, on land as opposed to in water, or on the ground as opposed to on another plant.''

*'''Transgenesis:'''

''Transgenesis is the process of introducing an exogenous gene - called a transgene - into a living organism so that the organism will exhibit a new property and transmit that property to its offspring.''

*'''Yolk:'''

''nutritive material of an ovum stored for the nutrition of an embryo''

*'''Zygote:'''

''The cell from which an organism develops, that results from the fertilization of the egg by the sperm.''

''Primary Resource "Biology- Online Dictionary''[http://www.biology-online.org/dictionary/Main_Page]

== References - Frog Embryology: ==

[[Image:Frog Research.jpg|thumb|left|Image details:[http://images.google.com.au/imgres?imgurl=http://www.odt.co.nz/files/story/2008/09/university_of_otago_zoology_senior_lecturer_phil_b_3343259744.jpg&imgrefurl=http://www.odt.co.nz/on-campus/university-otago/21670/dunedin-frog-man-wins-zoo-award&usg=__JvJJU5QfOnIwY2bk4xo64UXuJRs=&h=600&w=404&sz=22&hl=en&start=14&um=1&tbnid=AbsP89yWcUiilM:&tbnh=135&tbnw=91&prev=/images%3Fq%3Dfrog%2Bresearch%26hl%3Den%26um%3D1].jpg]]

1. Savage, J. M. (2002). The Amphibians and Reptiles of Costa Rica. University of Chicago Press, Chicago [http://www.springerlink.com/content/vv015277w1746llw/]

2. Ford, L.S.; D.C. Cannatella (1993). "The major clades of frogs". Herpetological Monographs 7: 94–117 [http://digimorph.org/specimens/Xenopus_laevis/]

3. Tyler, M. J. (1994). Australian Frogs A Natural History. Reed Books [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.gracilenta.html]

4. Cogger, H.G.; R.G. Zweifel, and D. Kirschner (2004). Encyclopedia of Reptiles & Amphibians Second Edition. Fog City Press [http://en.wikipedia.org/wiki/Microhylidae]

5. Beltz, Ellin (2005). Frogs: Inside their Remarkable World. Firefly Books [http://unjobs.org/authors/ellin-beltz]

6. Tyler, M. J. (1994). Australian Frogs A Natural History. Reed Books [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

7. Moury JD, Hanken J (1995) Early cranial neural crest migration in the direct-developing frog, Eleutherodactylus coqui. Acta
Anatomica (Basel) 153, 243-253.

8.Raynaud A (1985) Development of limbs and embryonic limb reduction. In Biology of the Reptilia (ed. Gans C, Billett F), pp.
59-148. New York: John Wiley.[http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=9309]

9. Hanken J (1986) Developmental evidence for amphibian origins. In Evolutionary Biology (ed. Hecht MK, Wallace B, Prance GT), 20, pp. 389-417. New York: Plenum Press. [Hanken J (1986) Developmental evidence for amphibian origins. In Evolutionary Biology (ed. Hecht MK, Wallace B, Prance GT), 20, pp. 389-417. New York: Plenum Press.]

10. Elinson RP (1990) Direct development in frogs : wiping the recapitulationist slate clean. Seminars in Developmental Biology
1, 263-270.

11. Beebee, T. J. C. 1996. Ecology and Conservation of Amphibians. Chapman and Hall. London. [http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V5X-3SVHMKH-1X&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=1021245355&_rerunOrigin=google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=825868e10cd178d16a8a0e5ad14dc5ef]

12. Lehtinen, R. M. 2002. The use of screw pines (Pandanus spp.) by amphibians and reptiles in Madagascar. Herpetological Bulletin 2002:20–25.

13. Parris, K. M. and M. A. McCarthy. 1999. What influences the structure of frog assemblages at forest streams. Australian Journal of Ecology 24:495–502. CrossRef

14. Zug, G. R. 1993. Herpetology: An Introductory Biology of Amphibians and Reptiles. Academic Press. San Diego, CA.

15. Slack,J.M.W., Darlington,B.G., Heath,J.K. and Godsave,S.F. (1987)Mesoderm induction in early Xenopus embryos by heparin-binding growth factors. Nature, 326, 197-200.

16. Melton,D.A. (1990) Activins are expressed early in Xenopus embryogenesis and can induce axial mesoderm and anterior structures. Cell, 63, 485-493.

17. Harland,R.M. and Misher,L. (1988) Stability of RNA in developing Xenopus embryos and identification of a destabilizing sequence in TFIIIA RNA. Development, 102, 837-852.

18. Cunliffe,V. and Smith,J.C. (1992) Ectopic mesoderm formation in Xenopus embryos caused by widespread expression of a Brachyury homologue. Nature, 358, 427-430.

19. Kinoshita,K., Bessho,T. and Asashima,M. (1993) Competence prepattern in the animal hemisphere of the 8-cell-stage Xenopus embryo. Devel. Biol., 160, 276-284.

20. LaBonne,C., Burke,B. and Whitman,M. (1995) Role of MAP kinase in mesoderm induction and axial patterning in Xenopus development. Development, 121, 1475-1486.

21. Green,J.B.A., New,H.V. and Smith,J.C. (1992) Responses of embryonic Xenopus cells to activin and FGF are separated by multiple dose thresholds and correspond to distinct axes of the mesoderm. Cell, 71, 731-739.

22. Grainger R., Blumberg B., Harland R., Amemiya C., Importance of Xenopus Tropicalis to biomedical and biological research, Benaroya Research Institute, Virginia Mason Research Center [http://www.genome.gov/Pages/Research/Sequencing/BACLibrary/xenopusTropicalis.pdf ]

23. Gregory, T.R. (2005). Animal Genome Size Database. [http://www.genomesize.com]

24. U.S Fish and Wildlife Services, ABNORMALITY CLASSIFICATION SOP, [http://www.fws.gov/contaminants/Amphibian/pdfs/AbnormalitySOP_woutpics_Jan08.pdf ]

25. Donald D. Brown*, Liquan Cai*, Biswajit Das*, Nicholas Marsh-Armstrong‡, Alexander M. Schreiber*, and Rejeanne Juste*(2005), Thyroid hormone controls multiple independent programs required for limb development in Xenopus laevis metamorphosis [http://www.pnas.org/content/102/35/12455.full]

26. Ogino, Hajime; Ochi, Haruki, Resources and transgenesis techniques for functional genomics in Xenopus, Development Growth & Differentiation, Volume 51, Number 4, May 2009 , pp. 387-401(15) [http://www.ingentaconnect.com/content/bsc/dgd/2009/00000051/00000004/art00001%3Bjsessionid=4ah96rms73gcu.alexandra]

27. Giles Newton (2004) Why the frog? The Human Genome, [http://genome.wellcome.ac.uk/doc_WTD020799.html]

28. Xenbase, [http://www.xenbase.org/common/]

29. Donders Center for Neuroscience & Nijmegen Center for Molecular Life Sciences (NCMLS), Beyond the genome (Xenopus transgenesis for functional genomics),Faculty of Science, Radboud University [http://molanphys.ruhosting.nl/transgenesis.htm]

== External Links ==
[[Image:Frog links.jpg|thumb|left|Image details:[http://images.google.com.au/imgres?imgurl=http://2.bp.blogspot.com/_o93AaY0GzH4/SjY_ZYv0PII/AAAAAAAAAgk/skruNc2yN78/s400/computer%2Bfrog.jpg&imgrefurl=http://hellaheaven-ana.blogspot.com/2009/06/talking-frog-contemporary-fairy-tale.html&usg=__oxji1TGLV2Fi7xe0dnlmuYk8gDo=&h=288&w=288&sz=16&hl=en&start=2&um=1&tbnid=ywZd4zpdxC5plM:&tbnh=115&tbnw=115&prev=/images%3Fq%3Dfrog%2Bon%2Bcomputer%26hl%3Den%26um%3D1].jpg]]

1. Frog embryology [http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/F/FrogEmbryology.html Frog Embryology]

2. Frog cellular materials [http://www.xenbase.org/xenbase/original/cell/cell.html xenbase]

3. The zoology of frog species [http://worms.zoology.wisc.edu/frogs/mainmenu.html zoology frogs]

4. Frog cycle [http://www.bioethics.gov/images/sc_images/frog_dev.gif bioethics frog] Just a little cycle of FROG'S life cycle

5. Frog Embryology [http://embryology.med.unsw.edu.au/OtherEmb/Frog.htm UNSW Embryology]

6. Frog Research [http://apps.carleton.edu/campus/library/now/exhibits/wallcharts/frog/ carleton library exhibit]

{{Template:Projects09}}
[[Category:Frog]]

2009 Group Project 5

2009-10-14T22:39:11Z

Z3258567: /* Cleavage */

== The Embryology of Frogs ==

== The Frog ==

[[Image: Frog species .jpg|thumb|left|Image details: Wikipedia (2009) Frog species[http://en.wikipedia.org/wiki/Frog#Uses_in_agriculture_and_research].jpg]]

Frogs are scientifically identified by the structure of their long posterior limbs, a petite framework, webbed fingers and feet, budged eyes and the lack of a tail. The majority of frog species are extensively recognized as outstanding jumpers, due to their long, dominant legs, which are adaptations to progress jumping performance during activities. The Frog is one of the most frequently studied species in experimental embryology and most anatomical sciences. ''The Frog is a practically effective model for human embryological development given that the Frog:''

- Comprises of genes which can be effectively manipulated.

- Comprises of similar homogeny with humans species.

- Reproduces a large quantity of offspring in a short period of time.

- Are small species which can be simply sustained.

- Are not extremely luxurious and expensive.

== The History of the uses in agriculture and research ==

[[Image: Frog experiments .jpg|thumb|right|Image details: Scans of chemically cleared and dyed preserved deformed frogs and toads [http://www.sat.qc.ca/upload/residence/frog-04.jpg].jpg]]

There are numerous types of frog species that have been manipulated in many developmental experiments. The frog was traditionally used by countless of the early embryology investigators and presently there are several diverse molecular mechanisms regarding progression of the frog. Theses include:

'''1.''' Food source; frog legs are a delicacy and are eaten in European countries and in many parts of South American regions.

'''2.''' Frogs have the finest biochemical dissection of phenomena that take place in the egg and oocyte. Frogs are the evolutionarily closest to mammals, commonly used as a vertebrate model.

'''3.''' Frogs lay thousands of outsized eggs, from which cell extracts can be readily prepared that is capable of recapitulating most molecular phenomena in a test tube.

'''4.''' Frogs have been commonly used as a laboratory system for a very long period, and have an extensive history of producing crucial observations in countless fields of biology.

'''5.''' Frogs have a important historical connection to the study of epigenetics (John Gurdon-vertebrate cloning and reprogramming) which has been mostly performed on frog species.

'''6.''' Frogs also have very strong evidence of pattern formation and early development, as the embryos are large in size and experimentally manipulative.

'''7.''' Recent research into the biochemistry of chromatin and epigenetics has been performed with frog species and mammalian cultured cells.

'''8.''' The biggest weakness of the Frog model system is the difficulty of performing genetic experiments and analysis, as frogs are allotetraploid, meaning they take approximately a year to fully develop to sexual maturity, and the genome has not been completely sequenced. Nevertheless, biochemical manipulations of cell extracts, such as immunodepletions and application of heterologous DNAs and nuclei can avoid the need for genetic exploitation.

----

== Growth and development of the Frog ==

[[Image: Mature develop frog.jpg|thumb|Image details: Wikipedia (2009) Red Eyed Tree Frog Figure 1 Primary source:[http://en.wikipedia.org/wiki/File:Red-eyed_Tree_Frog_-_Litoria_chloris_edit1].jpg]]

* The frog is a well recognised species, abundant predominantly in ponds, swamps, though various species may also exist in damp or shady environments distant from moist habitats.

* Eggs of specific frogs are easily obtained and may be examined in from the beginning of fertilization onwards. The phases of embryonic development differs in various chordates, yet the typical phases are basically apparent in all frog species. The differences are associated principally to the amount of yolk particles present in an egg.

* The yolk particles offer nourishment of the developing embryo. The process of frog development will be discussed from the phases of gametogenesis to the adult stage.

----

== The Egg ==
[[Image:Development of Poles in frog Fertilization.jpg|thumb|left|Development of Poles in Frog Fertilisation:J,Nassif 2009.jpg]]

- The embryology of a frog egg is a vast cell; its dimensions are approximately 1.4-1.6 million times larger than a typical aquatic species egg cell. Throughout the frog’s embryonic maturation period, the egg will be transformed into a tadpole encompassing millions of cells but still remains with its constant volume of genetic material, the vast prodction of cell have been illusttrated in the figure on the right revealing the production of eggs from female frogs. [http://en.wikipedia.org/wiki/Microhylidae]

- The early embryonic frog structure consists of three main segments the superior hemisphere known as the animal pole which is usually visible as a grey coloured area. The innermost layer appears to be between the outer two sections known as the gray crescent represented in black. Inferiorly, represents the vegetal pole typically lighter than the superior compartment illustrated in gold.

VIDEO RESOURCE: [http://www.youtube.com/watch?v=GO5YN_t1fqw&feature=related]

[[Image:Early Development of Frogs.jpg|thumb|left|Early Development of Frog:J,Nassif 2009.jpg]]

==History of frog embryology use ==

*'''1851''' - ''Henby Nelson''(MD): He identified a remarkable fact through the frog embryo. Henby observed the first cleavage of the yolk, in the egg of the frog. And cleaved structure corresponds in line of direction to the longitudinal axis of the body of the embryo of the frog species.

[[Image:Wilhelm Roux.jpg|thumb|right|Wilhelm Roux[http://images.google.com.au/imgres?imgurl=http://www.todayinsci.com/R/Roux_Wilhelm/RouxWilhelmThm.jpg&imgrefurl=http://www.todayinsci.com/6/6_09.htm&usg=__qRLTEMTHdZpAHxiNX12hWjcm9tA=&h=125&w=100&sz=4&hl=en&start=2&um=1&tbnid=LIKIwZTqCpk7MM:&tbnh=90&tbnw=72&prev=/images%3Fq%3DWilhelm%2BRoux%26gbv%3D2%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

*'''1888''' - ''Wilhelm Roux'': Wilhelm Roux attempted to solve the above observation by damaging one cell of a two-cell frog embryo with a hot needle. The cell stayed in place. However, it did not develop further. Its partner developed into a left or right half-embryo;

*'''1907''' - ''John Hopkins'' hospital: In order to identify the cellular source of neuronal fibres. Scientist placed small portions of frog embryo spinal cords in lymph on a microscope slide and was able to observe clear cut neuronal sprouting.

*'''1951''' - ''Robert Briggs'': Robert Briggs was able to clone a frog embryo by substituting the nucleus of an unfertilized frog egg cell with the nucleus of a frog embryo cell. This process is known as nuclear transplant, has formed the basis for all cloning.

*'''1952''' - ''Robert Briggs and T.J. King'': Robert Briggs and T.J. King used frog for test experiment. Because the size of the eggs in the frogs are enormous compared with those of mammals, which make them easier to manipulate.

*'''1976'''- Using the technique that had been successful in cloning frog embryos, the doctor transferred the nucleus of one cells into a donated egg cell. As an embryo began to develop, it was implanted into the uterus of a young woman.

*'''1997''' - ''Wilmut and Campbell'': Utilizing the cloning technique from frog embryo, Drs. Wilmut and Campbell tried the starvation technique on embryo cells to produce Megan and Morag, the world's first cloned sheep and, until now, the most famous sheep in history.

*'''2000''' - ''Tokyo University'': Scientists at Tokyo University have grown artificial eyeballs. Scientists formed them in tadpoles by using frog embryo cells.

*'''2001''' - ''Advanced Cell Technology'': Scientists from Advanced Cell Technology announced production of a human embryo clone. This is significant as its parthenogenesis has been artificially induced in frogs.

[[Image:John Gurdon .jpg|thumb|right|John Gurdon [http://images.google.com.au/imgres?imgurl=http://www.pnas.org/site/misc/images/gurdon.jpg&imgrefurl=http://www.pnas.org/site/misc/classics4.shtml&usg=__1p-GA1PdOYsxKL-cznMb3RHCm98=&h=526&w=400&sz=223&hl=en&start=1&um=1&tbnid=9k4lhuLssiWCAM:&tbnh=132&tbnw=100&prev=/images%3Fq%3DJohn%2BGurdon%26gbv%3D2%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

*'''2002''' - ''John Gurdon'': John Gurdon from Wellcome Cancer Research Institute in Cambridge experimented on cloned frog embryo.

== Gametogenesis ==

* The sexual reproduction occurs through the fusion of either mature reproductive cells or germ cells known as gametes, which include the sperm from the male frog and ova from female frog species so as to form a single cell, the fertilized zygote. The gametes are typically developed in parents of different sexes . [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

* Males gametes is a spermatozoon , the female frog gamete is an ovum. Each gamete is formed by a process, recognised as maturation or gametogenesis in gonads. The typical male frog gonads are testies in male, while the female gonads are ovaries. The synthesis of both gonads is associated with the process of fertilization. [http://en.wikipedia.org/wiki/Microhylidae]

* The zygote changes into a mature frog through the process of embryology and metamorphosis. Gametogenesis is a in progression which frog gametes are established from germ cells. Initial germ cells are called primordial germ cells, which can be recognised extremely early in the life of frog species.

----

== The Egg & Fertilization ==

[[Image:Fertilized and Unfertilised Eggs.jpg|thumb|left|Fertilized and Unfertilized Eggs:J,Nassif 2009.jpg]]

[[Image:Egg Development.jpg|thumb|left|Egg Development:J,Nassif 2009.jpg]]

- This occurs once the sperm cell has inserted, following the insertion of the sperm cells meiosis II is completed, there is a 30 degree position change of the cytoplasm, gray crescent allows this change to be visible in some amphibians, the gray crescent is able what determines the expect ted outline of how the frog will form. The sperm cell joins with the nuclei of the egg which forms the diploid zygote nucleus. --Sando Rashed 10:09, 24 September 2009 (EST)

- The early phases in the development of the egg is visible, but must be studied in tadpoles throughout maturation. In embryonic tadpoles of about 10 millimetres in length, soon after the opening of the oral cavity, a pair of longitudinal ridge-like thickenings of peritoneum becomes apparent along the posterior surface of the body cavity situated near to the mesentery and along the inner boundaries of the kidneys. Genital ridges are established in all tadpoles of this age, sex is not distinct until a later period. The development of the egg is illustrated in the figure on the left revealing the structure of a developed egg and a mature of egg.

[[Image:Fertilisation life cyle.jpg|thumb|Fertilization of Life cycle:Derived from primary source:[http://en.wikipedia.org/wiki/Frog]]]

== Maturation of the Egg ==

- The eggs have currently accomplished their full size, and develop from the exterior of the ovaries like a small shot, but they still have to pass through the course of maturation before they are prepared to be fertilised. This progression of maturation relates to the nucleus almost completely.

- The nucleus component, containing the nuclear fluid that excludes through the nuclear membrane into the substance of the egg, a great segment of the nuclear reticulum vanishes and becomes degraded into separate globules known as nucleoli, but a extremely small division remains in the midpoint as a slender intricately thread recognised as the nuclear skets.
Relative to the egg getting discharged from the ovary, the follicles shatter allowing the eggs to fall into the abdominal cavity of the frog species, the egg then passes forwards, directly by the contraction of the muscular wall, somewhat by the movement of the cilia of the peritoneum, to the apex of the oviduct, which positioned at the anterior compartment of the body cavity opposite to the roots of the respiratory organs.

- The terminal part of the oviduct establishes a thin-walled pouch capable of great swelling, inside which the eggs gathers in large numbers. In conclusion, the eggs are migrated out through the cloaca into water which the albuminous investments of the eggs rapidly augment to form the gelatinous mass of the frogs spawn.

== Maturation phases ==

'''1. Nuclear skein''', moves from the midpoint of the egg to its outer surface, which it reaches opposite the midpoint of the black pole. The skein, subsequently an unevenly twisted thread, now presumes the specific arrangement of a nuclear spindle, for instance may be visible in the nucleus of an epithelial or additional cell instantly prior to division of the cell occurs.[http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

'''2. The first Polar Body,''' regarding the instance the egg is laid, but prior to its fertilistion, the egg develops a considerably flattened appearance at its upper or black pole, a definite sum of fluid being exuded among the egg and the vitelline membrane. The nuclear spindle currently separate into two identical segments, one of which remains with the egg, and the supplementary is extruded as the first polar body, a small ovoidal white globule, which is situated on the surface of the egg surrounding the exuded peri-vitellline fluid.

'''3. The Second Polar Body''', half of the nuclear spindle that stay behind then splits into two equivalent divisions, one of which remains inside the egg as the female pronucleus, whereas the other segment is extruded as the second polar body, a small white globule extremely related to the first polar body, and like this positioned in the perivitelline fluid on the superior portion of the egg.

'''4. Fertilisation of the egg''', includes the synthesis of the spermatozoon with to egg, specifically, synthesis of the nuclei of these two bodies. The spermatozoa, subsequent to being shed over the seed by the male, distribute vigorously by means of their extended tails, break through the gelatinous investment of the female eggs, bore their way through the vitelline membrane and so go through into the eggs themselves, which they penetrate relative to the superior or black hemispheres.
* Subsequently, an hour following the spermatozoon has entered; a progression may be visible projecting within from the exterior segement of the egg, with a liquid spot in the mid point. This liquid centre is the nucleus of the spermatozoon, and is said to be the male pronucleus, it break through beyond into the female egg, transporting the specialised pigment into it, so that it appears bounded by a pigmented capsule linked with the exterior of the egg by a pigmented stalk.

* By this instance, the second polar body has been established and extruded, and the female pronucleus is merely the only component of the primary egg nucleus still present. Both the male and female pronuceli, which are at initially distance separate to each other, merge and after having enlarged significantly in size then fuse mutually about two and half hours after fertilisation has originated to produce the segmentation nucleus.
* The segmentation nucleus is a huge sphere-shaped vesicle embedded in delicately granular protoplasm, and bounded by a distinct capsule of pigment, its arrangement by the synthesis of the male and female pronuclei completes the action of fertilisation. Specifically female pronucleus may be observe as an imperfect nucleus, and consequently result in the course of fertilisation. The nucleus of the spermatozoon or male pronucleus, replaces the component of the egg- nucleus which has been misplaced as the polar bodies.

'''5. Segmentation of the Egg''', the initial phase of growth consist in constant separation of the egg, whereby it becomes transformed from the unicellular state, which is everlasting only in the lowest species, to muliticelluar state charactertics of all higher species. To these early processes of growth the names segmentation is specified. Shorty subsequent to the competition of fertilisation and arrangement of the segmentation nucleus this later misplaces its sphere-shaped appearance and develops to be spindle-shaped, the yolk granules at the equivalent instance showing a tendency to develop into lines distributing outwards from the distal segment of the spindle.
* The nucleus now split into two halves, which shift away from one another, the yolk granules are likely to combined themselves around the two nuclei, and a slender vertical plate of delicately granular substance is left, dividing the egg.[http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

* Superiorly the eggs depression now becomes visible, initially as a small cavity and then develops as a groove, which almost immediately extends all round, and speedily deepening, splits the egg into two entirely separate halves along a plane equivalent with the vertical plane.

* Shorty after, the two nuclei soon separate again into two, and therefore a second cleft is created in the same state as before, its additionally in the vertical plane, however in a plane at 90 degrees to the initial one, and on its finishing point the egg comprises of four accurately similar segments, each containing a nucleus. The third cleft is horizontal in shape, but not equal, lying closer to the superior than the lower pole, it segregates each of the four cells into, an superior smaller and a inferior larger pole

----

== Cleavage ==

[[Image: Frog Cleavage development.jpg|thumb|left|Cleavage Process details:[http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/F/FrogEmbryology.html].jpg]]

* The egg of the frog is scientifically identified as’ telolecithal’ meaning there is a outsized amount of yolk concentrated at a single pole, in contrast to the concentration of cytoplasm and the site of the nucleus. The cleavage phases are holoblastic, therefore the total and after the second cleavage they are asymmetrical .The initial cleavage stage appears about two and half to three hours after fertilization. It commences as a minor depression in close proximity to the centre of the animal hemisphere. It appears as if some interior force is pushing the surface the egg towards the centre. This small upturned fold steadily continues in the form of a channel until it surrounds the egg. This groove is shallow in the commencement, but develop into deeper eventually separating the fertilized egg into two halves recognised as the blastomeres. [The figure on the left symbolise the development and growth of the frog embryo during cleavage].

* Internally the separation is mitotic, consequently each daughter cell contains a nucleus resulting from the copulation nucleus of the fertilised egg. This cleavage is vertical, the two cells are indistinguishable in respect of cytoplasm, pigment and yolk. The subsequent cleavage appears about an hour after the first. The channel of this cleavage begins at the centre of the animal hemisphere, is at right angles to the first and is vertical. This divides the egg into four blastomeres. The fourth blastomere so produced are not qualitatively equal, since of these only two contain the material from the gray crescent. The cleavage begins about thirty minutes after the second is completed or four hours after fertilisation. the cleavage plane of the third furrow is horizontal and slightly above the equator. Thus the four upper cells are a little smaller than the four lower cells. The smaller blastomeres are called micromeres and the larger blastomeres are called macromeres. The fourth cleavages follow 20 minutes after the third and tend to be vertical. This is usually a double furrow.

* The cleavage rate is accelerated with each of the early divisions and since the blastomeres are of unequal size and have varying amounts of cytoplasm and yolk, synchronous cleavage is lost and there is an obvious overlapping of the division. The upper most cells divide more rapidly than the lowermost cells. From this point onwards perfect symmetry in cleavage and in blastomere is very rare, although the embryo developed perfectly. The fifth cleavage is also doubled, appearing first in the upper hemisphere and then in the lower.

* The cleavage thus far follows the rule that each cleavage plane comes in at right angles to the previous one. The subsequent divisions become so irregular that it is previous one. The subsequent division become so irregular that it is impossible to trace out any plan or procedure. The segmentation continues more rapidly in the pigmented regions, since at that place the protoplasm is most dense, whereas, yolk which is very abundant in the vegetal side delays cell division. The multicelluar embryo at this stage is called morula by some biologists.

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== Gastrulation ==

[[Image:FROG GASTRULATION .jpg|thumb|left|Figure Image details:[http://www.google.com.au/imgres?imgurl=http://bio1903.nicerweb.com/Locked/media/ch47/47_12FrogGastrulation.jpg&imgrefurl=http://bio1903.nicerweb.com/Locked/media/ch47/gastrulation-frog.html&h=540&w=480&sz=46&tbnid=N78sHjELreGGSM:&tbnh=132&tbnw=117&prev=/images%3Fq%3Dfrog%2B-%2Bgastrulation&hl=en&usg=__4VK9FYLft0W-4lBe6p5EtQAMiaI=&ei=qPy5SurtMJvE6wON8JmdAg&sa=X&oi=image_result&resnum=4&ct=image].jpg]]

''The phase of Blastulation is followed by the unique developmental progression of gastrulation. The process of frog gastrulation involves the following processes.''

'''1. Epiboly Phase'''

The pigmented cellular materials of blastula have the propensity to overgrow the yolk cells within the developing content. This course which is known as epiboly commences gradually in the final blastula and rapidly accelerates with advancing gastrulation development. The cellular matter within the animal pole reproduces and matures on all sides except in area surrounding the dorsal lip of the blastopore has been established.

'''2. Convergence'''

Scientists suggested that the unfolding was thought to result in spreading of the superficial cells over a substrate with suitable absorption properties. Consequently epiboly and convergence are an outcome to this spreading tendency, which is actually increased by a reduction in surface tension of the distributing cells.

'''3. Rotation'''

The epiboly phase is maintained until the region of the dorsal lip has migrated and is a to some extent greater than 90 degrees and the region of the white blastopore is reduced to small circular rings. This section will be positioned away from the developing vegetal pole. Laterally the complete developing gastrula has been rotated to a horizontal axis, allowing it to lie at right angles to the original median plane of the egg. Therefore, the course of rotation is such that the dorsal lip is practically pushed backwards in one direction as rapid or quicker than epiboly moves it forward in the other. The outcome will be that the blastopore produced at roughly the vegetal pole is posterior, and the dorsal and ventral lips are essentially dorsal and ventral. This in addition allows the eggs to form the antero-ventral side of the potential embryo whilst the area marked by the grey crescent is to develop the dorsal segment.

'''4. Invagination'''

Visible is a small fissure- like invagination which is apparent in the middle between the equator and the vegetal segment. The most superior or dorsal border of the cleft produce the dorsal lip of the blastopore. This imput move back and forth on the dorsal plane near the dorsal lip and migrates around the boundaries of the blastocoel in company with the extension of the lateral lips. This adapted invagination is maintained until the blastocoel cavity has been almost abolished; excluding the slender opening separating epiblasts from the hypoblast, the new segment formed is known as the archenteron cavity.

'''5. Involution'''

- Additional to previous course of action a distinct involution also occurs at the blastoporal borders. This is mainly dynamic at the median dorsal lip and gradually more less as it shifts across either side until it reaches the ventral lip where it constant.Throughout this progression, cells positioned beside the superior boundaries of the blastoporal lip migrate over the lip to the interior portion of the lip. These cells are remained within the embryo along the internal edge of the blastopore. This indicates the root of archenteron is composed of involuted cells and beyond this the external layer known as the ectoderm. The base and lateral sides are enclosed mainly of endodermal cellular material, which have been established from larger yolk cells, situated in the vegetal pole of the blastula.

- In the final phases of the gastrula development, the cells contributing to the floor of the archenteron, thin out significantly where they surround the blastocoel.
The hemispherical shaped dorsal lip of blastopore which become visible at the commencement of the gastruation stage carry on to augment, initially becoming semicircular, then transform into a horse shoe shaped and then finally forming into circular band. The band is the accomplished by the blastopore. Various yolk cells of vegetal pole present in the section are crowed into the blastoporal cavity where they form a gathering identified as a yolk plug. Blastopore rapidly reduces in size while the archenteron is still developing and becomes completely formed in the final stage; the yolk plug appears as only a small oval on the gastrula.

==Growth and Modification of Frog Species==

'''1. Changes in habits and habitats:'''

'''a)''' In frogs, metamorphosis is related with to the modifications and adaptations as a frog changes environmental habitats from an aquatic to a terrestrial mode. Metamorphosis has modified the adaption of frogs as this alteration it began during the aquatic adaptations in the surface of water to breathe air. Subsequently, it continues the terrestrial surroundings, therefore the frog species become abundant in vegetation area allowing the frog to transform in to amphibious species.

'''b)''' The transition during metamorphosis is linked with a change in food chain. The tadpoles being the embryonic origin of frogs are herbivorous, feeding on algae and green matter, which they collect by the adapted feature such as their teeth surrounding their mouths. Adult frogs, alternatively, are classified as carnivorous feeding on insects and worms. Occasionally, they also consume larger prey, for instance smaller frogs species and even little birds and rodents which they dominant and ingest.

[[Image:Development of frog from sperm to mature structure.jpg|thumb|left|Figure 9 Image details:J,Nassif 2009.jpg]]

'''2. Changes in Morphology'''

These include the decrease or complete absence of specific organs or structures which are essential during development of early frog embryology, but not critical in the mature frog species. The significant alterations of this nature include the following developmental structures.

'''a)''' The long tail of the tadpole alongside the fin folds is absorbed again during metamorphosis and becomes absent at the final stage of the metamorphosis.

'''b) '''The developing gills are resorted, the gill clefts are congested and the branchial cavities start to become absent. The reabsorbtion of gills also takes place by autolysis.

'''c)''' The teeth of the perioral disc additionally the homey lining of the jaws are shed.

'''d)''' The lateral line sense organs within the skin of tadpoles vanish throughout metamorphosis.

'''e)''' The cloacal tube begins to condensed and reduced.

'''f)''' Various blood vessels, together with parts of the aortic arches, are reduced during mature development.

(The figure on the left represents the transformation from a tadpole to a developing structure.)[http://science.jrank.org/pages/2862/Frogs-Adult-morphology.html]

'''3. Progressive or constructive changes'''

This process comprises of the development of specific organs which mature into functional systems only during metamorphosis.

'''a)''' During development the limbs continue to augment in size and differentiation. The forelimbs, which in the tadpole mature under the opercular membrane, which then break through to the exterior. Simultaneously there is a increase in the length and strength of the hind limbs, joints develop in them and the toes become visible.

'''b)''' The middle ear becomes apparent in relation with the first pharyngeal pouch. The tympanic membrane matures. It is bounded by circular tympanic cartilage which allows the frog to retain air.

'''c)''' The visual organs bulge up on the dorsal surface of the head developing the nictitating membrane.

'''d)''' There is augmentation of the tongue and the formation of thevomerina teeth.

[[Image: Growth model.jpg|thumb|Figure 10 Image details:J,Nassif2009:]]

'''4. Remodelling of some structures'''

Systematic organs which operate both in the early embryonic larva and the mature adult change their differentiation during metamorphosis so as to meet the requirements of the adult mode of life and due to the habitat adaptations. The figure on the right illustrates structures developing from specic germ cell layers.

'''a)''' The skin of the embryonic tadpole is lined with a double-layered epidermis. The number of layers of cells in the epidermis augments throughout metamorphosis. Superficial surface layers become cornified. Multicellular mucous and serous glands originate in the skin. The pigmentation of the skin continuously changes, new patterns and colour start to form.

'''b)''' There is a lengthening of the mouth gap as a result of rotation of the quadrate cartilage and the true jaws become functional.

'''c)''' The tongue rapidly progresses and becomes larger and more muscular.

'''d)''' The eyes become more specialised.

'''e)''' In early tadpoles, the GIT is extremely long and wound up into a spiral folds. The intestine become greatly lengthened in herbivorous species due to the vegetables food chain.[http://en.wikipedia.org/wiki/Frog]

'''5. Development of the reproductive system'''

(The figure below represents the reproductive and development cycle of a frog as it transform from egg to frog specie.)

In tadpoles, right after the mouth is being formed, two indentation like thickenings of peritoneum begin to appear near the body cavity (dorsal surface), which is nearest to the mesentery which is near the developing kidneys. These appear in all tadpoles.

These indentations appear here because of a change in the endothelial cells, everywhere else they are usually flat looking cells but they undergo a change and in this particular area become somewhat cuboidal/columnar.

Later on the indentations become more obvious due to the epithelial cells replicating numerously to form a thick layer. The posterior two thirds of the indentation for the female is the ovary and for the male it is the testis. The third that is left differentiates and becomes fat for the body.

[[Image: Mature frog life cyle.jpg|thumb|200px|left|Figure 11 Image details:Derived from primary source:http://www.scienceclarified.com/images/uesc_01_img0038.jpg]]

[[Image: Developing frog.jpg|thumb|Figure 12 Image details:
[[Image: Mature develop frog.jpg|thumb|Image details: Wikipedia (2009) TYPICAL FROG Primary source:[http://en.wikipedia.org/wiki/File:Red-eyed_Tree_Frog_-_Litoria_chloris_edit1.jpg]].jpg]]

===Delamination===

Delamination indicates a mass separating a group of cellular matter from other cellular groups. It has been illustrated that the division of notochord, mesoderm and endoderm tissues from each other to form distinct cellular masses is completed by the progression of delamination, subsequent to these materials moving to the inside throughout gastrulation. During the developing gastrula, the germ layers are all recognized. These distinct segments of the embryo develop from these germ tissue layers.

===Polarity and Rotation===

Throughout fertilisation to the beginning of gastrulation, the frog’s egg continues in the original location in relation to its polarity. Subsequent to gastrulation its polarity begins to differentiate. This progression is linked with migration of materials within the gastrula and can be responsible for the alterations of the centre of gravity.

===Closing of Blastopore===

Subsequent to the formation of the gastrula, the blastopore is visible as a tiny round circular filled cavity containing the yolk plug. As it continues to reduce in dimension, it represented as a pear-shaped outline through the mutual approach of its lateral lips. Through it final progression these fuse entirely to produce a longitudinal groove, the streak which continue dorsally and ventrally in a small aperture. The inferior aperture closes, resulting in a depression called the anal pit. The superior region remains open for some period and begins to as the neural groove is laid down.

===Post Gastrulation or Organogenesis===

Throughout the duration of pre-gastrulation, all tissues for different organs vanish from the surface of blastula and migrate inside to take their final arrangement in the embryo structure where organs are developed from their potential regions. Consequently organogenesis transfers an embryo into free larva structure.

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==Germ-layer origin of various body tissues==
[[Image: Development Models of Frog.jpg|thumb|right|Figure 13 Image details:Vertebrate Structure and Development.jpg]]

Ectoderm will give raise to structures such as skin, brain, spinal cord, neurons and sense receptors.
Mesoderm will give raise to structrues such as notochord, muscles, blood, bone and sex organs.
Endoderm will give raise to sturctures such as inner lining of gut, liver, pancreas, lungs and bladder, thyroid and parathyroid glands and thymus.

== Structures derived from Germ-layers of frog species ==

[[Image:Development of Frog Layers.jpg|thumb|left|Figure 14 Primary source[http://www.bio.miami.edu/~cmallery/150/physiol/sf19x11b.jpg]Image details:J,Nassif 2009.jpg]]

[[Image:Development of frog layers.jpg|thumb|left|Figure 15 Primary source [http://www.bio.miami.edu/~cmallery/150/physiol/sf19x11b.jpg]Image details:J,Nassif 2009.jpg]]

'''Ectoderm '''

''Establishes the epidermal segments and its derivatives, to the frog’s nervous system. The ectoderm also contributes to :''

1. The olfactory and auditory epithelium.

2. The retina and lens of the eye.

3. Sensory organs.

4. The epithelial lining of the oral cavity and the anus.

5. The pineal and pituitary body.

'''Mesoderm'''

''Mesoderm originates:''

1. Connective tissue.

2. Muscles, except the notochord.

3. Blood vessels.

4. Lymphatics.

5. The peritoneum and the urinary and reproductive system.

6. The dermis, parts of the eye excluding lens, cornea, and conjunctiva.

'''Endoderm'''

''From the endoderm arises:''

1. The epithelial lining to the gut and oesophagus, stomach, intestine, bile duct.

2. The hepatic cells of the liver, respiratory tract, larynx, trachea and lungs.

3. The lining of the urinary bladder, pancreas thyroid and thymus.

[The two figures reveal the development of structures deriving from the celluar components of the embryology of the frog].[Structures derived from Germ-layers of frog species ]

==Life cycle of a frog==

'''Fertilization-egg''':

The female lays eggs in the spring. A group of fertilized eggs is called spawn;

'''7-10 days''':

Fertilized egg feed on remaining yolk which is in its gut. Their gills, mouth and tail have poorly developed. Begin to swim and feed on algae;

'''10-30 days(4 weeks):'''

A layer of skin grows over gills. Teeth begin to appear. A coiled gut start to develop. This is aid in digestion;

'''30-60 days(6-9 weeks):'''

Legs being to grow and head is more distinct. Start to eat insects. Arms begin to grow;

'''60-80 days(12 weeks):'''

Resemble a frog. Still have remaining tail;

'''80-140 days(20 weeks):'''

Fully developed, spend most of time out of water. Majority of frog live between 4-15 years.

==Timeline of frog development==

Development of egg and embryo at temperature 18 degree celsius.

'''0 hours''' - fertilization of the egg

'''1 hours''' - formation of the gray crescent due to pigment migration

'''3.5 hours''' - early cleavage

'''4.5 hours''' - blastula stage(coeloblastula with eccentric blastocoel

'''26 hours''' - gastrulation

'''26 hours''' -'' early'' - crescent shaped dorsal lip

'''34 hours''' - ''middle''- semicircular blastoporal lip

'''42 hours''' - ''late'' - circular blastoporal lip

'''50 hours''' - neurulation

'''50 hours''' - ''early'' - medullary plate

'''62 hours''' -'' middle''- neural folds converging

'''67 hours''' - ''late'' - neural tube formed and ciliation of embryo

'''84 hours''' - tail bud stage(early organogeny)

'''96 hours''' - muscular response to tactile stimulation

'''118 hours''' - early heart beat, development of gill buds

'''140 hours''' - hatching and gill circulation

'''162 hours''' - mouth opens and cornea becomes transparent

'''192 hours''' - tail fin circulation established

'''216 hours''' - degeneration of external gills, formation of operculum, development of embryonic teeth

'''240 hours''' - opercular fold over brachial chamber except for spiracle and internal gills

'''255 hours''' - prolonged larval stage with refinement of organs

'''270 hours''' - development of hindlimbs, internal development of forelimbs in opercular cavity

'''275 hours''' - projection of forelimbs through operculum, left side first

'''280 hours''' - absorption of the tail and reduction in size of the gut

'''284 hours''' - metamorphosis complete, emergence from water as miniature, air breathing frog

==Stages of frog embryology==
--[[User:S8600021|Mark Hill]] 08:40, 9 October 2009 (EST) [[Talk:2009_Group_Project_5#Constructive_Criticism_of_Coordinator|see my comment on images]]

The rate of development of the egg and embryo will depend upon the temperature at which they are kept. The approximate schedule of development at 23 degree celsius is provided below.

{| border='1px'
|+ Table 1: Stages of frog development
!Stage !!Time since fertilisation (hours)!!Stage Characteristic !!Embryo characteristic !!Image of frog stage
|-
|1
|0.00-1.30
|fertilization of the egg, post fertilization
|animal hemisphere, gray crescent and vegetal hemisphere are present
|[[File:Stage01ventral.jpg|100px]]
|-
|2
|1.30-2.00
|splits into two cells
|appearance of first cleavage furrow
|[[File:Stage02ventral.jpg|100px]]
|-
|3
|2.00-2.15
|becomes four cells
|appearance of second cleavage furrow
|[[File:Stage03dorsolat.jpg|100px]]
|-
|4
|2.15-2.45
|becomes eight cells
|appearance of third cleavage furrow
|[[File:Stage04dorsolat.jpg|100px]]
|-
|5
|2.45-3.00
|becomes sixteen cells
|appearance of fourth cleavage furrow
|[[File:Stage05dorsal.jpg|100px]]
|-
|6
|3.00-3.30
|becomes thirty-two cells
|appearance of fifth cleavage furrow
|[[File:Stage06animal.jpg|100px]]
|-
|6.5
|3.30-4.00
|blastula stage
|Three dorsal folds become visible as a result of endoderm invagination. Pole cells no longer visible on surface
|[[File:Stage065dorsal.jpg|100px]]
|-
|7
|4.00-5.00
|Gastrulation stage
|two primary germ layers. epiblast and endoderm
|[[File:Stage07ventral.jpg|100px]]
|-
|8
|5.00-7.00
|neurulation
|medullary plate, neural folds and neural tube
|[[File:Stage08animal.jpg|100px]]
|-
|9
|7.00-9.00
|germ layer
|complete lip involution encircling yolk
|[[File:Stage09veg.jpg|100px]]
|-
|10
|9.00-11.00
|early gastrula
|two primary germ layers
|[[File:Stage10veg.jpg|100px]]
|-
|10.5
|11.00-11.45
|gastrula
|two germ layers
|[[File:Stage105vegb.jpg|100px]]
|-
|11
|11.45-12.30
|medulla plate
|Yolk sac protrudes dorsally, labium moves to midline on ventral side
|[[File:Stage11veg.jpg|100px]]
|-
|11.5
|12.30-13.15
|continuation of medulla plate
|start closing the plate
|[[File:Stage115veg.jpg|100px]]
|-
|12
|13.15-14.15
|early neurula
|thickened ectoderm give rise to CNS
|[[File:Stage12veg.jpg|100px]]
|-
|12.5
|14.15-14.45
|neural folds
|expansion of cavity
|[[File:Stage125postdors.jpg|100px]]
|-
|13
|14.45-16.15
|neural folds
|continue expanding cavity
|[[File:Stage13postdors.jpg|100px]]
|-
|14
|16.15-17.30
|neural folds
|continuation of cavity
|[[File:Stage14postdors.jpg|100px]]
|-
|15
|17.30-18.15
|tail bud stage
|early organogeny
|[[File:Stage15postdors.jpg|100px]]
|-
|16
|18.15-18.45
|tail bud stage
|posterior ventral view
|[[File:Stage16ant.jpg|100px]]
|-
|17
|18.45-19.45
|tail bud stage
|anterior view
|[[File:Stage17ant.jpg|100px]]
|-
|19
|20.45-21.45
|neural fold close complete
|dorsal view
|[[File:Stage19dorsal.jpg|100px]]
|-
|20
|21.45-22.30
|early tail bud
|anterior view
|[[File:Stage20dorsal.jpg|100px]]
|-
|21
|22.30-24.00
|termination of neural crest
|progress to next stage
|[[File:Stage21ant.jpg|100px]]
|-
|22
|24.00-24.45
|prolonged development
|elongation
|[[File:Stage22lat.jpg|100px]]
|-
|23
|24.45-26.15
|elongation of embryo
|later view
|[[File:Stage23lat.jpg|100px]]
|-
|24
|26.15-27.30
|continuation of elongation of embryo
|dorsal view
|[[File:Stage24latsmall.jpg|50px]]
|-
|25
|27.30-29.30
|organs development
|embryo elongates and develops dorsal thickening
|[[File:Stage25dorsal.jpg|50px]]
|-
|26
|29.30-31.15
|elongation
|dorsally forms neural and brain cavity
|[[File:Stage26lat.jpg|50px]]
|-
|27
|31.15-32.30
|elongation of embryo
|dorsal view
|[[File:Stage27lat.jpg|50px]]
|-
|28
|32.30-35.00
|further development
|lateral view
|[[File:Stage28lat.jpg|50px]]
|-
|29-30
|35.00-37.30
|tail bud
|growth
|[[File:Stage29-30lat.jpg|50px]]
|-
|31
|37.30-40.00
|prolonged development
|bud development
|[[File:Stage31lat.jpg|50px]]
|-
|32
|40.00-44.30
|early muscular development
|elongation
|[[File:Stage32lat.jpg|50px]]
|-
|33-34
|44.30-50.00
|muscular movement
|apparatus for locomotion
|[[File:Stage33-34lat.jpg|50px]]
|-
|35-36
|50.00-53.30
|muscular movement
|apparatus for locomotion
|[[File:Stage35-36lat.jpg|50px]]
|-
|37-38
|53.30-56.30
|heart beat
|develops apparatus
|[[File:Stage37-38lat.jpg|50px]]
|-
|39
|56.30-66.00
|mouth opens
|cornea transparent
|[[File:Stage39latsmall.jpg|50px]]
|-
|40
|66.00-76.00
|gill circulation
|hatching
|[[File:Stage40lat.jpg|50px]]
|-
|41
|76.00-80.00
|tail, fin circulation
|circulation
|[[File:Stage41lat.jpg|50px]]
|-
|42
|80.00-86.00
|internal gills, operculum
|opercular fold, teeth
|[[File:Stage42lat.jpg|50px]]
|-
|43
|86.00-98.00
|operculum complete
|operculum closed on right
|[[File:Stage43lat.jpg|50px]]
|-
|46
|98.00-106.00
|metamorphosis
|emergence from water as miniature, operculum complete|
|[[File:Stage46lat.jpg|50px]]
|-
|}

==Abnormalities of frog==

Abnormalities of frog could be caused by multiple factors. These include change in climate, predators, parasites, bacteria, fungi, viruses or pollution and contaminants such as pesticides, metals and fertilizer.[http://www.fws.gov/contaminants/documents/frogsrefup_septoct_2006.pdf]

The Abnormalities are further classified into different categories. These categories are:

===1. Infectious Diseases:===

'''Perkinsus Symptoms-''' caused by perkinsus-like protozoan organism. Symptoms include swollen viscera that leads to a bloated body and and infected swollen heart

'''Ichthyophonus symptoms-''' cause by parasitic genus, where symptoms include a swollen tail resorption site that matches the surrounding skin in color and translucency.

[[Image:Abnormalities of Frog species.jpg|thumb|left|Figure A Image details[waterwatchadelaide.net.au].jpg]]

===2. Surficial Abnormalities:===

Surficial abnormalities as the one that are visible on the surface of the skin. This includes abnormal pigmentation, , subcutaneous hemorrhaging, wounds due to trauma or from a predator
Edema is a fluid-filled swelling under skin whihc is also a surficial abnormality.

===3. Skeletal Abnormalities:===

This is further classified into three more categories:

'''a. Skeletal Malformations-'''

* Microcephaly (small head or blunt snout)
*Scoliosis (Curved spine in lateral direction)
*Shrunken Limb (Micromelia)
*Amelia (Completely missing limb with no stump)

'''b. Skeletal Abnormalities of Unclear Etiology-'''

This condition arises when a frog has ectromelia (missing limb), brachydactyly (missing digits) or other such condition with no visible trauma or external damage, then this will be classified as the Skeletal abnormality of unclear etiology.

'''c. Skeletal Injuries-'''

Any limb missing or broken due to trauma or other related reason which shows clear evidence of it is classified as skeletal injury

===4. Eye Abnormalities:===

Most common includes-

'''i. Anophthalmia:''' Skin covers the eye socket as there is no eye

'''ii. Abnormal Iris Coloration:''' Reduced pigment in either one eye or both resulting in two different colours of the iris at times

'''iii. Abnormal size or shape:''' Both eyes either deviating from each other or size of pupil or iris is different than the other eye

[http://www.fws.gov/contaminants/Amphibian/pdfs/AbnormalitySOP_woutpics_Jan08.pdf ]

==Genetics==

There are a wide variety of species that differ from each other when it comes to genetics and their functioning.

'''TAXONOMY:''' '''Phylum''' ''Chordata'' / '''Sub Phylum''' ''Vertebrata'' / '''Class''' ''Amphibia'' / '''Order''' ''Anura''

Their are more than two dozen different families of frogs, where suborders are:

'''1. ARCHAEBATRACHIA-''' most primitive frogs

'''2. MESOBATRACHIA-''' linked between the Archaebatrachia and Neobatrachia

'''3. NEOBATRACHIA-''' most modern frogs

{| border='4px'
|+ '''General Info:'''
! !!
|-
| '''Number of frogs' species'''
| 5280
|-
| '''Smallest frog genome size:'''
| 0.95pg, Ornate burrowing frog
|-
| '''Largest frog genome size:'''
| 13.40pg, Ornate horned frog
|-
| '''Mean of frogs' genome'''
| 4.68pg ± 0.13
|-
|}

[http://www.genomesize.com]

*Majority of frogs have only 22 to 26 chromosomes and polyploid is very common where they are almost bisexual.

*Polyploid Amphibians reduce their total cell number such that they acheive the same body size as diploids. One of the most unsual forms of polypoidy in amphibians is the water frog ''Rana esculenta'' from Europe and Western Asia.

* The species with larger genomes have more genes for e.g. the frog genus ''Xenopus'' includes 16 species, with genome sizes ranging from 3.5 x 10^9 bp to 1.6 x 10^10 bp. These differences have arisen by numerous events of polyploidization within the past 40 million years or so. The ancestral chromosome number for the genus seems to have been 18, but there are species with 36, 72 and 105 chromosomes [http://www.xenbase.org/common/]

{| border='4px'
|+ '''Difference within two families'''
! '''SPECIES''' !! ''X.LAEVIS'' !! ''X.TROPICALIS''
|-
| '''PLOIDY'''
| Allotetraploid
| Diploid
|-
| '''NO. OF CHROMOSOMES'''
| 36 chromosomes
| 20 chromosomes
|-
| '''GENOME SIZE'''
| 3.1 x 10^9 bp
| 1.7 x 10^9 bp
|-
| '''EGG SIZE'''
| 1-1.3 mm
| 0.7-0.8 mm
|-
| '''GENERATION TIME'''
| 1-2 years
| 4 months
|-
|}
[http://www.xenbase.org/common/]

===Genome Sequencing===

Since Frog has a huge family with many different species, only few main species that are used widely for the purposes of experiments have their genome sequenced.

''Xenopus tropicalis'' has one of the smallest genomes among amphibians and has the shortest generation time- four to six months and the only diploid genome among the 14 Xenopus species. This means it has no more than two copies of most genes, whereas the other species of Xenopus have four copies of most genes (pseudotetraploid). US Department of Energy's Joint Genome Institute (JGI) in Walnut Creek, California, initiated the X. tropicalis Genome Project, finding 1,700 million base pairs.
[http://www.genome.gov/Pages/Research/Sequencing/BACLibrary/xenopusTropicalis.pdf]

===Xenopus oocytes===

* The oocytes provide an important expression system for molecular biology.

* By injecting DNA or mRNA into the oocyte or developing embryo, scientists can study the protein products in a controlled system. This allows rapid functional expression of manipulated DNAs (or mRNA). This is particularly useful in electrophysiology, where the ease of recording from the oocyte makes expression of membrane channels attractive.

* One challenge of oocyte work is eliminating native proteins that might confound results, such as membrane channels native to the oocyte.

* Translation of proteins can be blocked or splicing of pre-mRNA can be modified by injection of Morpholino antisense oligos into the oocyte (for distribution throughout the embryo) or early embryo (for distribution only into daughter cells of the injected cell).
[http://www.staff.unibe.ch/sigel/xenopus.html]

===Xenopus Laevis===

* ''Xenopus Laevis'' is an important model organism in developmental biology. X. laevis is tetraploid and reaches sexual maturity in 1 to 2 years. What makes it important in developmental biology is its large and easily manipulable embryo.

* Extracts from the eggs of X. laevis frogs are also commonly used for biochemical studies of DNA replication and repair, as these extracts fully support DNA replication and other related processes in a cell-free environment which allows easier manipulation.

* The Human chorionic gonadotropin hormone (hCG) is present in the urine of the pregnant women in large quantities only. This hormone in the urine induces X.laevis oocyte production which formed the basis of first well-documented method of pregnancy testing X. laevis is also notable for its use as the first well-documented method of pregnancy testing when it was discovered. Today, commercially available HCG is injected into Xenopus males and females to induce mating behavior and breed these frogs in captivity at any time of the year.

===Gene cluster===

* The alpha and beta globin genes are closely linked in small cluster of frogs compared to human and chicken

* The similarity of architecture of two clusters found in X.laevis supports the tetraploid origin

* The two loci encoding the muscle specific creatine kinase isoenzymes and have large differences in developmental profile, therefore suggesting that duplicate loci that have not undergone silencing are not simply redundant copies but have acquired specialization.

* Contains twice number of genes for proteins i.e. haemoglobin and sarcomeric actin serum albumin compared with other species

----

==Current Embrology Research==

Currently, a number of fields have benefited from the development of frog embrology. These include cloning, verification of messenger RNA, and Cell cycle.

===Cloning===
[[Image:Robert Briggs.jpg|thumb|left|Figure 16 Image details:Robert Briggs.jpg]]

In 1952, Robert Briggs and Thomas J King cloned northern leopard frogs using a method of nuclear transfer. Briggs and King's experiment was similar to that envisioned - and piloted using salamanders - by Hans Spemann in his 1938 proposal for a 'fantastical experiment'. Later, John Gurdon extended this work and showed that nuclei from differentiated cells could support development, although less well than those from early embryos. [http://genome.wellcome.ac.uk/doc_WTD020799.html]

Lemaitre et a. (2005) from MRC Cancer Cell Unit, Cambridge, U.K. worked on experiments that demonstrated that importance of serial nuclear transplantation for the sucessful cloning of frogs. He demonstrated that exposure of somatic-cell nuclei (erythrocyte nuclei) and sperm nuclei to an extract of mitotic cell extract reorganizes the chromatin into shorter loops and allows replication at much shorter intervals along the DNA. This increases the efficiency of DNA replication in mammalian cell-free systems.

===Transgenesis techniques for functional genomics in Xenopus===

Transgenesis in Xenopus is made possible due to large embryos, a reliable fate map, ease of microinjection, ease of dissection/micromanipulation and existence of the neuroendocrine reflex of background adaptation as a model for activation/inact.

Recently, Hajime Ogino and Haruki Ochi from Nura Institute of Science and Technology in Japan focused on the genomic resources and principles of the transgenesis techniques in Xenopus, and discusses their applications to genome wide network analysis, with emphasis on the use of bioinformatics tools. This is will to understand the gene regulatory networks that control vertebrate development. [http://www.ingentaconnect.com/content/bsc/dgd/2009/00000051/00000004/art00001%3Bjsessionid=4ah96rms73gcu.alexandra]

Xenopus used to be a problem in earlier days when it came to transgenesis. Current methods involves isolated sperm nuclei from Xenopus testis that are microinjected into unfertilized eggs. The generated transgenic tadpoles contain 5-35 copies of the integrated plasmid that are expressed in all cells. If desired, expression of the transgene can be directed to the appropriate tissue and at the appropriate time by using specific promoters, mostly the Xenopus POMC gene promoter (isolated from a Xenopus genomic DNA library) to specifically direct expression of green fluorescent protein (GFP) at high levels to the intermediate pituitary cells, which can either be over expressed or inhibited.[http://molanphys.ruhosting.nl/transgenesis.htm]

[[File:Transgenesis.JPG]]

===Verification of messenger RNA===

While the existence and role of messenger RNA (mRNA) was known in bacteria, in the 1960s it was still debated whether it also existed in vertebrates. Taking haemoglobin mRNA from immature red blood cells and injecting it into a Xenopus oocyte, John Gurdon showed that the haemoglobin protein was indeed produced. Producing proteins in Xenopus oocytes has proved to be extremely useful in cell biology, in particular for the study of receptor proteins.[http://genome.wellcome.ac.uk/doc_WTD020799.html]

===Cell Cycle===

As they develop outside the mother, frog eggs are well stocked with the proteins needed to drive the development of the embryo. Studies of these processes has shed considerable light on the processes involved in cell division - termed the cell cycle. [http://genome.wellcome.ac.uk/doc_WTD020799.html]

===Limb development in Xenopus Laevis===

[[Image: Frog Limb development.jpg|thumb|right|Image details:Primary source:[http://images.google.com.au/imgres?imgurl=http://www.sciencedaily.com/images/2006/06/060616130718.jpg&imgrefurl=http://www.sciencedaily.com/releases/2006/06/060616130718.htm&usg=__xliPsPAvheUBME_kjv_q7auiFbo=&h=333&w=300&sz=11&hl=en&start=2&um=1&tbnid=y_ntJtmkRSK7WM:&tbnh=119&tbnw=107&prev=/images%3Fq%3DLimb%2Bdevelopment%2Bin%2BXenopus%2BLaevis%26ndsp%3D18%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

Donald D. Brown (2005),Department of Embryology, Carnegie Institution of Washington demonstrated factors related to limb development of Xenopus Laevis. Thyroid hormone (TH) is found to be required for limb development in this frog. Specific cell types in the growing limb were targeted for expression of a dominant negative form of the TH receptor by sperm-mediated transgenesis. Limb muscle development, the innervation of muscle from the spinal cord, and cartilage growth can be inhibited without affecting patterning of the limb or differentiation of other cell types. Remodeling of the skin occurs late in metamorphosis after the limb has formed. The coordination of these independent programs is affected in part by the control that TH exerts over DNA replication in all cell types of the limb. [http://www.pnas.org/content/102/35/12455.full]

----

== Glossary ==

[[Image: Frog species.jpg|thumb|left|Image details:Primary source:www.olympus.co.jp/.../080925/large/p02L.jpg].jpg]]

*'''Amphibian:'''

''Relating to or characteristic of animals of the class amphibia.Amphibians are found in the taxonomic class of amphibia, amphibians are capable of both occupying and successfully living in both land and aquatic communities.amphibian''

*'''Augmentation:'''

''Enlargement/Increase in cellular size.''

*'''Autolysis:'''

''breakdown of a part or whole cell or tissue by self-produced enzymes''

*'''Blastomeres:'''

''The undifferentiated cells formed by cleavage of the fertilised ovum. This includes cells in the cleavage, morula, and blastula stages of the embryo''

*'''Carnivorous:'''
''
Flesh-eating; subsisting on animals as food.''

*'''Cleavage:'''

''he repeated division of a fertilised ovum ''

* '''Cleft:'''

''an opening, fissure, or V-shaped indentation made by or as if by splitting''

*'''Chordate:'''

''Members of a diverse phylum of animals that, as embryos, possess a (1) notochord; (2) a dorsal, hollow nerve cord, (3) pharyngeal gill slits; and (4) a post-anal tail''

''The act or state of splitting or dividing of a cell, particularly during the telophase of (animal) cell division.''

*'''Cytoplasm:'''

''The cytoplasm (of both eukaryotes and prokaryotes) is where the functions for cell expansion, growth, metabolism, and replication are carried out''

* '''Epiboly:'''
''The expansion of one cell sheet over other cells, as takes place during gastrulation''

*'''Fertilization:'''

''A process in sexual reproduction that involves the union of male (sperm) and female (ovum) gametes (each with a single, haploid set of chromosomes) to produce a diploid zygote.''

*'''Gamete:'''
''A reproductive cell (male (sperm) or female (egg)) that has only half the usual number of chromosomes''

*'''Gametogenesis:'''

''process leading to the production of gametes. The development and maturation of sex cells through meiosis.Another name for meiosis where a diploid cell is divided into two haploid cells with half the chromosome content of the diploid parent cell.''

*'''Herbivorous:'''

''eating plants; of or pertaining to the herbivora.''

*'''Holoblastic:'''

''The complete division of an isolecithal or microlecithal egg into blastomeres''

*'''Invagination:'''

''One of the methods by which the various germinal layers of the ovum are differentiated.''

*'''Isoenzymes:'''

''Isozymes (also known as isoenzymes) are enzymes that differ in amino acid sequence but catalyze the same chemical reaction.''

*'''Mesentery:'''

'' membranous fold attaching various organs to the body wall.''

*'''Metamorphosis:'''

''A change in the form and often habits of an animal after the embryonic stage during normal development.''

*'''Neuroendocrine:'''

''Neuroendocrine [IPA nʊəroʊˈɛndəkrɪn] cells are cells that release a hormone into the circulating blood in response to a neural stimulus.''

*'''Organogenesis:'''

''The part of embryonic development where the body's main organs develop.''

*'''Peritoneum:'''

''The smooth serous membrane which lines the cavity of the abdomen, or the whole body cavity when there is no diaphragm, and, turning back, surrounds the viscera, forming a closed, or nearly closed, sac.''

*'''Perivitelline space:'''

''The perivitelline space is the space between the zona pellucida and the plasma membrane (sometimes called the vitelline membrane) in a fertilized ovum.''

*'''Polyploidy:'''

''Cells with three or more sets of chromosomes.''

*'''Pronucleus:'''

''the nucleus of the ovum or sperm after fertilization but before they fuse to form the nucleus of the zygote ''

*'''Protoplasm:'''

''The fluid living content of the cell that consists of two major divisions, the cytoplasm and the nucleoplasm (cell nucleus). It is composed mainly of nucleic acids, proteins, lipids, carbohydrates, and inorganic salts''

*'''Segmentation:'''

''division of some metazoan bodies (such as annelida and Arthropoda) into repeated parts, segments. Segmentation can be homomeric (more or less the same) or heteromeric(different from each other).''

*'''Terrestrial:'''

''Of or on the ground, of the habitat of a plant, on land as opposed to in water, or on the ground as opposed to on another plant.''

*'''Transgenesis:'''

''Transgenesis is the process of introducing an exogenous gene - called a transgene - into a living organism so that the organism will exhibit a new property and transmit that property to its offspring.''

*'''Yolk:'''

''nutritive material of an ovum stored for the nutrition of an embryo''

*'''Zygote:'''

''The cell from which an organism develops, that results from the fertilization of the egg by the sperm.''

''Primary Resource "Biology- Online Dictionary''[http://www.biology-online.org/dictionary/Main_Page]

== References - Frog Embryology: ==

[[Image:Frog Research.jpg|thumb|left|Image details:[http://images.google.com.au/imgres?imgurl=http://www.odt.co.nz/files/story/2008/09/university_of_otago_zoology_senior_lecturer_phil_b_3343259744.jpg&imgrefurl=http://www.odt.co.nz/on-campus/university-otago/21670/dunedin-frog-man-wins-zoo-award&usg=__JvJJU5QfOnIwY2bk4xo64UXuJRs=&h=600&w=404&sz=22&hl=en&start=14&um=1&tbnid=AbsP89yWcUiilM:&tbnh=135&tbnw=91&prev=/images%3Fq%3Dfrog%2Bresearch%26hl%3Den%26um%3D1].jpg]]

1. Savage, J. M. (2002). The Amphibians and Reptiles of Costa Rica. University of Chicago Press, Chicago [http://www.springerlink.com/content/vv015277w1746llw/]

2. Ford, L.S.; D.C. Cannatella (1993). "The major clades of frogs". Herpetological Monographs 7: 94–117 [http://digimorph.org/specimens/Xenopus_laevis/]

3. Tyler, M. J. (1994). Australian Frogs A Natural History. Reed Books [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.gracilenta.html]

4. Cogger, H.G.; R.G. Zweifel, and D. Kirschner (2004). Encyclopedia of Reptiles & Amphibians Second Edition. Fog City Press [http://en.wikipedia.org/wiki/Microhylidae]

5. Beltz, Ellin (2005). Frogs: Inside their Remarkable World. Firefly Books [http://unjobs.org/authors/ellin-beltz]

6. Tyler, M. J. (1994). Australian Frogs A Natural History. Reed Books [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

7. Moury JD, Hanken J (1995) Early cranial neural crest migration in the direct-developing frog, Eleutherodactylus coqui. Acta
Anatomica (Basel) 153, 243-253.

8.Raynaud A (1985) Development of limbs and embryonic limb reduction. In Biology of the Reptilia (ed. Gans C, Billett F), pp.
59-148. New York: John Wiley.[http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=9309]

9. Hanken J (1986) Developmental evidence for amphibian origins. In Evolutionary Biology (ed. Hecht MK, Wallace B, Prance GT), 20, pp. 389-417. New York: Plenum Press. [Hanken J (1986) Developmental evidence for amphibian origins. In Evolutionary Biology (ed. Hecht MK, Wallace B, Prance GT), 20, pp. 389-417. New York: Plenum Press.]

10. Elinson RP (1990) Direct development in frogs : wiping the recapitulationist slate clean. Seminars in Developmental Biology
1, 263-270.

11. Beebee, T. J. C. 1996. Ecology and Conservation of Amphibians. Chapman and Hall. London. [http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V5X-3SVHMKH-1X&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=1021245355&_rerunOrigin=google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=825868e10cd178d16a8a0e5ad14dc5ef]

12. Lehtinen, R. M. 2002. The use of screw pines (Pandanus spp.) by amphibians and reptiles in Madagascar. Herpetological Bulletin 2002:20–25.

13. Parris, K. M. and M. A. McCarthy. 1999. What influences the structure of frog assemblages at forest streams. Australian Journal of Ecology 24:495–502. CrossRef

14. Zug, G. R. 1993. Herpetology: An Introductory Biology of Amphibians and Reptiles. Academic Press. San Diego, CA.

15. Slack,J.M.W., Darlington,B.G., Heath,J.K. and Godsave,S.F. (1987)Mesoderm induction in early Xenopus embryos by heparin-binding growth factors. Nature, 326, 197-200.

16. Melton,D.A. (1990) Activins are expressed early in Xenopus embryogenesis and can induce axial mesoderm and anterior structures. Cell, 63, 485-493.

17. Harland,R.M. and Misher,L. (1988) Stability of RNA in developing Xenopus embryos and identification of a destabilizing sequence in TFIIIA RNA. Development, 102, 837-852.

18. Cunliffe,V. and Smith,J.C. (1992) Ectopic mesoderm formation in Xenopus embryos caused by widespread expression of a Brachyury homologue. Nature, 358, 427-430.

19. Kinoshita,K., Bessho,T. and Asashima,M. (1993) Competence prepattern in the animal hemisphere of the 8-cell-stage Xenopus embryo. Devel. Biol., 160, 276-284.

20. LaBonne,C., Burke,B. and Whitman,M. (1995) Role of MAP kinase in mesoderm induction and axial patterning in Xenopus development. Development, 121, 1475-1486.

21. Green,J.B.A., New,H.V. and Smith,J.C. (1992) Responses of embryonic Xenopus cells to activin and FGF are separated by multiple dose thresholds and correspond to distinct axes of the mesoderm. Cell, 71, 731-739.

22. Grainger R., Blumberg B., Harland R., Amemiya C., Importance of Xenopus Tropicalis to biomedical and biological research, Benaroya Research Institute, Virginia Mason Research Center [http://www.genome.gov/Pages/Research/Sequencing/BACLibrary/xenopusTropicalis.pdf ]

23. Gregory, T.R. (2005). Animal Genome Size Database. [http://www.genomesize.com]

24. U.S Fish and Wildlife Services, ABNORMALITY CLASSIFICATION SOP, [http://www.fws.gov/contaminants/Amphibian/pdfs/AbnormalitySOP_woutpics_Jan08.pdf ]

25. Donald D. Brown*, Liquan Cai*, Biswajit Das*, Nicholas Marsh-Armstrong‡, Alexander M. Schreiber*, and Rejeanne Juste*(2005), Thyroid hormone controls multiple independent programs required for limb development in Xenopus laevis metamorphosis [http://www.pnas.org/content/102/35/12455.full]

26. Ogino, Hajime; Ochi, Haruki, Resources and transgenesis techniques for functional genomics in Xenopus, Development Growth & Differentiation, Volume 51, Number 4, May 2009 , pp. 387-401(15) [http://www.ingentaconnect.com/content/bsc/dgd/2009/00000051/00000004/art00001%3Bjsessionid=4ah96rms73gcu.alexandra]

27. Giles Newton (2004) Why the frog? The Human Genome, [http://genome.wellcome.ac.uk/doc_WTD020799.html]

28. Xenbase, [http://www.xenbase.org/common/]

29. Donders Center for Neuroscience & Nijmegen Center for Molecular Life Sciences (NCMLS), Beyond the genome (Xenopus transgenesis for functional genomics),Faculty of Science, Radboud University [http://molanphys.ruhosting.nl/transgenesis.htm]

== External Links ==
[[Image:Frog links.jpg|thumb|left|Image details:[http://images.google.com.au/imgres?imgurl=http://2.bp.blogspot.com/_o93AaY0GzH4/SjY_ZYv0PII/AAAAAAAAAgk/skruNc2yN78/s400/computer%2Bfrog.jpg&imgrefurl=http://hellaheaven-ana.blogspot.com/2009/06/talking-frog-contemporary-fairy-tale.html&usg=__oxji1TGLV2Fi7xe0dnlmuYk8gDo=&h=288&w=288&sz=16&hl=en&start=2&um=1&tbnid=ywZd4zpdxC5plM:&tbnh=115&tbnw=115&prev=/images%3Fq%3Dfrog%2Bon%2Bcomputer%26hl%3Den%26um%3D1].jpg]]

1. Frog embryology [http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/F/FrogEmbryology.html Frog Embryology]

2. Frog cellular materials [http://www.xenbase.org/xenbase/original/cell/cell.html xenbase]

3. The zoology of frog species [http://worms.zoology.wisc.edu/frogs/mainmenu.html zoology frogs]

4. Frog cycle [http://www.bioethics.gov/images/sc_images/frog_dev.gif bioethics frog] Just a little cycle of FROG'S life cycle

5. Frog Embryology [http://embryology.med.unsw.edu.au/OtherEmb/Frog.htm UNSW Embryology]

6. Frog Research [http://apps.carleton.edu/campus/library/now/exhibits/wallcharts/frog/ carleton library exhibit]

{{Template:Projects09}}
[[Category:Frog]]

2009 Group Project 5

2009-10-14T22:38:09Z

Z3258567: /* The Egg & Fertilization */

== The Embryology of Frogs ==

== The Frog ==

[[Image: Frog species .jpg|thumb|left|Image details: Wikipedia (2009) Frog species[http://en.wikipedia.org/wiki/Frog#Uses_in_agriculture_and_research].jpg]]

Frogs are scientifically identified by the structure of their long posterior limbs, a petite framework, webbed fingers and feet, budged eyes and the lack of a tail. The majority of frog species are extensively recognized as outstanding jumpers, due to their long, dominant legs, which are adaptations to progress jumping performance during activities. The Frog is one of the most frequently studied species in experimental embryology and most anatomical sciences. ''The Frog is a practically effective model for human embryological development given that the Frog:''

- Comprises of genes which can be effectively manipulated.

- Comprises of similar homogeny with humans species.

- Reproduces a large quantity of offspring in a short period of time.

- Are small species which can be simply sustained.

- Are not extremely luxurious and expensive.

== The History of the uses in agriculture and research ==

[[Image: Frog experiments .jpg|thumb|right|Image details: Scans of chemically cleared and dyed preserved deformed frogs and toads [http://www.sat.qc.ca/upload/residence/frog-04.jpg].jpg]]

There are numerous types of frog species that have been manipulated in many developmental experiments. The frog was traditionally used by countless of the early embryology investigators and presently there are several diverse molecular mechanisms regarding progression of the frog. Theses include:

'''1.''' Food source; frog legs are a delicacy and are eaten in European countries and in many parts of South American regions.

'''2.''' Frogs have the finest biochemical dissection of phenomena that take place in the egg and oocyte. Frogs are the evolutionarily closest to mammals, commonly used as a vertebrate model.

'''3.''' Frogs lay thousands of outsized eggs, from which cell extracts can be readily prepared that is capable of recapitulating most molecular phenomena in a test tube.

'''4.''' Frogs have been commonly used as a laboratory system for a very long period, and have an extensive history of producing crucial observations in countless fields of biology.

'''5.''' Frogs have a important historical connection to the study of epigenetics (John Gurdon-vertebrate cloning and reprogramming) which has been mostly performed on frog species.

'''6.''' Frogs also have very strong evidence of pattern formation and early development, as the embryos are large in size and experimentally manipulative.

'''7.''' Recent research into the biochemistry of chromatin and epigenetics has been performed with frog species and mammalian cultured cells.

'''8.''' The biggest weakness of the Frog model system is the difficulty of performing genetic experiments and analysis, as frogs are allotetraploid, meaning they take approximately a year to fully develop to sexual maturity, and the genome has not been completely sequenced. Nevertheless, biochemical manipulations of cell extracts, such as immunodepletions and application of heterologous DNAs and nuclei can avoid the need for genetic exploitation.

----

== Growth and development of the Frog ==

[[Image: Mature develop frog.jpg|thumb|Image details: Wikipedia (2009) Red Eyed Tree Frog Figure 1 Primary source:[http://en.wikipedia.org/wiki/File:Red-eyed_Tree_Frog_-_Litoria_chloris_edit1].jpg]]

* The frog is a well recognised species, abundant predominantly in ponds, swamps, though various species may also exist in damp or shady environments distant from moist habitats.

* Eggs of specific frogs are easily obtained and may be examined in from the beginning of fertilization onwards. The phases of embryonic development differs in various chordates, yet the typical phases are basically apparent in all frog species. The differences are associated principally to the amount of yolk particles present in an egg.

* The yolk particles offer nourishment of the developing embryo. The process of frog development will be discussed from the phases of gametogenesis to the adult stage.

----

== The Egg ==
[[Image:Development of Poles in frog Fertilization.jpg|thumb|left|Development of Poles in Frog Fertilisation:J,Nassif 2009.jpg]]

- The embryology of a frog egg is a vast cell; its dimensions are approximately 1.4-1.6 million times larger than a typical aquatic species egg cell. Throughout the frog’s embryonic maturation period, the egg will be transformed into a tadpole encompassing millions of cells but still remains with its constant volume of genetic material, the vast prodction of cell have been illusttrated in the figure on the right revealing the production of eggs from female frogs. [http://en.wikipedia.org/wiki/Microhylidae]

- The early embryonic frog structure consists of three main segments the superior hemisphere known as the animal pole which is usually visible as a grey coloured area. The innermost layer appears to be between the outer two sections known as the gray crescent represented in black. Inferiorly, represents the vegetal pole typically lighter than the superior compartment illustrated in gold.

VIDEO RESOURCE: [http://www.youtube.com/watch?v=GO5YN_t1fqw&feature=related]

[[Image:Early Development of Frogs.jpg|thumb|left|Early Development of Frog:J,Nassif 2009.jpg]]

==History of frog embryology use ==

*'''1851''' - ''Henby Nelson''(MD): He identified a remarkable fact through the frog embryo. Henby observed the first cleavage of the yolk, in the egg of the frog. And cleaved structure corresponds in line of direction to the longitudinal axis of the body of the embryo of the frog species.

[[Image:Wilhelm Roux.jpg|thumb|right|Wilhelm Roux[http://images.google.com.au/imgres?imgurl=http://www.todayinsci.com/R/Roux_Wilhelm/RouxWilhelmThm.jpg&imgrefurl=http://www.todayinsci.com/6/6_09.htm&usg=__qRLTEMTHdZpAHxiNX12hWjcm9tA=&h=125&w=100&sz=4&hl=en&start=2&um=1&tbnid=LIKIwZTqCpk7MM:&tbnh=90&tbnw=72&prev=/images%3Fq%3DWilhelm%2BRoux%26gbv%3D2%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

*'''1888''' - ''Wilhelm Roux'': Wilhelm Roux attempted to solve the above observation by damaging one cell of a two-cell frog embryo with a hot needle. The cell stayed in place. However, it did not develop further. Its partner developed into a left or right half-embryo;

*'''1907''' - ''John Hopkins'' hospital: In order to identify the cellular source of neuronal fibres. Scientist placed small portions of frog embryo spinal cords in lymph on a microscope slide and was able to observe clear cut neuronal sprouting.

*'''1951''' - ''Robert Briggs'': Robert Briggs was able to clone a frog embryo by substituting the nucleus of an unfertilized frog egg cell with the nucleus of a frog embryo cell. This process is known as nuclear transplant, has formed the basis for all cloning.

*'''1952''' - ''Robert Briggs and T.J. King'': Robert Briggs and T.J. King used frog for test experiment. Because the size of the eggs in the frogs are enormous compared with those of mammals, which make them easier to manipulate.

*'''1976'''- Using the technique that had been successful in cloning frog embryos, the doctor transferred the nucleus of one cells into a donated egg cell. As an embryo began to develop, it was implanted into the uterus of a young woman.

*'''1997''' - ''Wilmut and Campbell'': Utilizing the cloning technique from frog embryo, Drs. Wilmut and Campbell tried the starvation technique on embryo cells to produce Megan and Morag, the world's first cloned sheep and, until now, the most famous sheep in history.

*'''2000''' - ''Tokyo University'': Scientists at Tokyo University have grown artificial eyeballs. Scientists formed them in tadpoles by using frog embryo cells.

*'''2001''' - ''Advanced Cell Technology'': Scientists from Advanced Cell Technology announced production of a human embryo clone. This is significant as its parthenogenesis has been artificially induced in frogs.

[[Image:John Gurdon .jpg|thumb|right|John Gurdon [http://images.google.com.au/imgres?imgurl=http://www.pnas.org/site/misc/images/gurdon.jpg&imgrefurl=http://www.pnas.org/site/misc/classics4.shtml&usg=__1p-GA1PdOYsxKL-cznMb3RHCm98=&h=526&w=400&sz=223&hl=en&start=1&um=1&tbnid=9k4lhuLssiWCAM:&tbnh=132&tbnw=100&prev=/images%3Fq%3DJohn%2BGurdon%26gbv%3D2%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

*'''2002''' - ''John Gurdon'': John Gurdon from Wellcome Cancer Research Institute in Cambridge experimented on cloned frog embryo.

== Gametogenesis ==

* The sexual reproduction occurs through the fusion of either mature reproductive cells or germ cells known as gametes, which include the sperm from the male frog and ova from female frog species so as to form a single cell, the fertilized zygote. The gametes are typically developed in parents of different sexes . [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

* Males gametes is a spermatozoon , the female frog gamete is an ovum. Each gamete is formed by a process, recognised as maturation or gametogenesis in gonads. The typical male frog gonads are testies in male, while the female gonads are ovaries. The synthesis of both gonads is associated with the process of fertilization. [http://en.wikipedia.org/wiki/Microhylidae]

* The zygote changes into a mature frog through the process of embryology and metamorphosis. Gametogenesis is a in progression which frog gametes are established from germ cells. Initial germ cells are called primordial germ cells, which can be recognised extremely early in the life of frog species.

----

== The Egg & Fertilization ==

[[Image:Fertilized and Unfertilised Eggs.jpg|thumb|left|Fertilized and Unfertilized Eggs:J,Nassif 2009.jpg]]

[[Image:Egg Development.jpg|thumb|left|Egg Development:J,Nassif 2009.jpg]]

- This occurs once the sperm cell has inserted, following the insertion of the sperm cells meiosis II is completed, there is a 30 degree position change of the cytoplasm, gray crescent allows this change to be visible in some amphibians, the gray crescent is able what determines the expect ted outline of how the frog will form. The sperm cell joins with the nuclei of the egg which forms the diploid zygote nucleus. --Sando Rashed 10:09, 24 September 2009 (EST)

- The early phases in the development of the egg is visible, but must be studied in tadpoles throughout maturation. In embryonic tadpoles of about 10 millimetres in length, soon after the opening of the oral cavity, a pair of longitudinal ridge-like thickenings of peritoneum becomes apparent along the posterior surface of the body cavity situated near to the mesentery and along the inner boundaries of the kidneys. Genital ridges are established in all tadpoles of this age, sex is not distinct until a later period. The development of the egg is illustrated in the figure on the left revealing the structure of a developed egg and a mature of egg.

[[Image:Fertilisation life cyle.jpg|thumb|Fertilization of Life cycle:Derived from primary source:[http://en.wikipedia.org/wiki/Frog]]]

== Maturation of the Egg ==

- The eggs have currently accomplished their full size, and develop from the exterior of the ovaries like a small shot, but they still have to pass through the course of maturation before they are prepared to be fertilised. This progression of maturation relates to the nucleus almost completely.

- The nucleus component, containing the nuclear fluid that excludes through the nuclear membrane into the substance of the egg, a great segment of the nuclear reticulum vanishes and becomes degraded into separate globules known as nucleoli, but a extremely small division remains in the midpoint as a slender intricately thread recognised as the nuclear skets.
Relative to the egg getting discharged from the ovary, the follicles shatter allowing the eggs to fall into the abdominal cavity of the frog species, the egg then passes forwards, directly by the contraction of the muscular wall, somewhat by the movement of the cilia of the peritoneum, to the apex of the oviduct, which positioned at the anterior compartment of the body cavity opposite to the roots of the respiratory organs.

- The terminal part of the oviduct establishes a thin-walled pouch capable of great swelling, inside which the eggs gathers in large numbers. In conclusion, the eggs are migrated out through the cloaca into water which the albuminous investments of the eggs rapidly augment to form the gelatinous mass of the frogs spawn.

== Maturation phases ==

'''1. Nuclear skein''', moves from the midpoint of the egg to its outer surface, which it reaches opposite the midpoint of the black pole. The skein, subsequently an unevenly twisted thread, now presumes the specific arrangement of a nuclear spindle, for instance may be visible in the nucleus of an epithelial or additional cell instantly prior to division of the cell occurs.[http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

'''2. The first Polar Body,''' regarding the instance the egg is laid, but prior to its fertilistion, the egg develops a considerably flattened appearance at its upper or black pole, a definite sum of fluid being exuded among the egg and the vitelline membrane. The nuclear spindle currently separate into two identical segments, one of which remains with the egg, and the supplementary is extruded as the first polar body, a small ovoidal white globule, which is situated on the surface of the egg surrounding the exuded peri-vitellline fluid.

'''3. The Second Polar Body''', half of the nuclear spindle that stay behind then splits into two equivalent divisions, one of which remains inside the egg as the female pronucleus, whereas the other segment is extruded as the second polar body, a small white globule extremely related to the first polar body, and like this positioned in the perivitelline fluid on the superior portion of the egg.

'''4. Fertilisation of the egg''', includes the synthesis of the spermatozoon with to egg, specifically, synthesis of the nuclei of these two bodies. The spermatozoa, subsequent to being shed over the seed by the male, distribute vigorously by means of their extended tails, break through the gelatinous investment of the female eggs, bore their way through the vitelline membrane and so go through into the eggs themselves, which they penetrate relative to the superior or black hemispheres.
* Subsequently, an hour following the spermatozoon has entered; a progression may be visible projecting within from the exterior segement of the egg, with a liquid spot in the mid point. This liquid centre is the nucleus of the spermatozoon, and is said to be the male pronucleus, it break through beyond into the female egg, transporting the specialised pigment into it, so that it appears bounded by a pigmented capsule linked with the exterior of the egg by a pigmented stalk.

* By this instance, the second polar body has been established and extruded, and the female pronucleus is merely the only component of the primary egg nucleus still present. Both the male and female pronuceli, which are at initially distance separate to each other, merge and after having enlarged significantly in size then fuse mutually about two and half hours after fertilisation has originated to produce the segmentation nucleus.
* The segmentation nucleus is a huge sphere-shaped vesicle embedded in delicately granular protoplasm, and bounded by a distinct capsule of pigment, its arrangement by the synthesis of the male and female pronuclei completes the action of fertilisation. Specifically female pronucleus may be observe as an imperfect nucleus, and consequently result in the course of fertilisation. The nucleus of the spermatozoon or male pronucleus, replaces the component of the egg- nucleus which has been misplaced as the polar bodies.

'''5. Segmentation of the Egg''', the initial phase of growth consist in constant separation of the egg, whereby it becomes transformed from the unicellular state, which is everlasting only in the lowest species, to muliticelluar state charactertics of all higher species. To these early processes of growth the names segmentation is specified. Shorty subsequent to the competition of fertilisation and arrangement of the segmentation nucleus this later misplaces its sphere-shaped appearance and develops to be spindle-shaped, the yolk granules at the equivalent instance showing a tendency to develop into lines distributing outwards from the distal segment of the spindle.
* The nucleus now split into two halves, which shift away from one another, the yolk granules are likely to combined themselves around the two nuclei, and a slender vertical plate of delicately granular substance is left, dividing the egg.[http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

* Superiorly the eggs depression now becomes visible, initially as a small cavity and then develops as a groove, which almost immediately extends all round, and speedily deepening, splits the egg into two entirely separate halves along a plane equivalent with the vertical plane.

* Shorty after, the two nuclei soon separate again into two, and therefore a second cleft is created in the same state as before, its additionally in the vertical plane, however in a plane at 90 degrees to the initial one, and on its finishing point the egg comprises of four accurately similar segments, each containing a nucleus. The third cleft is horizontal in shape, but not equal, lying closer to the superior than the lower pole, it segregates each of the four cells into, an superior smaller and a inferior larger pole

----

== Cleavage ==

[[Image: Frog Cleavage development.jpg|thumb|left|Figure 8.1 Image details:[http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/F/FrogEmbryology.html].jpg]]

* The egg of the frog is scientifically identified as’ telolecithal’ meaning there is a outsized amount of yolk concentrated at a single pole, in contrast to the concentration of cytoplasm and the site of the nucleus. The cleavage phases are holoblastic, therefore the total and after the second cleavage they are asymmetrical .The initial cleavage stage appears about two and half to three hours after fertilization. It commences as a minor depression in close proximity to the centre of the animal hemisphere. It appears as if some interior force is pushing the surface the egg towards the centre. This small upturned fold steadily continues in the form of a channel until it surrounds the egg. This groove is shallow in the commencement, but develop into deeper eventually separating the fertilized egg into two halves recognised as the blastomeres. [The figure on the left symbolise the development and growth of the frog embryo during cleavage].

* Internally the separation is mitotic, consequently each daughter cell contains a nucleus resulting from the copulation nucleus of the fertilised egg. This cleavage is vertical, the two cells are indistinguishable in respect of cytoplasm, pigment and yolk. The subsequent cleavage appears about an hour after the first. The channel of this cleavage begins at the centre of the animal hemisphere, is at right angles to the first and is vertical. This divides the egg into four blastomeres. The fourth blastomere so produced are not qualitatively equal, since of these only two contain the material from the gray crescent. The cleavage begins about thirty minutes after the second is completed or four hours after fertilisation. the cleavage plane of the third furrow is horizontal and slightly above the equator. Thus the four upper cells are a little smaller than the four lower cells. The smaller blastomeres are called micromeres and the larger blastomeres are called macromeres. The fourth cleavages follow 20 minutes after the third and tend to be vertical. This is usually a double furrow.

* The cleavage rate is accelerated with each of the early divisions and since the blastomeres are of unequal size and have varying amounts of cytoplasm and yolk, synchronous cleavage is lost and there is an obvious overlapping of the division. The upper most cells divide more rapidly than the lowermost cells. From this point onwards perfect symmetry in cleavage and in blastomere is very rare, although the embryo developed perfectly. The fifth cleavage is also doubled, appearing first in the upper hemisphere and then in the lower.

* The cleavage thus far follows the rule that each cleavage plane comes in at right angles to the previous one. The subsequent divisions become so irregular that it is previous one. The subsequent division become so irregular that it is impossible to trace out any plan or procedure. The segmentation continues more rapidly in the pigmented regions, since at that place the protoplasm is most dense, whereas, yolk which is very abundant in the vegetal side delays cell division. The multicelluar embryo at this stage is called morula by some biologists.

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== Gastrulation ==

[[Image:FROG GASTRULATION .jpg|thumb|left|Figure Image details:[http://www.google.com.au/imgres?imgurl=http://bio1903.nicerweb.com/Locked/media/ch47/47_12FrogGastrulation.jpg&imgrefurl=http://bio1903.nicerweb.com/Locked/media/ch47/gastrulation-frog.html&h=540&w=480&sz=46&tbnid=N78sHjELreGGSM:&tbnh=132&tbnw=117&prev=/images%3Fq%3Dfrog%2B-%2Bgastrulation&hl=en&usg=__4VK9FYLft0W-4lBe6p5EtQAMiaI=&ei=qPy5SurtMJvE6wON8JmdAg&sa=X&oi=image_result&resnum=4&ct=image].jpg]]

''The phase of Blastulation is followed by the unique developmental progression of gastrulation. The process of frog gastrulation involves the following processes.''

'''1. Epiboly Phase'''

The pigmented cellular materials of blastula have the propensity to overgrow the yolk cells within the developing content. This course which is known as epiboly commences gradually in the final blastula and rapidly accelerates with advancing gastrulation development. The cellular matter within the animal pole reproduces and matures on all sides except in area surrounding the dorsal lip of the blastopore has been established.

'''2. Convergence'''

Scientists suggested that the unfolding was thought to result in spreading of the superficial cells over a substrate with suitable absorption properties. Consequently epiboly and convergence are an outcome to this spreading tendency, which is actually increased by a reduction in surface tension of the distributing cells.

'''3. Rotation'''

The epiboly phase is maintained until the region of the dorsal lip has migrated and is a to some extent greater than 90 degrees and the region of the white blastopore is reduced to small circular rings. This section will be positioned away from the developing vegetal pole. Laterally the complete developing gastrula has been rotated to a horizontal axis, allowing it to lie at right angles to the original median plane of the egg. Therefore, the course of rotation is such that the dorsal lip is practically pushed backwards in one direction as rapid or quicker than epiboly moves it forward in the other. The outcome will be that the blastopore produced at roughly the vegetal pole is posterior, and the dorsal and ventral lips are essentially dorsal and ventral. This in addition allows the eggs to form the antero-ventral side of the potential embryo whilst the area marked by the grey crescent is to develop the dorsal segment.

'''4. Invagination'''

Visible is a small fissure- like invagination which is apparent in the middle between the equator and the vegetal segment. The most superior or dorsal border of the cleft produce the dorsal lip of the blastopore. This imput move back and forth on the dorsal plane near the dorsal lip and migrates around the boundaries of the blastocoel in company with the extension of the lateral lips. This adapted invagination is maintained until the blastocoel cavity has been almost abolished; excluding the slender opening separating epiblasts from the hypoblast, the new segment formed is known as the archenteron cavity.

'''5. Involution'''

- Additional to previous course of action a distinct involution also occurs at the blastoporal borders. This is mainly dynamic at the median dorsal lip and gradually more less as it shifts across either side until it reaches the ventral lip where it constant.Throughout this progression, cells positioned beside the superior boundaries of the blastoporal lip migrate over the lip to the interior portion of the lip. These cells are remained within the embryo along the internal edge of the blastopore. This indicates the root of archenteron is composed of involuted cells and beyond this the external layer known as the ectoderm. The base and lateral sides are enclosed mainly of endodermal cellular material, which have been established from larger yolk cells, situated in the vegetal pole of the blastula.

- In the final phases of the gastrula development, the cells contributing to the floor of the archenteron, thin out significantly where they surround the blastocoel.
The hemispherical shaped dorsal lip of blastopore which become visible at the commencement of the gastruation stage carry on to augment, initially becoming semicircular, then transform into a horse shoe shaped and then finally forming into circular band. The band is the accomplished by the blastopore. Various yolk cells of vegetal pole present in the section are crowed into the blastoporal cavity where they form a gathering identified as a yolk plug. Blastopore rapidly reduces in size while the archenteron is still developing and becomes completely formed in the final stage; the yolk plug appears as only a small oval on the gastrula.

==Growth and Modification of Frog Species==

'''1. Changes in habits and habitats:'''

'''a)''' In frogs, metamorphosis is related with to the modifications and adaptations as a frog changes environmental habitats from an aquatic to a terrestrial mode. Metamorphosis has modified the adaption of frogs as this alteration it began during the aquatic adaptations in the surface of water to breathe air. Subsequently, it continues the terrestrial surroundings, therefore the frog species become abundant in vegetation area allowing the frog to transform in to amphibious species.

'''b)''' The transition during metamorphosis is linked with a change in food chain. The tadpoles being the embryonic origin of frogs are herbivorous, feeding on algae and green matter, which they collect by the adapted feature such as their teeth surrounding their mouths. Adult frogs, alternatively, are classified as carnivorous feeding on insects and worms. Occasionally, they also consume larger prey, for instance smaller frogs species and even little birds and rodents which they dominant and ingest.

[[Image:Development of frog from sperm to mature structure.jpg|thumb|left|Figure 9 Image details:J,Nassif 2009.jpg]]

'''2. Changes in Morphology'''

These include the decrease or complete absence of specific organs or structures which are essential during development of early frog embryology, but not critical in the mature frog species. The significant alterations of this nature include the following developmental structures.

'''a)''' The long tail of the tadpole alongside the fin folds is absorbed again during metamorphosis and becomes absent at the final stage of the metamorphosis.

'''b) '''The developing gills are resorted, the gill clefts are congested and the branchial cavities start to become absent. The reabsorbtion of gills also takes place by autolysis.

'''c)''' The teeth of the perioral disc additionally the homey lining of the jaws are shed.

'''d)''' The lateral line sense organs within the skin of tadpoles vanish throughout metamorphosis.

'''e)''' The cloacal tube begins to condensed and reduced.

'''f)''' Various blood vessels, together with parts of the aortic arches, are reduced during mature development.

(The figure on the left represents the transformation from a tadpole to a developing structure.)[http://science.jrank.org/pages/2862/Frogs-Adult-morphology.html]

'''3. Progressive or constructive changes'''

This process comprises of the development of specific organs which mature into functional systems only during metamorphosis.

'''a)''' During development the limbs continue to augment in size and differentiation. The forelimbs, which in the tadpole mature under the opercular membrane, which then break through to the exterior. Simultaneously there is a increase in the length and strength of the hind limbs, joints develop in them and the toes become visible.

'''b)''' The middle ear becomes apparent in relation with the first pharyngeal pouch. The tympanic membrane matures. It is bounded by circular tympanic cartilage which allows the frog to retain air.

'''c)''' The visual organs bulge up on the dorsal surface of the head developing the nictitating membrane.

'''d)''' There is augmentation of the tongue and the formation of thevomerina teeth.

[[Image: Growth model.jpg|thumb|Figure 10 Image details:J,Nassif2009:]]

'''4. Remodelling of some structures'''

Systematic organs which operate both in the early embryonic larva and the mature adult change their differentiation during metamorphosis so as to meet the requirements of the adult mode of life and due to the habitat adaptations. The figure on the right illustrates structures developing from specic germ cell layers.

'''a)''' The skin of the embryonic tadpole is lined with a double-layered epidermis. The number of layers of cells in the epidermis augments throughout metamorphosis. Superficial surface layers become cornified. Multicellular mucous and serous glands originate in the skin. The pigmentation of the skin continuously changes, new patterns and colour start to form.

'''b)''' There is a lengthening of the mouth gap as a result of rotation of the quadrate cartilage and the true jaws become functional.

'''c)''' The tongue rapidly progresses and becomes larger and more muscular.

'''d)''' The eyes become more specialised.

'''e)''' In early tadpoles, the GIT is extremely long and wound up into a spiral folds. The intestine become greatly lengthened in herbivorous species due to the vegetables food chain.[http://en.wikipedia.org/wiki/Frog]

'''5. Development of the reproductive system'''

(The figure below represents the reproductive and development cycle of a frog as it transform from egg to frog specie.)

In tadpoles, right after the mouth is being formed, two indentation like thickenings of peritoneum begin to appear near the body cavity (dorsal surface), which is nearest to the mesentery which is near the developing kidneys. These appear in all tadpoles.

These indentations appear here because of a change in the endothelial cells, everywhere else they are usually flat looking cells but they undergo a change and in this particular area become somewhat cuboidal/columnar.

Later on the indentations become more obvious due to the epithelial cells replicating numerously to form a thick layer. The posterior two thirds of the indentation for the female is the ovary and for the male it is the testis. The third that is left differentiates and becomes fat for the body.

[[Image: Mature frog life cyle.jpg|thumb|200px|left|Figure 11 Image details:Derived from primary source:http://www.scienceclarified.com/images/uesc_01_img0038.jpg]]

[[Image: Developing frog.jpg|thumb|Figure 12 Image details:
[[Image: Mature develop frog.jpg|thumb|Image details: Wikipedia (2009) TYPICAL FROG Primary source:[http://en.wikipedia.org/wiki/File:Red-eyed_Tree_Frog_-_Litoria_chloris_edit1.jpg]].jpg]]

===Delamination===

Delamination indicates a mass separating a group of cellular matter from other cellular groups. It has been illustrated that the division of notochord, mesoderm and endoderm tissues from each other to form distinct cellular masses is completed by the progression of delamination, subsequent to these materials moving to the inside throughout gastrulation. During the developing gastrula, the germ layers are all recognized. These distinct segments of the embryo develop from these germ tissue layers.

===Polarity and Rotation===

Throughout fertilisation to the beginning of gastrulation, the frog’s egg continues in the original location in relation to its polarity. Subsequent to gastrulation its polarity begins to differentiate. This progression is linked with migration of materials within the gastrula and can be responsible for the alterations of the centre of gravity.

===Closing of Blastopore===

Subsequent to the formation of the gastrula, the blastopore is visible as a tiny round circular filled cavity containing the yolk plug. As it continues to reduce in dimension, it represented as a pear-shaped outline through the mutual approach of its lateral lips. Through it final progression these fuse entirely to produce a longitudinal groove, the streak which continue dorsally and ventrally in a small aperture. The inferior aperture closes, resulting in a depression called the anal pit. The superior region remains open for some period and begins to as the neural groove is laid down.

===Post Gastrulation or Organogenesis===

Throughout the duration of pre-gastrulation, all tissues for different organs vanish from the surface of blastula and migrate inside to take their final arrangement in the embryo structure where organs are developed from their potential regions. Consequently organogenesis transfers an embryo into free larva structure.

----

==Germ-layer origin of various body tissues==
[[Image: Development Models of Frog.jpg|thumb|right|Figure 13 Image details:Vertebrate Structure and Development.jpg]]

Ectoderm will give raise to structures such as skin, brain, spinal cord, neurons and sense receptors.
Mesoderm will give raise to structrues such as notochord, muscles, blood, bone and sex organs.
Endoderm will give raise to sturctures such as inner lining of gut, liver, pancreas, lungs and bladder, thyroid and parathyroid glands and thymus.

== Structures derived from Germ-layers of frog species ==

[[Image:Development of Frog Layers.jpg|thumb|left|Figure 14 Primary source[http://www.bio.miami.edu/~cmallery/150/physiol/sf19x11b.jpg]Image details:J,Nassif 2009.jpg]]

[[Image:Development of frog layers.jpg|thumb|left|Figure 15 Primary source [http://www.bio.miami.edu/~cmallery/150/physiol/sf19x11b.jpg]Image details:J,Nassif 2009.jpg]]

'''Ectoderm '''

''Establishes the epidermal segments and its derivatives, to the frog’s nervous system. The ectoderm also contributes to :''

1. The olfactory and auditory epithelium.

2. The retina and lens of the eye.

3. Sensory organs.

4. The epithelial lining of the oral cavity and the anus.

5. The pineal and pituitary body.

'''Mesoderm'''

''Mesoderm originates:''

1. Connective tissue.

2. Muscles, except the notochord.

3. Blood vessels.

4. Lymphatics.

5. The peritoneum and the urinary and reproductive system.

6. The dermis, parts of the eye excluding lens, cornea, and conjunctiva.

'''Endoderm'''

''From the endoderm arises:''

1. The epithelial lining to the gut and oesophagus, stomach, intestine, bile duct.

2. The hepatic cells of the liver, respiratory tract, larynx, trachea and lungs.

3. The lining of the urinary bladder, pancreas thyroid and thymus.

[The two figures reveal the development of structures deriving from the celluar components of the embryology of the frog].[Structures derived from Germ-layers of frog species ]

==Life cycle of a frog==

'''Fertilization-egg''':

The female lays eggs in the spring. A group of fertilized eggs is called spawn;

'''7-10 days''':

Fertilized egg feed on remaining yolk which is in its gut. Their gills, mouth and tail have poorly developed. Begin to swim and feed on algae;

'''10-30 days(4 weeks):'''

A layer of skin grows over gills. Teeth begin to appear. A coiled gut start to develop. This is aid in digestion;

'''30-60 days(6-9 weeks):'''

Legs being to grow and head is more distinct. Start to eat insects. Arms begin to grow;

'''60-80 days(12 weeks):'''

Resemble a frog. Still have remaining tail;

'''80-140 days(20 weeks):'''

Fully developed, spend most of time out of water. Majority of frog live between 4-15 years.

==Timeline of frog development==

Development of egg and embryo at temperature 18 degree celsius.

'''0 hours''' - fertilization of the egg

'''1 hours''' - formation of the gray crescent due to pigment migration

'''3.5 hours''' - early cleavage

'''4.5 hours''' - blastula stage(coeloblastula with eccentric blastocoel

'''26 hours''' - gastrulation

'''26 hours''' -'' early'' - crescent shaped dorsal lip

'''34 hours''' - ''middle''- semicircular blastoporal lip

'''42 hours''' - ''late'' - circular blastoporal lip

'''50 hours''' - neurulation

'''50 hours''' - ''early'' - medullary plate

'''62 hours''' -'' middle''- neural folds converging

'''67 hours''' - ''late'' - neural tube formed and ciliation of embryo

'''84 hours''' - tail bud stage(early organogeny)

'''96 hours''' - muscular response to tactile stimulation

'''118 hours''' - early heart beat, development of gill buds

'''140 hours''' - hatching and gill circulation

'''162 hours''' - mouth opens and cornea becomes transparent

'''192 hours''' - tail fin circulation established

'''216 hours''' - degeneration of external gills, formation of operculum, development of embryonic teeth

'''240 hours''' - opercular fold over brachial chamber except for spiracle and internal gills

'''255 hours''' - prolonged larval stage with refinement of organs

'''270 hours''' - development of hindlimbs, internal development of forelimbs in opercular cavity

'''275 hours''' - projection of forelimbs through operculum, left side first

'''280 hours''' - absorption of the tail and reduction in size of the gut

'''284 hours''' - metamorphosis complete, emergence from water as miniature, air breathing frog

==Stages of frog embryology==
--[[User:S8600021|Mark Hill]] 08:40, 9 October 2009 (EST) [[Talk:2009_Group_Project_5#Constructive_Criticism_of_Coordinator|see my comment on images]]

The rate of development of the egg and embryo will depend upon the temperature at which they are kept. The approximate schedule of development at 23 degree celsius is provided below.

{| border='1px'
|+ Table 1: Stages of frog development
!Stage !!Time since fertilisation (hours)!!Stage Characteristic !!Embryo characteristic !!Image of frog stage
|-
|1
|0.00-1.30
|fertilization of the egg, post fertilization
|animal hemisphere, gray crescent and vegetal hemisphere are present
|[[File:Stage01ventral.jpg|100px]]
|-
|2
|1.30-2.00
|splits into two cells
|appearance of first cleavage furrow
|[[File:Stage02ventral.jpg|100px]]
|-
|3
|2.00-2.15
|becomes four cells
|appearance of second cleavage furrow
|[[File:Stage03dorsolat.jpg|100px]]
|-
|4
|2.15-2.45
|becomes eight cells
|appearance of third cleavage furrow
|[[File:Stage04dorsolat.jpg|100px]]
|-
|5
|2.45-3.00
|becomes sixteen cells
|appearance of fourth cleavage furrow
|[[File:Stage05dorsal.jpg|100px]]
|-
|6
|3.00-3.30
|becomes thirty-two cells
|appearance of fifth cleavage furrow
|[[File:Stage06animal.jpg|100px]]
|-
|6.5
|3.30-4.00
|blastula stage
|Three dorsal folds become visible as a result of endoderm invagination. Pole cells no longer visible on surface
|[[File:Stage065dorsal.jpg|100px]]
|-
|7
|4.00-5.00
|Gastrulation stage
|two primary germ layers. epiblast and endoderm
|[[File:Stage07ventral.jpg|100px]]
|-
|8
|5.00-7.00
|neurulation
|medullary plate, neural folds and neural tube
|[[File:Stage08animal.jpg|100px]]
|-
|9
|7.00-9.00
|germ layer
|complete lip involution encircling yolk
|[[File:Stage09veg.jpg|100px]]
|-
|10
|9.00-11.00
|early gastrula
|two primary germ layers
|[[File:Stage10veg.jpg|100px]]
|-
|10.5
|11.00-11.45
|gastrula
|two germ layers
|[[File:Stage105vegb.jpg|100px]]
|-
|11
|11.45-12.30
|medulla plate
|Yolk sac protrudes dorsally, labium moves to midline on ventral side
|[[File:Stage11veg.jpg|100px]]
|-
|11.5
|12.30-13.15
|continuation of medulla plate
|start closing the plate
|[[File:Stage115veg.jpg|100px]]
|-
|12
|13.15-14.15
|early neurula
|thickened ectoderm give rise to CNS
|[[File:Stage12veg.jpg|100px]]
|-
|12.5
|14.15-14.45
|neural folds
|expansion of cavity
|[[File:Stage125postdors.jpg|100px]]
|-
|13
|14.45-16.15
|neural folds
|continue expanding cavity
|[[File:Stage13postdors.jpg|100px]]
|-
|14
|16.15-17.30
|neural folds
|continuation of cavity
|[[File:Stage14postdors.jpg|100px]]
|-
|15
|17.30-18.15
|tail bud stage
|early organogeny
|[[File:Stage15postdors.jpg|100px]]
|-
|16
|18.15-18.45
|tail bud stage
|posterior ventral view
|[[File:Stage16ant.jpg|100px]]
|-
|17
|18.45-19.45
|tail bud stage
|anterior view
|[[File:Stage17ant.jpg|100px]]
|-
|19
|20.45-21.45
|neural fold close complete
|dorsal view
|[[File:Stage19dorsal.jpg|100px]]
|-
|20
|21.45-22.30
|early tail bud
|anterior view
|[[File:Stage20dorsal.jpg|100px]]
|-
|21
|22.30-24.00
|termination of neural crest
|progress to next stage
|[[File:Stage21ant.jpg|100px]]
|-
|22
|24.00-24.45
|prolonged development
|elongation
|[[File:Stage22lat.jpg|100px]]
|-
|23
|24.45-26.15
|elongation of embryo
|later view
|[[File:Stage23lat.jpg|100px]]
|-
|24
|26.15-27.30
|continuation of elongation of embryo
|dorsal view
|[[File:Stage24latsmall.jpg|50px]]
|-
|25
|27.30-29.30
|organs development
|embryo elongates and develops dorsal thickening
|[[File:Stage25dorsal.jpg|50px]]
|-
|26
|29.30-31.15
|elongation
|dorsally forms neural and brain cavity
|[[File:Stage26lat.jpg|50px]]
|-
|27
|31.15-32.30
|elongation of embryo
|dorsal view
|[[File:Stage27lat.jpg|50px]]
|-
|28
|32.30-35.00
|further development
|lateral view
|[[File:Stage28lat.jpg|50px]]
|-
|29-30
|35.00-37.30
|tail bud
|growth
|[[File:Stage29-30lat.jpg|50px]]
|-
|31
|37.30-40.00
|prolonged development
|bud development
|[[File:Stage31lat.jpg|50px]]
|-
|32
|40.00-44.30
|early muscular development
|elongation
|[[File:Stage32lat.jpg|50px]]
|-
|33-34
|44.30-50.00
|muscular movement
|apparatus for locomotion
|[[File:Stage33-34lat.jpg|50px]]
|-
|35-36
|50.00-53.30
|muscular movement
|apparatus for locomotion
|[[File:Stage35-36lat.jpg|50px]]
|-
|37-38
|53.30-56.30
|heart beat
|develops apparatus
|[[File:Stage37-38lat.jpg|50px]]
|-
|39
|56.30-66.00
|mouth opens
|cornea transparent
|[[File:Stage39latsmall.jpg|50px]]
|-
|40
|66.00-76.00
|gill circulation
|hatching
|[[File:Stage40lat.jpg|50px]]
|-
|41
|76.00-80.00
|tail, fin circulation
|circulation
|[[File:Stage41lat.jpg|50px]]
|-
|42
|80.00-86.00
|internal gills, operculum
|opercular fold, teeth
|[[File:Stage42lat.jpg|50px]]
|-
|43
|86.00-98.00
|operculum complete
|operculum closed on right
|[[File:Stage43lat.jpg|50px]]
|-
|46
|98.00-106.00
|metamorphosis
|emergence from water as miniature, operculum complete|
|[[File:Stage46lat.jpg|50px]]
|-
|}

==Abnormalities of frog==

Abnormalities of frog could be caused by multiple factors. These include change in climate, predators, parasites, bacteria, fungi, viruses or pollution and contaminants such as pesticides, metals and fertilizer.[http://www.fws.gov/contaminants/documents/frogsrefup_septoct_2006.pdf]

The Abnormalities are further classified into different categories. These categories are:

===1. Infectious Diseases:===

'''Perkinsus Symptoms-''' caused by perkinsus-like protozoan organism. Symptoms include swollen viscera that leads to a bloated body and and infected swollen heart

'''Ichthyophonus symptoms-''' cause by parasitic genus, where symptoms include a swollen tail resorption site that matches the surrounding skin in color and translucency.

[[Image:Abnormalities of Frog species.jpg|thumb|left|Figure A Image details[waterwatchadelaide.net.au].jpg]]

===2. Surficial Abnormalities:===

Surficial abnormalities as the one that are visible on the surface of the skin. This includes abnormal pigmentation, , subcutaneous hemorrhaging, wounds due to trauma or from a predator
Edema is a fluid-filled swelling under skin whihc is also a surficial abnormality.

===3. Skeletal Abnormalities:===

This is further classified into three more categories:

'''a. Skeletal Malformations-'''

* Microcephaly (small head or blunt snout)
*Scoliosis (Curved spine in lateral direction)
*Shrunken Limb (Micromelia)
*Amelia (Completely missing limb with no stump)

'''b. Skeletal Abnormalities of Unclear Etiology-'''

This condition arises when a frog has ectromelia (missing limb), brachydactyly (missing digits) or other such condition with no visible trauma or external damage, then this will be classified as the Skeletal abnormality of unclear etiology.

'''c. Skeletal Injuries-'''

Any limb missing or broken due to trauma or other related reason which shows clear evidence of it is classified as skeletal injury

===4. Eye Abnormalities:===

Most common includes-

'''i. Anophthalmia:''' Skin covers the eye socket as there is no eye

'''ii. Abnormal Iris Coloration:''' Reduced pigment in either one eye or both resulting in two different colours of the iris at times

'''iii. Abnormal size or shape:''' Both eyes either deviating from each other or size of pupil or iris is different than the other eye

[http://www.fws.gov/contaminants/Amphibian/pdfs/AbnormalitySOP_woutpics_Jan08.pdf ]

==Genetics==

There are a wide variety of species that differ from each other when it comes to genetics and their functioning.

'''TAXONOMY:''' '''Phylum''' ''Chordata'' / '''Sub Phylum''' ''Vertebrata'' / '''Class''' ''Amphibia'' / '''Order''' ''Anura''

Their are more than two dozen different families of frogs, where suborders are:

'''1. ARCHAEBATRACHIA-''' most primitive frogs

'''2. MESOBATRACHIA-''' linked between the Archaebatrachia and Neobatrachia

'''3. NEOBATRACHIA-''' most modern frogs

{| border='4px'
|+ '''General Info:'''
! !!
|-
| '''Number of frogs' species'''
| 5280
|-
| '''Smallest frog genome size:'''
| 0.95pg, Ornate burrowing frog
|-
| '''Largest frog genome size:'''
| 13.40pg, Ornate horned frog
|-
| '''Mean of frogs' genome'''
| 4.68pg ± 0.13
|-
|}

[http://www.genomesize.com]

*Majority of frogs have only 22 to 26 chromosomes and polyploid is very common where they are almost bisexual.

*Polyploid Amphibians reduce their total cell number such that they acheive the same body size as diploids. One of the most unsual forms of polypoidy in amphibians is the water frog ''Rana esculenta'' from Europe and Western Asia.

* The species with larger genomes have more genes for e.g. the frog genus ''Xenopus'' includes 16 species, with genome sizes ranging from 3.5 x 10^9 bp to 1.6 x 10^10 bp. These differences have arisen by numerous events of polyploidization within the past 40 million years or so. The ancestral chromosome number for the genus seems to have been 18, but there are species with 36, 72 and 105 chromosomes [http://www.xenbase.org/common/]

{| border='4px'
|+ '''Difference within two families'''
! '''SPECIES''' !! ''X.LAEVIS'' !! ''X.TROPICALIS''
|-
| '''PLOIDY'''
| Allotetraploid
| Diploid
|-
| '''NO. OF CHROMOSOMES'''
| 36 chromosomes
| 20 chromosomes
|-
| '''GENOME SIZE'''
| 3.1 x 10^9 bp
| 1.7 x 10^9 bp
|-
| '''EGG SIZE'''
| 1-1.3 mm
| 0.7-0.8 mm
|-
| '''GENERATION TIME'''
| 1-2 years
| 4 months
|-
|}
[http://www.xenbase.org/common/]

===Genome Sequencing===

Since Frog has a huge family with many different species, only few main species that are used widely for the purposes of experiments have their genome sequenced.

''Xenopus tropicalis'' has one of the smallest genomes among amphibians and has the shortest generation time- four to six months and the only diploid genome among the 14 Xenopus species. This means it has no more than two copies of most genes, whereas the other species of Xenopus have four copies of most genes (pseudotetraploid). US Department of Energy's Joint Genome Institute (JGI) in Walnut Creek, California, initiated the X. tropicalis Genome Project, finding 1,700 million base pairs.
[http://www.genome.gov/Pages/Research/Sequencing/BACLibrary/xenopusTropicalis.pdf]

===Xenopus oocytes===

* The oocytes provide an important expression system for molecular biology.

* By injecting DNA or mRNA into the oocyte or developing embryo, scientists can study the protein products in a controlled system. This allows rapid functional expression of manipulated DNAs (or mRNA). This is particularly useful in electrophysiology, where the ease of recording from the oocyte makes expression of membrane channels attractive.

* One challenge of oocyte work is eliminating native proteins that might confound results, such as membrane channels native to the oocyte.

* Translation of proteins can be blocked or splicing of pre-mRNA can be modified by injection of Morpholino antisense oligos into the oocyte (for distribution throughout the embryo) or early embryo (for distribution only into daughter cells of the injected cell).
[http://www.staff.unibe.ch/sigel/xenopus.html]

===Xenopus Laevis===

* ''Xenopus Laevis'' is an important model organism in developmental biology. X. laevis is tetraploid and reaches sexual maturity in 1 to 2 years. What makes it important in developmental biology is its large and easily manipulable embryo.

* Extracts from the eggs of X. laevis frogs are also commonly used for biochemical studies of DNA replication and repair, as these extracts fully support DNA replication and other related processes in a cell-free environment which allows easier manipulation.

* The Human chorionic gonadotropin hormone (hCG) is present in the urine of the pregnant women in large quantities only. This hormone in the urine induces X.laevis oocyte production which formed the basis of first well-documented method of pregnancy testing X. laevis is also notable for its use as the first well-documented method of pregnancy testing when it was discovered. Today, commercially available HCG is injected into Xenopus males and females to induce mating behavior and breed these frogs in captivity at any time of the year.

===Gene cluster===

* The alpha and beta globin genes are closely linked in small cluster of frogs compared to human and chicken

* The similarity of architecture of two clusters found in X.laevis supports the tetraploid origin

* The two loci encoding the muscle specific creatine kinase isoenzymes and have large differences in developmental profile, therefore suggesting that duplicate loci that have not undergone silencing are not simply redundant copies but have acquired specialization.

* Contains twice number of genes for proteins i.e. haemoglobin and sarcomeric actin serum albumin compared with other species

----

==Current Embrology Research==

Currently, a number of fields have benefited from the development of frog embrology. These include cloning, verification of messenger RNA, and Cell cycle.

===Cloning===
[[Image:Robert Briggs.jpg|thumb|left|Figure 16 Image details:Robert Briggs.jpg]]

In 1952, Robert Briggs and Thomas J King cloned northern leopard frogs using a method of nuclear transfer. Briggs and King's experiment was similar to that envisioned - and piloted using salamanders - by Hans Spemann in his 1938 proposal for a 'fantastical experiment'. Later, John Gurdon extended this work and showed that nuclei from differentiated cells could support development, although less well than those from early embryos. [http://genome.wellcome.ac.uk/doc_WTD020799.html]

Lemaitre et a. (2005) from MRC Cancer Cell Unit, Cambridge, U.K. worked on experiments that demonstrated that importance of serial nuclear transplantation for the sucessful cloning of frogs. He demonstrated that exposure of somatic-cell nuclei (erythrocyte nuclei) and sperm nuclei to an extract of mitotic cell extract reorganizes the chromatin into shorter loops and allows replication at much shorter intervals along the DNA. This increases the efficiency of DNA replication in mammalian cell-free systems.

===Transgenesis techniques for functional genomics in Xenopus===

Transgenesis in Xenopus is made possible due to large embryos, a reliable fate map, ease of microinjection, ease of dissection/micromanipulation and existence of the neuroendocrine reflex of background adaptation as a model for activation/inact.

Recently, Hajime Ogino and Haruki Ochi from Nura Institute of Science and Technology in Japan focused on the genomic resources and principles of the transgenesis techniques in Xenopus, and discusses their applications to genome wide network analysis, with emphasis on the use of bioinformatics tools. This is will to understand the gene regulatory networks that control vertebrate development. [http://www.ingentaconnect.com/content/bsc/dgd/2009/00000051/00000004/art00001%3Bjsessionid=4ah96rms73gcu.alexandra]

Xenopus used to be a problem in earlier days when it came to transgenesis. Current methods involves isolated sperm nuclei from Xenopus testis that are microinjected into unfertilized eggs. The generated transgenic tadpoles contain 5-35 copies of the integrated plasmid that are expressed in all cells. If desired, expression of the transgene can be directed to the appropriate tissue and at the appropriate time by using specific promoters, mostly the Xenopus POMC gene promoter (isolated from a Xenopus genomic DNA library) to specifically direct expression of green fluorescent protein (GFP) at high levels to the intermediate pituitary cells, which can either be over expressed or inhibited.[http://molanphys.ruhosting.nl/transgenesis.htm]

[[File:Transgenesis.JPG]]

===Verification of messenger RNA===

While the existence and role of messenger RNA (mRNA) was known in bacteria, in the 1960s it was still debated whether it also existed in vertebrates. Taking haemoglobin mRNA from immature red blood cells and injecting it into a Xenopus oocyte, John Gurdon showed that the haemoglobin protein was indeed produced. Producing proteins in Xenopus oocytes has proved to be extremely useful in cell biology, in particular for the study of receptor proteins.[http://genome.wellcome.ac.uk/doc_WTD020799.html]

===Cell Cycle===

As they develop outside the mother, frog eggs are well stocked with the proteins needed to drive the development of the embryo. Studies of these processes has shed considerable light on the processes involved in cell division - termed the cell cycle. [http://genome.wellcome.ac.uk/doc_WTD020799.html]

===Limb development in Xenopus Laevis===

[[Image: Frog Limb development.jpg|thumb|right|Image details:Primary source:[http://images.google.com.au/imgres?imgurl=http://www.sciencedaily.com/images/2006/06/060616130718.jpg&imgrefurl=http://www.sciencedaily.com/releases/2006/06/060616130718.htm&usg=__xliPsPAvheUBME_kjv_q7auiFbo=&h=333&w=300&sz=11&hl=en&start=2&um=1&tbnid=y_ntJtmkRSK7WM:&tbnh=119&tbnw=107&prev=/images%3Fq%3DLimb%2Bdevelopment%2Bin%2BXenopus%2BLaevis%26ndsp%3D18%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

Donald D. Brown (2005),Department of Embryology, Carnegie Institution of Washington demonstrated factors related to limb development of Xenopus Laevis. Thyroid hormone (TH) is found to be required for limb development in this frog. Specific cell types in the growing limb were targeted for expression of a dominant negative form of the TH receptor by sperm-mediated transgenesis. Limb muscle development, the innervation of muscle from the spinal cord, and cartilage growth can be inhibited without affecting patterning of the limb or differentiation of other cell types. Remodeling of the skin occurs late in metamorphosis after the limb has formed. The coordination of these independent programs is affected in part by the control that TH exerts over DNA replication in all cell types of the limb. [http://www.pnas.org/content/102/35/12455.full]

----

== Glossary ==

[[Image: Frog species.jpg|thumb|left|Image details:Primary source:www.olympus.co.jp/.../080925/large/p02L.jpg].jpg]]

*'''Amphibian:'''

''Relating to or characteristic of animals of the class amphibia.Amphibians are found in the taxonomic class of amphibia, amphibians are capable of both occupying and successfully living in both land and aquatic communities.amphibian''

*'''Augmentation:'''

''Enlargement/Increase in cellular size.''

*'''Autolysis:'''

''breakdown of a part or whole cell or tissue by self-produced enzymes''

*'''Blastomeres:'''

''The undifferentiated cells formed by cleavage of the fertilised ovum. This includes cells in the cleavage, morula, and blastula stages of the embryo''

*'''Carnivorous:'''
''
Flesh-eating; subsisting on animals as food.''

*'''Cleavage:'''

''he repeated division of a fertilised ovum ''

* '''Cleft:'''

''an opening, fissure, or V-shaped indentation made by or as if by splitting''

*'''Chordate:'''

''Members of a diverse phylum of animals that, as embryos, possess a (1) notochord; (2) a dorsal, hollow nerve cord, (3) pharyngeal gill slits; and (4) a post-anal tail''

''The act or state of splitting or dividing of a cell, particularly during the telophase of (animal) cell division.''

*'''Cytoplasm:'''

''The cytoplasm (of both eukaryotes and prokaryotes) is where the functions for cell expansion, growth, metabolism, and replication are carried out''

* '''Epiboly:'''
''The expansion of one cell sheet over other cells, as takes place during gastrulation''

*'''Fertilization:'''

''A process in sexual reproduction that involves the union of male (sperm) and female (ovum) gametes (each with a single, haploid set of chromosomes) to produce a diploid zygote.''

*'''Gamete:'''
''A reproductive cell (male (sperm) or female (egg)) that has only half the usual number of chromosomes''

*'''Gametogenesis:'''

''process leading to the production of gametes. The development and maturation of sex cells through meiosis.Another name for meiosis where a diploid cell is divided into two haploid cells with half the chromosome content of the diploid parent cell.''

*'''Herbivorous:'''

''eating plants; of or pertaining to the herbivora.''

*'''Holoblastic:'''

''The complete division of an isolecithal or microlecithal egg into blastomeres''

*'''Invagination:'''

''One of the methods by which the various germinal layers of the ovum are differentiated.''

*'''Isoenzymes:'''

''Isozymes (also known as isoenzymes) are enzymes that differ in amino acid sequence but catalyze the same chemical reaction.''

*'''Mesentery:'''

'' membranous fold attaching various organs to the body wall.''

*'''Metamorphosis:'''

''A change in the form and often habits of an animal after the embryonic stage during normal development.''

*'''Neuroendocrine:'''

''Neuroendocrine [IPA nʊəroʊˈɛndəkrɪn] cells are cells that release a hormone into the circulating blood in response to a neural stimulus.''

*'''Organogenesis:'''

''The part of embryonic development where the body's main organs develop.''

*'''Peritoneum:'''

''The smooth serous membrane which lines the cavity of the abdomen, or the whole body cavity when there is no diaphragm, and, turning back, surrounds the viscera, forming a closed, or nearly closed, sac.''

*'''Perivitelline space:'''

''The perivitelline space is the space between the zona pellucida and the plasma membrane (sometimes called the vitelline membrane) in a fertilized ovum.''

*'''Polyploidy:'''

''Cells with three or more sets of chromosomes.''

*'''Pronucleus:'''

''the nucleus of the ovum or sperm after fertilization but before they fuse to form the nucleus of the zygote ''

*'''Protoplasm:'''

''The fluid living content of the cell that consists of two major divisions, the cytoplasm and the nucleoplasm (cell nucleus). It is composed mainly of nucleic acids, proteins, lipids, carbohydrates, and inorganic salts''

*'''Segmentation:'''

''division of some metazoan bodies (such as annelida and Arthropoda) into repeated parts, segments. Segmentation can be homomeric (more or less the same) or heteromeric(different from each other).''

*'''Terrestrial:'''

''Of or on the ground, of the habitat of a plant, on land as opposed to in water, or on the ground as opposed to on another plant.''

*'''Transgenesis:'''

''Transgenesis is the process of introducing an exogenous gene - called a transgene - into a living organism so that the organism will exhibit a new property and transmit that property to its offspring.''

*'''Yolk:'''

''nutritive material of an ovum stored for the nutrition of an embryo''

*'''Zygote:'''

''The cell from which an organism develops, that results from the fertilization of the egg by the sperm.''

''Primary Resource "Biology- Online Dictionary''[http://www.biology-online.org/dictionary/Main_Page]

== References - Frog Embryology: ==

[[Image:Frog Research.jpg|thumb|left|Image details:[http://images.google.com.au/imgres?imgurl=http://www.odt.co.nz/files/story/2008/09/university_of_otago_zoology_senior_lecturer_phil_b_3343259744.jpg&imgrefurl=http://www.odt.co.nz/on-campus/university-otago/21670/dunedin-frog-man-wins-zoo-award&usg=__JvJJU5QfOnIwY2bk4xo64UXuJRs=&h=600&w=404&sz=22&hl=en&start=14&um=1&tbnid=AbsP89yWcUiilM:&tbnh=135&tbnw=91&prev=/images%3Fq%3Dfrog%2Bresearch%26hl%3Den%26um%3D1].jpg]]

1. Savage, J. M. (2002). The Amphibians and Reptiles of Costa Rica. University of Chicago Press, Chicago [http://www.springerlink.com/content/vv015277w1746llw/]

2. Ford, L.S.; D.C. Cannatella (1993). "The major clades of frogs". Herpetological Monographs 7: 94–117 [http://digimorph.org/specimens/Xenopus_laevis/]

3. Tyler, M. J. (1994). Australian Frogs A Natural History. Reed Books [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.gracilenta.html]

4. Cogger, H.G.; R.G. Zweifel, and D. Kirschner (2004). Encyclopedia of Reptiles & Amphibians Second Edition. Fog City Press [http://en.wikipedia.org/wiki/Microhylidae]

5. Beltz, Ellin (2005). Frogs: Inside their Remarkable World. Firefly Books [http://unjobs.org/authors/ellin-beltz]

6. Tyler, M. J. (1994). Australian Frogs A Natural History. Reed Books [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

7. Moury JD, Hanken J (1995) Early cranial neural crest migration in the direct-developing frog, Eleutherodactylus coqui. Acta
Anatomica (Basel) 153, 243-253.

8.Raynaud A (1985) Development of limbs and embryonic limb reduction. In Biology of the Reptilia (ed. Gans C, Billett F), pp.
59-148. New York: John Wiley.[http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=9309]

9. Hanken J (1986) Developmental evidence for amphibian origins. In Evolutionary Biology (ed. Hecht MK, Wallace B, Prance GT), 20, pp. 389-417. New York: Plenum Press. [Hanken J (1986) Developmental evidence for amphibian origins. In Evolutionary Biology (ed. Hecht MK, Wallace B, Prance GT), 20, pp. 389-417. New York: Plenum Press.]

10. Elinson RP (1990) Direct development in frogs : wiping the recapitulationist slate clean. Seminars in Developmental Biology
1, 263-270.

11. Beebee, T. J. C. 1996. Ecology and Conservation of Amphibians. Chapman and Hall. London. [http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V5X-3SVHMKH-1X&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=1021245355&_rerunOrigin=google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=825868e10cd178d16a8a0e5ad14dc5ef]

12. Lehtinen, R. M. 2002. The use of screw pines (Pandanus spp.) by amphibians and reptiles in Madagascar. Herpetological Bulletin 2002:20–25.

13. Parris, K. M. and M. A. McCarthy. 1999. What influences the structure of frog assemblages at forest streams. Australian Journal of Ecology 24:495–502. CrossRef

14. Zug, G. R. 1993. Herpetology: An Introductory Biology of Amphibians and Reptiles. Academic Press. San Diego, CA.

15. Slack,J.M.W., Darlington,B.G., Heath,J.K. and Godsave,S.F. (1987)Mesoderm induction in early Xenopus embryos by heparin-binding growth factors. Nature, 326, 197-200.

16. Melton,D.A. (1990) Activins are expressed early in Xenopus embryogenesis and can induce axial mesoderm and anterior structures. Cell, 63, 485-493.

17. Harland,R.M. and Misher,L. (1988) Stability of RNA in developing Xenopus embryos and identification of a destabilizing sequence in TFIIIA RNA. Development, 102, 837-852.

18. Cunliffe,V. and Smith,J.C. (1992) Ectopic mesoderm formation in Xenopus embryos caused by widespread expression of a Brachyury homologue. Nature, 358, 427-430.

19. Kinoshita,K., Bessho,T. and Asashima,M. (1993) Competence prepattern in the animal hemisphere of the 8-cell-stage Xenopus embryo. Devel. Biol., 160, 276-284.

20. LaBonne,C., Burke,B. and Whitman,M. (1995) Role of MAP kinase in mesoderm induction and axial patterning in Xenopus development. Development, 121, 1475-1486.

21. Green,J.B.A., New,H.V. and Smith,J.C. (1992) Responses of embryonic Xenopus cells to activin and FGF are separated by multiple dose thresholds and correspond to distinct axes of the mesoderm. Cell, 71, 731-739.

22. Grainger R., Blumberg B., Harland R., Amemiya C., Importance of Xenopus Tropicalis to biomedical and biological research, Benaroya Research Institute, Virginia Mason Research Center [http://www.genome.gov/Pages/Research/Sequencing/BACLibrary/xenopusTropicalis.pdf ]

23. Gregory, T.R. (2005). Animal Genome Size Database. [http://www.genomesize.com]

24. U.S Fish and Wildlife Services, ABNORMALITY CLASSIFICATION SOP, [http://www.fws.gov/contaminants/Amphibian/pdfs/AbnormalitySOP_woutpics_Jan08.pdf ]

25. Donald D. Brown*, Liquan Cai*, Biswajit Das*, Nicholas Marsh-Armstrong‡, Alexander M. Schreiber*, and Rejeanne Juste*(2005), Thyroid hormone controls multiple independent programs required for limb development in Xenopus laevis metamorphosis [http://www.pnas.org/content/102/35/12455.full]

26. Ogino, Hajime; Ochi, Haruki, Resources and transgenesis techniques for functional genomics in Xenopus, Development Growth & Differentiation, Volume 51, Number 4, May 2009 , pp. 387-401(15) [http://www.ingentaconnect.com/content/bsc/dgd/2009/00000051/00000004/art00001%3Bjsessionid=4ah96rms73gcu.alexandra]

27. Giles Newton (2004) Why the frog? The Human Genome, [http://genome.wellcome.ac.uk/doc_WTD020799.html]

28. Xenbase, [http://www.xenbase.org/common/]

29. Donders Center for Neuroscience & Nijmegen Center for Molecular Life Sciences (NCMLS), Beyond the genome (Xenopus transgenesis for functional genomics),Faculty of Science, Radboud University [http://molanphys.ruhosting.nl/transgenesis.htm]

== External Links ==
[[Image:Frog links.jpg|thumb|left|Image details:[http://images.google.com.au/imgres?imgurl=http://2.bp.blogspot.com/_o93AaY0GzH4/SjY_ZYv0PII/AAAAAAAAAgk/skruNc2yN78/s400/computer%2Bfrog.jpg&imgrefurl=http://hellaheaven-ana.blogspot.com/2009/06/talking-frog-contemporary-fairy-tale.html&usg=__oxji1TGLV2Fi7xe0dnlmuYk8gDo=&h=288&w=288&sz=16&hl=en&start=2&um=1&tbnid=ywZd4zpdxC5plM:&tbnh=115&tbnw=115&prev=/images%3Fq%3Dfrog%2Bon%2Bcomputer%26hl%3Den%26um%3D1].jpg]]

1. Frog embryology [http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/F/FrogEmbryology.html Frog Embryology]

2. Frog cellular materials [http://www.xenbase.org/xenbase/original/cell/cell.html xenbase]

3. The zoology of frog species [http://worms.zoology.wisc.edu/frogs/mainmenu.html zoology frogs]

4. Frog cycle [http://www.bioethics.gov/images/sc_images/frog_dev.gif bioethics frog] Just a little cycle of FROG'S life cycle

5. Frog Embryology [http://embryology.med.unsw.edu.au/OtherEmb/Frog.htm UNSW Embryology]

6. Frog Research [http://apps.carleton.edu/campus/library/now/exhibits/wallcharts/frog/ carleton library exhibit]

{{Template:Projects09}}
[[Category:Frog]]

2009 Group Project 5

2009-10-14T22:37:27Z

Z3258567: /* The Egg & Fertilization */

== The Embryology of Frogs ==

== The Frog ==

[[Image: Frog species .jpg|thumb|left|Image details: Wikipedia (2009) Frog species[http://en.wikipedia.org/wiki/Frog#Uses_in_agriculture_and_research].jpg]]

Frogs are scientifically identified by the structure of their long posterior limbs, a petite framework, webbed fingers and feet, budged eyes and the lack of a tail. The majority of frog species are extensively recognized as outstanding jumpers, due to their long, dominant legs, which are adaptations to progress jumping performance during activities. The Frog is one of the most frequently studied species in experimental embryology and most anatomical sciences. ''The Frog is a practically effective model for human embryological development given that the Frog:''

- Comprises of genes which can be effectively manipulated.

- Comprises of similar homogeny with humans species.

- Reproduces a large quantity of offspring in a short period of time.

- Are small species which can be simply sustained.

- Are not extremely luxurious and expensive.

== The History of the uses in agriculture and research ==

[[Image: Frog experiments .jpg|thumb|right|Image details: Scans of chemically cleared and dyed preserved deformed frogs and toads [http://www.sat.qc.ca/upload/residence/frog-04.jpg].jpg]]

There are numerous types of frog species that have been manipulated in many developmental experiments. The frog was traditionally used by countless of the early embryology investigators and presently there are several diverse molecular mechanisms regarding progression of the frog. Theses include:

'''1.''' Food source; frog legs are a delicacy and are eaten in European countries and in many parts of South American regions.

'''2.''' Frogs have the finest biochemical dissection of phenomena that take place in the egg and oocyte. Frogs are the evolutionarily closest to mammals, commonly used as a vertebrate model.

'''3.''' Frogs lay thousands of outsized eggs, from which cell extracts can be readily prepared that is capable of recapitulating most molecular phenomena in a test tube.

'''4.''' Frogs have been commonly used as a laboratory system for a very long period, and have an extensive history of producing crucial observations in countless fields of biology.

'''5.''' Frogs have a important historical connection to the study of epigenetics (John Gurdon-vertebrate cloning and reprogramming) which has been mostly performed on frog species.

'''6.''' Frogs also have very strong evidence of pattern formation and early development, as the embryos are large in size and experimentally manipulative.

'''7.''' Recent research into the biochemistry of chromatin and epigenetics has been performed with frog species and mammalian cultured cells.

'''8.''' The biggest weakness of the Frog model system is the difficulty of performing genetic experiments and analysis, as frogs are allotetraploid, meaning they take approximately a year to fully develop to sexual maturity, and the genome has not been completely sequenced. Nevertheless, biochemical manipulations of cell extracts, such as immunodepletions and application of heterologous DNAs and nuclei can avoid the need for genetic exploitation.

----

== Growth and development of the Frog ==

[[Image: Mature develop frog.jpg|thumb|Image details: Wikipedia (2009) Red Eyed Tree Frog Figure 1 Primary source:[http://en.wikipedia.org/wiki/File:Red-eyed_Tree_Frog_-_Litoria_chloris_edit1].jpg]]

* The frog is a well recognised species, abundant predominantly in ponds, swamps, though various species may also exist in damp or shady environments distant from moist habitats.

* Eggs of specific frogs are easily obtained and may be examined in from the beginning of fertilization onwards. The phases of embryonic development differs in various chordates, yet the typical phases are basically apparent in all frog species. The differences are associated principally to the amount of yolk particles present in an egg.

* The yolk particles offer nourishment of the developing embryo. The process of frog development will be discussed from the phases of gametogenesis to the adult stage.

----

== The Egg ==
[[Image:Development of Poles in frog Fertilization.jpg|thumb|left|Development of Poles in Frog Fertilisation:J,Nassif 2009.jpg]]

- The embryology of a frog egg is a vast cell; its dimensions are approximately 1.4-1.6 million times larger than a typical aquatic species egg cell. Throughout the frog’s embryonic maturation period, the egg will be transformed into a tadpole encompassing millions of cells but still remains with its constant volume of genetic material, the vast prodction of cell have been illusttrated in the figure on the right revealing the production of eggs from female frogs. [http://en.wikipedia.org/wiki/Microhylidae]

- The early embryonic frog structure consists of three main segments the superior hemisphere known as the animal pole which is usually visible as a grey coloured area. The innermost layer appears to be between the outer two sections known as the gray crescent represented in black. Inferiorly, represents the vegetal pole typically lighter than the superior compartment illustrated in gold.

VIDEO RESOURCE: [http://www.youtube.com/watch?v=GO5YN_t1fqw&feature=related]

[[Image:Early Development of Frogs.jpg|thumb|left|Early Development of Frog:J,Nassif 2009.jpg]]

==History of frog embryology use ==

*'''1851''' - ''Henby Nelson''(MD): He identified a remarkable fact through the frog embryo. Henby observed the first cleavage of the yolk, in the egg of the frog. And cleaved structure corresponds in line of direction to the longitudinal axis of the body of the embryo of the frog species.

[[Image:Wilhelm Roux.jpg|thumb|right|Wilhelm Roux[http://images.google.com.au/imgres?imgurl=http://www.todayinsci.com/R/Roux_Wilhelm/RouxWilhelmThm.jpg&imgrefurl=http://www.todayinsci.com/6/6_09.htm&usg=__qRLTEMTHdZpAHxiNX12hWjcm9tA=&h=125&w=100&sz=4&hl=en&start=2&um=1&tbnid=LIKIwZTqCpk7MM:&tbnh=90&tbnw=72&prev=/images%3Fq%3DWilhelm%2BRoux%26gbv%3D2%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

*'''1888''' - ''Wilhelm Roux'': Wilhelm Roux attempted to solve the above observation by damaging one cell of a two-cell frog embryo with a hot needle. The cell stayed in place. However, it did not develop further. Its partner developed into a left or right half-embryo;

*'''1907''' - ''John Hopkins'' hospital: In order to identify the cellular source of neuronal fibres. Scientist placed small portions of frog embryo spinal cords in lymph on a microscope slide and was able to observe clear cut neuronal sprouting.

*'''1951''' - ''Robert Briggs'': Robert Briggs was able to clone a frog embryo by substituting the nucleus of an unfertilized frog egg cell with the nucleus of a frog embryo cell. This process is known as nuclear transplant, has formed the basis for all cloning.

*'''1952''' - ''Robert Briggs and T.J. King'': Robert Briggs and T.J. King used frog for test experiment. Because the size of the eggs in the frogs are enormous compared with those of mammals, which make them easier to manipulate.

*'''1976'''- Using the technique that had been successful in cloning frog embryos, the doctor transferred the nucleus of one cells into a donated egg cell. As an embryo began to develop, it was implanted into the uterus of a young woman.

*'''1997''' - ''Wilmut and Campbell'': Utilizing the cloning technique from frog embryo, Drs. Wilmut and Campbell tried the starvation technique on embryo cells to produce Megan and Morag, the world's first cloned sheep and, until now, the most famous sheep in history.

*'''2000''' - ''Tokyo University'': Scientists at Tokyo University have grown artificial eyeballs. Scientists formed them in tadpoles by using frog embryo cells.

*'''2001''' - ''Advanced Cell Technology'': Scientists from Advanced Cell Technology announced production of a human embryo clone. This is significant as its parthenogenesis has been artificially induced in frogs.

[[Image:John Gurdon .jpg|thumb|right|John Gurdon [http://images.google.com.au/imgres?imgurl=http://www.pnas.org/site/misc/images/gurdon.jpg&imgrefurl=http://www.pnas.org/site/misc/classics4.shtml&usg=__1p-GA1PdOYsxKL-cznMb3RHCm98=&h=526&w=400&sz=223&hl=en&start=1&um=1&tbnid=9k4lhuLssiWCAM:&tbnh=132&tbnw=100&prev=/images%3Fq%3DJohn%2BGurdon%26gbv%3D2%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

*'''2002''' - ''John Gurdon'': John Gurdon from Wellcome Cancer Research Institute in Cambridge experimented on cloned frog embryo.

== Gametogenesis ==

* The sexual reproduction occurs through the fusion of either mature reproductive cells or germ cells known as gametes, which include the sperm from the male frog and ova from female frog species so as to form a single cell, the fertilized zygote. The gametes are typically developed in parents of different sexes . [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

* Males gametes is a spermatozoon , the female frog gamete is an ovum. Each gamete is formed by a process, recognised as maturation or gametogenesis in gonads. The typical male frog gonads are testies in male, while the female gonads are ovaries. The synthesis of both gonads is associated with the process of fertilization. [http://en.wikipedia.org/wiki/Microhylidae]

* The zygote changes into a mature frog through the process of embryology and metamorphosis. Gametogenesis is a in progression which frog gametes are established from germ cells. Initial germ cells are called primordial germ cells, which can be recognised extremely early in the life of frog species.

----

== The Egg & Fertilization ==

[[Image:Fertilized and Unfertilised Eggs.jpg|thumb|left|Fertilized and Unfertilized Eggs:J,Nassif 2009.jpg]]

[[Image:Egg Development.jpg|thumb|left|Figure 7 Image details:J,Nassif 2009.jpg]]

- This occurs once the sperm cell has inserted, following the insertion of the sperm cells meiosis II is completed, there is a 30 degree position change of the cytoplasm, gray crescent allows this change to be visible in some amphibians, the gray crescent is able what determines the expect ted outline of how the frog will form. The sperm cell joins with the nuclei of the egg which forms the diploid zygote nucleus. --Sando Rashed 10:09, 24 September 2009 (EST)

- The early phases in the development of the egg is visible, but must be studied in tadpoles throughout maturation. In embryonic tadpoles of about 10 millimetres in length, soon after the opening of the oral cavity, a pair of longitudinal ridge-like thickenings of peritoneum becomes apparent along the posterior surface of the body cavity situated near to the mesentery and along the inner boundaries of the kidneys. Genital ridges are established in all tadpoles of this age, sex is not distinct until a later period. The development of the egg is illustrated in the figure on the left revealing the structure of a developed egg and a mature of egg.

[[Image:Fertilisation life cyle.jpg|thumb|Fertilization of Life cycle:Derived from primary source:[http://en.wikipedia.org/wiki/Frog]]]

== Maturation of the Egg ==

- The eggs have currently accomplished their full size, and develop from the exterior of the ovaries like a small shot, but they still have to pass through the course of maturation before they are prepared to be fertilised. This progression of maturation relates to the nucleus almost completely.

- The nucleus component, containing the nuclear fluid that excludes through the nuclear membrane into the substance of the egg, a great segment of the nuclear reticulum vanishes and becomes degraded into separate globules known as nucleoli, but a extremely small division remains in the midpoint as a slender intricately thread recognised as the nuclear skets.
Relative to the egg getting discharged from the ovary, the follicles shatter allowing the eggs to fall into the abdominal cavity of the frog species, the egg then passes forwards, directly by the contraction of the muscular wall, somewhat by the movement of the cilia of the peritoneum, to the apex of the oviduct, which positioned at the anterior compartment of the body cavity opposite to the roots of the respiratory organs.

- The terminal part of the oviduct establishes a thin-walled pouch capable of great swelling, inside which the eggs gathers in large numbers. In conclusion, the eggs are migrated out through the cloaca into water which the albuminous investments of the eggs rapidly augment to form the gelatinous mass of the frogs spawn.

== Maturation phases ==

'''1. Nuclear skein''', moves from the midpoint of the egg to its outer surface, which it reaches opposite the midpoint of the black pole. The skein, subsequently an unevenly twisted thread, now presumes the specific arrangement of a nuclear spindle, for instance may be visible in the nucleus of an epithelial or additional cell instantly prior to division of the cell occurs.[http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

'''2. The first Polar Body,''' regarding the instance the egg is laid, but prior to its fertilistion, the egg develops a considerably flattened appearance at its upper or black pole, a definite sum of fluid being exuded among the egg and the vitelline membrane. The nuclear spindle currently separate into two identical segments, one of which remains with the egg, and the supplementary is extruded as the first polar body, a small ovoidal white globule, which is situated on the surface of the egg surrounding the exuded peri-vitellline fluid.

'''3. The Second Polar Body''', half of the nuclear spindle that stay behind then splits into two equivalent divisions, one of which remains inside the egg as the female pronucleus, whereas the other segment is extruded as the second polar body, a small white globule extremely related to the first polar body, and like this positioned in the perivitelline fluid on the superior portion of the egg.

'''4. Fertilisation of the egg''', includes the synthesis of the spermatozoon with to egg, specifically, synthesis of the nuclei of these two bodies. The spermatozoa, subsequent to being shed over the seed by the male, distribute vigorously by means of their extended tails, break through the gelatinous investment of the female eggs, bore their way through the vitelline membrane and so go through into the eggs themselves, which they penetrate relative to the superior or black hemispheres.
* Subsequently, an hour following the spermatozoon has entered; a progression may be visible projecting within from the exterior segement of the egg, with a liquid spot in the mid point. This liquid centre is the nucleus of the spermatozoon, and is said to be the male pronucleus, it break through beyond into the female egg, transporting the specialised pigment into it, so that it appears bounded by a pigmented capsule linked with the exterior of the egg by a pigmented stalk.

* By this instance, the second polar body has been established and extruded, and the female pronucleus is merely the only component of the primary egg nucleus still present. Both the male and female pronuceli, which are at initially distance separate to each other, merge and after having enlarged significantly in size then fuse mutually about two and half hours after fertilisation has originated to produce the segmentation nucleus.
* The segmentation nucleus is a huge sphere-shaped vesicle embedded in delicately granular protoplasm, and bounded by a distinct capsule of pigment, its arrangement by the synthesis of the male and female pronuclei completes the action of fertilisation. Specifically female pronucleus may be observe as an imperfect nucleus, and consequently result in the course of fertilisation. The nucleus of the spermatozoon or male pronucleus, replaces the component of the egg- nucleus which has been misplaced as the polar bodies.

'''5. Segmentation of the Egg''', the initial phase of growth consist in constant separation of the egg, whereby it becomes transformed from the unicellular state, which is everlasting only in the lowest species, to muliticelluar state charactertics of all higher species. To these early processes of growth the names segmentation is specified. Shorty subsequent to the competition of fertilisation and arrangement of the segmentation nucleus this later misplaces its sphere-shaped appearance and develops to be spindle-shaped, the yolk granules at the equivalent instance showing a tendency to develop into lines distributing outwards from the distal segment of the spindle.
* The nucleus now split into two halves, which shift away from one another, the yolk granules are likely to combined themselves around the two nuclei, and a slender vertical plate of delicately granular substance is left, dividing the egg.[http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

* Superiorly the eggs depression now becomes visible, initially as a small cavity and then develops as a groove, which almost immediately extends all round, and speedily deepening, splits the egg into two entirely separate halves along a plane equivalent with the vertical plane.

* Shorty after, the two nuclei soon separate again into two, and therefore a second cleft is created in the same state as before, its additionally in the vertical plane, however in a plane at 90 degrees to the initial one, and on its finishing point the egg comprises of four accurately similar segments, each containing a nucleus. The third cleft is horizontal in shape, but not equal, lying closer to the superior than the lower pole, it segregates each of the four cells into, an superior smaller and a inferior larger pole

----

== Cleavage ==

[[Image: Frog Cleavage development.jpg|thumb|left|Figure 8.1 Image details:[http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/F/FrogEmbryology.html].jpg]]

* The egg of the frog is scientifically identified as’ telolecithal’ meaning there is a outsized amount of yolk concentrated at a single pole, in contrast to the concentration of cytoplasm and the site of the nucleus. The cleavage phases are holoblastic, therefore the total and after the second cleavage they are asymmetrical .The initial cleavage stage appears about two and half to three hours after fertilization. It commences as a minor depression in close proximity to the centre of the animal hemisphere. It appears as if some interior force is pushing the surface the egg towards the centre. This small upturned fold steadily continues in the form of a channel until it surrounds the egg. This groove is shallow in the commencement, but develop into deeper eventually separating the fertilized egg into two halves recognised as the blastomeres. [The figure on the left symbolise the development and growth of the frog embryo during cleavage].

* Internally the separation is mitotic, consequently each daughter cell contains a nucleus resulting from the copulation nucleus of the fertilised egg. This cleavage is vertical, the two cells are indistinguishable in respect of cytoplasm, pigment and yolk. The subsequent cleavage appears about an hour after the first. The channel of this cleavage begins at the centre of the animal hemisphere, is at right angles to the first and is vertical. This divides the egg into four blastomeres. The fourth blastomere so produced are not qualitatively equal, since of these only two contain the material from the gray crescent. The cleavage begins about thirty minutes after the second is completed or four hours after fertilisation. the cleavage plane of the third furrow is horizontal and slightly above the equator. Thus the four upper cells are a little smaller than the four lower cells. The smaller blastomeres are called micromeres and the larger blastomeres are called macromeres. The fourth cleavages follow 20 minutes after the third and tend to be vertical. This is usually a double furrow.

* The cleavage rate is accelerated with each of the early divisions and since the blastomeres are of unequal size and have varying amounts of cytoplasm and yolk, synchronous cleavage is lost and there is an obvious overlapping of the division. The upper most cells divide more rapidly than the lowermost cells. From this point onwards perfect symmetry in cleavage and in blastomere is very rare, although the embryo developed perfectly. The fifth cleavage is also doubled, appearing first in the upper hemisphere and then in the lower.

* The cleavage thus far follows the rule that each cleavage plane comes in at right angles to the previous one. The subsequent divisions become so irregular that it is previous one. The subsequent division become so irregular that it is impossible to trace out any plan or procedure. The segmentation continues more rapidly in the pigmented regions, since at that place the protoplasm is most dense, whereas, yolk which is very abundant in the vegetal side delays cell division. The multicelluar embryo at this stage is called morula by some biologists.

----

== Gastrulation ==

[[Image:FROG GASTRULATION .jpg|thumb|left|Figure Image details:[http://www.google.com.au/imgres?imgurl=http://bio1903.nicerweb.com/Locked/media/ch47/47_12FrogGastrulation.jpg&imgrefurl=http://bio1903.nicerweb.com/Locked/media/ch47/gastrulation-frog.html&h=540&w=480&sz=46&tbnid=N78sHjELreGGSM:&tbnh=132&tbnw=117&prev=/images%3Fq%3Dfrog%2B-%2Bgastrulation&hl=en&usg=__4VK9FYLft0W-4lBe6p5EtQAMiaI=&ei=qPy5SurtMJvE6wON8JmdAg&sa=X&oi=image_result&resnum=4&ct=image].jpg]]

''The phase of Blastulation is followed by the unique developmental progression of gastrulation. The process of frog gastrulation involves the following processes.''

'''1. Epiboly Phase'''

The pigmented cellular materials of blastula have the propensity to overgrow the yolk cells within the developing content. This course which is known as epiboly commences gradually in the final blastula and rapidly accelerates with advancing gastrulation development. The cellular matter within the animal pole reproduces and matures on all sides except in area surrounding the dorsal lip of the blastopore has been established.

'''2. Convergence'''

Scientists suggested that the unfolding was thought to result in spreading of the superficial cells over a substrate with suitable absorption properties. Consequently epiboly and convergence are an outcome to this spreading tendency, which is actually increased by a reduction in surface tension of the distributing cells.

'''3. Rotation'''

The epiboly phase is maintained until the region of the dorsal lip has migrated and is a to some extent greater than 90 degrees and the region of the white blastopore is reduced to small circular rings. This section will be positioned away from the developing vegetal pole. Laterally the complete developing gastrula has been rotated to a horizontal axis, allowing it to lie at right angles to the original median plane of the egg. Therefore, the course of rotation is such that the dorsal lip is practically pushed backwards in one direction as rapid or quicker than epiboly moves it forward in the other. The outcome will be that the blastopore produced at roughly the vegetal pole is posterior, and the dorsal and ventral lips are essentially dorsal and ventral. This in addition allows the eggs to form the antero-ventral side of the potential embryo whilst the area marked by the grey crescent is to develop the dorsal segment.

'''4. Invagination'''

Visible is a small fissure- like invagination which is apparent in the middle between the equator and the vegetal segment. The most superior or dorsal border of the cleft produce the dorsal lip of the blastopore. This imput move back and forth on the dorsal plane near the dorsal lip and migrates around the boundaries of the blastocoel in company with the extension of the lateral lips. This adapted invagination is maintained until the blastocoel cavity has been almost abolished; excluding the slender opening separating epiblasts from the hypoblast, the new segment formed is known as the archenteron cavity.

'''5. Involution'''

- Additional to previous course of action a distinct involution also occurs at the blastoporal borders. This is mainly dynamic at the median dorsal lip and gradually more less as it shifts across either side until it reaches the ventral lip where it constant.Throughout this progression, cells positioned beside the superior boundaries of the blastoporal lip migrate over the lip to the interior portion of the lip. These cells are remained within the embryo along the internal edge of the blastopore. This indicates the root of archenteron is composed of involuted cells and beyond this the external layer known as the ectoderm. The base and lateral sides are enclosed mainly of endodermal cellular material, which have been established from larger yolk cells, situated in the vegetal pole of the blastula.

- In the final phases of the gastrula development, the cells contributing to the floor of the archenteron, thin out significantly where they surround the blastocoel.
The hemispherical shaped dorsal lip of blastopore which become visible at the commencement of the gastruation stage carry on to augment, initially becoming semicircular, then transform into a horse shoe shaped and then finally forming into circular band. The band is the accomplished by the blastopore. Various yolk cells of vegetal pole present in the section are crowed into the blastoporal cavity where they form a gathering identified as a yolk plug. Blastopore rapidly reduces in size while the archenteron is still developing and becomes completely formed in the final stage; the yolk plug appears as only a small oval on the gastrula.

==Growth and Modification of Frog Species==

'''1. Changes in habits and habitats:'''

'''a)''' In frogs, metamorphosis is related with to the modifications and adaptations as a frog changes environmental habitats from an aquatic to a terrestrial mode. Metamorphosis has modified the adaption of frogs as this alteration it began during the aquatic adaptations in the surface of water to breathe air. Subsequently, it continues the terrestrial surroundings, therefore the frog species become abundant in vegetation area allowing the frog to transform in to amphibious species.

'''b)''' The transition during metamorphosis is linked with a change in food chain. The tadpoles being the embryonic origin of frogs are herbivorous, feeding on algae and green matter, which they collect by the adapted feature such as their teeth surrounding their mouths. Adult frogs, alternatively, are classified as carnivorous feeding on insects and worms. Occasionally, they also consume larger prey, for instance smaller frogs species and even little birds and rodents which they dominant and ingest.

[[Image:Development of frog from sperm to mature structure.jpg|thumb|left|Figure 9 Image details:J,Nassif 2009.jpg]]

'''2. Changes in Morphology'''

These include the decrease or complete absence of specific organs or structures which are essential during development of early frog embryology, but not critical in the mature frog species. The significant alterations of this nature include the following developmental structures.

'''a)''' The long tail of the tadpole alongside the fin folds is absorbed again during metamorphosis and becomes absent at the final stage of the metamorphosis.

'''b) '''The developing gills are resorted, the gill clefts are congested and the branchial cavities start to become absent. The reabsorbtion of gills also takes place by autolysis.

'''c)''' The teeth of the perioral disc additionally the homey lining of the jaws are shed.

'''d)''' The lateral line sense organs within the skin of tadpoles vanish throughout metamorphosis.

'''e)''' The cloacal tube begins to condensed and reduced.

'''f)''' Various blood vessels, together with parts of the aortic arches, are reduced during mature development.

(The figure on the left represents the transformation from a tadpole to a developing structure.)[http://science.jrank.org/pages/2862/Frogs-Adult-morphology.html]

'''3. Progressive or constructive changes'''

This process comprises of the development of specific organs which mature into functional systems only during metamorphosis.

'''a)''' During development the limbs continue to augment in size and differentiation. The forelimbs, which in the tadpole mature under the opercular membrane, which then break through to the exterior. Simultaneously there is a increase in the length and strength of the hind limbs, joints develop in them and the toes become visible.

'''b)''' The middle ear becomes apparent in relation with the first pharyngeal pouch. The tympanic membrane matures. It is bounded by circular tympanic cartilage which allows the frog to retain air.

'''c)''' The visual organs bulge up on the dorsal surface of the head developing the nictitating membrane.

'''d)''' There is augmentation of the tongue and the formation of thevomerina teeth.

[[Image: Growth model.jpg|thumb|Figure 10 Image details:J,Nassif2009:]]

'''4. Remodelling of some structures'''

Systematic organs which operate both in the early embryonic larva and the mature adult change their differentiation during metamorphosis so as to meet the requirements of the adult mode of life and due to the habitat adaptations. The figure on the right illustrates structures developing from specic germ cell layers.

'''a)''' The skin of the embryonic tadpole is lined with a double-layered epidermis. The number of layers of cells in the epidermis augments throughout metamorphosis. Superficial surface layers become cornified. Multicellular mucous and serous glands originate in the skin. The pigmentation of the skin continuously changes, new patterns and colour start to form.

'''b)''' There is a lengthening of the mouth gap as a result of rotation of the quadrate cartilage and the true jaws become functional.

'''c)''' The tongue rapidly progresses and becomes larger and more muscular.

'''d)''' The eyes become more specialised.

'''e)''' In early tadpoles, the GIT is extremely long and wound up into a spiral folds. The intestine become greatly lengthened in herbivorous species due to the vegetables food chain.[http://en.wikipedia.org/wiki/Frog]

'''5. Development of the reproductive system'''

(The figure below represents the reproductive and development cycle of a frog as it transform from egg to frog specie.)

In tadpoles, right after the mouth is being formed, two indentation like thickenings of peritoneum begin to appear near the body cavity (dorsal surface), which is nearest to the mesentery which is near the developing kidneys. These appear in all tadpoles.

These indentations appear here because of a change in the endothelial cells, everywhere else they are usually flat looking cells but they undergo a change and in this particular area become somewhat cuboidal/columnar.

Later on the indentations become more obvious due to the epithelial cells replicating numerously to form a thick layer. The posterior two thirds of the indentation for the female is the ovary and for the male it is the testis. The third that is left differentiates and becomes fat for the body.

[[Image: Mature frog life cyle.jpg|thumb|200px|left|Figure 11 Image details:Derived from primary source:http://www.scienceclarified.com/images/uesc_01_img0038.jpg]]

[[Image: Developing frog.jpg|thumb|Figure 12 Image details:
[[Image: Mature develop frog.jpg|thumb|Image details: Wikipedia (2009) TYPICAL FROG Primary source:[http://en.wikipedia.org/wiki/File:Red-eyed_Tree_Frog_-_Litoria_chloris_edit1.jpg]].jpg]]

===Delamination===

Delamination indicates a mass separating a group of cellular matter from other cellular groups. It has been illustrated that the division of notochord, mesoderm and endoderm tissues from each other to form distinct cellular masses is completed by the progression of delamination, subsequent to these materials moving to the inside throughout gastrulation. During the developing gastrula, the germ layers are all recognized. These distinct segments of the embryo develop from these germ tissue layers.

===Polarity and Rotation===

Throughout fertilisation to the beginning of gastrulation, the frog’s egg continues in the original location in relation to its polarity. Subsequent to gastrulation its polarity begins to differentiate. This progression is linked with migration of materials within the gastrula and can be responsible for the alterations of the centre of gravity.

===Closing of Blastopore===

Subsequent to the formation of the gastrula, the blastopore is visible as a tiny round circular filled cavity containing the yolk plug. As it continues to reduce in dimension, it represented as a pear-shaped outline through the mutual approach of its lateral lips. Through it final progression these fuse entirely to produce a longitudinal groove, the streak which continue dorsally and ventrally in a small aperture. The inferior aperture closes, resulting in a depression called the anal pit. The superior region remains open for some period and begins to as the neural groove is laid down.

===Post Gastrulation or Organogenesis===

Throughout the duration of pre-gastrulation, all tissues for different organs vanish from the surface of blastula and migrate inside to take their final arrangement in the embryo structure where organs are developed from their potential regions. Consequently organogenesis transfers an embryo into free larva structure.

----

==Germ-layer origin of various body tissues==
[[Image: Development Models of Frog.jpg|thumb|right|Figure 13 Image details:Vertebrate Structure and Development.jpg]]

Ectoderm will give raise to structures such as skin, brain, spinal cord, neurons and sense receptors.
Mesoderm will give raise to structrues such as notochord, muscles, blood, bone and sex organs.
Endoderm will give raise to sturctures such as inner lining of gut, liver, pancreas, lungs and bladder, thyroid and parathyroid glands and thymus.

== Structures derived from Germ-layers of frog species ==

[[Image:Development of Frog Layers.jpg|thumb|left|Figure 14 Primary source[http://www.bio.miami.edu/~cmallery/150/physiol/sf19x11b.jpg]Image details:J,Nassif 2009.jpg]]

[[Image:Development of frog layers.jpg|thumb|left|Figure 15 Primary source [http://www.bio.miami.edu/~cmallery/150/physiol/sf19x11b.jpg]Image details:J,Nassif 2009.jpg]]

'''Ectoderm '''

''Establishes the epidermal segments and its derivatives, to the frog’s nervous system. The ectoderm also contributes to :''

1. The olfactory and auditory epithelium.

2. The retina and lens of the eye.

3. Sensory organs.

4. The epithelial lining of the oral cavity and the anus.

5. The pineal and pituitary body.

'''Mesoderm'''

''Mesoderm originates:''

1. Connective tissue.

2. Muscles, except the notochord.

3. Blood vessels.

4. Lymphatics.

5. The peritoneum and the urinary and reproductive system.

6. The dermis, parts of the eye excluding lens, cornea, and conjunctiva.

'''Endoderm'''

''From the endoderm arises:''

1. The epithelial lining to the gut and oesophagus, stomach, intestine, bile duct.

2. The hepatic cells of the liver, respiratory tract, larynx, trachea and lungs.

3. The lining of the urinary bladder, pancreas thyroid and thymus.

[The two figures reveal the development of structures deriving from the celluar components of the embryology of the frog].[Structures derived from Germ-layers of frog species ]

==Life cycle of a frog==

'''Fertilization-egg''':

The female lays eggs in the spring. A group of fertilized eggs is called spawn;

'''7-10 days''':

Fertilized egg feed on remaining yolk which is in its gut. Their gills, mouth and tail have poorly developed. Begin to swim and feed on algae;

'''10-30 days(4 weeks):'''

A layer of skin grows over gills. Teeth begin to appear. A coiled gut start to develop. This is aid in digestion;

'''30-60 days(6-9 weeks):'''

Legs being to grow and head is more distinct. Start to eat insects. Arms begin to grow;

'''60-80 days(12 weeks):'''

Resemble a frog. Still have remaining tail;

'''80-140 days(20 weeks):'''

Fully developed, spend most of time out of water. Majority of frog live between 4-15 years.

==Timeline of frog development==

Development of egg and embryo at temperature 18 degree celsius.

'''0 hours''' - fertilization of the egg

'''1 hours''' - formation of the gray crescent due to pigment migration

'''3.5 hours''' - early cleavage

'''4.5 hours''' - blastula stage(coeloblastula with eccentric blastocoel

'''26 hours''' - gastrulation

'''26 hours''' -'' early'' - crescent shaped dorsal lip

'''34 hours''' - ''middle''- semicircular blastoporal lip

'''42 hours''' - ''late'' - circular blastoporal lip

'''50 hours''' - neurulation

'''50 hours''' - ''early'' - medullary plate

'''62 hours''' -'' middle''- neural folds converging

'''67 hours''' - ''late'' - neural tube formed and ciliation of embryo

'''84 hours''' - tail bud stage(early organogeny)

'''96 hours''' - muscular response to tactile stimulation

'''118 hours''' - early heart beat, development of gill buds

'''140 hours''' - hatching and gill circulation

'''162 hours''' - mouth opens and cornea becomes transparent

'''192 hours''' - tail fin circulation established

'''216 hours''' - degeneration of external gills, formation of operculum, development of embryonic teeth

'''240 hours''' - opercular fold over brachial chamber except for spiracle and internal gills

'''255 hours''' - prolonged larval stage with refinement of organs

'''270 hours''' - development of hindlimbs, internal development of forelimbs in opercular cavity

'''275 hours''' - projection of forelimbs through operculum, left side first

'''280 hours''' - absorption of the tail and reduction in size of the gut

'''284 hours''' - metamorphosis complete, emergence from water as miniature, air breathing frog

==Stages of frog embryology==
--[[User:S8600021|Mark Hill]] 08:40, 9 October 2009 (EST) [[Talk:2009_Group_Project_5#Constructive_Criticism_of_Coordinator|see my comment on images]]

The rate of development of the egg and embryo will depend upon the temperature at which they are kept. The approximate schedule of development at 23 degree celsius is provided below.

{| border='1px'
|+ Table 1: Stages of frog development
!Stage !!Time since fertilisation (hours)!!Stage Characteristic !!Embryo characteristic !!Image of frog stage
|-
|1
|0.00-1.30
|fertilization of the egg, post fertilization
|animal hemisphere, gray crescent and vegetal hemisphere are present
|[[File:Stage01ventral.jpg|100px]]
|-
|2
|1.30-2.00
|splits into two cells
|appearance of first cleavage furrow
|[[File:Stage02ventral.jpg|100px]]
|-
|3
|2.00-2.15
|becomes four cells
|appearance of second cleavage furrow
|[[File:Stage03dorsolat.jpg|100px]]
|-
|4
|2.15-2.45
|becomes eight cells
|appearance of third cleavage furrow
|[[File:Stage04dorsolat.jpg|100px]]
|-
|5
|2.45-3.00
|becomes sixteen cells
|appearance of fourth cleavage furrow
|[[File:Stage05dorsal.jpg|100px]]
|-
|6
|3.00-3.30
|becomes thirty-two cells
|appearance of fifth cleavage furrow
|[[File:Stage06animal.jpg|100px]]
|-
|6.5
|3.30-4.00
|blastula stage
|Three dorsal folds become visible as a result of endoderm invagination. Pole cells no longer visible on surface
|[[File:Stage065dorsal.jpg|100px]]
|-
|7
|4.00-5.00
|Gastrulation stage
|two primary germ layers. epiblast and endoderm
|[[File:Stage07ventral.jpg|100px]]
|-
|8
|5.00-7.00
|neurulation
|medullary plate, neural folds and neural tube
|[[File:Stage08animal.jpg|100px]]
|-
|9
|7.00-9.00
|germ layer
|complete lip involution encircling yolk
|[[File:Stage09veg.jpg|100px]]
|-
|10
|9.00-11.00
|early gastrula
|two primary germ layers
|[[File:Stage10veg.jpg|100px]]
|-
|10.5
|11.00-11.45
|gastrula
|two germ layers
|[[File:Stage105vegb.jpg|100px]]
|-
|11
|11.45-12.30
|medulla plate
|Yolk sac protrudes dorsally, labium moves to midline on ventral side
|[[File:Stage11veg.jpg|100px]]
|-
|11.5
|12.30-13.15
|continuation of medulla plate
|start closing the plate
|[[File:Stage115veg.jpg|100px]]
|-
|12
|13.15-14.15
|early neurula
|thickened ectoderm give rise to CNS
|[[File:Stage12veg.jpg|100px]]
|-
|12.5
|14.15-14.45
|neural folds
|expansion of cavity
|[[File:Stage125postdors.jpg|100px]]
|-
|13
|14.45-16.15
|neural folds
|continue expanding cavity
|[[File:Stage13postdors.jpg|100px]]
|-
|14
|16.15-17.30
|neural folds
|continuation of cavity
|[[File:Stage14postdors.jpg|100px]]
|-
|15
|17.30-18.15
|tail bud stage
|early organogeny
|[[File:Stage15postdors.jpg|100px]]
|-
|16
|18.15-18.45
|tail bud stage
|posterior ventral view
|[[File:Stage16ant.jpg|100px]]
|-
|17
|18.45-19.45
|tail bud stage
|anterior view
|[[File:Stage17ant.jpg|100px]]
|-
|19
|20.45-21.45
|neural fold close complete
|dorsal view
|[[File:Stage19dorsal.jpg|100px]]
|-
|20
|21.45-22.30
|early tail bud
|anterior view
|[[File:Stage20dorsal.jpg|100px]]
|-
|21
|22.30-24.00
|termination of neural crest
|progress to next stage
|[[File:Stage21ant.jpg|100px]]
|-
|22
|24.00-24.45
|prolonged development
|elongation
|[[File:Stage22lat.jpg|100px]]
|-
|23
|24.45-26.15
|elongation of embryo
|later view
|[[File:Stage23lat.jpg|100px]]
|-
|24
|26.15-27.30
|continuation of elongation of embryo
|dorsal view
|[[File:Stage24latsmall.jpg|50px]]
|-
|25
|27.30-29.30
|organs development
|embryo elongates and develops dorsal thickening
|[[File:Stage25dorsal.jpg|50px]]
|-
|26
|29.30-31.15
|elongation
|dorsally forms neural and brain cavity
|[[File:Stage26lat.jpg|50px]]
|-
|27
|31.15-32.30
|elongation of embryo
|dorsal view
|[[File:Stage27lat.jpg|50px]]
|-
|28
|32.30-35.00
|further development
|lateral view
|[[File:Stage28lat.jpg|50px]]
|-
|29-30
|35.00-37.30
|tail bud
|growth
|[[File:Stage29-30lat.jpg|50px]]
|-
|31
|37.30-40.00
|prolonged development
|bud development
|[[File:Stage31lat.jpg|50px]]
|-
|32
|40.00-44.30
|early muscular development
|elongation
|[[File:Stage32lat.jpg|50px]]
|-
|33-34
|44.30-50.00
|muscular movement
|apparatus for locomotion
|[[File:Stage33-34lat.jpg|50px]]
|-
|35-36
|50.00-53.30
|muscular movement
|apparatus for locomotion
|[[File:Stage35-36lat.jpg|50px]]
|-
|37-38
|53.30-56.30
|heart beat
|develops apparatus
|[[File:Stage37-38lat.jpg|50px]]
|-
|39
|56.30-66.00
|mouth opens
|cornea transparent
|[[File:Stage39latsmall.jpg|50px]]
|-
|40
|66.00-76.00
|gill circulation
|hatching
|[[File:Stage40lat.jpg|50px]]
|-
|41
|76.00-80.00
|tail, fin circulation
|circulation
|[[File:Stage41lat.jpg|50px]]
|-
|42
|80.00-86.00
|internal gills, operculum
|opercular fold, teeth
|[[File:Stage42lat.jpg|50px]]
|-
|43
|86.00-98.00
|operculum complete
|operculum closed on right
|[[File:Stage43lat.jpg|50px]]
|-
|46
|98.00-106.00
|metamorphosis
|emergence from water as miniature, operculum complete|
|[[File:Stage46lat.jpg|50px]]
|-
|}

==Abnormalities of frog==

Abnormalities of frog could be caused by multiple factors. These include change in climate, predators, parasites, bacteria, fungi, viruses or pollution and contaminants such as pesticides, metals and fertilizer.[http://www.fws.gov/contaminants/documents/frogsrefup_septoct_2006.pdf]

The Abnormalities are further classified into different categories. These categories are:

===1. Infectious Diseases:===

'''Perkinsus Symptoms-''' caused by perkinsus-like protozoan organism. Symptoms include swollen viscera that leads to a bloated body and and infected swollen heart

'''Ichthyophonus symptoms-''' cause by parasitic genus, where symptoms include a swollen tail resorption site that matches the surrounding skin in color and translucency.

[[Image:Abnormalities of Frog species.jpg|thumb|left|Figure A Image details[waterwatchadelaide.net.au].jpg]]

===2. Surficial Abnormalities:===

Surficial abnormalities as the one that are visible on the surface of the skin. This includes abnormal pigmentation, , subcutaneous hemorrhaging, wounds due to trauma or from a predator
Edema is a fluid-filled swelling under skin whihc is also a surficial abnormality.

===3. Skeletal Abnormalities:===

This is further classified into three more categories:

'''a. Skeletal Malformations-'''

* Microcephaly (small head or blunt snout)
*Scoliosis (Curved spine in lateral direction)
*Shrunken Limb (Micromelia)
*Amelia (Completely missing limb with no stump)

'''b. Skeletal Abnormalities of Unclear Etiology-'''

This condition arises when a frog has ectromelia (missing limb), brachydactyly (missing digits) or other such condition with no visible trauma or external damage, then this will be classified as the Skeletal abnormality of unclear etiology.

'''c. Skeletal Injuries-'''

Any limb missing or broken due to trauma or other related reason which shows clear evidence of it is classified as skeletal injury

===4. Eye Abnormalities:===

Most common includes-

'''i. Anophthalmia:''' Skin covers the eye socket as there is no eye

'''ii. Abnormal Iris Coloration:''' Reduced pigment in either one eye or both resulting in two different colours of the iris at times

'''iii. Abnormal size or shape:''' Both eyes either deviating from each other or size of pupil or iris is different than the other eye

[http://www.fws.gov/contaminants/Amphibian/pdfs/AbnormalitySOP_woutpics_Jan08.pdf ]

==Genetics==

There are a wide variety of species that differ from each other when it comes to genetics and their functioning.

'''TAXONOMY:''' '''Phylum''' ''Chordata'' / '''Sub Phylum''' ''Vertebrata'' / '''Class''' ''Amphibia'' / '''Order''' ''Anura''

Their are more than two dozen different families of frogs, where suborders are:

'''1. ARCHAEBATRACHIA-''' most primitive frogs

'''2. MESOBATRACHIA-''' linked between the Archaebatrachia and Neobatrachia

'''3. NEOBATRACHIA-''' most modern frogs

{| border='4px'
|+ '''General Info:'''
! !!
|-
| '''Number of frogs' species'''
| 5280
|-
| '''Smallest frog genome size:'''
| 0.95pg, Ornate burrowing frog
|-
| '''Largest frog genome size:'''
| 13.40pg, Ornate horned frog
|-
| '''Mean of frogs' genome'''
| 4.68pg ± 0.13
|-
|}

[http://www.genomesize.com]

*Majority of frogs have only 22 to 26 chromosomes and polyploid is very common where they are almost bisexual.

*Polyploid Amphibians reduce their total cell number such that they acheive the same body size as diploids. One of the most unsual forms of polypoidy in amphibians is the water frog ''Rana esculenta'' from Europe and Western Asia.

* The species with larger genomes have more genes for e.g. the frog genus ''Xenopus'' includes 16 species, with genome sizes ranging from 3.5 x 10^9 bp to 1.6 x 10^10 bp. These differences have arisen by numerous events of polyploidization within the past 40 million years or so. The ancestral chromosome number for the genus seems to have been 18, but there are species with 36, 72 and 105 chromosomes [http://www.xenbase.org/common/]

{| border='4px'
|+ '''Difference within two families'''
! '''SPECIES''' !! ''X.LAEVIS'' !! ''X.TROPICALIS''
|-
| '''PLOIDY'''
| Allotetraploid
| Diploid
|-
| '''NO. OF CHROMOSOMES'''
| 36 chromosomes
| 20 chromosomes
|-
| '''GENOME SIZE'''
| 3.1 x 10^9 bp
| 1.7 x 10^9 bp
|-
| '''EGG SIZE'''
| 1-1.3 mm
| 0.7-0.8 mm
|-
| '''GENERATION TIME'''
| 1-2 years
| 4 months
|-
|}
[http://www.xenbase.org/common/]

===Genome Sequencing===

Since Frog has a huge family with many different species, only few main species that are used widely for the purposes of experiments have their genome sequenced.

''Xenopus tropicalis'' has one of the smallest genomes among amphibians and has the shortest generation time- four to six months and the only diploid genome among the 14 Xenopus species. This means it has no more than two copies of most genes, whereas the other species of Xenopus have four copies of most genes (pseudotetraploid). US Department of Energy's Joint Genome Institute (JGI) in Walnut Creek, California, initiated the X. tropicalis Genome Project, finding 1,700 million base pairs.
[http://www.genome.gov/Pages/Research/Sequencing/BACLibrary/xenopusTropicalis.pdf]

===Xenopus oocytes===

* The oocytes provide an important expression system for molecular biology.

* By injecting DNA or mRNA into the oocyte or developing embryo, scientists can study the protein products in a controlled system. This allows rapid functional expression of manipulated DNAs (or mRNA). This is particularly useful in electrophysiology, where the ease of recording from the oocyte makes expression of membrane channels attractive.

* One challenge of oocyte work is eliminating native proteins that might confound results, such as membrane channels native to the oocyte.

* Translation of proteins can be blocked or splicing of pre-mRNA can be modified by injection of Morpholino antisense oligos into the oocyte (for distribution throughout the embryo) or early embryo (for distribution only into daughter cells of the injected cell).
[http://www.staff.unibe.ch/sigel/xenopus.html]

===Xenopus Laevis===

* ''Xenopus Laevis'' is an important model organism in developmental biology. X. laevis is tetraploid and reaches sexual maturity in 1 to 2 years. What makes it important in developmental biology is its large and easily manipulable embryo.

* Extracts from the eggs of X. laevis frogs are also commonly used for biochemical studies of DNA replication and repair, as these extracts fully support DNA replication and other related processes in a cell-free environment which allows easier manipulation.

* The Human chorionic gonadotropin hormone (hCG) is present in the urine of the pregnant women in large quantities only. This hormone in the urine induces X.laevis oocyte production which formed the basis of first well-documented method of pregnancy testing X. laevis is also notable for its use as the first well-documented method of pregnancy testing when it was discovered. Today, commercially available HCG is injected into Xenopus males and females to induce mating behavior and breed these frogs in captivity at any time of the year.

===Gene cluster===

* The alpha and beta globin genes are closely linked in small cluster of frogs compared to human and chicken

* The similarity of architecture of two clusters found in X.laevis supports the tetraploid origin

* The two loci encoding the muscle specific creatine kinase isoenzymes and have large differences in developmental profile, therefore suggesting that duplicate loci that have not undergone silencing are not simply redundant copies but have acquired specialization.

* Contains twice number of genes for proteins i.e. haemoglobin and sarcomeric actin serum albumin compared with other species

----

==Current Embrology Research==

Currently, a number of fields have benefited from the development of frog embrology. These include cloning, verification of messenger RNA, and Cell cycle.

===Cloning===
[[Image:Robert Briggs.jpg|thumb|left|Figure 16 Image details:Robert Briggs.jpg]]

In 1952, Robert Briggs and Thomas J King cloned northern leopard frogs using a method of nuclear transfer. Briggs and King's experiment was similar to that envisioned - and piloted using salamanders - by Hans Spemann in his 1938 proposal for a 'fantastical experiment'. Later, John Gurdon extended this work and showed that nuclei from differentiated cells could support development, although less well than those from early embryos. [http://genome.wellcome.ac.uk/doc_WTD020799.html]

Lemaitre et a. (2005) from MRC Cancer Cell Unit, Cambridge, U.K. worked on experiments that demonstrated that importance of serial nuclear transplantation for the sucessful cloning of frogs. He demonstrated that exposure of somatic-cell nuclei (erythrocyte nuclei) and sperm nuclei to an extract of mitotic cell extract reorganizes the chromatin into shorter loops and allows replication at much shorter intervals along the DNA. This increases the efficiency of DNA replication in mammalian cell-free systems.

===Transgenesis techniques for functional genomics in Xenopus===

Transgenesis in Xenopus is made possible due to large embryos, a reliable fate map, ease of microinjection, ease of dissection/micromanipulation and existence of the neuroendocrine reflex of background adaptation as a model for activation/inact.

Recently, Hajime Ogino and Haruki Ochi from Nura Institute of Science and Technology in Japan focused on the genomic resources and principles of the transgenesis techniques in Xenopus, and discusses their applications to genome wide network analysis, with emphasis on the use of bioinformatics tools. This is will to understand the gene regulatory networks that control vertebrate development. [http://www.ingentaconnect.com/content/bsc/dgd/2009/00000051/00000004/art00001%3Bjsessionid=4ah96rms73gcu.alexandra]

Xenopus used to be a problem in earlier days when it came to transgenesis. Current methods involves isolated sperm nuclei from Xenopus testis that are microinjected into unfertilized eggs. The generated transgenic tadpoles contain 5-35 copies of the integrated plasmid that are expressed in all cells. If desired, expression of the transgene can be directed to the appropriate tissue and at the appropriate time by using specific promoters, mostly the Xenopus POMC gene promoter (isolated from a Xenopus genomic DNA library) to specifically direct expression of green fluorescent protein (GFP) at high levels to the intermediate pituitary cells, which can either be over expressed or inhibited.[http://molanphys.ruhosting.nl/transgenesis.htm]

[[File:Transgenesis.JPG]]

===Verification of messenger RNA===

While the existence and role of messenger RNA (mRNA) was known in bacteria, in the 1960s it was still debated whether it also existed in vertebrates. Taking haemoglobin mRNA from immature red blood cells and injecting it into a Xenopus oocyte, John Gurdon showed that the haemoglobin protein was indeed produced. Producing proteins in Xenopus oocytes has proved to be extremely useful in cell biology, in particular for the study of receptor proteins.[http://genome.wellcome.ac.uk/doc_WTD020799.html]

===Cell Cycle===

As they develop outside the mother, frog eggs are well stocked with the proteins needed to drive the development of the embryo. Studies of these processes has shed considerable light on the processes involved in cell division - termed the cell cycle. [http://genome.wellcome.ac.uk/doc_WTD020799.html]

===Limb development in Xenopus Laevis===

[[Image: Frog Limb development.jpg|thumb|right|Image details:Primary source:[http://images.google.com.au/imgres?imgurl=http://www.sciencedaily.com/images/2006/06/060616130718.jpg&imgrefurl=http://www.sciencedaily.com/releases/2006/06/060616130718.htm&usg=__xliPsPAvheUBME_kjv_q7auiFbo=&h=333&w=300&sz=11&hl=en&start=2&um=1&tbnid=y_ntJtmkRSK7WM:&tbnh=119&tbnw=107&prev=/images%3Fq%3DLimb%2Bdevelopment%2Bin%2BXenopus%2BLaevis%26ndsp%3D18%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

Donald D. Brown (2005),Department of Embryology, Carnegie Institution of Washington demonstrated factors related to limb development of Xenopus Laevis. Thyroid hormone (TH) is found to be required for limb development in this frog. Specific cell types in the growing limb were targeted for expression of a dominant negative form of the TH receptor by sperm-mediated transgenesis. Limb muscle development, the innervation of muscle from the spinal cord, and cartilage growth can be inhibited without affecting patterning of the limb or differentiation of other cell types. Remodeling of the skin occurs late in metamorphosis after the limb has formed. The coordination of these independent programs is affected in part by the control that TH exerts over DNA replication in all cell types of the limb. [http://www.pnas.org/content/102/35/12455.full]

----

== Glossary ==

[[Image: Frog species.jpg|thumb|left|Image details:Primary source:www.olympus.co.jp/.../080925/large/p02L.jpg].jpg]]

*'''Amphibian:'''

''Relating to or characteristic of animals of the class amphibia.Amphibians are found in the taxonomic class of amphibia, amphibians are capable of both occupying and successfully living in both land and aquatic communities.amphibian''

*'''Augmentation:'''

''Enlargement/Increase in cellular size.''

*'''Autolysis:'''

''breakdown of a part or whole cell or tissue by self-produced enzymes''

*'''Blastomeres:'''

''The undifferentiated cells formed by cleavage of the fertilised ovum. This includes cells in the cleavage, morula, and blastula stages of the embryo''

*'''Carnivorous:'''
''
Flesh-eating; subsisting on animals as food.''

*'''Cleavage:'''

''he repeated division of a fertilised ovum ''

* '''Cleft:'''

''an opening, fissure, or V-shaped indentation made by or as if by splitting''

*'''Chordate:'''

''Members of a diverse phylum of animals that, as embryos, possess a (1) notochord; (2) a dorsal, hollow nerve cord, (3) pharyngeal gill slits; and (4) a post-anal tail''

''The act or state of splitting or dividing of a cell, particularly during the telophase of (animal) cell division.''

*'''Cytoplasm:'''

''The cytoplasm (of both eukaryotes and prokaryotes) is where the functions for cell expansion, growth, metabolism, and replication are carried out''

* '''Epiboly:'''
''The expansion of one cell sheet over other cells, as takes place during gastrulation''

*'''Fertilization:'''

''A process in sexual reproduction that involves the union of male (sperm) and female (ovum) gametes (each with a single, haploid set of chromosomes) to produce a diploid zygote.''

*'''Gamete:'''
''A reproductive cell (male (sperm) or female (egg)) that has only half the usual number of chromosomes''

*'''Gametogenesis:'''

''process leading to the production of gametes. The development and maturation of sex cells through meiosis.Another name for meiosis where a diploid cell is divided into two haploid cells with half the chromosome content of the diploid parent cell.''

*'''Herbivorous:'''

''eating plants; of or pertaining to the herbivora.''

*'''Holoblastic:'''

''The complete division of an isolecithal or microlecithal egg into blastomeres''

*'''Invagination:'''

''One of the methods by which the various germinal layers of the ovum are differentiated.''

*'''Isoenzymes:'''

''Isozymes (also known as isoenzymes) are enzymes that differ in amino acid sequence but catalyze the same chemical reaction.''

*'''Mesentery:'''

'' membranous fold attaching various organs to the body wall.''

*'''Metamorphosis:'''

''A change in the form and often habits of an animal after the embryonic stage during normal development.''

*'''Neuroendocrine:'''

''Neuroendocrine [IPA nʊəroʊˈɛndəkrɪn] cells are cells that release a hormone into the circulating blood in response to a neural stimulus.''

*'''Organogenesis:'''

''The part of embryonic development where the body's main organs develop.''

*'''Peritoneum:'''

''The smooth serous membrane which lines the cavity of the abdomen, or the whole body cavity when there is no diaphragm, and, turning back, surrounds the viscera, forming a closed, or nearly closed, sac.''

*'''Perivitelline space:'''

''The perivitelline space is the space between the zona pellucida and the plasma membrane (sometimes called the vitelline membrane) in a fertilized ovum.''

*'''Polyploidy:'''

''Cells with three or more sets of chromosomes.''

*'''Pronucleus:'''

''the nucleus of the ovum or sperm after fertilization but before they fuse to form the nucleus of the zygote ''

*'''Protoplasm:'''

''The fluid living content of the cell that consists of two major divisions, the cytoplasm and the nucleoplasm (cell nucleus). It is composed mainly of nucleic acids, proteins, lipids, carbohydrates, and inorganic salts''

*'''Segmentation:'''

''division of some metazoan bodies (such as annelida and Arthropoda) into repeated parts, segments. Segmentation can be homomeric (more or less the same) or heteromeric(different from each other).''

*'''Terrestrial:'''

''Of or on the ground, of the habitat of a plant, on land as opposed to in water, or on the ground as opposed to on another plant.''

*'''Transgenesis:'''

''Transgenesis is the process of introducing an exogenous gene - called a transgene - into a living organism so that the organism will exhibit a new property and transmit that property to its offspring.''

*'''Yolk:'''

''nutritive material of an ovum stored for the nutrition of an embryo''

*'''Zygote:'''

''The cell from which an organism develops, that results from the fertilization of the egg by the sperm.''

''Primary Resource "Biology- Online Dictionary''[http://www.biology-online.org/dictionary/Main_Page]

== References - Frog Embryology: ==

[[Image:Frog Research.jpg|thumb|left|Image details:[http://images.google.com.au/imgres?imgurl=http://www.odt.co.nz/files/story/2008/09/university_of_otago_zoology_senior_lecturer_phil_b_3343259744.jpg&imgrefurl=http://www.odt.co.nz/on-campus/university-otago/21670/dunedin-frog-man-wins-zoo-award&usg=__JvJJU5QfOnIwY2bk4xo64UXuJRs=&h=600&w=404&sz=22&hl=en&start=14&um=1&tbnid=AbsP89yWcUiilM:&tbnh=135&tbnw=91&prev=/images%3Fq%3Dfrog%2Bresearch%26hl%3Den%26um%3D1].jpg]]

1. Savage, J. M. (2002). The Amphibians and Reptiles of Costa Rica. University of Chicago Press, Chicago [http://www.springerlink.com/content/vv015277w1746llw/]

2. Ford, L.S.; D.C. Cannatella (1993). "The major clades of frogs". Herpetological Monographs 7: 94–117 [http://digimorph.org/specimens/Xenopus_laevis/]

3. Tyler, M. J. (1994). Australian Frogs A Natural History. Reed Books [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.gracilenta.html]

4. Cogger, H.G.; R.G. Zweifel, and D. Kirschner (2004). Encyclopedia of Reptiles & Amphibians Second Edition. Fog City Press [http://en.wikipedia.org/wiki/Microhylidae]

5. Beltz, Ellin (2005). Frogs: Inside their Remarkable World. Firefly Books [http://unjobs.org/authors/ellin-beltz]

6. Tyler, M. J. (1994). Australian Frogs A Natural History. Reed Books [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

7. Moury JD, Hanken J (1995) Early cranial neural crest migration in the direct-developing frog, Eleutherodactylus coqui. Acta
Anatomica (Basel) 153, 243-253.

8.Raynaud A (1985) Development of limbs and embryonic limb reduction. In Biology of the Reptilia (ed. Gans C, Billett F), pp.
59-148. New York: John Wiley.[http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=9309]

9. Hanken J (1986) Developmental evidence for amphibian origins. In Evolutionary Biology (ed. Hecht MK, Wallace B, Prance GT), 20, pp. 389-417. New York: Plenum Press. [Hanken J (1986) Developmental evidence for amphibian origins. In Evolutionary Biology (ed. Hecht MK, Wallace B, Prance GT), 20, pp. 389-417. New York: Plenum Press.]

10. Elinson RP (1990) Direct development in frogs : wiping the recapitulationist slate clean. Seminars in Developmental Biology
1, 263-270.

11. Beebee, T. J. C. 1996. Ecology and Conservation of Amphibians. Chapman and Hall. London. [http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V5X-3SVHMKH-1X&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=1021245355&_rerunOrigin=google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=825868e10cd178d16a8a0e5ad14dc5ef]

12. Lehtinen, R. M. 2002. The use of screw pines (Pandanus spp.) by amphibians and reptiles in Madagascar. Herpetological Bulletin 2002:20–25.

13. Parris, K. M. and M. A. McCarthy. 1999. What influences the structure of frog assemblages at forest streams. Australian Journal of Ecology 24:495–502. CrossRef

14. Zug, G. R. 1993. Herpetology: An Introductory Biology of Amphibians and Reptiles. Academic Press. San Diego, CA.

15. Slack,J.M.W., Darlington,B.G., Heath,J.K. and Godsave,S.F. (1987)Mesoderm induction in early Xenopus embryos by heparin-binding growth factors. Nature, 326, 197-200.

16. Melton,D.A. (1990) Activins are expressed early in Xenopus embryogenesis and can induce axial mesoderm and anterior structures. Cell, 63, 485-493.

17. Harland,R.M. and Misher,L. (1988) Stability of RNA in developing Xenopus embryos and identification of a destabilizing sequence in TFIIIA RNA. Development, 102, 837-852.

18. Cunliffe,V. and Smith,J.C. (1992) Ectopic mesoderm formation in Xenopus embryos caused by widespread expression of a Brachyury homologue. Nature, 358, 427-430.

19. Kinoshita,K., Bessho,T. and Asashima,M. (1993) Competence prepattern in the animal hemisphere of the 8-cell-stage Xenopus embryo. Devel. Biol., 160, 276-284.

20. LaBonne,C., Burke,B. and Whitman,M. (1995) Role of MAP kinase in mesoderm induction and axial patterning in Xenopus development. Development, 121, 1475-1486.

21. Green,J.B.A., New,H.V. and Smith,J.C. (1992) Responses of embryonic Xenopus cells to activin and FGF are separated by multiple dose thresholds and correspond to distinct axes of the mesoderm. Cell, 71, 731-739.

22. Grainger R., Blumberg B., Harland R., Amemiya C., Importance of Xenopus Tropicalis to biomedical and biological research, Benaroya Research Institute, Virginia Mason Research Center [http://www.genome.gov/Pages/Research/Sequencing/BACLibrary/xenopusTropicalis.pdf ]

23. Gregory, T.R. (2005). Animal Genome Size Database. [http://www.genomesize.com]

24. U.S Fish and Wildlife Services, ABNORMALITY CLASSIFICATION SOP, [http://www.fws.gov/contaminants/Amphibian/pdfs/AbnormalitySOP_woutpics_Jan08.pdf ]

25. Donald D. Brown*, Liquan Cai*, Biswajit Das*, Nicholas Marsh-Armstrong‡, Alexander M. Schreiber*, and Rejeanne Juste*(2005), Thyroid hormone controls multiple independent programs required for limb development in Xenopus laevis metamorphosis [http://www.pnas.org/content/102/35/12455.full]

26. Ogino, Hajime; Ochi, Haruki, Resources and transgenesis techniques for functional genomics in Xenopus, Development Growth & Differentiation, Volume 51, Number 4, May 2009 , pp. 387-401(15) [http://www.ingentaconnect.com/content/bsc/dgd/2009/00000051/00000004/art00001%3Bjsessionid=4ah96rms73gcu.alexandra]

27. Giles Newton (2004) Why the frog? The Human Genome, [http://genome.wellcome.ac.uk/doc_WTD020799.html]

28. Xenbase, [http://www.xenbase.org/common/]

29. Donders Center for Neuroscience & Nijmegen Center for Molecular Life Sciences (NCMLS), Beyond the genome (Xenopus transgenesis for functional genomics),Faculty of Science, Radboud University [http://molanphys.ruhosting.nl/transgenesis.htm]

== External Links ==
[[Image:Frog links.jpg|thumb|left|Image details:[http://images.google.com.au/imgres?imgurl=http://2.bp.blogspot.com/_o93AaY0GzH4/SjY_ZYv0PII/AAAAAAAAAgk/skruNc2yN78/s400/computer%2Bfrog.jpg&imgrefurl=http://hellaheaven-ana.blogspot.com/2009/06/talking-frog-contemporary-fairy-tale.html&usg=__oxji1TGLV2Fi7xe0dnlmuYk8gDo=&h=288&w=288&sz=16&hl=en&start=2&um=1&tbnid=ywZd4zpdxC5plM:&tbnh=115&tbnw=115&prev=/images%3Fq%3Dfrog%2Bon%2Bcomputer%26hl%3Den%26um%3D1].jpg]]

1. Frog embryology [http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/F/FrogEmbryology.html Frog Embryology]

2. Frog cellular materials [http://www.xenbase.org/xenbase/original/cell/cell.html xenbase]

3. The zoology of frog species [http://worms.zoology.wisc.edu/frogs/mainmenu.html zoology frogs]

4. Frog cycle [http://www.bioethics.gov/images/sc_images/frog_dev.gif bioethics frog] Just a little cycle of FROG'S life cycle

5. Frog Embryology [http://embryology.med.unsw.edu.au/OtherEmb/Frog.htm UNSW Embryology]

6. Frog Research [http://apps.carleton.edu/campus/library/now/exhibits/wallcharts/frog/ carleton library exhibit]

{{Template:Projects09}}
[[Category:Frog]]

2009 Group Project 5

2009-10-14T22:36:49Z

Z3258567: /* The Egg */

== The Embryology of Frogs ==

== The Frog ==

[[Image: Frog species .jpg|thumb|left|Image details: Wikipedia (2009) Frog species[http://en.wikipedia.org/wiki/Frog#Uses_in_agriculture_and_research].jpg]]

Frogs are scientifically identified by the structure of their long posterior limbs, a petite framework, webbed fingers and feet, budged eyes and the lack of a tail. The majority of frog species are extensively recognized as outstanding jumpers, due to their long, dominant legs, which are adaptations to progress jumping performance during activities. The Frog is one of the most frequently studied species in experimental embryology and most anatomical sciences. ''The Frog is a practically effective model for human embryological development given that the Frog:''

- Comprises of genes which can be effectively manipulated.

- Comprises of similar homogeny with humans species.

- Reproduces a large quantity of offspring in a short period of time.

- Are small species which can be simply sustained.

- Are not extremely luxurious and expensive.

== The History of the uses in agriculture and research ==

[[Image: Frog experiments .jpg|thumb|right|Image details: Scans of chemically cleared and dyed preserved deformed frogs and toads [http://www.sat.qc.ca/upload/residence/frog-04.jpg].jpg]]

There are numerous types of frog species that have been manipulated in many developmental experiments. The frog was traditionally used by countless of the early embryology investigators and presently there are several diverse molecular mechanisms regarding progression of the frog. Theses include:

'''1.''' Food source; frog legs are a delicacy and are eaten in European countries and in many parts of South American regions.

'''2.''' Frogs have the finest biochemical dissection of phenomena that take place in the egg and oocyte. Frogs are the evolutionarily closest to mammals, commonly used as a vertebrate model.

'''3.''' Frogs lay thousands of outsized eggs, from which cell extracts can be readily prepared that is capable of recapitulating most molecular phenomena in a test tube.

'''4.''' Frogs have been commonly used as a laboratory system for a very long period, and have an extensive history of producing crucial observations in countless fields of biology.

'''5.''' Frogs have a important historical connection to the study of epigenetics (John Gurdon-vertebrate cloning and reprogramming) which has been mostly performed on frog species.

'''6.''' Frogs also have very strong evidence of pattern formation and early development, as the embryos are large in size and experimentally manipulative.

'''7.''' Recent research into the biochemistry of chromatin and epigenetics has been performed with frog species and mammalian cultured cells.

'''8.''' The biggest weakness of the Frog model system is the difficulty of performing genetic experiments and analysis, as frogs are allotetraploid, meaning they take approximately a year to fully develop to sexual maturity, and the genome has not been completely sequenced. Nevertheless, biochemical manipulations of cell extracts, such as immunodepletions and application of heterologous DNAs and nuclei can avoid the need for genetic exploitation.

----

== Growth and development of the Frog ==

[[Image: Mature develop frog.jpg|thumb|Image details: Wikipedia (2009) Red Eyed Tree Frog Figure 1 Primary source:[http://en.wikipedia.org/wiki/File:Red-eyed_Tree_Frog_-_Litoria_chloris_edit1].jpg]]

* The frog is a well recognised species, abundant predominantly in ponds, swamps, though various species may also exist in damp or shady environments distant from moist habitats.

* Eggs of specific frogs are easily obtained and may be examined in from the beginning of fertilization onwards. The phases of embryonic development differs in various chordates, yet the typical phases are basically apparent in all frog species. The differences are associated principally to the amount of yolk particles present in an egg.

* The yolk particles offer nourishment of the developing embryo. The process of frog development will be discussed from the phases of gametogenesis to the adult stage.

----

== The Egg ==
[[Image:Development of Poles in frog Fertilization.jpg|thumb|left|Development of Poles in Frog Fertilisation:J,Nassif 2009.jpg]]

- The embryology of a frog egg is a vast cell; its dimensions are approximately 1.4-1.6 million times larger than a typical aquatic species egg cell. Throughout the frog’s embryonic maturation period, the egg will be transformed into a tadpole encompassing millions of cells but still remains with its constant volume of genetic material, the vast prodction of cell have been illusttrated in the figure on the right revealing the production of eggs from female frogs. [http://en.wikipedia.org/wiki/Microhylidae]

- The early embryonic frog structure consists of three main segments the superior hemisphere known as the animal pole which is usually visible as a grey coloured area. The innermost layer appears to be between the outer two sections known as the gray crescent represented in black. Inferiorly, represents the vegetal pole typically lighter than the superior compartment illustrated in gold.

VIDEO RESOURCE: [http://www.youtube.com/watch?v=GO5YN_t1fqw&feature=related]

[[Image:Early Development of Frogs.jpg|thumb|left|Early Development of Frog:J,Nassif 2009.jpg]]

==History of frog embryology use ==

*'''1851''' - ''Henby Nelson''(MD): He identified a remarkable fact through the frog embryo. Henby observed the first cleavage of the yolk, in the egg of the frog. And cleaved structure corresponds in line of direction to the longitudinal axis of the body of the embryo of the frog species.

[[Image:Wilhelm Roux.jpg|thumb|right|Wilhelm Roux[http://images.google.com.au/imgres?imgurl=http://www.todayinsci.com/R/Roux_Wilhelm/RouxWilhelmThm.jpg&imgrefurl=http://www.todayinsci.com/6/6_09.htm&usg=__qRLTEMTHdZpAHxiNX12hWjcm9tA=&h=125&w=100&sz=4&hl=en&start=2&um=1&tbnid=LIKIwZTqCpk7MM:&tbnh=90&tbnw=72&prev=/images%3Fq%3DWilhelm%2BRoux%26gbv%3D2%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

*'''1888''' - ''Wilhelm Roux'': Wilhelm Roux attempted to solve the above observation by damaging one cell of a two-cell frog embryo with a hot needle. The cell stayed in place. However, it did not develop further. Its partner developed into a left or right half-embryo;

*'''1907''' - ''John Hopkins'' hospital: In order to identify the cellular source of neuronal fibres. Scientist placed small portions of frog embryo spinal cords in lymph on a microscope slide and was able to observe clear cut neuronal sprouting.

*'''1951''' - ''Robert Briggs'': Robert Briggs was able to clone a frog embryo by substituting the nucleus of an unfertilized frog egg cell with the nucleus of a frog embryo cell. This process is known as nuclear transplant, has formed the basis for all cloning.

*'''1952''' - ''Robert Briggs and T.J. King'': Robert Briggs and T.J. King used frog for test experiment. Because the size of the eggs in the frogs are enormous compared with those of mammals, which make them easier to manipulate.

*'''1976'''- Using the technique that had been successful in cloning frog embryos, the doctor transferred the nucleus of one cells into a donated egg cell. As an embryo began to develop, it was implanted into the uterus of a young woman.

*'''1997''' - ''Wilmut and Campbell'': Utilizing the cloning technique from frog embryo, Drs. Wilmut and Campbell tried the starvation technique on embryo cells to produce Megan and Morag, the world's first cloned sheep and, until now, the most famous sheep in history.

*'''2000''' - ''Tokyo University'': Scientists at Tokyo University have grown artificial eyeballs. Scientists formed them in tadpoles by using frog embryo cells.

*'''2001''' - ''Advanced Cell Technology'': Scientists from Advanced Cell Technology announced production of a human embryo clone. This is significant as its parthenogenesis has been artificially induced in frogs.

[[Image:John Gurdon .jpg|thumb|right|John Gurdon [http://images.google.com.au/imgres?imgurl=http://www.pnas.org/site/misc/images/gurdon.jpg&imgrefurl=http://www.pnas.org/site/misc/classics4.shtml&usg=__1p-GA1PdOYsxKL-cznMb3RHCm98=&h=526&w=400&sz=223&hl=en&start=1&um=1&tbnid=9k4lhuLssiWCAM:&tbnh=132&tbnw=100&prev=/images%3Fq%3DJohn%2BGurdon%26gbv%3D2%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

*'''2002''' - ''John Gurdon'': John Gurdon from Wellcome Cancer Research Institute in Cambridge experimented on cloned frog embryo.

== Gametogenesis ==

* The sexual reproduction occurs through the fusion of either mature reproductive cells or germ cells known as gametes, which include the sperm from the male frog and ova from female frog species so as to form a single cell, the fertilized zygote. The gametes are typically developed in parents of different sexes . [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

* Males gametes is a spermatozoon , the female frog gamete is an ovum. Each gamete is formed by a process, recognised as maturation or gametogenesis in gonads. The typical male frog gonads are testies in male, while the female gonads are ovaries. The synthesis of both gonads is associated with the process of fertilization. [http://en.wikipedia.org/wiki/Microhylidae]

* The zygote changes into a mature frog through the process of embryology and metamorphosis. Gametogenesis is a in progression which frog gametes are established from germ cells. Initial germ cells are called primordial germ cells, which can be recognised extremely early in the life of frog species.

----

== The Egg & Fertilization ==

[[Image:Fertilized and Unfertilised Eggs.jpg|thumb|left|Figure 6 Image details:J,Nassif 2009.jpg]]

[[Image:Egg Development.jpg|thumb|left|Figure 7 Image details:J,Nassif 2009.jpg]]

- This occurs once the sperm cell has inserted, following the insertion of the sperm cells meiosis II is completed, there is a 30 degree position change of the cytoplasm, gray crescent allows this change to be visible in some amphibians, the gray crescent is able what determines the expect ted outline of how the frog will form. The sperm cell joins with the nuclei of the egg which forms the diploid zygote nucleus. --Sando Rashed 10:09, 24 September 2009 (EST)

- The early phases in the development of the egg is visible, but must be studied in tadpoles throughout maturation. In embryonic tadpoles of about 10 millimetres in length, soon after the opening of the oral cavity, a pair of longitudinal ridge-like thickenings of peritoneum becomes apparent along the posterior surface of the body cavity situated near to the mesentery and along the inner boundaries of the kidneys. Genital ridges are established in all tadpoles of this age, sex is not distinct until a later period. The development of the egg is illustrated in the figure on the left revealing the structure of a developed egg and a mature of egg.

[[Image:Fertilisation life cyle.jpg|thumb|Figure 8 Image details:Derived from primary source:[http://en.wikipedia.org/wiki/Frog]]]

== Maturation of the Egg ==

- The eggs have currently accomplished their full size, and develop from the exterior of the ovaries like a small shot, but they still have to pass through the course of maturation before they are prepared to be fertilised. This progression of maturation relates to the nucleus almost completely.

- The nucleus component, containing the nuclear fluid that excludes through the nuclear membrane into the substance of the egg, a great segment of the nuclear reticulum vanishes and becomes degraded into separate globules known as nucleoli, but a extremely small division remains in the midpoint as a slender intricately thread recognised as the nuclear skets.
Relative to the egg getting discharged from the ovary, the follicles shatter allowing the eggs to fall into the abdominal cavity of the frog species, the egg then passes forwards, directly by the contraction of the muscular wall, somewhat by the movement of the cilia of the peritoneum, to the apex of the oviduct, which positioned at the anterior compartment of the body cavity opposite to the roots of the respiratory organs.

- The terminal part of the oviduct establishes a thin-walled pouch capable of great swelling, inside which the eggs gathers in large numbers. In conclusion, the eggs are migrated out through the cloaca into water which the albuminous investments of the eggs rapidly augment to form the gelatinous mass of the frogs spawn.

== Maturation phases ==

'''1. Nuclear skein''', moves from the midpoint of the egg to its outer surface, which it reaches opposite the midpoint of the black pole. The skein, subsequently an unevenly twisted thread, now presumes the specific arrangement of a nuclear spindle, for instance may be visible in the nucleus of an epithelial or additional cell instantly prior to division of the cell occurs.[http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

'''2. The first Polar Body,''' regarding the instance the egg is laid, but prior to its fertilistion, the egg develops a considerably flattened appearance at its upper or black pole, a definite sum of fluid being exuded among the egg and the vitelline membrane. The nuclear spindle currently separate into two identical segments, one of which remains with the egg, and the supplementary is extruded as the first polar body, a small ovoidal white globule, which is situated on the surface of the egg surrounding the exuded peri-vitellline fluid.

'''3. The Second Polar Body''', half of the nuclear spindle that stay behind then splits into two equivalent divisions, one of which remains inside the egg as the female pronucleus, whereas the other segment is extruded as the second polar body, a small white globule extremely related to the first polar body, and like this positioned in the perivitelline fluid on the superior portion of the egg.

'''4. Fertilisation of the egg''', includes the synthesis of the spermatozoon with to egg, specifically, synthesis of the nuclei of these two bodies. The spermatozoa, subsequent to being shed over the seed by the male, distribute vigorously by means of their extended tails, break through the gelatinous investment of the female eggs, bore their way through the vitelline membrane and so go through into the eggs themselves, which they penetrate relative to the superior or black hemispheres.
* Subsequently, an hour following the spermatozoon has entered; a progression may be visible projecting within from the exterior segement of the egg, with a liquid spot in the mid point. This liquid centre is the nucleus of the spermatozoon, and is said to be the male pronucleus, it break through beyond into the female egg, transporting the specialised pigment into it, so that it appears bounded by a pigmented capsule linked with the exterior of the egg by a pigmented stalk.

* By this instance, the second polar body has been established and extruded, and the female pronucleus is merely the only component of the primary egg nucleus still present. Both the male and female pronuceli, which are at initially distance separate to each other, merge and after having enlarged significantly in size then fuse mutually about two and half hours after fertilisation has originated to produce the segmentation nucleus.
* The segmentation nucleus is a huge sphere-shaped vesicle embedded in delicately granular protoplasm, and bounded by a distinct capsule of pigment, its arrangement by the synthesis of the male and female pronuclei completes the action of fertilisation. Specifically female pronucleus may be observe as an imperfect nucleus, and consequently result in the course of fertilisation. The nucleus of the spermatozoon or male pronucleus, replaces the component of the egg- nucleus which has been misplaced as the polar bodies.

'''5. Segmentation of the Egg''', the initial phase of growth consist in constant separation of the egg, whereby it becomes transformed from the unicellular state, which is everlasting only in the lowest species, to muliticelluar state charactertics of all higher species. To these early processes of growth the names segmentation is specified. Shorty subsequent to the competition of fertilisation and arrangement of the segmentation nucleus this later misplaces its sphere-shaped appearance and develops to be spindle-shaped, the yolk granules at the equivalent instance showing a tendency to develop into lines distributing outwards from the distal segment of the spindle.
* The nucleus now split into two halves, which shift away from one another, the yolk granules are likely to combined themselves around the two nuclei, and a slender vertical plate of delicately granular substance is left, dividing the egg.[http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

* Superiorly the eggs depression now becomes visible, initially as a small cavity and then develops as a groove, which almost immediately extends all round, and speedily deepening, splits the egg into two entirely separate halves along a plane equivalent with the vertical plane.

* Shorty after, the two nuclei soon separate again into two, and therefore a second cleft is created in the same state as before, its additionally in the vertical plane, however in a plane at 90 degrees to the initial one, and on its finishing point the egg comprises of four accurately similar segments, each containing a nucleus. The third cleft is horizontal in shape, but not equal, lying closer to the superior than the lower pole, it segregates each of the four cells into, an superior smaller and a inferior larger pole

----

== Cleavage ==

[[Image: Frog Cleavage development.jpg|thumb|left|Figure 8.1 Image details:[http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/F/FrogEmbryology.html].jpg]]

* The egg of the frog is scientifically identified as’ telolecithal’ meaning there is a outsized amount of yolk concentrated at a single pole, in contrast to the concentration of cytoplasm and the site of the nucleus. The cleavage phases are holoblastic, therefore the total and after the second cleavage they are asymmetrical .The initial cleavage stage appears about two and half to three hours after fertilization. It commences as a minor depression in close proximity to the centre of the animal hemisphere. It appears as if some interior force is pushing the surface the egg towards the centre. This small upturned fold steadily continues in the form of a channel until it surrounds the egg. This groove is shallow in the commencement, but develop into deeper eventually separating the fertilized egg into two halves recognised as the blastomeres. [The figure on the left symbolise the development and growth of the frog embryo during cleavage].

* Internally the separation is mitotic, consequently each daughter cell contains a nucleus resulting from the copulation nucleus of the fertilised egg. This cleavage is vertical, the two cells are indistinguishable in respect of cytoplasm, pigment and yolk. The subsequent cleavage appears about an hour after the first. The channel of this cleavage begins at the centre of the animal hemisphere, is at right angles to the first and is vertical. This divides the egg into four blastomeres. The fourth blastomere so produced are not qualitatively equal, since of these only two contain the material from the gray crescent. The cleavage begins about thirty minutes after the second is completed or four hours after fertilisation. the cleavage plane of the third furrow is horizontal and slightly above the equator. Thus the four upper cells are a little smaller than the four lower cells. The smaller blastomeres are called micromeres and the larger blastomeres are called macromeres. The fourth cleavages follow 20 minutes after the third and tend to be vertical. This is usually a double furrow.

* The cleavage rate is accelerated with each of the early divisions and since the blastomeres are of unequal size and have varying amounts of cytoplasm and yolk, synchronous cleavage is lost and there is an obvious overlapping of the division. The upper most cells divide more rapidly than the lowermost cells. From this point onwards perfect symmetry in cleavage and in blastomere is very rare, although the embryo developed perfectly. The fifth cleavage is also doubled, appearing first in the upper hemisphere and then in the lower.

* The cleavage thus far follows the rule that each cleavage plane comes in at right angles to the previous one. The subsequent divisions become so irregular that it is previous one. The subsequent division become so irregular that it is impossible to trace out any plan or procedure. The segmentation continues more rapidly in the pigmented regions, since at that place the protoplasm is most dense, whereas, yolk which is very abundant in the vegetal side delays cell division. The multicelluar embryo at this stage is called morula by some biologists.

----

== Gastrulation ==

[[Image:FROG GASTRULATION .jpg|thumb|left|Figure Image details:[http://www.google.com.au/imgres?imgurl=http://bio1903.nicerweb.com/Locked/media/ch47/47_12FrogGastrulation.jpg&imgrefurl=http://bio1903.nicerweb.com/Locked/media/ch47/gastrulation-frog.html&h=540&w=480&sz=46&tbnid=N78sHjELreGGSM:&tbnh=132&tbnw=117&prev=/images%3Fq%3Dfrog%2B-%2Bgastrulation&hl=en&usg=__4VK9FYLft0W-4lBe6p5EtQAMiaI=&ei=qPy5SurtMJvE6wON8JmdAg&sa=X&oi=image_result&resnum=4&ct=image].jpg]]

''The phase of Blastulation is followed by the unique developmental progression of gastrulation. The process of frog gastrulation involves the following processes.''

'''1. Epiboly Phase'''

The pigmented cellular materials of blastula have the propensity to overgrow the yolk cells within the developing content. This course which is known as epiboly commences gradually in the final blastula and rapidly accelerates with advancing gastrulation development. The cellular matter within the animal pole reproduces and matures on all sides except in area surrounding the dorsal lip of the blastopore has been established.

'''2. Convergence'''

Scientists suggested that the unfolding was thought to result in spreading of the superficial cells over a substrate with suitable absorption properties. Consequently epiboly and convergence are an outcome to this spreading tendency, which is actually increased by a reduction in surface tension of the distributing cells.

'''3. Rotation'''

The epiboly phase is maintained until the region of the dorsal lip has migrated and is a to some extent greater than 90 degrees and the region of the white blastopore is reduced to small circular rings. This section will be positioned away from the developing vegetal pole. Laterally the complete developing gastrula has been rotated to a horizontal axis, allowing it to lie at right angles to the original median plane of the egg. Therefore, the course of rotation is such that the dorsal lip is practically pushed backwards in one direction as rapid or quicker than epiboly moves it forward in the other. The outcome will be that the blastopore produced at roughly the vegetal pole is posterior, and the dorsal and ventral lips are essentially dorsal and ventral. This in addition allows the eggs to form the antero-ventral side of the potential embryo whilst the area marked by the grey crescent is to develop the dorsal segment.

'''4. Invagination'''

Visible is a small fissure- like invagination which is apparent in the middle between the equator and the vegetal segment. The most superior or dorsal border of the cleft produce the dorsal lip of the blastopore. This imput move back and forth on the dorsal plane near the dorsal lip and migrates around the boundaries of the blastocoel in company with the extension of the lateral lips. This adapted invagination is maintained until the blastocoel cavity has been almost abolished; excluding the slender opening separating epiblasts from the hypoblast, the new segment formed is known as the archenteron cavity.

'''5. Involution'''

- Additional to previous course of action a distinct involution also occurs at the blastoporal borders. This is mainly dynamic at the median dorsal lip and gradually more less as it shifts across either side until it reaches the ventral lip where it constant.Throughout this progression, cells positioned beside the superior boundaries of the blastoporal lip migrate over the lip to the interior portion of the lip. These cells are remained within the embryo along the internal edge of the blastopore. This indicates the root of archenteron is composed of involuted cells and beyond this the external layer known as the ectoderm. The base and lateral sides are enclosed mainly of endodermal cellular material, which have been established from larger yolk cells, situated in the vegetal pole of the blastula.

- In the final phases of the gastrula development, the cells contributing to the floor of the archenteron, thin out significantly where they surround the blastocoel.
The hemispherical shaped dorsal lip of blastopore which become visible at the commencement of the gastruation stage carry on to augment, initially becoming semicircular, then transform into a horse shoe shaped and then finally forming into circular band. The band is the accomplished by the blastopore. Various yolk cells of vegetal pole present in the section are crowed into the blastoporal cavity where they form a gathering identified as a yolk plug. Blastopore rapidly reduces in size while the archenteron is still developing and becomes completely formed in the final stage; the yolk plug appears as only a small oval on the gastrula.

==Growth and Modification of Frog Species==

'''1. Changes in habits and habitats:'''

'''a)''' In frogs, metamorphosis is related with to the modifications and adaptations as a frog changes environmental habitats from an aquatic to a terrestrial mode. Metamorphosis has modified the adaption of frogs as this alteration it began during the aquatic adaptations in the surface of water to breathe air. Subsequently, it continues the terrestrial surroundings, therefore the frog species become abundant in vegetation area allowing the frog to transform in to amphibious species.

'''b)''' The transition during metamorphosis is linked with a change in food chain. The tadpoles being the embryonic origin of frogs are herbivorous, feeding on algae and green matter, which they collect by the adapted feature such as their teeth surrounding their mouths. Adult frogs, alternatively, are classified as carnivorous feeding on insects and worms. Occasionally, they also consume larger prey, for instance smaller frogs species and even little birds and rodents which they dominant and ingest.

[[Image:Development of frog from sperm to mature structure.jpg|thumb|left|Figure 9 Image details:J,Nassif 2009.jpg]]

'''2. Changes in Morphology'''

These include the decrease or complete absence of specific organs or structures which are essential during development of early frog embryology, but not critical in the mature frog species. The significant alterations of this nature include the following developmental structures.

'''a)''' The long tail of the tadpole alongside the fin folds is absorbed again during metamorphosis and becomes absent at the final stage of the metamorphosis.

'''b) '''The developing gills are resorted, the gill clefts are congested and the branchial cavities start to become absent. The reabsorbtion of gills also takes place by autolysis.

'''c)''' The teeth of the perioral disc additionally the homey lining of the jaws are shed.

'''d)''' The lateral line sense organs within the skin of tadpoles vanish throughout metamorphosis.

'''e)''' The cloacal tube begins to condensed and reduced.

'''f)''' Various blood vessels, together with parts of the aortic arches, are reduced during mature development.

(The figure on the left represents the transformation from a tadpole to a developing structure.)[http://science.jrank.org/pages/2862/Frogs-Adult-morphology.html]

'''3. Progressive or constructive changes'''

This process comprises of the development of specific organs which mature into functional systems only during metamorphosis.

'''a)''' During development the limbs continue to augment in size and differentiation. The forelimbs, which in the tadpole mature under the opercular membrane, which then break through to the exterior. Simultaneously there is a increase in the length and strength of the hind limbs, joints develop in them and the toes become visible.

'''b)''' The middle ear becomes apparent in relation with the first pharyngeal pouch. The tympanic membrane matures. It is bounded by circular tympanic cartilage which allows the frog to retain air.

'''c)''' The visual organs bulge up on the dorsal surface of the head developing the nictitating membrane.

'''d)''' There is augmentation of the tongue and the formation of thevomerina teeth.

[[Image: Growth model.jpg|thumb|Figure 10 Image details:J,Nassif2009:]]

'''4. Remodelling of some structures'''

Systematic organs which operate both in the early embryonic larva and the mature adult change their differentiation during metamorphosis so as to meet the requirements of the adult mode of life and due to the habitat adaptations. The figure on the right illustrates structures developing from specic germ cell layers.

'''a)''' The skin of the embryonic tadpole is lined with a double-layered epidermis. The number of layers of cells in the epidermis augments throughout metamorphosis. Superficial surface layers become cornified. Multicellular mucous and serous glands originate in the skin. The pigmentation of the skin continuously changes, new patterns and colour start to form.

'''b)''' There is a lengthening of the mouth gap as a result of rotation of the quadrate cartilage and the true jaws become functional.

'''c)''' The tongue rapidly progresses and becomes larger and more muscular.

'''d)''' The eyes become more specialised.

'''e)''' In early tadpoles, the GIT is extremely long and wound up into a spiral folds. The intestine become greatly lengthened in herbivorous species due to the vegetables food chain.[http://en.wikipedia.org/wiki/Frog]

'''5. Development of the reproductive system'''

(The figure below represents the reproductive and development cycle of a frog as it transform from egg to frog specie.)

In tadpoles, right after the mouth is being formed, two indentation like thickenings of peritoneum begin to appear near the body cavity (dorsal surface), which is nearest to the mesentery which is near the developing kidneys. These appear in all tadpoles.

These indentations appear here because of a change in the endothelial cells, everywhere else they are usually flat looking cells but they undergo a change and in this particular area become somewhat cuboidal/columnar.

Later on the indentations become more obvious due to the epithelial cells replicating numerously to form a thick layer. The posterior two thirds of the indentation for the female is the ovary and for the male it is the testis. The third that is left differentiates and becomes fat for the body.

[[Image: Mature frog life cyle.jpg|thumb|200px|left|Figure 11 Image details:Derived from primary source:http://www.scienceclarified.com/images/uesc_01_img0038.jpg]]

[[Image: Developing frog.jpg|thumb|Figure 12 Image details:
[[Image: Mature develop frog.jpg|thumb|Image details: Wikipedia (2009) TYPICAL FROG Primary source:[http://en.wikipedia.org/wiki/File:Red-eyed_Tree_Frog_-_Litoria_chloris_edit1.jpg]].jpg]]

===Delamination===

Delamination indicates a mass separating a group of cellular matter from other cellular groups. It has been illustrated that the division of notochord, mesoderm and endoderm tissues from each other to form distinct cellular masses is completed by the progression of delamination, subsequent to these materials moving to the inside throughout gastrulation. During the developing gastrula, the germ layers are all recognized. These distinct segments of the embryo develop from these germ tissue layers.

===Polarity and Rotation===

Throughout fertilisation to the beginning of gastrulation, the frog’s egg continues in the original location in relation to its polarity. Subsequent to gastrulation its polarity begins to differentiate. This progression is linked with migration of materials within the gastrula and can be responsible for the alterations of the centre of gravity.

===Closing of Blastopore===

Subsequent to the formation of the gastrula, the blastopore is visible as a tiny round circular filled cavity containing the yolk plug. As it continues to reduce in dimension, it represented as a pear-shaped outline through the mutual approach of its lateral lips. Through it final progression these fuse entirely to produce a longitudinal groove, the streak which continue dorsally and ventrally in a small aperture. The inferior aperture closes, resulting in a depression called the anal pit. The superior region remains open for some period and begins to as the neural groove is laid down.

===Post Gastrulation or Organogenesis===

Throughout the duration of pre-gastrulation, all tissues for different organs vanish from the surface of blastula and migrate inside to take their final arrangement in the embryo structure where organs are developed from their potential regions. Consequently organogenesis transfers an embryo into free larva structure.

----

==Germ-layer origin of various body tissues==
[[Image: Development Models of Frog.jpg|thumb|right|Figure 13 Image details:Vertebrate Structure and Development.jpg]]

Ectoderm will give raise to structures such as skin, brain, spinal cord, neurons and sense receptors.
Mesoderm will give raise to structrues such as notochord, muscles, blood, bone and sex organs.
Endoderm will give raise to sturctures such as inner lining of gut, liver, pancreas, lungs and bladder, thyroid and parathyroid glands and thymus.

== Structures derived from Germ-layers of frog species ==

[[Image:Development of Frog Layers.jpg|thumb|left|Figure 14 Primary source[http://www.bio.miami.edu/~cmallery/150/physiol/sf19x11b.jpg]Image details:J,Nassif 2009.jpg]]

[[Image:Development of frog layers.jpg|thumb|left|Figure 15 Primary source [http://www.bio.miami.edu/~cmallery/150/physiol/sf19x11b.jpg]Image details:J,Nassif 2009.jpg]]

'''Ectoderm '''

''Establishes the epidermal segments and its derivatives, to the frog’s nervous system. The ectoderm also contributes to :''

1. The olfactory and auditory epithelium.

2. The retina and lens of the eye.

3. Sensory organs.

4. The epithelial lining of the oral cavity and the anus.

5. The pineal and pituitary body.

'''Mesoderm'''

''Mesoderm originates:''

1. Connective tissue.

2. Muscles, except the notochord.

3. Blood vessels.

4. Lymphatics.

5. The peritoneum and the urinary and reproductive system.

6. The dermis, parts of the eye excluding lens, cornea, and conjunctiva.

'''Endoderm'''

''From the endoderm arises:''

1. The epithelial lining to the gut and oesophagus, stomach, intestine, bile duct.

2. The hepatic cells of the liver, respiratory tract, larynx, trachea and lungs.

3. The lining of the urinary bladder, pancreas thyroid and thymus.

[The two figures reveal the development of structures deriving from the celluar components of the embryology of the frog].[Structures derived from Germ-layers of frog species ]

==Life cycle of a frog==

'''Fertilization-egg''':

The female lays eggs in the spring. A group of fertilized eggs is called spawn;

'''7-10 days''':

Fertilized egg feed on remaining yolk which is in its gut. Their gills, mouth and tail have poorly developed. Begin to swim and feed on algae;

'''10-30 days(4 weeks):'''

A layer of skin grows over gills. Teeth begin to appear. A coiled gut start to develop. This is aid in digestion;

'''30-60 days(6-9 weeks):'''

Legs being to grow and head is more distinct. Start to eat insects. Arms begin to grow;

'''60-80 days(12 weeks):'''

Resemble a frog. Still have remaining tail;

'''80-140 days(20 weeks):'''

Fully developed, spend most of time out of water. Majority of frog live between 4-15 years.

==Timeline of frog development==

Development of egg and embryo at temperature 18 degree celsius.

'''0 hours''' - fertilization of the egg

'''1 hours''' - formation of the gray crescent due to pigment migration

'''3.5 hours''' - early cleavage

'''4.5 hours''' - blastula stage(coeloblastula with eccentric blastocoel

'''26 hours''' - gastrulation

'''26 hours''' -'' early'' - crescent shaped dorsal lip

'''34 hours''' - ''middle''- semicircular blastoporal lip

'''42 hours''' - ''late'' - circular blastoporal lip

'''50 hours''' - neurulation

'''50 hours''' - ''early'' - medullary plate

'''62 hours''' -'' middle''- neural folds converging

'''67 hours''' - ''late'' - neural tube formed and ciliation of embryo

'''84 hours''' - tail bud stage(early organogeny)

'''96 hours''' - muscular response to tactile stimulation

'''118 hours''' - early heart beat, development of gill buds

'''140 hours''' - hatching and gill circulation

'''162 hours''' - mouth opens and cornea becomes transparent

'''192 hours''' - tail fin circulation established

'''216 hours''' - degeneration of external gills, formation of operculum, development of embryonic teeth

'''240 hours''' - opercular fold over brachial chamber except for spiracle and internal gills

'''255 hours''' - prolonged larval stage with refinement of organs

'''270 hours''' - development of hindlimbs, internal development of forelimbs in opercular cavity

'''275 hours''' - projection of forelimbs through operculum, left side first

'''280 hours''' - absorption of the tail and reduction in size of the gut

'''284 hours''' - metamorphosis complete, emergence from water as miniature, air breathing frog

==Stages of frog embryology==
--[[User:S8600021|Mark Hill]] 08:40, 9 October 2009 (EST) [[Talk:2009_Group_Project_5#Constructive_Criticism_of_Coordinator|see my comment on images]]

The rate of development of the egg and embryo will depend upon the temperature at which they are kept. The approximate schedule of development at 23 degree celsius is provided below.

{| border='1px'
|+ Table 1: Stages of frog development
!Stage !!Time since fertilisation (hours)!!Stage Characteristic !!Embryo characteristic !!Image of frog stage
|-
|1
|0.00-1.30
|fertilization of the egg, post fertilization
|animal hemisphere, gray crescent and vegetal hemisphere are present
|[[File:Stage01ventral.jpg|100px]]
|-
|2
|1.30-2.00
|splits into two cells
|appearance of first cleavage furrow
|[[File:Stage02ventral.jpg|100px]]
|-
|3
|2.00-2.15
|becomes four cells
|appearance of second cleavage furrow
|[[File:Stage03dorsolat.jpg|100px]]
|-
|4
|2.15-2.45
|becomes eight cells
|appearance of third cleavage furrow
|[[File:Stage04dorsolat.jpg|100px]]
|-
|5
|2.45-3.00
|becomes sixteen cells
|appearance of fourth cleavage furrow
|[[File:Stage05dorsal.jpg|100px]]
|-
|6
|3.00-3.30
|becomes thirty-two cells
|appearance of fifth cleavage furrow
|[[File:Stage06animal.jpg|100px]]
|-
|6.5
|3.30-4.00
|blastula stage
|Three dorsal folds become visible as a result of endoderm invagination. Pole cells no longer visible on surface
|[[File:Stage065dorsal.jpg|100px]]
|-
|7
|4.00-5.00
|Gastrulation stage
|two primary germ layers. epiblast and endoderm
|[[File:Stage07ventral.jpg|100px]]
|-
|8
|5.00-7.00
|neurulation
|medullary plate, neural folds and neural tube
|[[File:Stage08animal.jpg|100px]]
|-
|9
|7.00-9.00
|germ layer
|complete lip involution encircling yolk
|[[File:Stage09veg.jpg|100px]]
|-
|10
|9.00-11.00
|early gastrula
|two primary germ layers
|[[File:Stage10veg.jpg|100px]]
|-
|10.5
|11.00-11.45
|gastrula
|two germ layers
|[[File:Stage105vegb.jpg|100px]]
|-
|11
|11.45-12.30
|medulla plate
|Yolk sac protrudes dorsally, labium moves to midline on ventral side
|[[File:Stage11veg.jpg|100px]]
|-
|11.5
|12.30-13.15
|continuation of medulla plate
|start closing the plate
|[[File:Stage115veg.jpg|100px]]
|-
|12
|13.15-14.15
|early neurula
|thickened ectoderm give rise to CNS
|[[File:Stage12veg.jpg|100px]]
|-
|12.5
|14.15-14.45
|neural folds
|expansion of cavity
|[[File:Stage125postdors.jpg|100px]]
|-
|13
|14.45-16.15
|neural folds
|continue expanding cavity
|[[File:Stage13postdors.jpg|100px]]
|-
|14
|16.15-17.30
|neural folds
|continuation of cavity
|[[File:Stage14postdors.jpg|100px]]
|-
|15
|17.30-18.15
|tail bud stage
|early organogeny
|[[File:Stage15postdors.jpg|100px]]
|-
|16
|18.15-18.45
|tail bud stage
|posterior ventral view
|[[File:Stage16ant.jpg|100px]]
|-
|17
|18.45-19.45
|tail bud stage
|anterior view
|[[File:Stage17ant.jpg|100px]]
|-
|19
|20.45-21.45
|neural fold close complete
|dorsal view
|[[File:Stage19dorsal.jpg|100px]]
|-
|20
|21.45-22.30
|early tail bud
|anterior view
|[[File:Stage20dorsal.jpg|100px]]
|-
|21
|22.30-24.00
|termination of neural crest
|progress to next stage
|[[File:Stage21ant.jpg|100px]]
|-
|22
|24.00-24.45
|prolonged development
|elongation
|[[File:Stage22lat.jpg|100px]]
|-
|23
|24.45-26.15
|elongation of embryo
|later view
|[[File:Stage23lat.jpg|100px]]
|-
|24
|26.15-27.30
|continuation of elongation of embryo
|dorsal view
|[[File:Stage24latsmall.jpg|50px]]
|-
|25
|27.30-29.30
|organs development
|embryo elongates and develops dorsal thickening
|[[File:Stage25dorsal.jpg|50px]]
|-
|26
|29.30-31.15
|elongation
|dorsally forms neural and brain cavity
|[[File:Stage26lat.jpg|50px]]
|-
|27
|31.15-32.30
|elongation of embryo
|dorsal view
|[[File:Stage27lat.jpg|50px]]
|-
|28
|32.30-35.00
|further development
|lateral view
|[[File:Stage28lat.jpg|50px]]
|-
|29-30
|35.00-37.30
|tail bud
|growth
|[[File:Stage29-30lat.jpg|50px]]
|-
|31
|37.30-40.00
|prolonged development
|bud development
|[[File:Stage31lat.jpg|50px]]
|-
|32
|40.00-44.30
|early muscular development
|elongation
|[[File:Stage32lat.jpg|50px]]
|-
|33-34
|44.30-50.00
|muscular movement
|apparatus for locomotion
|[[File:Stage33-34lat.jpg|50px]]
|-
|35-36
|50.00-53.30
|muscular movement
|apparatus for locomotion
|[[File:Stage35-36lat.jpg|50px]]
|-
|37-38
|53.30-56.30
|heart beat
|develops apparatus
|[[File:Stage37-38lat.jpg|50px]]
|-
|39
|56.30-66.00
|mouth opens
|cornea transparent
|[[File:Stage39latsmall.jpg|50px]]
|-
|40
|66.00-76.00
|gill circulation
|hatching
|[[File:Stage40lat.jpg|50px]]
|-
|41
|76.00-80.00
|tail, fin circulation
|circulation
|[[File:Stage41lat.jpg|50px]]
|-
|42
|80.00-86.00
|internal gills, operculum
|opercular fold, teeth
|[[File:Stage42lat.jpg|50px]]
|-
|43
|86.00-98.00
|operculum complete
|operculum closed on right
|[[File:Stage43lat.jpg|50px]]
|-
|46
|98.00-106.00
|metamorphosis
|emergence from water as miniature, operculum complete|
|[[File:Stage46lat.jpg|50px]]
|-
|}

==Abnormalities of frog==

Abnormalities of frog could be caused by multiple factors. These include change in climate, predators, parasites, bacteria, fungi, viruses or pollution and contaminants such as pesticides, metals and fertilizer.[http://www.fws.gov/contaminants/documents/frogsrefup_septoct_2006.pdf]

The Abnormalities are further classified into different categories. These categories are:

===1. Infectious Diseases:===

'''Perkinsus Symptoms-''' caused by perkinsus-like protozoan organism. Symptoms include swollen viscera that leads to a bloated body and and infected swollen heart

'''Ichthyophonus symptoms-''' cause by parasitic genus, where symptoms include a swollen tail resorption site that matches the surrounding skin in color and translucency.

[[Image:Abnormalities of Frog species.jpg|thumb|left|Figure A Image details[waterwatchadelaide.net.au].jpg]]

===2. Surficial Abnormalities:===

Surficial abnormalities as the one that are visible on the surface of the skin. This includes abnormal pigmentation, , subcutaneous hemorrhaging, wounds due to trauma or from a predator
Edema is a fluid-filled swelling under skin whihc is also a surficial abnormality.

===3. Skeletal Abnormalities:===

This is further classified into three more categories:

'''a. Skeletal Malformations-'''

* Microcephaly (small head or blunt snout)
*Scoliosis (Curved spine in lateral direction)
*Shrunken Limb (Micromelia)
*Amelia (Completely missing limb with no stump)

'''b. Skeletal Abnormalities of Unclear Etiology-'''

This condition arises when a frog has ectromelia (missing limb), brachydactyly (missing digits) or other such condition with no visible trauma or external damage, then this will be classified as the Skeletal abnormality of unclear etiology.

'''c. Skeletal Injuries-'''

Any limb missing or broken due to trauma or other related reason which shows clear evidence of it is classified as skeletal injury

===4. Eye Abnormalities:===

Most common includes-

'''i. Anophthalmia:''' Skin covers the eye socket as there is no eye

'''ii. Abnormal Iris Coloration:''' Reduced pigment in either one eye or both resulting in two different colours of the iris at times

'''iii. Abnormal size or shape:''' Both eyes either deviating from each other or size of pupil or iris is different than the other eye

[http://www.fws.gov/contaminants/Amphibian/pdfs/AbnormalitySOP_woutpics_Jan08.pdf ]

==Genetics==

There are a wide variety of species that differ from each other when it comes to genetics and their functioning.

'''TAXONOMY:''' '''Phylum''' ''Chordata'' / '''Sub Phylum''' ''Vertebrata'' / '''Class''' ''Amphibia'' / '''Order''' ''Anura''

Their are more than two dozen different families of frogs, where suborders are:

'''1. ARCHAEBATRACHIA-''' most primitive frogs

'''2. MESOBATRACHIA-''' linked between the Archaebatrachia and Neobatrachia

'''3. NEOBATRACHIA-''' most modern frogs

{| border='4px'
|+ '''General Info:'''
! !!
|-
| '''Number of frogs' species'''
| 5280
|-
| '''Smallest frog genome size:'''
| 0.95pg, Ornate burrowing frog
|-
| '''Largest frog genome size:'''
| 13.40pg, Ornate horned frog
|-
| '''Mean of frogs' genome'''
| 4.68pg ± 0.13
|-
|}

[http://www.genomesize.com]

*Majority of frogs have only 22 to 26 chromosomes and polyploid is very common where they are almost bisexual.

*Polyploid Amphibians reduce their total cell number such that they acheive the same body size as diploids. One of the most unsual forms of polypoidy in amphibians is the water frog ''Rana esculenta'' from Europe and Western Asia.

* The species with larger genomes have more genes for e.g. the frog genus ''Xenopus'' includes 16 species, with genome sizes ranging from 3.5 x 10^9 bp to 1.6 x 10^10 bp. These differences have arisen by numerous events of polyploidization within the past 40 million years or so. The ancestral chromosome number for the genus seems to have been 18, but there are species with 36, 72 and 105 chromosomes [http://www.xenbase.org/common/]

{| border='4px'
|+ '''Difference within two families'''
! '''SPECIES''' !! ''X.LAEVIS'' !! ''X.TROPICALIS''
|-
| '''PLOIDY'''
| Allotetraploid
| Diploid
|-
| '''NO. OF CHROMOSOMES'''
| 36 chromosomes
| 20 chromosomes
|-
| '''GENOME SIZE'''
| 3.1 x 10^9 bp
| 1.7 x 10^9 bp
|-
| '''EGG SIZE'''
| 1-1.3 mm
| 0.7-0.8 mm
|-
| '''GENERATION TIME'''
| 1-2 years
| 4 months
|-
|}
[http://www.xenbase.org/common/]

===Genome Sequencing===

Since Frog has a huge family with many different species, only few main species that are used widely for the purposes of experiments have their genome sequenced.

''Xenopus tropicalis'' has one of the smallest genomes among amphibians and has the shortest generation time- four to six months and the only diploid genome among the 14 Xenopus species. This means it has no more than two copies of most genes, whereas the other species of Xenopus have four copies of most genes (pseudotetraploid). US Department of Energy's Joint Genome Institute (JGI) in Walnut Creek, California, initiated the X. tropicalis Genome Project, finding 1,700 million base pairs.
[http://www.genome.gov/Pages/Research/Sequencing/BACLibrary/xenopusTropicalis.pdf]

===Xenopus oocytes===

* The oocytes provide an important expression system for molecular biology.

* By injecting DNA or mRNA into the oocyte or developing embryo, scientists can study the protein products in a controlled system. This allows rapid functional expression of manipulated DNAs (or mRNA). This is particularly useful in electrophysiology, where the ease of recording from the oocyte makes expression of membrane channels attractive.

* One challenge of oocyte work is eliminating native proteins that might confound results, such as membrane channels native to the oocyte.

* Translation of proteins can be blocked or splicing of pre-mRNA can be modified by injection of Morpholino antisense oligos into the oocyte (for distribution throughout the embryo) or early embryo (for distribution only into daughter cells of the injected cell).
[http://www.staff.unibe.ch/sigel/xenopus.html]

===Xenopus Laevis===

* ''Xenopus Laevis'' is an important model organism in developmental biology. X. laevis is tetraploid and reaches sexual maturity in 1 to 2 years. What makes it important in developmental biology is its large and easily manipulable embryo.

* Extracts from the eggs of X. laevis frogs are also commonly used for biochemical studies of DNA replication and repair, as these extracts fully support DNA replication and other related processes in a cell-free environment which allows easier manipulation.

* The Human chorionic gonadotropin hormone (hCG) is present in the urine of the pregnant women in large quantities only. This hormone in the urine induces X.laevis oocyte production which formed the basis of first well-documented method of pregnancy testing X. laevis is also notable for its use as the first well-documented method of pregnancy testing when it was discovered. Today, commercially available HCG is injected into Xenopus males and females to induce mating behavior and breed these frogs in captivity at any time of the year.

===Gene cluster===

* The alpha and beta globin genes are closely linked in small cluster of frogs compared to human and chicken

* The similarity of architecture of two clusters found in X.laevis supports the tetraploid origin

* The two loci encoding the muscle specific creatine kinase isoenzymes and have large differences in developmental profile, therefore suggesting that duplicate loci that have not undergone silencing are not simply redundant copies but have acquired specialization.

* Contains twice number of genes for proteins i.e. haemoglobin and sarcomeric actin serum albumin compared with other species

----

==Current Embrology Research==

Currently, a number of fields have benefited from the development of frog embrology. These include cloning, verification of messenger RNA, and Cell cycle.

===Cloning===
[[Image:Robert Briggs.jpg|thumb|left|Figure 16 Image details:Robert Briggs.jpg]]

In 1952, Robert Briggs and Thomas J King cloned northern leopard frogs using a method of nuclear transfer. Briggs and King's experiment was similar to that envisioned - and piloted using salamanders - by Hans Spemann in his 1938 proposal for a 'fantastical experiment'. Later, John Gurdon extended this work and showed that nuclei from differentiated cells could support development, although less well than those from early embryos. [http://genome.wellcome.ac.uk/doc_WTD020799.html]

Lemaitre et a. (2005) from MRC Cancer Cell Unit, Cambridge, U.K. worked on experiments that demonstrated that importance of serial nuclear transplantation for the sucessful cloning of frogs. He demonstrated that exposure of somatic-cell nuclei (erythrocyte nuclei) and sperm nuclei to an extract of mitotic cell extract reorganizes the chromatin into shorter loops and allows replication at much shorter intervals along the DNA. This increases the efficiency of DNA replication in mammalian cell-free systems.

===Transgenesis techniques for functional genomics in Xenopus===

Transgenesis in Xenopus is made possible due to large embryos, a reliable fate map, ease of microinjection, ease of dissection/micromanipulation and existence of the neuroendocrine reflex of background adaptation as a model for activation/inact.

Recently, Hajime Ogino and Haruki Ochi from Nura Institute of Science and Technology in Japan focused on the genomic resources and principles of the transgenesis techniques in Xenopus, and discusses their applications to genome wide network analysis, with emphasis on the use of bioinformatics tools. This is will to understand the gene regulatory networks that control vertebrate development. [http://www.ingentaconnect.com/content/bsc/dgd/2009/00000051/00000004/art00001%3Bjsessionid=4ah96rms73gcu.alexandra]

Xenopus used to be a problem in earlier days when it came to transgenesis. Current methods involves isolated sperm nuclei from Xenopus testis that are microinjected into unfertilized eggs. The generated transgenic tadpoles contain 5-35 copies of the integrated plasmid that are expressed in all cells. If desired, expression of the transgene can be directed to the appropriate tissue and at the appropriate time by using specific promoters, mostly the Xenopus POMC gene promoter (isolated from a Xenopus genomic DNA library) to specifically direct expression of green fluorescent protein (GFP) at high levels to the intermediate pituitary cells, which can either be over expressed or inhibited.[http://molanphys.ruhosting.nl/transgenesis.htm]

[[File:Transgenesis.JPG]]

===Verification of messenger RNA===

While the existence and role of messenger RNA (mRNA) was known in bacteria, in the 1960s it was still debated whether it also existed in vertebrates. Taking haemoglobin mRNA from immature red blood cells and injecting it into a Xenopus oocyte, John Gurdon showed that the haemoglobin protein was indeed produced. Producing proteins in Xenopus oocytes has proved to be extremely useful in cell biology, in particular for the study of receptor proteins.[http://genome.wellcome.ac.uk/doc_WTD020799.html]

===Cell Cycle===

As they develop outside the mother, frog eggs are well stocked with the proteins needed to drive the development of the embryo. Studies of these processes has shed considerable light on the processes involved in cell division - termed the cell cycle. [http://genome.wellcome.ac.uk/doc_WTD020799.html]

===Limb development in Xenopus Laevis===

[[Image: Frog Limb development.jpg|thumb|right|Image details:Primary source:[http://images.google.com.au/imgres?imgurl=http://www.sciencedaily.com/images/2006/06/060616130718.jpg&imgrefurl=http://www.sciencedaily.com/releases/2006/06/060616130718.htm&usg=__xliPsPAvheUBME_kjv_q7auiFbo=&h=333&w=300&sz=11&hl=en&start=2&um=1&tbnid=y_ntJtmkRSK7WM:&tbnh=119&tbnw=107&prev=/images%3Fq%3DLimb%2Bdevelopment%2Bin%2BXenopus%2BLaevis%26ndsp%3D18%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

Donald D. Brown (2005),Department of Embryology, Carnegie Institution of Washington demonstrated factors related to limb development of Xenopus Laevis. Thyroid hormone (TH) is found to be required for limb development in this frog. Specific cell types in the growing limb were targeted for expression of a dominant negative form of the TH receptor by sperm-mediated transgenesis. Limb muscle development, the innervation of muscle from the spinal cord, and cartilage growth can be inhibited without affecting patterning of the limb or differentiation of other cell types. Remodeling of the skin occurs late in metamorphosis after the limb has formed. The coordination of these independent programs is affected in part by the control that TH exerts over DNA replication in all cell types of the limb. [http://www.pnas.org/content/102/35/12455.full]

----

== Glossary ==

[[Image: Frog species.jpg|thumb|left|Image details:Primary source:www.olympus.co.jp/.../080925/large/p02L.jpg].jpg]]

*'''Amphibian:'''

''Relating to or characteristic of animals of the class amphibia.Amphibians are found in the taxonomic class of amphibia, amphibians are capable of both occupying and successfully living in both land and aquatic communities.amphibian''

*'''Augmentation:'''

''Enlargement/Increase in cellular size.''

*'''Autolysis:'''

''breakdown of a part or whole cell or tissue by self-produced enzymes''

*'''Blastomeres:'''

''The undifferentiated cells formed by cleavage of the fertilised ovum. This includes cells in the cleavage, morula, and blastula stages of the embryo''

*'''Carnivorous:'''
''
Flesh-eating; subsisting on animals as food.''

*'''Cleavage:'''

''he repeated division of a fertilised ovum ''

* '''Cleft:'''

''an opening, fissure, or V-shaped indentation made by or as if by splitting''

*'''Chordate:'''

''Members of a diverse phylum of animals that, as embryos, possess a (1) notochord; (2) a dorsal, hollow nerve cord, (3) pharyngeal gill slits; and (4) a post-anal tail''

''The act or state of splitting or dividing of a cell, particularly during the telophase of (animal) cell division.''

*'''Cytoplasm:'''

''The cytoplasm (of both eukaryotes and prokaryotes) is where the functions for cell expansion, growth, metabolism, and replication are carried out''

* '''Epiboly:'''
''The expansion of one cell sheet over other cells, as takes place during gastrulation''

*'''Fertilization:'''

''A process in sexual reproduction that involves the union of male (sperm) and female (ovum) gametes (each with a single, haploid set of chromosomes) to produce a diploid zygote.''

*'''Gamete:'''
''A reproductive cell (male (sperm) or female (egg)) that has only half the usual number of chromosomes''

*'''Gametogenesis:'''

''process leading to the production of gametes. The development and maturation of sex cells through meiosis.Another name for meiosis where a diploid cell is divided into two haploid cells with half the chromosome content of the diploid parent cell.''

*'''Herbivorous:'''

''eating plants; of or pertaining to the herbivora.''

*'''Holoblastic:'''

''The complete division of an isolecithal or microlecithal egg into blastomeres''

*'''Invagination:'''

''One of the methods by which the various germinal layers of the ovum are differentiated.''

*'''Isoenzymes:'''

''Isozymes (also known as isoenzymes) are enzymes that differ in amino acid sequence but catalyze the same chemical reaction.''

*'''Mesentery:'''

'' membranous fold attaching various organs to the body wall.''

*'''Metamorphosis:'''

''A change in the form and often habits of an animal after the embryonic stage during normal development.''

*'''Neuroendocrine:'''

''Neuroendocrine [IPA nʊəroʊˈɛndəkrɪn] cells are cells that release a hormone into the circulating blood in response to a neural stimulus.''

*'''Organogenesis:'''

''The part of embryonic development where the body's main organs develop.''

*'''Peritoneum:'''

''The smooth serous membrane which lines the cavity of the abdomen, or the whole body cavity when there is no diaphragm, and, turning back, surrounds the viscera, forming a closed, or nearly closed, sac.''

*'''Perivitelline space:'''

''The perivitelline space is the space between the zona pellucida and the plasma membrane (sometimes called the vitelline membrane) in a fertilized ovum.''

*'''Polyploidy:'''

''Cells with three or more sets of chromosomes.''

*'''Pronucleus:'''

''the nucleus of the ovum or sperm after fertilization but before they fuse to form the nucleus of the zygote ''

*'''Protoplasm:'''

''The fluid living content of the cell that consists of two major divisions, the cytoplasm and the nucleoplasm (cell nucleus). It is composed mainly of nucleic acids, proteins, lipids, carbohydrates, and inorganic salts''

*'''Segmentation:'''

''division of some metazoan bodies (such as annelida and Arthropoda) into repeated parts, segments. Segmentation can be homomeric (more or less the same) or heteromeric(different from each other).''

*'''Terrestrial:'''

''Of or on the ground, of the habitat of a plant, on land as opposed to in water, or on the ground as opposed to on another plant.''

*'''Transgenesis:'''

''Transgenesis is the process of introducing an exogenous gene - called a transgene - into a living organism so that the organism will exhibit a new property and transmit that property to its offspring.''

*'''Yolk:'''

''nutritive material of an ovum stored for the nutrition of an embryo''

*'''Zygote:'''

''The cell from which an organism develops, that results from the fertilization of the egg by the sperm.''

''Primary Resource "Biology- Online Dictionary''[http://www.biology-online.org/dictionary/Main_Page]

== References - Frog Embryology: ==

[[Image:Frog Research.jpg|thumb|left|Image details:[http://images.google.com.au/imgres?imgurl=http://www.odt.co.nz/files/story/2008/09/university_of_otago_zoology_senior_lecturer_phil_b_3343259744.jpg&imgrefurl=http://www.odt.co.nz/on-campus/university-otago/21670/dunedin-frog-man-wins-zoo-award&usg=__JvJJU5QfOnIwY2bk4xo64UXuJRs=&h=600&w=404&sz=22&hl=en&start=14&um=1&tbnid=AbsP89yWcUiilM:&tbnh=135&tbnw=91&prev=/images%3Fq%3Dfrog%2Bresearch%26hl%3Den%26um%3D1].jpg]]

1. Savage, J. M. (2002). The Amphibians and Reptiles of Costa Rica. University of Chicago Press, Chicago [http://www.springerlink.com/content/vv015277w1746llw/]

2. Ford, L.S.; D.C. Cannatella (1993). "The major clades of frogs". Herpetological Monographs 7: 94–117 [http://digimorph.org/specimens/Xenopus_laevis/]

3. Tyler, M. J. (1994). Australian Frogs A Natural History. Reed Books [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.gracilenta.html]

4. Cogger, H.G.; R.G. Zweifel, and D. Kirschner (2004). Encyclopedia of Reptiles & Amphibians Second Edition. Fog City Press [http://en.wikipedia.org/wiki/Microhylidae]

5. Beltz, Ellin (2005). Frogs: Inside their Remarkable World. Firefly Books [http://unjobs.org/authors/ellin-beltz]

6. Tyler, M. J. (1994). Australian Frogs A Natural History. Reed Books [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

7. Moury JD, Hanken J (1995) Early cranial neural crest migration in the direct-developing frog, Eleutherodactylus coqui. Acta
Anatomica (Basel) 153, 243-253.

8.Raynaud A (1985) Development of limbs and embryonic limb reduction. In Biology of the Reptilia (ed. Gans C, Billett F), pp.
59-148. New York: John Wiley.[http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=9309]

9. Hanken J (1986) Developmental evidence for amphibian origins. In Evolutionary Biology (ed. Hecht MK, Wallace B, Prance GT), 20, pp. 389-417. New York: Plenum Press. [Hanken J (1986) Developmental evidence for amphibian origins. In Evolutionary Biology (ed. Hecht MK, Wallace B, Prance GT), 20, pp. 389-417. New York: Plenum Press.]

10. Elinson RP (1990) Direct development in frogs : wiping the recapitulationist slate clean. Seminars in Developmental Biology
1, 263-270.

11. Beebee, T. J. C. 1996. Ecology and Conservation of Amphibians. Chapman and Hall. London. [http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V5X-3SVHMKH-1X&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=1021245355&_rerunOrigin=google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=825868e10cd178d16a8a0e5ad14dc5ef]

12. Lehtinen, R. M. 2002. The use of screw pines (Pandanus spp.) by amphibians and reptiles in Madagascar. Herpetological Bulletin 2002:20–25.

13. Parris, K. M. and M. A. McCarthy. 1999. What influences the structure of frog assemblages at forest streams. Australian Journal of Ecology 24:495–502. CrossRef

14. Zug, G. R. 1993. Herpetology: An Introductory Biology of Amphibians and Reptiles. Academic Press. San Diego, CA.

15. Slack,J.M.W., Darlington,B.G., Heath,J.K. and Godsave,S.F. (1987)Mesoderm induction in early Xenopus embryos by heparin-binding growth factors. Nature, 326, 197-200.

16. Melton,D.A. (1990) Activins are expressed early in Xenopus embryogenesis and can induce axial mesoderm and anterior structures. Cell, 63, 485-493.

17. Harland,R.M. and Misher,L. (1988) Stability of RNA in developing Xenopus embryos and identification of a destabilizing sequence in TFIIIA RNA. Development, 102, 837-852.

18. Cunliffe,V. and Smith,J.C. (1992) Ectopic mesoderm formation in Xenopus embryos caused by widespread expression of a Brachyury homologue. Nature, 358, 427-430.

19. Kinoshita,K., Bessho,T. and Asashima,M. (1993) Competence prepattern in the animal hemisphere of the 8-cell-stage Xenopus embryo. Devel. Biol., 160, 276-284.

20. LaBonne,C., Burke,B. and Whitman,M. (1995) Role of MAP kinase in mesoderm induction and axial patterning in Xenopus development. Development, 121, 1475-1486.

21. Green,J.B.A., New,H.V. and Smith,J.C. (1992) Responses of embryonic Xenopus cells to activin and FGF are separated by multiple dose thresholds and correspond to distinct axes of the mesoderm. Cell, 71, 731-739.

22. Grainger R., Blumberg B., Harland R., Amemiya C., Importance of Xenopus Tropicalis to biomedical and biological research, Benaroya Research Institute, Virginia Mason Research Center [http://www.genome.gov/Pages/Research/Sequencing/BACLibrary/xenopusTropicalis.pdf ]

23. Gregory, T.R. (2005). Animal Genome Size Database. [http://www.genomesize.com]

24. U.S Fish and Wildlife Services, ABNORMALITY CLASSIFICATION SOP, [http://www.fws.gov/contaminants/Amphibian/pdfs/AbnormalitySOP_woutpics_Jan08.pdf ]

25. Donald D. Brown*, Liquan Cai*, Biswajit Das*, Nicholas Marsh-Armstrong‡, Alexander M. Schreiber*, and Rejeanne Juste*(2005), Thyroid hormone controls multiple independent programs required for limb development in Xenopus laevis metamorphosis [http://www.pnas.org/content/102/35/12455.full]

26. Ogino, Hajime; Ochi, Haruki, Resources and transgenesis techniques for functional genomics in Xenopus, Development Growth & Differentiation, Volume 51, Number 4, May 2009 , pp. 387-401(15) [http://www.ingentaconnect.com/content/bsc/dgd/2009/00000051/00000004/art00001%3Bjsessionid=4ah96rms73gcu.alexandra]

27. Giles Newton (2004) Why the frog? The Human Genome, [http://genome.wellcome.ac.uk/doc_WTD020799.html]

28. Xenbase, [http://www.xenbase.org/common/]

29. Donders Center for Neuroscience & Nijmegen Center for Molecular Life Sciences (NCMLS), Beyond the genome (Xenopus transgenesis for functional genomics),Faculty of Science, Radboud University [http://molanphys.ruhosting.nl/transgenesis.htm]

== External Links ==
[[Image:Frog links.jpg|thumb|left|Image details:[http://images.google.com.au/imgres?imgurl=http://2.bp.blogspot.com/_o93AaY0GzH4/SjY_ZYv0PII/AAAAAAAAAgk/skruNc2yN78/s400/computer%2Bfrog.jpg&imgrefurl=http://hellaheaven-ana.blogspot.com/2009/06/talking-frog-contemporary-fairy-tale.html&usg=__oxji1TGLV2Fi7xe0dnlmuYk8gDo=&h=288&w=288&sz=16&hl=en&start=2&um=1&tbnid=ywZd4zpdxC5plM:&tbnh=115&tbnw=115&prev=/images%3Fq%3Dfrog%2Bon%2Bcomputer%26hl%3Den%26um%3D1].jpg]]

1. Frog embryology [http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/F/FrogEmbryology.html Frog Embryology]

2. Frog cellular materials [http://www.xenbase.org/xenbase/original/cell/cell.html xenbase]

3. The zoology of frog species [http://worms.zoology.wisc.edu/frogs/mainmenu.html zoology frogs]

4. Frog cycle [http://www.bioethics.gov/images/sc_images/frog_dev.gif bioethics frog] Just a little cycle of FROG'S life cycle

5. Frog Embryology [http://embryology.med.unsw.edu.au/OtherEmb/Frog.htm UNSW Embryology]

6. Frog Research [http://apps.carleton.edu/campus/library/now/exhibits/wallcharts/frog/ carleton library exhibit]

{{Template:Projects09}}
[[Category:Frog]]

2009 Group Project 5

2009-10-14T22:36:23Z

Z3258567: /* History of frog embryology use */

== The Embryology of Frogs ==

== The Frog ==

[[Image: Frog species .jpg|thumb|left|Image details: Wikipedia (2009) Frog species[http://en.wikipedia.org/wiki/Frog#Uses_in_agriculture_and_research].jpg]]

Frogs are scientifically identified by the structure of their long posterior limbs, a petite framework, webbed fingers and feet, budged eyes and the lack of a tail. The majority of frog species are extensively recognized as outstanding jumpers, due to their long, dominant legs, which are adaptations to progress jumping performance during activities. The Frog is one of the most frequently studied species in experimental embryology and most anatomical sciences. ''The Frog is a practically effective model for human embryological development given that the Frog:''

- Comprises of genes which can be effectively manipulated.

- Comprises of similar homogeny with humans species.

- Reproduces a large quantity of offspring in a short period of time.

- Are small species which can be simply sustained.

- Are not extremely luxurious and expensive.

== The History of the uses in agriculture and research ==

[[Image: Frog experiments .jpg|thumb|right|Image details: Scans of chemically cleared and dyed preserved deformed frogs and toads [http://www.sat.qc.ca/upload/residence/frog-04.jpg].jpg]]

There are numerous types of frog species that have been manipulated in many developmental experiments. The frog was traditionally used by countless of the early embryology investigators and presently there are several diverse molecular mechanisms regarding progression of the frog. Theses include:

'''1.''' Food source; frog legs are a delicacy and are eaten in European countries and in many parts of South American regions.

'''2.''' Frogs have the finest biochemical dissection of phenomena that take place in the egg and oocyte. Frogs are the evolutionarily closest to mammals, commonly used as a vertebrate model.

'''3.''' Frogs lay thousands of outsized eggs, from which cell extracts can be readily prepared that is capable of recapitulating most molecular phenomena in a test tube.

'''4.''' Frogs have been commonly used as a laboratory system for a very long period, and have an extensive history of producing crucial observations in countless fields of biology.

'''5.''' Frogs have a important historical connection to the study of epigenetics (John Gurdon-vertebrate cloning and reprogramming) which has been mostly performed on frog species.

'''6.''' Frogs also have very strong evidence of pattern formation and early development, as the embryos are large in size and experimentally manipulative.

'''7.''' Recent research into the biochemistry of chromatin and epigenetics has been performed with frog species and mammalian cultured cells.

'''8.''' The biggest weakness of the Frog model system is the difficulty of performing genetic experiments and analysis, as frogs are allotetraploid, meaning they take approximately a year to fully develop to sexual maturity, and the genome has not been completely sequenced. Nevertheless, biochemical manipulations of cell extracts, such as immunodepletions and application of heterologous DNAs and nuclei can avoid the need for genetic exploitation.

----

== Growth and development of the Frog ==

[[Image: Mature develop frog.jpg|thumb|Image details: Wikipedia (2009) Red Eyed Tree Frog Figure 1 Primary source:[http://en.wikipedia.org/wiki/File:Red-eyed_Tree_Frog_-_Litoria_chloris_edit1].jpg]]

* The frog is a well recognised species, abundant predominantly in ponds, swamps, though various species may also exist in damp or shady environments distant from moist habitats.

* Eggs of specific frogs are easily obtained and may be examined in from the beginning of fertilization onwards. The phases of embryonic development differs in various chordates, yet the typical phases are basically apparent in all frog species. The differences are associated principally to the amount of yolk particles present in an egg.

* The yolk particles offer nourishment of the developing embryo. The process of frog development will be discussed from the phases of gametogenesis to the adult stage.

----

== The Egg ==
[[Image:Development of Poles in frog Fertilization.jpg|thumb|left|Development of Poles in Frog Fertilisation:J,Nassif 2009.jpg]]

- The embryology of a frog egg is a vast cell; its dimensions are approximately 1.4-1.6 million times larger than a typical aquatic species egg cell. Throughout the frog’s embryonic maturation period, the egg will be transformed into a tadpole encompassing millions of cells but still remains with its constant volume of genetic material, the vast prodction of cell have been illusttrated in the figure on the right revealing the production of eggs from female frogs. [http://en.wikipedia.org/wiki/Microhylidae]

- The early embryonic frog structure consists of three main segments the superior hemisphere known as the animal pole which is usually visible as a grey coloured area. The innermost layer appears to be between the outer two sections known as the gray crescent represented in black. Inferiorly, represents the vegetal pole typically lighter than the superior compartment illustrated in gold.

VIDEO RESOURCE: [http://www.youtube.com/watch?v=GO5YN_t1fqw&feature=related]

[[Image:Early Development of Frogs.jpg|thumb|left|Figure 3 Image details:J,Nassif 2009.jpg]]

==History of frog embryology use ==

*'''1851''' - ''Henby Nelson''(MD): He identified a remarkable fact through the frog embryo. Henby observed the first cleavage of the yolk, in the egg of the frog. And cleaved structure corresponds in line of direction to the longitudinal axis of the body of the embryo of the frog species.

[[Image:Wilhelm Roux.jpg|thumb|right|Wilhelm Roux[http://images.google.com.au/imgres?imgurl=http://www.todayinsci.com/R/Roux_Wilhelm/RouxWilhelmThm.jpg&imgrefurl=http://www.todayinsci.com/6/6_09.htm&usg=__qRLTEMTHdZpAHxiNX12hWjcm9tA=&h=125&w=100&sz=4&hl=en&start=2&um=1&tbnid=LIKIwZTqCpk7MM:&tbnh=90&tbnw=72&prev=/images%3Fq%3DWilhelm%2BRoux%26gbv%3D2%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

*'''1888''' - ''Wilhelm Roux'': Wilhelm Roux attempted to solve the above observation by damaging one cell of a two-cell frog embryo with a hot needle. The cell stayed in place. However, it did not develop further. Its partner developed into a left or right half-embryo;

*'''1907''' - ''John Hopkins'' hospital: In order to identify the cellular source of neuronal fibres. Scientist placed small portions of frog embryo spinal cords in lymph on a microscope slide and was able to observe clear cut neuronal sprouting.

*'''1951''' - ''Robert Briggs'': Robert Briggs was able to clone a frog embryo by substituting the nucleus of an unfertilized frog egg cell with the nucleus of a frog embryo cell. This process is known as nuclear transplant, has formed the basis for all cloning.

*'''1952''' - ''Robert Briggs and T.J. King'': Robert Briggs and T.J. King used frog for test experiment. Because the size of the eggs in the frogs are enormous compared with those of mammals, which make them easier to manipulate.

*'''1976'''- Using the technique that had been successful in cloning frog embryos, the doctor transferred the nucleus of one cells into a donated egg cell. As an embryo began to develop, it was implanted into the uterus of a young woman.

*'''1997''' - ''Wilmut and Campbell'': Utilizing the cloning technique from frog embryo, Drs. Wilmut and Campbell tried the starvation technique on embryo cells to produce Megan and Morag, the world's first cloned sheep and, until now, the most famous sheep in history.

*'''2000''' - ''Tokyo University'': Scientists at Tokyo University have grown artificial eyeballs. Scientists formed them in tadpoles by using frog embryo cells.

*'''2001''' - ''Advanced Cell Technology'': Scientists from Advanced Cell Technology announced production of a human embryo clone. This is significant as its parthenogenesis has been artificially induced in frogs.

[[Image:John Gurdon .jpg|thumb|right|John Gurdon [http://images.google.com.au/imgres?imgurl=http://www.pnas.org/site/misc/images/gurdon.jpg&imgrefurl=http://www.pnas.org/site/misc/classics4.shtml&usg=__1p-GA1PdOYsxKL-cznMb3RHCm98=&h=526&w=400&sz=223&hl=en&start=1&um=1&tbnid=9k4lhuLssiWCAM:&tbnh=132&tbnw=100&prev=/images%3Fq%3DJohn%2BGurdon%26gbv%3D2%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

*'''2002''' - ''John Gurdon'': John Gurdon from Wellcome Cancer Research Institute in Cambridge experimented on cloned frog embryo.

== Gametogenesis ==

* The sexual reproduction occurs through the fusion of either mature reproductive cells or germ cells known as gametes, which include the sperm from the male frog and ova from female frog species so as to form a single cell, the fertilized zygote. The gametes are typically developed in parents of different sexes . [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

* Males gametes is a spermatozoon , the female frog gamete is an ovum. Each gamete is formed by a process, recognised as maturation or gametogenesis in gonads. The typical male frog gonads are testies in male, while the female gonads are ovaries. The synthesis of both gonads is associated with the process of fertilization. [http://en.wikipedia.org/wiki/Microhylidae]

* The zygote changes into a mature frog through the process of embryology and metamorphosis. Gametogenesis is a in progression which frog gametes are established from germ cells. Initial germ cells are called primordial germ cells, which can be recognised extremely early in the life of frog species.

----

== The Egg & Fertilization ==

[[Image:Fertilized and Unfertilised Eggs.jpg|thumb|left|Figure 6 Image details:J,Nassif 2009.jpg]]

[[Image:Egg Development.jpg|thumb|left|Figure 7 Image details:J,Nassif 2009.jpg]]

- This occurs once the sperm cell has inserted, following the insertion of the sperm cells meiosis II is completed, there is a 30 degree position change of the cytoplasm, gray crescent allows this change to be visible in some amphibians, the gray crescent is able what determines the expect ted outline of how the frog will form. The sperm cell joins with the nuclei of the egg which forms the diploid zygote nucleus. --Sando Rashed 10:09, 24 September 2009 (EST)

- The early phases in the development of the egg is visible, but must be studied in tadpoles throughout maturation. In embryonic tadpoles of about 10 millimetres in length, soon after the opening of the oral cavity, a pair of longitudinal ridge-like thickenings of peritoneum becomes apparent along the posterior surface of the body cavity situated near to the mesentery and along the inner boundaries of the kidneys. Genital ridges are established in all tadpoles of this age, sex is not distinct until a later period. The development of the egg is illustrated in the figure on the left revealing the structure of a developed egg and a mature of egg.

[[Image:Fertilisation life cyle.jpg|thumb|Figure 8 Image details:Derived from primary source:[http://en.wikipedia.org/wiki/Frog]]]

== Maturation of the Egg ==

- The eggs have currently accomplished their full size, and develop from the exterior of the ovaries like a small shot, but they still have to pass through the course of maturation before they are prepared to be fertilised. This progression of maturation relates to the nucleus almost completely.

- The nucleus component, containing the nuclear fluid that excludes through the nuclear membrane into the substance of the egg, a great segment of the nuclear reticulum vanishes and becomes degraded into separate globules known as nucleoli, but a extremely small division remains in the midpoint as a slender intricately thread recognised as the nuclear skets.
Relative to the egg getting discharged from the ovary, the follicles shatter allowing the eggs to fall into the abdominal cavity of the frog species, the egg then passes forwards, directly by the contraction of the muscular wall, somewhat by the movement of the cilia of the peritoneum, to the apex of the oviduct, which positioned at the anterior compartment of the body cavity opposite to the roots of the respiratory organs.

- The terminal part of the oviduct establishes a thin-walled pouch capable of great swelling, inside which the eggs gathers in large numbers. In conclusion, the eggs are migrated out through the cloaca into water which the albuminous investments of the eggs rapidly augment to form the gelatinous mass of the frogs spawn.

== Maturation phases ==

'''1. Nuclear skein''', moves from the midpoint of the egg to its outer surface, which it reaches opposite the midpoint of the black pole. The skein, subsequently an unevenly twisted thread, now presumes the specific arrangement of a nuclear spindle, for instance may be visible in the nucleus of an epithelial or additional cell instantly prior to division of the cell occurs.[http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

'''2. The first Polar Body,''' regarding the instance the egg is laid, but prior to its fertilistion, the egg develops a considerably flattened appearance at its upper or black pole, a definite sum of fluid being exuded among the egg and the vitelline membrane. The nuclear spindle currently separate into two identical segments, one of which remains with the egg, and the supplementary is extruded as the first polar body, a small ovoidal white globule, which is situated on the surface of the egg surrounding the exuded peri-vitellline fluid.

'''3. The Second Polar Body''', half of the nuclear spindle that stay behind then splits into two equivalent divisions, one of which remains inside the egg as the female pronucleus, whereas the other segment is extruded as the second polar body, a small white globule extremely related to the first polar body, and like this positioned in the perivitelline fluid on the superior portion of the egg.

'''4. Fertilisation of the egg''', includes the synthesis of the spermatozoon with to egg, specifically, synthesis of the nuclei of these two bodies. The spermatozoa, subsequent to being shed over the seed by the male, distribute vigorously by means of their extended tails, break through the gelatinous investment of the female eggs, bore their way through the vitelline membrane and so go through into the eggs themselves, which they penetrate relative to the superior or black hemispheres.
* Subsequently, an hour following the spermatozoon has entered; a progression may be visible projecting within from the exterior segement of the egg, with a liquid spot in the mid point. This liquid centre is the nucleus of the spermatozoon, and is said to be the male pronucleus, it break through beyond into the female egg, transporting the specialised pigment into it, so that it appears bounded by a pigmented capsule linked with the exterior of the egg by a pigmented stalk.

* By this instance, the second polar body has been established and extruded, and the female pronucleus is merely the only component of the primary egg nucleus still present. Both the male and female pronuceli, which are at initially distance separate to each other, merge and after having enlarged significantly in size then fuse mutually about two and half hours after fertilisation has originated to produce the segmentation nucleus.
* The segmentation nucleus is a huge sphere-shaped vesicle embedded in delicately granular protoplasm, and bounded by a distinct capsule of pigment, its arrangement by the synthesis of the male and female pronuclei completes the action of fertilisation. Specifically female pronucleus may be observe as an imperfect nucleus, and consequently result in the course of fertilisation. The nucleus of the spermatozoon or male pronucleus, replaces the component of the egg- nucleus which has been misplaced as the polar bodies.

'''5. Segmentation of the Egg''', the initial phase of growth consist in constant separation of the egg, whereby it becomes transformed from the unicellular state, which is everlasting only in the lowest species, to muliticelluar state charactertics of all higher species. To these early processes of growth the names segmentation is specified. Shorty subsequent to the competition of fertilisation and arrangement of the segmentation nucleus this later misplaces its sphere-shaped appearance and develops to be spindle-shaped, the yolk granules at the equivalent instance showing a tendency to develop into lines distributing outwards from the distal segment of the spindle.
* The nucleus now split into two halves, which shift away from one another, the yolk granules are likely to combined themselves around the two nuclei, and a slender vertical plate of delicately granular substance is left, dividing the egg.[http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

* Superiorly the eggs depression now becomes visible, initially as a small cavity and then develops as a groove, which almost immediately extends all round, and speedily deepening, splits the egg into two entirely separate halves along a plane equivalent with the vertical plane.

* Shorty after, the two nuclei soon separate again into two, and therefore a second cleft is created in the same state as before, its additionally in the vertical plane, however in a plane at 90 degrees to the initial one, and on its finishing point the egg comprises of four accurately similar segments, each containing a nucleus. The third cleft is horizontal in shape, but not equal, lying closer to the superior than the lower pole, it segregates each of the four cells into, an superior smaller and a inferior larger pole

----

== Cleavage ==

[[Image: Frog Cleavage development.jpg|thumb|left|Figure 8.1 Image details:[http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/F/FrogEmbryology.html].jpg]]

* The egg of the frog is scientifically identified as’ telolecithal’ meaning there is a outsized amount of yolk concentrated at a single pole, in contrast to the concentration of cytoplasm and the site of the nucleus. The cleavage phases are holoblastic, therefore the total and after the second cleavage they are asymmetrical .The initial cleavage stage appears about two and half to three hours after fertilization. It commences as a minor depression in close proximity to the centre of the animal hemisphere. It appears as if some interior force is pushing the surface the egg towards the centre. This small upturned fold steadily continues in the form of a channel until it surrounds the egg. This groove is shallow in the commencement, but develop into deeper eventually separating the fertilized egg into two halves recognised as the blastomeres. [The figure on the left symbolise the development and growth of the frog embryo during cleavage].

* Internally the separation is mitotic, consequently each daughter cell contains a nucleus resulting from the copulation nucleus of the fertilised egg. This cleavage is vertical, the two cells are indistinguishable in respect of cytoplasm, pigment and yolk. The subsequent cleavage appears about an hour after the first. The channel of this cleavage begins at the centre of the animal hemisphere, is at right angles to the first and is vertical. This divides the egg into four blastomeres. The fourth blastomere so produced are not qualitatively equal, since of these only two contain the material from the gray crescent. The cleavage begins about thirty minutes after the second is completed or four hours after fertilisation. the cleavage plane of the third furrow is horizontal and slightly above the equator. Thus the four upper cells are a little smaller than the four lower cells. The smaller blastomeres are called micromeres and the larger blastomeres are called macromeres. The fourth cleavages follow 20 minutes after the third and tend to be vertical. This is usually a double furrow.

* The cleavage rate is accelerated with each of the early divisions and since the blastomeres are of unequal size and have varying amounts of cytoplasm and yolk, synchronous cleavage is lost and there is an obvious overlapping of the division. The upper most cells divide more rapidly than the lowermost cells. From this point onwards perfect symmetry in cleavage and in blastomere is very rare, although the embryo developed perfectly. The fifth cleavage is also doubled, appearing first in the upper hemisphere and then in the lower.

* The cleavage thus far follows the rule that each cleavage plane comes in at right angles to the previous one. The subsequent divisions become so irregular that it is previous one. The subsequent division become so irregular that it is impossible to trace out any plan or procedure. The segmentation continues more rapidly in the pigmented regions, since at that place the protoplasm is most dense, whereas, yolk which is very abundant in the vegetal side delays cell division. The multicelluar embryo at this stage is called morula by some biologists.

----

== Gastrulation ==

[[Image:FROG GASTRULATION .jpg|thumb|left|Figure Image details:[http://www.google.com.au/imgres?imgurl=http://bio1903.nicerweb.com/Locked/media/ch47/47_12FrogGastrulation.jpg&imgrefurl=http://bio1903.nicerweb.com/Locked/media/ch47/gastrulation-frog.html&h=540&w=480&sz=46&tbnid=N78sHjELreGGSM:&tbnh=132&tbnw=117&prev=/images%3Fq%3Dfrog%2B-%2Bgastrulation&hl=en&usg=__4VK9FYLft0W-4lBe6p5EtQAMiaI=&ei=qPy5SurtMJvE6wON8JmdAg&sa=X&oi=image_result&resnum=4&ct=image].jpg]]

''The phase of Blastulation is followed by the unique developmental progression of gastrulation. The process of frog gastrulation involves the following processes.''

'''1. Epiboly Phase'''

The pigmented cellular materials of blastula have the propensity to overgrow the yolk cells within the developing content. This course which is known as epiboly commences gradually in the final blastula and rapidly accelerates with advancing gastrulation development. The cellular matter within the animal pole reproduces and matures on all sides except in area surrounding the dorsal lip of the blastopore has been established.

'''2. Convergence'''

Scientists suggested that the unfolding was thought to result in spreading of the superficial cells over a substrate with suitable absorption properties. Consequently epiboly and convergence are an outcome to this spreading tendency, which is actually increased by a reduction in surface tension of the distributing cells.

'''3. Rotation'''

The epiboly phase is maintained until the region of the dorsal lip has migrated and is a to some extent greater than 90 degrees and the region of the white blastopore is reduced to small circular rings. This section will be positioned away from the developing vegetal pole. Laterally the complete developing gastrula has been rotated to a horizontal axis, allowing it to lie at right angles to the original median plane of the egg. Therefore, the course of rotation is such that the dorsal lip is practically pushed backwards in one direction as rapid or quicker than epiboly moves it forward in the other. The outcome will be that the blastopore produced at roughly the vegetal pole is posterior, and the dorsal and ventral lips are essentially dorsal and ventral. This in addition allows the eggs to form the antero-ventral side of the potential embryo whilst the area marked by the grey crescent is to develop the dorsal segment.

'''4. Invagination'''

Visible is a small fissure- like invagination which is apparent in the middle between the equator and the vegetal segment. The most superior or dorsal border of the cleft produce the dorsal lip of the blastopore. This imput move back and forth on the dorsal plane near the dorsal lip and migrates around the boundaries of the blastocoel in company with the extension of the lateral lips. This adapted invagination is maintained until the blastocoel cavity has been almost abolished; excluding the slender opening separating epiblasts from the hypoblast, the new segment formed is known as the archenteron cavity.

'''5. Involution'''

- Additional to previous course of action a distinct involution also occurs at the blastoporal borders. This is mainly dynamic at the median dorsal lip and gradually more less as it shifts across either side until it reaches the ventral lip where it constant.Throughout this progression, cells positioned beside the superior boundaries of the blastoporal lip migrate over the lip to the interior portion of the lip. These cells are remained within the embryo along the internal edge of the blastopore. This indicates the root of archenteron is composed of involuted cells and beyond this the external layer known as the ectoderm. The base and lateral sides are enclosed mainly of endodermal cellular material, which have been established from larger yolk cells, situated in the vegetal pole of the blastula.

- In the final phases of the gastrula development, the cells contributing to the floor of the archenteron, thin out significantly where they surround the blastocoel.
The hemispherical shaped dorsal lip of blastopore which become visible at the commencement of the gastruation stage carry on to augment, initially becoming semicircular, then transform into a horse shoe shaped and then finally forming into circular band. The band is the accomplished by the blastopore. Various yolk cells of vegetal pole present in the section are crowed into the blastoporal cavity where they form a gathering identified as a yolk plug. Blastopore rapidly reduces in size while the archenteron is still developing and becomes completely formed in the final stage; the yolk plug appears as only a small oval on the gastrula.

==Growth and Modification of Frog Species==

'''1. Changes in habits and habitats:'''

'''a)''' In frogs, metamorphosis is related with to the modifications and adaptations as a frog changes environmental habitats from an aquatic to a terrestrial mode. Metamorphosis has modified the adaption of frogs as this alteration it began during the aquatic adaptations in the surface of water to breathe air. Subsequently, it continues the terrestrial surroundings, therefore the frog species become abundant in vegetation area allowing the frog to transform in to amphibious species.

'''b)''' The transition during metamorphosis is linked with a change in food chain. The tadpoles being the embryonic origin of frogs are herbivorous, feeding on algae and green matter, which they collect by the adapted feature such as their teeth surrounding their mouths. Adult frogs, alternatively, are classified as carnivorous feeding on insects and worms. Occasionally, they also consume larger prey, for instance smaller frogs species and even little birds and rodents which they dominant and ingest.

[[Image:Development of frog from sperm to mature structure.jpg|thumb|left|Figure 9 Image details:J,Nassif 2009.jpg]]

'''2. Changes in Morphology'''

These include the decrease or complete absence of specific organs or structures which are essential during development of early frog embryology, but not critical in the mature frog species. The significant alterations of this nature include the following developmental structures.

'''a)''' The long tail of the tadpole alongside the fin folds is absorbed again during metamorphosis and becomes absent at the final stage of the metamorphosis.

'''b) '''The developing gills are resorted, the gill clefts are congested and the branchial cavities start to become absent. The reabsorbtion of gills also takes place by autolysis.

'''c)''' The teeth of the perioral disc additionally the homey lining of the jaws are shed.

'''d)''' The lateral line sense organs within the skin of tadpoles vanish throughout metamorphosis.

'''e)''' The cloacal tube begins to condensed and reduced.

'''f)''' Various blood vessels, together with parts of the aortic arches, are reduced during mature development.

(The figure on the left represents the transformation from a tadpole to a developing structure.)[http://science.jrank.org/pages/2862/Frogs-Adult-morphology.html]

'''3. Progressive or constructive changes'''

This process comprises of the development of specific organs which mature into functional systems only during metamorphosis.

'''a)''' During development the limbs continue to augment in size and differentiation. The forelimbs, which in the tadpole mature under the opercular membrane, which then break through to the exterior. Simultaneously there is a increase in the length and strength of the hind limbs, joints develop in them and the toes become visible.

'''b)''' The middle ear becomes apparent in relation with the first pharyngeal pouch. The tympanic membrane matures. It is bounded by circular tympanic cartilage which allows the frog to retain air.

'''c)''' The visual organs bulge up on the dorsal surface of the head developing the nictitating membrane.

'''d)''' There is augmentation of the tongue and the formation of thevomerina teeth.

[[Image: Growth model.jpg|thumb|Figure 10 Image details:J,Nassif2009:]]

'''4. Remodelling of some structures'''

Systematic organs which operate both in the early embryonic larva and the mature adult change their differentiation during metamorphosis so as to meet the requirements of the adult mode of life and due to the habitat adaptations. The figure on the right illustrates structures developing from specic germ cell layers.

'''a)''' The skin of the embryonic tadpole is lined with a double-layered epidermis. The number of layers of cells in the epidermis augments throughout metamorphosis. Superficial surface layers become cornified. Multicellular mucous and serous glands originate in the skin. The pigmentation of the skin continuously changes, new patterns and colour start to form.

'''b)''' There is a lengthening of the mouth gap as a result of rotation of the quadrate cartilage and the true jaws become functional.

'''c)''' The tongue rapidly progresses and becomes larger and more muscular.

'''d)''' The eyes become more specialised.

'''e)''' In early tadpoles, the GIT is extremely long and wound up into a spiral folds. The intestine become greatly lengthened in herbivorous species due to the vegetables food chain.[http://en.wikipedia.org/wiki/Frog]

'''5. Development of the reproductive system'''

(The figure below represents the reproductive and development cycle of a frog as it transform from egg to frog specie.)

In tadpoles, right after the mouth is being formed, two indentation like thickenings of peritoneum begin to appear near the body cavity (dorsal surface), which is nearest to the mesentery which is near the developing kidneys. These appear in all tadpoles.

These indentations appear here because of a change in the endothelial cells, everywhere else they are usually flat looking cells but they undergo a change and in this particular area become somewhat cuboidal/columnar.

Later on the indentations become more obvious due to the epithelial cells replicating numerously to form a thick layer. The posterior two thirds of the indentation for the female is the ovary and for the male it is the testis. The third that is left differentiates and becomes fat for the body.

[[Image: Mature frog life cyle.jpg|thumb|200px|left|Figure 11 Image details:Derived from primary source:http://www.scienceclarified.com/images/uesc_01_img0038.jpg]]

[[Image: Developing frog.jpg|thumb|Figure 12 Image details:
[[Image: Mature develop frog.jpg|thumb|Image details: Wikipedia (2009) TYPICAL FROG Primary source:[http://en.wikipedia.org/wiki/File:Red-eyed_Tree_Frog_-_Litoria_chloris_edit1.jpg]].jpg]]

===Delamination===

Delamination indicates a mass separating a group of cellular matter from other cellular groups. It has been illustrated that the division of notochord, mesoderm and endoderm tissues from each other to form distinct cellular masses is completed by the progression of delamination, subsequent to these materials moving to the inside throughout gastrulation. During the developing gastrula, the germ layers are all recognized. These distinct segments of the embryo develop from these germ tissue layers.

===Polarity and Rotation===

Throughout fertilisation to the beginning of gastrulation, the frog’s egg continues in the original location in relation to its polarity. Subsequent to gastrulation its polarity begins to differentiate. This progression is linked with migration of materials within the gastrula and can be responsible for the alterations of the centre of gravity.

===Closing of Blastopore===

Subsequent to the formation of the gastrula, the blastopore is visible as a tiny round circular filled cavity containing the yolk plug. As it continues to reduce in dimension, it represented as a pear-shaped outline through the mutual approach of its lateral lips. Through it final progression these fuse entirely to produce a longitudinal groove, the streak which continue dorsally and ventrally in a small aperture. The inferior aperture closes, resulting in a depression called the anal pit. The superior region remains open for some period and begins to as the neural groove is laid down.

===Post Gastrulation or Organogenesis===

Throughout the duration of pre-gastrulation, all tissues for different organs vanish from the surface of blastula and migrate inside to take their final arrangement in the embryo structure where organs are developed from their potential regions. Consequently organogenesis transfers an embryo into free larva structure.

----

==Germ-layer origin of various body tissues==
[[Image: Development Models of Frog.jpg|thumb|right|Figure 13 Image details:Vertebrate Structure and Development.jpg]]

Ectoderm will give raise to structures such as skin, brain, spinal cord, neurons and sense receptors.
Mesoderm will give raise to structrues such as notochord, muscles, blood, bone and sex organs.
Endoderm will give raise to sturctures such as inner lining of gut, liver, pancreas, lungs and bladder, thyroid and parathyroid glands and thymus.

== Structures derived from Germ-layers of frog species ==

[[Image:Development of Frog Layers.jpg|thumb|left|Figure 14 Primary source[http://www.bio.miami.edu/~cmallery/150/physiol/sf19x11b.jpg]Image details:J,Nassif 2009.jpg]]

[[Image:Development of frog layers.jpg|thumb|left|Figure 15 Primary source [http://www.bio.miami.edu/~cmallery/150/physiol/sf19x11b.jpg]Image details:J,Nassif 2009.jpg]]

'''Ectoderm '''

''Establishes the epidermal segments and its derivatives, to the frog’s nervous system. The ectoderm also contributes to :''

1. The olfactory and auditory epithelium.

2. The retina and lens of the eye.

3. Sensory organs.

4. The epithelial lining of the oral cavity and the anus.

5. The pineal and pituitary body.

'''Mesoderm'''

''Mesoderm originates:''

1. Connective tissue.

2. Muscles, except the notochord.

3. Blood vessels.

4. Lymphatics.

5. The peritoneum and the urinary and reproductive system.

6. The dermis, parts of the eye excluding lens, cornea, and conjunctiva.

'''Endoderm'''

''From the endoderm arises:''

1. The epithelial lining to the gut and oesophagus, stomach, intestine, bile duct.

2. The hepatic cells of the liver, respiratory tract, larynx, trachea and lungs.

3. The lining of the urinary bladder, pancreas thyroid and thymus.

[The two figures reveal the development of structures deriving from the celluar components of the embryology of the frog].[Structures derived from Germ-layers of frog species ]

==Life cycle of a frog==

'''Fertilization-egg''':

The female lays eggs in the spring. A group of fertilized eggs is called spawn;

'''7-10 days''':

Fertilized egg feed on remaining yolk which is in its gut. Their gills, mouth and tail have poorly developed. Begin to swim and feed on algae;

'''10-30 days(4 weeks):'''

A layer of skin grows over gills. Teeth begin to appear. A coiled gut start to develop. This is aid in digestion;

'''30-60 days(6-9 weeks):'''

Legs being to grow and head is more distinct. Start to eat insects. Arms begin to grow;

'''60-80 days(12 weeks):'''

Resemble a frog. Still have remaining tail;

'''80-140 days(20 weeks):'''

Fully developed, spend most of time out of water. Majority of frog live between 4-15 years.

==Timeline of frog development==

Development of egg and embryo at temperature 18 degree celsius.

'''0 hours''' - fertilization of the egg

'''1 hours''' - formation of the gray crescent due to pigment migration

'''3.5 hours''' - early cleavage

'''4.5 hours''' - blastula stage(coeloblastula with eccentric blastocoel

'''26 hours''' - gastrulation

'''26 hours''' -'' early'' - crescent shaped dorsal lip

'''34 hours''' - ''middle''- semicircular blastoporal lip

'''42 hours''' - ''late'' - circular blastoporal lip

'''50 hours''' - neurulation

'''50 hours''' - ''early'' - medullary plate

'''62 hours''' -'' middle''- neural folds converging

'''67 hours''' - ''late'' - neural tube formed and ciliation of embryo

'''84 hours''' - tail bud stage(early organogeny)

'''96 hours''' - muscular response to tactile stimulation

'''118 hours''' - early heart beat, development of gill buds

'''140 hours''' - hatching and gill circulation

'''162 hours''' - mouth opens and cornea becomes transparent

'''192 hours''' - tail fin circulation established

'''216 hours''' - degeneration of external gills, formation of operculum, development of embryonic teeth

'''240 hours''' - opercular fold over brachial chamber except for spiracle and internal gills

'''255 hours''' - prolonged larval stage with refinement of organs

'''270 hours''' - development of hindlimbs, internal development of forelimbs in opercular cavity

'''275 hours''' - projection of forelimbs through operculum, left side first

'''280 hours''' - absorption of the tail and reduction in size of the gut

'''284 hours''' - metamorphosis complete, emergence from water as miniature, air breathing frog

==Stages of frog embryology==
--[[User:S8600021|Mark Hill]] 08:40, 9 October 2009 (EST) [[Talk:2009_Group_Project_5#Constructive_Criticism_of_Coordinator|see my comment on images]]

The rate of development of the egg and embryo will depend upon the temperature at which they are kept. The approximate schedule of development at 23 degree celsius is provided below.

{| border='1px'
|+ Table 1: Stages of frog development
!Stage !!Time since fertilisation (hours)!!Stage Characteristic !!Embryo characteristic !!Image of frog stage
|-
|1
|0.00-1.30
|fertilization of the egg, post fertilization
|animal hemisphere, gray crescent and vegetal hemisphere are present
|[[File:Stage01ventral.jpg|100px]]
|-
|2
|1.30-2.00
|splits into two cells
|appearance of first cleavage furrow
|[[File:Stage02ventral.jpg|100px]]
|-
|3
|2.00-2.15
|becomes four cells
|appearance of second cleavage furrow
|[[File:Stage03dorsolat.jpg|100px]]
|-
|4
|2.15-2.45
|becomes eight cells
|appearance of third cleavage furrow
|[[File:Stage04dorsolat.jpg|100px]]
|-
|5
|2.45-3.00
|becomes sixteen cells
|appearance of fourth cleavage furrow
|[[File:Stage05dorsal.jpg|100px]]
|-
|6
|3.00-3.30
|becomes thirty-two cells
|appearance of fifth cleavage furrow
|[[File:Stage06animal.jpg|100px]]
|-
|6.5
|3.30-4.00
|blastula stage
|Three dorsal folds become visible as a result of endoderm invagination. Pole cells no longer visible on surface
|[[File:Stage065dorsal.jpg|100px]]
|-
|7
|4.00-5.00
|Gastrulation stage
|two primary germ layers. epiblast and endoderm
|[[File:Stage07ventral.jpg|100px]]
|-
|8
|5.00-7.00
|neurulation
|medullary plate, neural folds and neural tube
|[[File:Stage08animal.jpg|100px]]
|-
|9
|7.00-9.00
|germ layer
|complete lip involution encircling yolk
|[[File:Stage09veg.jpg|100px]]
|-
|10
|9.00-11.00
|early gastrula
|two primary germ layers
|[[File:Stage10veg.jpg|100px]]
|-
|10.5
|11.00-11.45
|gastrula
|two germ layers
|[[File:Stage105vegb.jpg|100px]]
|-
|11
|11.45-12.30
|medulla plate
|Yolk sac protrudes dorsally, labium moves to midline on ventral side
|[[File:Stage11veg.jpg|100px]]
|-
|11.5
|12.30-13.15
|continuation of medulla plate
|start closing the plate
|[[File:Stage115veg.jpg|100px]]
|-
|12
|13.15-14.15
|early neurula
|thickened ectoderm give rise to CNS
|[[File:Stage12veg.jpg|100px]]
|-
|12.5
|14.15-14.45
|neural folds
|expansion of cavity
|[[File:Stage125postdors.jpg|100px]]
|-
|13
|14.45-16.15
|neural folds
|continue expanding cavity
|[[File:Stage13postdors.jpg|100px]]
|-
|14
|16.15-17.30
|neural folds
|continuation of cavity
|[[File:Stage14postdors.jpg|100px]]
|-
|15
|17.30-18.15
|tail bud stage
|early organogeny
|[[File:Stage15postdors.jpg|100px]]
|-
|16
|18.15-18.45
|tail bud stage
|posterior ventral view
|[[File:Stage16ant.jpg|100px]]
|-
|17
|18.45-19.45
|tail bud stage
|anterior view
|[[File:Stage17ant.jpg|100px]]
|-
|19
|20.45-21.45
|neural fold close complete
|dorsal view
|[[File:Stage19dorsal.jpg|100px]]
|-
|20
|21.45-22.30
|early tail bud
|anterior view
|[[File:Stage20dorsal.jpg|100px]]
|-
|21
|22.30-24.00
|termination of neural crest
|progress to next stage
|[[File:Stage21ant.jpg|100px]]
|-
|22
|24.00-24.45
|prolonged development
|elongation
|[[File:Stage22lat.jpg|100px]]
|-
|23
|24.45-26.15
|elongation of embryo
|later view
|[[File:Stage23lat.jpg|100px]]
|-
|24
|26.15-27.30
|continuation of elongation of embryo
|dorsal view
|[[File:Stage24latsmall.jpg|50px]]
|-
|25
|27.30-29.30
|organs development
|embryo elongates and develops dorsal thickening
|[[File:Stage25dorsal.jpg|50px]]
|-
|26
|29.30-31.15
|elongation
|dorsally forms neural and brain cavity
|[[File:Stage26lat.jpg|50px]]
|-
|27
|31.15-32.30
|elongation of embryo
|dorsal view
|[[File:Stage27lat.jpg|50px]]
|-
|28
|32.30-35.00
|further development
|lateral view
|[[File:Stage28lat.jpg|50px]]
|-
|29-30
|35.00-37.30
|tail bud
|growth
|[[File:Stage29-30lat.jpg|50px]]
|-
|31
|37.30-40.00
|prolonged development
|bud development
|[[File:Stage31lat.jpg|50px]]
|-
|32
|40.00-44.30
|early muscular development
|elongation
|[[File:Stage32lat.jpg|50px]]
|-
|33-34
|44.30-50.00
|muscular movement
|apparatus for locomotion
|[[File:Stage33-34lat.jpg|50px]]
|-
|35-36
|50.00-53.30
|muscular movement
|apparatus for locomotion
|[[File:Stage35-36lat.jpg|50px]]
|-
|37-38
|53.30-56.30
|heart beat
|develops apparatus
|[[File:Stage37-38lat.jpg|50px]]
|-
|39
|56.30-66.00
|mouth opens
|cornea transparent
|[[File:Stage39latsmall.jpg|50px]]
|-
|40
|66.00-76.00
|gill circulation
|hatching
|[[File:Stage40lat.jpg|50px]]
|-
|41
|76.00-80.00
|tail, fin circulation
|circulation
|[[File:Stage41lat.jpg|50px]]
|-
|42
|80.00-86.00
|internal gills, operculum
|opercular fold, teeth
|[[File:Stage42lat.jpg|50px]]
|-
|43
|86.00-98.00
|operculum complete
|operculum closed on right
|[[File:Stage43lat.jpg|50px]]
|-
|46
|98.00-106.00
|metamorphosis
|emergence from water as miniature, operculum complete|
|[[File:Stage46lat.jpg|50px]]
|-
|}

==Abnormalities of frog==

Abnormalities of frog could be caused by multiple factors. These include change in climate, predators, parasites, bacteria, fungi, viruses or pollution and contaminants such as pesticides, metals and fertilizer.[http://www.fws.gov/contaminants/documents/frogsrefup_septoct_2006.pdf]

The Abnormalities are further classified into different categories. These categories are:

===1. Infectious Diseases:===

'''Perkinsus Symptoms-''' caused by perkinsus-like protozoan organism. Symptoms include swollen viscera that leads to a bloated body and and infected swollen heart

'''Ichthyophonus symptoms-''' cause by parasitic genus, where symptoms include a swollen tail resorption site that matches the surrounding skin in color and translucency.

[[Image:Abnormalities of Frog species.jpg|thumb|left|Figure A Image details[waterwatchadelaide.net.au].jpg]]

===2. Surficial Abnormalities:===

Surficial abnormalities as the one that are visible on the surface of the skin. This includes abnormal pigmentation, , subcutaneous hemorrhaging, wounds due to trauma or from a predator
Edema is a fluid-filled swelling under skin whihc is also a surficial abnormality.

===3. Skeletal Abnormalities:===

This is further classified into three more categories:

'''a. Skeletal Malformations-'''

* Microcephaly (small head or blunt snout)
*Scoliosis (Curved spine in lateral direction)
*Shrunken Limb (Micromelia)
*Amelia (Completely missing limb with no stump)

'''b. Skeletal Abnormalities of Unclear Etiology-'''

This condition arises when a frog has ectromelia (missing limb), brachydactyly (missing digits) or other such condition with no visible trauma or external damage, then this will be classified as the Skeletal abnormality of unclear etiology.

'''c. Skeletal Injuries-'''

Any limb missing or broken due to trauma or other related reason which shows clear evidence of it is classified as skeletal injury

===4. Eye Abnormalities:===

Most common includes-

'''i. Anophthalmia:''' Skin covers the eye socket as there is no eye

'''ii. Abnormal Iris Coloration:''' Reduced pigment in either one eye or both resulting in two different colours of the iris at times

'''iii. Abnormal size or shape:''' Both eyes either deviating from each other or size of pupil or iris is different than the other eye

[http://www.fws.gov/contaminants/Amphibian/pdfs/AbnormalitySOP_woutpics_Jan08.pdf ]

==Genetics==

There are a wide variety of species that differ from each other when it comes to genetics and their functioning.

'''TAXONOMY:''' '''Phylum''' ''Chordata'' / '''Sub Phylum''' ''Vertebrata'' / '''Class''' ''Amphibia'' / '''Order''' ''Anura''

Their are more than two dozen different families of frogs, where suborders are:

'''1. ARCHAEBATRACHIA-''' most primitive frogs

'''2. MESOBATRACHIA-''' linked between the Archaebatrachia and Neobatrachia

'''3. NEOBATRACHIA-''' most modern frogs

{| border='4px'
|+ '''General Info:'''
! !!
|-
| '''Number of frogs' species'''
| 5280
|-
| '''Smallest frog genome size:'''
| 0.95pg, Ornate burrowing frog
|-
| '''Largest frog genome size:'''
| 13.40pg, Ornate horned frog
|-
| '''Mean of frogs' genome'''
| 4.68pg ± 0.13
|-
|}

[http://www.genomesize.com]

*Majority of frogs have only 22 to 26 chromosomes and polyploid is very common where they are almost bisexual.

*Polyploid Amphibians reduce their total cell number such that they acheive the same body size as diploids. One of the most unsual forms of polypoidy in amphibians is the water frog ''Rana esculenta'' from Europe and Western Asia.

* The species with larger genomes have more genes for e.g. the frog genus ''Xenopus'' includes 16 species, with genome sizes ranging from 3.5 x 10^9 bp to 1.6 x 10^10 bp. These differences have arisen by numerous events of polyploidization within the past 40 million years or so. The ancestral chromosome number for the genus seems to have been 18, but there are species with 36, 72 and 105 chromosomes [http://www.xenbase.org/common/]

{| border='4px'
|+ '''Difference within two families'''
! '''SPECIES''' !! ''X.LAEVIS'' !! ''X.TROPICALIS''
|-
| '''PLOIDY'''
| Allotetraploid
| Diploid
|-
| '''NO. OF CHROMOSOMES'''
| 36 chromosomes
| 20 chromosomes
|-
| '''GENOME SIZE'''
| 3.1 x 10^9 bp
| 1.7 x 10^9 bp
|-
| '''EGG SIZE'''
| 1-1.3 mm
| 0.7-0.8 mm
|-
| '''GENERATION TIME'''
| 1-2 years
| 4 months
|-
|}
[http://www.xenbase.org/common/]

===Genome Sequencing===

Since Frog has a huge family with many different species, only few main species that are used widely for the purposes of experiments have their genome sequenced.

''Xenopus tropicalis'' has one of the smallest genomes among amphibians and has the shortest generation time- four to six months and the only diploid genome among the 14 Xenopus species. This means it has no more than two copies of most genes, whereas the other species of Xenopus have four copies of most genes (pseudotetraploid). US Department of Energy's Joint Genome Institute (JGI) in Walnut Creek, California, initiated the X. tropicalis Genome Project, finding 1,700 million base pairs.
[http://www.genome.gov/Pages/Research/Sequencing/BACLibrary/xenopusTropicalis.pdf]

===Xenopus oocytes===

* The oocytes provide an important expression system for molecular biology.

* By injecting DNA or mRNA into the oocyte or developing embryo, scientists can study the protein products in a controlled system. This allows rapid functional expression of manipulated DNAs (or mRNA). This is particularly useful in electrophysiology, where the ease of recording from the oocyte makes expression of membrane channels attractive.

* One challenge of oocyte work is eliminating native proteins that might confound results, such as membrane channels native to the oocyte.

* Translation of proteins can be blocked or splicing of pre-mRNA can be modified by injection of Morpholino antisense oligos into the oocyte (for distribution throughout the embryo) or early embryo (for distribution only into daughter cells of the injected cell).
[http://www.staff.unibe.ch/sigel/xenopus.html]

===Xenopus Laevis===

* ''Xenopus Laevis'' is an important model organism in developmental biology. X. laevis is tetraploid and reaches sexual maturity in 1 to 2 years. What makes it important in developmental biology is its large and easily manipulable embryo.

* Extracts from the eggs of X. laevis frogs are also commonly used for biochemical studies of DNA replication and repair, as these extracts fully support DNA replication and other related processes in a cell-free environment which allows easier manipulation.

* The Human chorionic gonadotropin hormone (hCG) is present in the urine of the pregnant women in large quantities only. This hormone in the urine induces X.laevis oocyte production which formed the basis of first well-documented method of pregnancy testing X. laevis is also notable for its use as the first well-documented method of pregnancy testing when it was discovered. Today, commercially available HCG is injected into Xenopus males and females to induce mating behavior and breed these frogs in captivity at any time of the year.

===Gene cluster===

* The alpha and beta globin genes are closely linked in small cluster of frogs compared to human and chicken

* The similarity of architecture of two clusters found in X.laevis supports the tetraploid origin

* The two loci encoding the muscle specific creatine kinase isoenzymes and have large differences in developmental profile, therefore suggesting that duplicate loci that have not undergone silencing are not simply redundant copies but have acquired specialization.

* Contains twice number of genes for proteins i.e. haemoglobin and sarcomeric actin serum albumin compared with other species

----

==Current Embrology Research==

Currently, a number of fields have benefited from the development of frog embrology. These include cloning, verification of messenger RNA, and Cell cycle.

===Cloning===
[[Image:Robert Briggs.jpg|thumb|left|Figure 16 Image details:Robert Briggs.jpg]]

In 1952, Robert Briggs and Thomas J King cloned northern leopard frogs using a method of nuclear transfer. Briggs and King's experiment was similar to that envisioned - and piloted using salamanders - by Hans Spemann in his 1938 proposal for a 'fantastical experiment'. Later, John Gurdon extended this work and showed that nuclei from differentiated cells could support development, although less well than those from early embryos. [http://genome.wellcome.ac.uk/doc_WTD020799.html]

Lemaitre et a. (2005) from MRC Cancer Cell Unit, Cambridge, U.K. worked on experiments that demonstrated that importance of serial nuclear transplantation for the sucessful cloning of frogs. He demonstrated that exposure of somatic-cell nuclei (erythrocyte nuclei) and sperm nuclei to an extract of mitotic cell extract reorganizes the chromatin into shorter loops and allows replication at much shorter intervals along the DNA. This increases the efficiency of DNA replication in mammalian cell-free systems.

===Transgenesis techniques for functional genomics in Xenopus===

Transgenesis in Xenopus is made possible due to large embryos, a reliable fate map, ease of microinjection, ease of dissection/micromanipulation and existence of the neuroendocrine reflex of background adaptation as a model for activation/inact.

Recently, Hajime Ogino and Haruki Ochi from Nura Institute of Science and Technology in Japan focused on the genomic resources and principles of the transgenesis techniques in Xenopus, and discusses their applications to genome wide network analysis, with emphasis on the use of bioinformatics tools. This is will to understand the gene regulatory networks that control vertebrate development. [http://www.ingentaconnect.com/content/bsc/dgd/2009/00000051/00000004/art00001%3Bjsessionid=4ah96rms73gcu.alexandra]

Xenopus used to be a problem in earlier days when it came to transgenesis. Current methods involves isolated sperm nuclei from Xenopus testis that are microinjected into unfertilized eggs. The generated transgenic tadpoles contain 5-35 copies of the integrated plasmid that are expressed in all cells. If desired, expression of the transgene can be directed to the appropriate tissue and at the appropriate time by using specific promoters, mostly the Xenopus POMC gene promoter (isolated from a Xenopus genomic DNA library) to specifically direct expression of green fluorescent protein (GFP) at high levels to the intermediate pituitary cells, which can either be over expressed or inhibited.[http://molanphys.ruhosting.nl/transgenesis.htm]

[[File:Transgenesis.JPG]]

===Verification of messenger RNA===

While the existence and role of messenger RNA (mRNA) was known in bacteria, in the 1960s it was still debated whether it also existed in vertebrates. Taking haemoglobin mRNA from immature red blood cells and injecting it into a Xenopus oocyte, John Gurdon showed that the haemoglobin protein was indeed produced. Producing proteins in Xenopus oocytes has proved to be extremely useful in cell biology, in particular for the study of receptor proteins.[http://genome.wellcome.ac.uk/doc_WTD020799.html]

===Cell Cycle===

As they develop outside the mother, frog eggs are well stocked with the proteins needed to drive the development of the embryo. Studies of these processes has shed considerable light on the processes involved in cell division - termed the cell cycle. [http://genome.wellcome.ac.uk/doc_WTD020799.html]

===Limb development in Xenopus Laevis===

[[Image: Frog Limb development.jpg|thumb|right|Image details:Primary source:[http://images.google.com.au/imgres?imgurl=http://www.sciencedaily.com/images/2006/06/060616130718.jpg&imgrefurl=http://www.sciencedaily.com/releases/2006/06/060616130718.htm&usg=__xliPsPAvheUBME_kjv_q7auiFbo=&h=333&w=300&sz=11&hl=en&start=2&um=1&tbnid=y_ntJtmkRSK7WM:&tbnh=119&tbnw=107&prev=/images%3Fq%3DLimb%2Bdevelopment%2Bin%2BXenopus%2BLaevis%26ndsp%3D18%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

Donald D. Brown (2005),Department of Embryology, Carnegie Institution of Washington demonstrated factors related to limb development of Xenopus Laevis. Thyroid hormone (TH) is found to be required for limb development in this frog. Specific cell types in the growing limb were targeted for expression of a dominant negative form of the TH receptor by sperm-mediated transgenesis. Limb muscle development, the innervation of muscle from the spinal cord, and cartilage growth can be inhibited without affecting patterning of the limb or differentiation of other cell types. Remodeling of the skin occurs late in metamorphosis after the limb has formed. The coordination of these independent programs is affected in part by the control that TH exerts over DNA replication in all cell types of the limb. [http://www.pnas.org/content/102/35/12455.full]

----

== Glossary ==

[[Image: Frog species.jpg|thumb|left|Image details:Primary source:www.olympus.co.jp/.../080925/large/p02L.jpg].jpg]]

*'''Amphibian:'''

''Relating to or characteristic of animals of the class amphibia.Amphibians are found in the taxonomic class of amphibia, amphibians are capable of both occupying and successfully living in both land and aquatic communities.amphibian''

*'''Augmentation:'''

''Enlargement/Increase in cellular size.''

*'''Autolysis:'''

''breakdown of a part or whole cell or tissue by self-produced enzymes''

*'''Blastomeres:'''

''The undifferentiated cells formed by cleavage of the fertilised ovum. This includes cells in the cleavage, morula, and blastula stages of the embryo''

*'''Carnivorous:'''
''
Flesh-eating; subsisting on animals as food.''

*'''Cleavage:'''

''he repeated division of a fertilised ovum ''

* '''Cleft:'''

''an opening, fissure, or V-shaped indentation made by or as if by splitting''

*'''Chordate:'''

''Members of a diverse phylum of animals that, as embryos, possess a (1) notochord; (2) a dorsal, hollow nerve cord, (3) pharyngeal gill slits; and (4) a post-anal tail''

''The act or state of splitting or dividing of a cell, particularly during the telophase of (animal) cell division.''

*'''Cytoplasm:'''

''The cytoplasm (of both eukaryotes and prokaryotes) is where the functions for cell expansion, growth, metabolism, and replication are carried out''

* '''Epiboly:'''
''The expansion of one cell sheet over other cells, as takes place during gastrulation''

*'''Fertilization:'''

''A process in sexual reproduction that involves the union of male (sperm) and female (ovum) gametes (each with a single, haploid set of chromosomes) to produce a diploid zygote.''

*'''Gamete:'''
''A reproductive cell (male (sperm) or female (egg)) that has only half the usual number of chromosomes''

*'''Gametogenesis:'''

''process leading to the production of gametes. The development and maturation of sex cells through meiosis.Another name for meiosis where a diploid cell is divided into two haploid cells with half the chromosome content of the diploid parent cell.''

*'''Herbivorous:'''

''eating plants; of or pertaining to the herbivora.''

*'''Holoblastic:'''

''The complete division of an isolecithal or microlecithal egg into blastomeres''

*'''Invagination:'''

''One of the methods by which the various germinal layers of the ovum are differentiated.''

*'''Isoenzymes:'''

''Isozymes (also known as isoenzymes) are enzymes that differ in amino acid sequence but catalyze the same chemical reaction.''

*'''Mesentery:'''

'' membranous fold attaching various organs to the body wall.''

*'''Metamorphosis:'''

''A change in the form and often habits of an animal after the embryonic stage during normal development.''

*'''Neuroendocrine:'''

''Neuroendocrine [IPA nʊəroʊˈɛndəkrɪn] cells are cells that release a hormone into the circulating blood in response to a neural stimulus.''

*'''Organogenesis:'''

''The part of embryonic development where the body's main organs develop.''

*'''Peritoneum:'''

''The smooth serous membrane which lines the cavity of the abdomen, or the whole body cavity when there is no diaphragm, and, turning back, surrounds the viscera, forming a closed, or nearly closed, sac.''

*'''Perivitelline space:'''

''The perivitelline space is the space between the zona pellucida and the plasma membrane (sometimes called the vitelline membrane) in a fertilized ovum.''

*'''Polyploidy:'''

''Cells with three or more sets of chromosomes.''

*'''Pronucleus:'''

''the nucleus of the ovum or sperm after fertilization but before they fuse to form the nucleus of the zygote ''

*'''Protoplasm:'''

''The fluid living content of the cell that consists of two major divisions, the cytoplasm and the nucleoplasm (cell nucleus). It is composed mainly of nucleic acids, proteins, lipids, carbohydrates, and inorganic salts''

*'''Segmentation:'''

''division of some metazoan bodies (such as annelida and Arthropoda) into repeated parts, segments. Segmentation can be homomeric (more or less the same) or heteromeric(different from each other).''

*'''Terrestrial:'''

''Of or on the ground, of the habitat of a plant, on land as opposed to in water, or on the ground as opposed to on another plant.''

*'''Transgenesis:'''

''Transgenesis is the process of introducing an exogenous gene - called a transgene - into a living organism so that the organism will exhibit a new property and transmit that property to its offspring.''

*'''Yolk:'''

''nutritive material of an ovum stored for the nutrition of an embryo''

*'''Zygote:'''

''The cell from which an organism develops, that results from the fertilization of the egg by the sperm.''

''Primary Resource "Biology- Online Dictionary''[http://www.biology-online.org/dictionary/Main_Page]

== References - Frog Embryology: ==

[[Image:Frog Research.jpg|thumb|left|Image details:[http://images.google.com.au/imgres?imgurl=http://www.odt.co.nz/files/story/2008/09/university_of_otago_zoology_senior_lecturer_phil_b_3343259744.jpg&imgrefurl=http://www.odt.co.nz/on-campus/university-otago/21670/dunedin-frog-man-wins-zoo-award&usg=__JvJJU5QfOnIwY2bk4xo64UXuJRs=&h=600&w=404&sz=22&hl=en&start=14&um=1&tbnid=AbsP89yWcUiilM:&tbnh=135&tbnw=91&prev=/images%3Fq%3Dfrog%2Bresearch%26hl%3Den%26um%3D1].jpg]]

1. Savage, J. M. (2002). The Amphibians and Reptiles of Costa Rica. University of Chicago Press, Chicago [http://www.springerlink.com/content/vv015277w1746llw/]

2. Ford, L.S.; D.C. Cannatella (1993). "The major clades of frogs". Herpetological Monographs 7: 94–117 [http://digimorph.org/specimens/Xenopus_laevis/]

3. Tyler, M. J. (1994). Australian Frogs A Natural History. Reed Books [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.gracilenta.html]

4. Cogger, H.G.; R.G. Zweifel, and D. Kirschner (2004). Encyclopedia of Reptiles & Amphibians Second Edition. Fog City Press [http://en.wikipedia.org/wiki/Microhylidae]

5. Beltz, Ellin (2005). Frogs: Inside their Remarkable World. Firefly Books [http://unjobs.org/authors/ellin-beltz]

6. Tyler, M. J. (1994). Australian Frogs A Natural History. Reed Books [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

7. Moury JD, Hanken J (1995) Early cranial neural crest migration in the direct-developing frog, Eleutherodactylus coqui. Acta
Anatomica (Basel) 153, 243-253.

8.Raynaud A (1985) Development of limbs and embryonic limb reduction. In Biology of the Reptilia (ed. Gans C, Billett F), pp.
59-148. New York: John Wiley.[http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=9309]

9. Hanken J (1986) Developmental evidence for amphibian origins. In Evolutionary Biology (ed. Hecht MK, Wallace B, Prance GT), 20, pp. 389-417. New York: Plenum Press. [Hanken J (1986) Developmental evidence for amphibian origins. In Evolutionary Biology (ed. Hecht MK, Wallace B, Prance GT), 20, pp. 389-417. New York: Plenum Press.]

10. Elinson RP (1990) Direct development in frogs : wiping the recapitulationist slate clean. Seminars in Developmental Biology
1, 263-270.

11. Beebee, T. J. C. 1996. Ecology and Conservation of Amphibians. Chapman and Hall. London. [http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V5X-3SVHMKH-1X&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=1021245355&_rerunOrigin=google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=825868e10cd178d16a8a0e5ad14dc5ef]

12. Lehtinen, R. M. 2002. The use of screw pines (Pandanus spp.) by amphibians and reptiles in Madagascar. Herpetological Bulletin 2002:20–25.

13. Parris, K. M. and M. A. McCarthy. 1999. What influences the structure of frog assemblages at forest streams. Australian Journal of Ecology 24:495–502. CrossRef

14. Zug, G. R. 1993. Herpetology: An Introductory Biology of Amphibians and Reptiles. Academic Press. San Diego, CA.

15. Slack,J.M.W., Darlington,B.G., Heath,J.K. and Godsave,S.F. (1987)Mesoderm induction in early Xenopus embryos by heparin-binding growth factors. Nature, 326, 197-200.

16. Melton,D.A. (1990) Activins are expressed early in Xenopus embryogenesis and can induce axial mesoderm and anterior structures. Cell, 63, 485-493.

17. Harland,R.M. and Misher,L. (1988) Stability of RNA in developing Xenopus embryos and identification of a destabilizing sequence in TFIIIA RNA. Development, 102, 837-852.

18. Cunliffe,V. and Smith,J.C. (1992) Ectopic mesoderm formation in Xenopus embryos caused by widespread expression of a Brachyury homologue. Nature, 358, 427-430.

19. Kinoshita,K., Bessho,T. and Asashima,M. (1993) Competence prepattern in the animal hemisphere of the 8-cell-stage Xenopus embryo. Devel. Biol., 160, 276-284.

20. LaBonne,C., Burke,B. and Whitman,M. (1995) Role of MAP kinase in mesoderm induction and axial patterning in Xenopus development. Development, 121, 1475-1486.

21. Green,J.B.A., New,H.V. and Smith,J.C. (1992) Responses of embryonic Xenopus cells to activin and FGF are separated by multiple dose thresholds and correspond to distinct axes of the mesoderm. Cell, 71, 731-739.

22. Grainger R., Blumberg B., Harland R., Amemiya C., Importance of Xenopus Tropicalis to biomedical and biological research, Benaroya Research Institute, Virginia Mason Research Center [http://www.genome.gov/Pages/Research/Sequencing/BACLibrary/xenopusTropicalis.pdf ]

23. Gregory, T.R. (2005). Animal Genome Size Database. [http://www.genomesize.com]

24. U.S Fish and Wildlife Services, ABNORMALITY CLASSIFICATION SOP, [http://www.fws.gov/contaminants/Amphibian/pdfs/AbnormalitySOP_woutpics_Jan08.pdf ]

25. Donald D. Brown*, Liquan Cai*, Biswajit Das*, Nicholas Marsh-Armstrong‡, Alexander M. Schreiber*, and Rejeanne Juste*(2005), Thyroid hormone controls multiple independent programs required for limb development in Xenopus laevis metamorphosis [http://www.pnas.org/content/102/35/12455.full]

26. Ogino, Hajime; Ochi, Haruki, Resources and transgenesis techniques for functional genomics in Xenopus, Development Growth & Differentiation, Volume 51, Number 4, May 2009 , pp. 387-401(15) [http://www.ingentaconnect.com/content/bsc/dgd/2009/00000051/00000004/art00001%3Bjsessionid=4ah96rms73gcu.alexandra]

27. Giles Newton (2004) Why the frog? The Human Genome, [http://genome.wellcome.ac.uk/doc_WTD020799.html]

28. Xenbase, [http://www.xenbase.org/common/]

29. Donders Center for Neuroscience & Nijmegen Center for Molecular Life Sciences (NCMLS), Beyond the genome (Xenopus transgenesis for functional genomics),Faculty of Science, Radboud University [http://molanphys.ruhosting.nl/transgenesis.htm]

== External Links ==
[[Image:Frog links.jpg|thumb|left|Image details:[http://images.google.com.au/imgres?imgurl=http://2.bp.blogspot.com/_o93AaY0GzH4/SjY_ZYv0PII/AAAAAAAAAgk/skruNc2yN78/s400/computer%2Bfrog.jpg&imgrefurl=http://hellaheaven-ana.blogspot.com/2009/06/talking-frog-contemporary-fairy-tale.html&usg=__oxji1TGLV2Fi7xe0dnlmuYk8gDo=&h=288&w=288&sz=16&hl=en&start=2&um=1&tbnid=ywZd4zpdxC5plM:&tbnh=115&tbnw=115&prev=/images%3Fq%3Dfrog%2Bon%2Bcomputer%26hl%3Den%26um%3D1].jpg]]

1. Frog embryology [http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/F/FrogEmbryology.html Frog Embryology]

2. Frog cellular materials [http://www.xenbase.org/xenbase/original/cell/cell.html xenbase]

3. The zoology of frog species [http://worms.zoology.wisc.edu/frogs/mainmenu.html zoology frogs]

4. Frog cycle [http://www.bioethics.gov/images/sc_images/frog_dev.gif bioethics frog] Just a little cycle of FROG'S life cycle

5. Frog Embryology [http://embryology.med.unsw.edu.au/OtherEmb/Frog.htm UNSW Embryology]

6. Frog Research [http://apps.carleton.edu/campus/library/now/exhibits/wallcharts/frog/ carleton library exhibit]

{{Template:Projects09}}
[[Category:Frog]]

2009 Group Project 5

2009-10-14T22:35:41Z

Z3258567: /* The Egg */

== The Embryology of Frogs ==

== The Frog ==

[[Image: Frog species .jpg|thumb|left|Image details: Wikipedia (2009) Frog species[http://en.wikipedia.org/wiki/Frog#Uses_in_agriculture_and_research].jpg]]

Frogs are scientifically identified by the structure of their long posterior limbs, a petite framework, webbed fingers and feet, budged eyes and the lack of a tail. The majority of frog species are extensively recognized as outstanding jumpers, due to their long, dominant legs, which are adaptations to progress jumping performance during activities. The Frog is one of the most frequently studied species in experimental embryology and most anatomical sciences. ''The Frog is a practically effective model for human embryological development given that the Frog:''

- Comprises of genes which can be effectively manipulated.

- Comprises of similar homogeny with humans species.

- Reproduces a large quantity of offspring in a short period of time.

- Are small species which can be simply sustained.

- Are not extremely luxurious and expensive.

== The History of the uses in agriculture and research ==

[[Image: Frog experiments .jpg|thumb|right|Image details: Scans of chemically cleared and dyed preserved deformed frogs and toads [http://www.sat.qc.ca/upload/residence/frog-04.jpg].jpg]]

There are numerous types of frog species that have been manipulated in many developmental experiments. The frog was traditionally used by countless of the early embryology investigators and presently there are several diverse molecular mechanisms regarding progression of the frog. Theses include:

'''1.''' Food source; frog legs are a delicacy and are eaten in European countries and in many parts of South American regions.

'''2.''' Frogs have the finest biochemical dissection of phenomena that take place in the egg and oocyte. Frogs are the evolutionarily closest to mammals, commonly used as a vertebrate model.

'''3.''' Frogs lay thousands of outsized eggs, from which cell extracts can be readily prepared that is capable of recapitulating most molecular phenomena in a test tube.

'''4.''' Frogs have been commonly used as a laboratory system for a very long period, and have an extensive history of producing crucial observations in countless fields of biology.

'''5.''' Frogs have a important historical connection to the study of epigenetics (John Gurdon-vertebrate cloning and reprogramming) which has been mostly performed on frog species.

'''6.''' Frogs also have very strong evidence of pattern formation and early development, as the embryos are large in size and experimentally manipulative.

'''7.''' Recent research into the biochemistry of chromatin and epigenetics has been performed with frog species and mammalian cultured cells.

'''8.''' The biggest weakness of the Frog model system is the difficulty of performing genetic experiments and analysis, as frogs are allotetraploid, meaning they take approximately a year to fully develop to sexual maturity, and the genome has not been completely sequenced. Nevertheless, biochemical manipulations of cell extracts, such as immunodepletions and application of heterologous DNAs and nuclei can avoid the need for genetic exploitation.

----

== Growth and development of the Frog ==

[[Image: Mature develop frog.jpg|thumb|Image details: Wikipedia (2009) Red Eyed Tree Frog Figure 1 Primary source:[http://en.wikipedia.org/wiki/File:Red-eyed_Tree_Frog_-_Litoria_chloris_edit1].jpg]]

* The frog is a well recognised species, abundant predominantly in ponds, swamps, though various species may also exist in damp or shady environments distant from moist habitats.

* Eggs of specific frogs are easily obtained and may be examined in from the beginning of fertilization onwards. The phases of embryonic development differs in various chordates, yet the typical phases are basically apparent in all frog species. The differences are associated principally to the amount of yolk particles present in an egg.

* The yolk particles offer nourishment of the developing embryo. The process of frog development will be discussed from the phases of gametogenesis to the adult stage.

----

== The Egg ==
[[Image:Development of Poles in frog Fertilization.jpg|thumb|left|Development of Poles in Frog Fertilisation:J,Nassif 2009.jpg]]

- The embryology of a frog egg is a vast cell; its dimensions are approximately 1.4-1.6 million times larger than a typical aquatic species egg cell. Throughout the frog’s embryonic maturation period, the egg will be transformed into a tadpole encompassing millions of cells but still remains with its constant volume of genetic material, the vast prodction of cell have been illusttrated in the figure on the right revealing the production of eggs from female frogs. [http://en.wikipedia.org/wiki/Microhylidae]

- The early embryonic frog structure consists of three main segments the superior hemisphere known as the animal pole which is usually visible as a grey coloured area. The innermost layer appears to be between the outer two sections known as the gray crescent represented in black. Inferiorly, represents the vegetal pole typically lighter than the superior compartment illustrated in gold.

VIDEO RESOURCE: [http://www.youtube.com/watch?v=GO5YN_t1fqw&feature=related]

[[Image:Early Development of Frogs.jpg|thumb|left|Figure 3 Image details:J,Nassif 2009.jpg]]

==History of frog embryology use ==

*'''1851''' - ''Henby Nelson''(MD): He identified a remarkable fact through the frog embryo. Henby observed the first cleavage of the yolk, in the egg of the frog. And cleaved structure corresponds in line of direction to the longitudinal axis of the body of the embryo of the frog species.

[[Image:Wilhelm Roux.jpg|thumb|right|Wilhelm Roux[http://images.google.com.au/imgres?imgurl=http://www.todayinsci.com/R/Roux_Wilhelm/RouxWilhelmThm.jpg&imgrefurl=http://www.todayinsci.com/6/6_09.htm&usg=__qRLTEMTHdZpAHxiNX12hWjcm9tA=&h=125&w=100&sz=4&hl=en&start=2&um=1&tbnid=LIKIwZTqCpk7MM:&tbnh=90&tbnw=72&prev=/images%3Fq%3DWilhelm%2BRoux%26gbv%3D2%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

*'''1888''' - ''Wilhelm Roux'': Wilhelm Roux attempted to solve the above observation by damaging one cell of a two-cell frog embryo with a hot needle. The cell stayed in place. However, it did not develop further. Its partner developed into a left or right half-embryo;

*'''1907''' - ''John Hopkins'' hospital: In order to identify the cellular source of neuronal fibres. Scientist placed small portions of frog embryo spinal cords in lymph on a microscope slide and was able to observe clear cut neuronal sprouting.

*'''1951''' - ''Robert Briggs'': Robert Briggs was able to clone a frog embryo by substituting the nucleus of an unfertilized frog egg cell with the nucleus of a frog embryo cell. This process is known as nuclear transplant, has formed the basis for all cloning.

*'''1952''' - ''Robert Briggs and T.J. King'': Robert Briggs and T.J. King used frog for test experiment. Because the size of the eggs in the frogs are enormous compared with those of mammals, which make them easier to manipulate.

*'''1976'''- Using the technique that had been successful in cloning frog embryos, the doctor transferred the nucleus of one cells into a donated egg cell. As an embryo began to develop, it was implanted into the uterus of a young woman.

*'''1997''' - ''Wilmut and Campbell'': Utilizing the cloning technique from frog embryo, Drs. Wilmut and Campbell tried the starvation technique on embryo cells to produce Megan and Morag, the world's first cloned sheep and, until now, the most famous sheep in history.

*'''2000''' - ''Tokyo University'': Scientists at Tokyo University have grown artificial eyeballs. Scientists formed them in tadpoles by using frog embryo cells.

*'''2001''' - ''Advanced Cell Technology'': Scientists from Advanced Cell Technology announced production of a human embryo clone. This is significant as its parthenogenesis has been artificially induced in frogs.

[[Image:John Gurdon .jpg|thumb|right|John Gurdon [http://images.google.com.au/imgres?imgurl=http://www.pnas.org/site/misc/images/gurdon.jpg&imgrefurl=http://www.pnas.org/site/misc/classics4.shtml&usg=__1p-GA1PdOYsxKL-cznMb3RHCm98=&h=526&w=400&sz=223&hl=en&start=1&um=1&tbnid=9k4lhuLssiWCAM:&tbnh=132&tbnw=100&prev=/images%3Fq%3DJohn%2BGurdon%26gbv%3D2%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

*'''2002''' - ''John Gurdon'': John Gurdon from Wellcome Cancer Research Institute in Cambridge experimented on cloned frog embryo.

== Gametogenesis ==

* The sexual reproduction occurs through the fusion of either mature reproductive cells or germ cells known as gametes, which include the sperm from the male frog and ova from female frog species so as to form a single cell, the fertilized zygote. The gametes are typically developed in parents of different sexes . [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

* Males gametes is a spermatozoon , the female frog gamete is an ovum. Each gamete is formed by a process, recognised as maturation or gametogenesis in gonads. The typical male frog gonads are testies in male, while the female gonads are ovaries. The synthesis of both gonads is associated with the process of fertilization. [http://en.wikipedia.org/wiki/Microhylidae]

* The zygote changes into a mature frog through the process of embryology and metamorphosis. Gametogenesis is a in progression which frog gametes are established from germ cells. Initial germ cells are called primordial germ cells, which can be recognised extremely early in the life of frog species.

----

== The Egg & Fertilization ==

[[Image:Fertilized and Unfertilised Eggs.jpg|thumb|left|Figure 6 Image details:J,Nassif 2009.jpg]]

[[Image:Egg Development.jpg|thumb|left|Figure 7 Image details:J,Nassif 2009.jpg]]

- This occurs once the sperm cell has inserted, following the insertion of the sperm cells meiosis II is completed, there is a 30 degree position change of the cytoplasm, gray crescent allows this change to be visible in some amphibians, the gray crescent is able what determines the expect ted outline of how the frog will form. The sperm cell joins with the nuclei of the egg which forms the diploid zygote nucleus. --Sando Rashed 10:09, 24 September 2009 (EST)

- The early phases in the development of the egg is visible, but must be studied in tadpoles throughout maturation. In embryonic tadpoles of about 10 millimetres in length, soon after the opening of the oral cavity, a pair of longitudinal ridge-like thickenings of peritoneum becomes apparent along the posterior surface of the body cavity situated near to the mesentery and along the inner boundaries of the kidneys. Genital ridges are established in all tadpoles of this age, sex is not distinct until a later period. The development of the egg is illustrated in the figure on the left revealing the structure of a developed egg and a mature of egg.

[[Image:Fertilisation life cyle.jpg|thumb|Figure 8 Image details:Derived from primary source:[http://en.wikipedia.org/wiki/Frog]]]

== Maturation of the Egg ==

- The eggs have currently accomplished their full size, and develop from the exterior of the ovaries like a small shot, but they still have to pass through the course of maturation before they are prepared to be fertilised. This progression of maturation relates to the nucleus almost completely.

- The nucleus component, containing the nuclear fluid that excludes through the nuclear membrane into the substance of the egg, a great segment of the nuclear reticulum vanishes and becomes degraded into separate globules known as nucleoli, but a extremely small division remains in the midpoint as a slender intricately thread recognised as the nuclear skets.
Relative to the egg getting discharged from the ovary, the follicles shatter allowing the eggs to fall into the abdominal cavity of the frog species, the egg then passes forwards, directly by the contraction of the muscular wall, somewhat by the movement of the cilia of the peritoneum, to the apex of the oviduct, which positioned at the anterior compartment of the body cavity opposite to the roots of the respiratory organs.

- The terminal part of the oviduct establishes a thin-walled pouch capable of great swelling, inside which the eggs gathers in large numbers. In conclusion, the eggs are migrated out through the cloaca into water which the albuminous investments of the eggs rapidly augment to form the gelatinous mass of the frogs spawn.

== Maturation phases ==

'''1. Nuclear skein''', moves from the midpoint of the egg to its outer surface, which it reaches opposite the midpoint of the black pole. The skein, subsequently an unevenly twisted thread, now presumes the specific arrangement of a nuclear spindle, for instance may be visible in the nucleus of an epithelial or additional cell instantly prior to division of the cell occurs.[http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

'''2. The first Polar Body,''' regarding the instance the egg is laid, but prior to its fertilistion, the egg develops a considerably flattened appearance at its upper or black pole, a definite sum of fluid being exuded among the egg and the vitelline membrane. The nuclear spindle currently separate into two identical segments, one of which remains with the egg, and the supplementary is extruded as the first polar body, a small ovoidal white globule, which is situated on the surface of the egg surrounding the exuded peri-vitellline fluid.

'''3. The Second Polar Body''', half of the nuclear spindle that stay behind then splits into two equivalent divisions, one of which remains inside the egg as the female pronucleus, whereas the other segment is extruded as the second polar body, a small white globule extremely related to the first polar body, and like this positioned in the perivitelline fluid on the superior portion of the egg.

'''4. Fertilisation of the egg''', includes the synthesis of the spermatozoon with to egg, specifically, synthesis of the nuclei of these two bodies. The spermatozoa, subsequent to being shed over the seed by the male, distribute vigorously by means of their extended tails, break through the gelatinous investment of the female eggs, bore their way through the vitelline membrane and so go through into the eggs themselves, which they penetrate relative to the superior or black hemispheres.
* Subsequently, an hour following the spermatozoon has entered; a progression may be visible projecting within from the exterior segement of the egg, with a liquid spot in the mid point. This liquid centre is the nucleus of the spermatozoon, and is said to be the male pronucleus, it break through beyond into the female egg, transporting the specialised pigment into it, so that it appears bounded by a pigmented capsule linked with the exterior of the egg by a pigmented stalk.

* By this instance, the second polar body has been established and extruded, and the female pronucleus is merely the only component of the primary egg nucleus still present. Both the male and female pronuceli, which are at initially distance separate to each other, merge and after having enlarged significantly in size then fuse mutually about two and half hours after fertilisation has originated to produce the segmentation nucleus.
* The segmentation nucleus is a huge sphere-shaped vesicle embedded in delicately granular protoplasm, and bounded by a distinct capsule of pigment, its arrangement by the synthesis of the male and female pronuclei completes the action of fertilisation. Specifically female pronucleus may be observe as an imperfect nucleus, and consequently result in the course of fertilisation. The nucleus of the spermatozoon or male pronucleus, replaces the component of the egg- nucleus which has been misplaced as the polar bodies.

'''5. Segmentation of the Egg''', the initial phase of growth consist in constant separation of the egg, whereby it becomes transformed from the unicellular state, which is everlasting only in the lowest species, to muliticelluar state charactertics of all higher species. To these early processes of growth the names segmentation is specified. Shorty subsequent to the competition of fertilisation and arrangement of the segmentation nucleus this later misplaces its sphere-shaped appearance and develops to be spindle-shaped, the yolk granules at the equivalent instance showing a tendency to develop into lines distributing outwards from the distal segment of the spindle.
* The nucleus now split into two halves, which shift away from one another, the yolk granules are likely to combined themselves around the two nuclei, and a slender vertical plate of delicately granular substance is left, dividing the egg.[http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

* Superiorly the eggs depression now becomes visible, initially as a small cavity and then develops as a groove, which almost immediately extends all round, and speedily deepening, splits the egg into two entirely separate halves along a plane equivalent with the vertical plane.

* Shorty after, the two nuclei soon separate again into two, and therefore a second cleft is created in the same state as before, its additionally in the vertical plane, however in a plane at 90 degrees to the initial one, and on its finishing point the egg comprises of four accurately similar segments, each containing a nucleus. The third cleft is horizontal in shape, but not equal, lying closer to the superior than the lower pole, it segregates each of the four cells into, an superior smaller and a inferior larger pole

----

== Cleavage ==

[[Image: Frog Cleavage development.jpg|thumb|left|Figure 8.1 Image details:[http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/F/FrogEmbryology.html].jpg]]

* The egg of the frog is scientifically identified as’ telolecithal’ meaning there is a outsized amount of yolk concentrated at a single pole, in contrast to the concentration of cytoplasm and the site of the nucleus. The cleavage phases are holoblastic, therefore the total and after the second cleavage they are asymmetrical .The initial cleavage stage appears about two and half to three hours after fertilization. It commences as a minor depression in close proximity to the centre of the animal hemisphere. It appears as if some interior force is pushing the surface the egg towards the centre. This small upturned fold steadily continues in the form of a channel until it surrounds the egg. This groove is shallow in the commencement, but develop into deeper eventually separating the fertilized egg into two halves recognised as the blastomeres. [The figure on the left symbolise the development and growth of the frog embryo during cleavage].

* Internally the separation is mitotic, consequently each daughter cell contains a nucleus resulting from the copulation nucleus of the fertilised egg. This cleavage is vertical, the two cells are indistinguishable in respect of cytoplasm, pigment and yolk. The subsequent cleavage appears about an hour after the first. The channel of this cleavage begins at the centre of the animal hemisphere, is at right angles to the first and is vertical. This divides the egg into four blastomeres. The fourth blastomere so produced are not qualitatively equal, since of these only two contain the material from the gray crescent. The cleavage begins about thirty minutes after the second is completed or four hours after fertilisation. the cleavage plane of the third furrow is horizontal and slightly above the equator. Thus the four upper cells are a little smaller than the four lower cells. The smaller blastomeres are called micromeres and the larger blastomeres are called macromeres. The fourth cleavages follow 20 minutes after the third and tend to be vertical. This is usually a double furrow.

* The cleavage rate is accelerated with each of the early divisions and since the blastomeres are of unequal size and have varying amounts of cytoplasm and yolk, synchronous cleavage is lost and there is an obvious overlapping of the division. The upper most cells divide more rapidly than the lowermost cells. From this point onwards perfect symmetry in cleavage and in blastomere is very rare, although the embryo developed perfectly. The fifth cleavage is also doubled, appearing first in the upper hemisphere and then in the lower.

* The cleavage thus far follows the rule that each cleavage plane comes in at right angles to the previous one. The subsequent divisions become so irregular that it is previous one. The subsequent division become so irregular that it is impossible to trace out any plan or procedure. The segmentation continues more rapidly in the pigmented regions, since at that place the protoplasm is most dense, whereas, yolk which is very abundant in the vegetal side delays cell division. The multicelluar embryo at this stage is called morula by some biologists.

----

== Gastrulation ==

[[Image:FROG GASTRULATION .jpg|thumb|left|Figure Image details:[http://www.google.com.au/imgres?imgurl=http://bio1903.nicerweb.com/Locked/media/ch47/47_12FrogGastrulation.jpg&imgrefurl=http://bio1903.nicerweb.com/Locked/media/ch47/gastrulation-frog.html&h=540&w=480&sz=46&tbnid=N78sHjELreGGSM:&tbnh=132&tbnw=117&prev=/images%3Fq%3Dfrog%2B-%2Bgastrulation&hl=en&usg=__4VK9FYLft0W-4lBe6p5EtQAMiaI=&ei=qPy5SurtMJvE6wON8JmdAg&sa=X&oi=image_result&resnum=4&ct=image].jpg]]

''The phase of Blastulation is followed by the unique developmental progression of gastrulation. The process of frog gastrulation involves the following processes.''

'''1. Epiboly Phase'''

The pigmented cellular materials of blastula have the propensity to overgrow the yolk cells within the developing content. This course which is known as epiboly commences gradually in the final blastula and rapidly accelerates with advancing gastrulation development. The cellular matter within the animal pole reproduces and matures on all sides except in area surrounding the dorsal lip of the blastopore has been established.

'''2. Convergence'''

Scientists suggested that the unfolding was thought to result in spreading of the superficial cells over a substrate with suitable absorption properties. Consequently epiboly and convergence are an outcome to this spreading tendency, which is actually increased by a reduction in surface tension of the distributing cells.

'''3. Rotation'''

The epiboly phase is maintained until the region of the dorsal lip has migrated and is a to some extent greater than 90 degrees and the region of the white blastopore is reduced to small circular rings. This section will be positioned away from the developing vegetal pole. Laterally the complete developing gastrula has been rotated to a horizontal axis, allowing it to lie at right angles to the original median plane of the egg. Therefore, the course of rotation is such that the dorsal lip is practically pushed backwards in one direction as rapid or quicker than epiboly moves it forward in the other. The outcome will be that the blastopore produced at roughly the vegetal pole is posterior, and the dorsal and ventral lips are essentially dorsal and ventral. This in addition allows the eggs to form the antero-ventral side of the potential embryo whilst the area marked by the grey crescent is to develop the dorsal segment.

'''4. Invagination'''

Visible is a small fissure- like invagination which is apparent in the middle between the equator and the vegetal segment. The most superior or dorsal border of the cleft produce the dorsal lip of the blastopore. This imput move back and forth on the dorsal plane near the dorsal lip and migrates around the boundaries of the blastocoel in company with the extension of the lateral lips. This adapted invagination is maintained until the blastocoel cavity has been almost abolished; excluding the slender opening separating epiblasts from the hypoblast, the new segment formed is known as the archenteron cavity.

'''5. Involution'''

- Additional to previous course of action a distinct involution also occurs at the blastoporal borders. This is mainly dynamic at the median dorsal lip and gradually more less as it shifts across either side until it reaches the ventral lip where it constant.Throughout this progression, cells positioned beside the superior boundaries of the blastoporal lip migrate over the lip to the interior portion of the lip. These cells are remained within the embryo along the internal edge of the blastopore. This indicates the root of archenteron is composed of involuted cells and beyond this the external layer known as the ectoderm. The base and lateral sides are enclosed mainly of endodermal cellular material, which have been established from larger yolk cells, situated in the vegetal pole of the blastula.

- In the final phases of the gastrula development, the cells contributing to the floor of the archenteron, thin out significantly where they surround the blastocoel.
The hemispherical shaped dorsal lip of blastopore which become visible at the commencement of the gastruation stage carry on to augment, initially becoming semicircular, then transform into a horse shoe shaped and then finally forming into circular band. The band is the accomplished by the blastopore. Various yolk cells of vegetal pole present in the section are crowed into the blastoporal cavity where they form a gathering identified as a yolk plug. Blastopore rapidly reduces in size while the archenteron is still developing and becomes completely formed in the final stage; the yolk plug appears as only a small oval on the gastrula.

==Growth and Modification of Frog Species==

'''1. Changes in habits and habitats:'''

'''a)''' In frogs, metamorphosis is related with to the modifications and adaptations as a frog changes environmental habitats from an aquatic to a terrestrial mode. Metamorphosis has modified the adaption of frogs as this alteration it began during the aquatic adaptations in the surface of water to breathe air. Subsequently, it continues the terrestrial surroundings, therefore the frog species become abundant in vegetation area allowing the frog to transform in to amphibious species.

'''b)''' The transition during metamorphosis is linked with a change in food chain. The tadpoles being the embryonic origin of frogs are herbivorous, feeding on algae and green matter, which they collect by the adapted feature such as their teeth surrounding their mouths. Adult frogs, alternatively, are classified as carnivorous feeding on insects and worms. Occasionally, they also consume larger prey, for instance smaller frogs species and even little birds and rodents which they dominant and ingest.

[[Image:Development of frog from sperm to mature structure.jpg|thumb|left|Figure 9 Image details:J,Nassif 2009.jpg]]

'''2. Changes in Morphology'''

These include the decrease or complete absence of specific organs or structures which are essential during development of early frog embryology, but not critical in the mature frog species. The significant alterations of this nature include the following developmental structures.

'''a)''' The long tail of the tadpole alongside the fin folds is absorbed again during metamorphosis and becomes absent at the final stage of the metamorphosis.

'''b) '''The developing gills are resorted, the gill clefts are congested and the branchial cavities start to become absent. The reabsorbtion of gills also takes place by autolysis.

'''c)''' The teeth of the perioral disc additionally the homey lining of the jaws are shed.

'''d)''' The lateral line sense organs within the skin of tadpoles vanish throughout metamorphosis.

'''e)''' The cloacal tube begins to condensed and reduced.

'''f)''' Various blood vessels, together with parts of the aortic arches, are reduced during mature development.

(The figure on the left represents the transformation from a tadpole to a developing structure.)[http://science.jrank.org/pages/2862/Frogs-Adult-morphology.html]

'''3. Progressive or constructive changes'''

This process comprises of the development of specific organs which mature into functional systems only during metamorphosis.

'''a)''' During development the limbs continue to augment in size and differentiation. The forelimbs, which in the tadpole mature under the opercular membrane, which then break through to the exterior. Simultaneously there is a increase in the length and strength of the hind limbs, joints develop in them and the toes become visible.

'''b)''' The middle ear becomes apparent in relation with the first pharyngeal pouch. The tympanic membrane matures. It is bounded by circular tympanic cartilage which allows the frog to retain air.

'''c)''' The visual organs bulge up on the dorsal surface of the head developing the nictitating membrane.

'''d)''' There is augmentation of the tongue and the formation of thevomerina teeth.

[[Image: Growth model.jpg|thumb|Figure 10 Image details:J,Nassif2009:]]

'''4. Remodelling of some structures'''

Systematic organs which operate both in the early embryonic larva and the mature adult change their differentiation during metamorphosis so as to meet the requirements of the adult mode of life and due to the habitat adaptations. The figure on the right illustrates structures developing from specic germ cell layers.

'''a)''' The skin of the embryonic tadpole is lined with a double-layered epidermis. The number of layers of cells in the epidermis augments throughout metamorphosis. Superficial surface layers become cornified. Multicellular mucous and serous glands originate in the skin. The pigmentation of the skin continuously changes, new patterns and colour start to form.

'''b)''' There is a lengthening of the mouth gap as a result of rotation of the quadrate cartilage and the true jaws become functional.

'''c)''' The tongue rapidly progresses and becomes larger and more muscular.

'''d)''' The eyes become more specialised.

'''e)''' In early tadpoles, the GIT is extremely long and wound up into a spiral folds. The intestine become greatly lengthened in herbivorous species due to the vegetables food chain.[http://en.wikipedia.org/wiki/Frog]

'''5. Development of the reproductive system'''

(The figure below represents the reproductive and development cycle of a frog as it transform from egg to frog specie.)

In tadpoles, right after the mouth is being formed, two indentation like thickenings of peritoneum begin to appear near the body cavity (dorsal surface), which is nearest to the mesentery which is near the developing kidneys. These appear in all tadpoles.

These indentations appear here because of a change in the endothelial cells, everywhere else they are usually flat looking cells but they undergo a change and in this particular area become somewhat cuboidal/columnar.

Later on the indentations become more obvious due to the epithelial cells replicating numerously to form a thick layer. The posterior two thirds of the indentation for the female is the ovary and for the male it is the testis. The third that is left differentiates and becomes fat for the body.

[[Image: Mature frog life cyle.jpg|thumb|200px|left|Figure 11 Image details:Derived from primary source:http://www.scienceclarified.com/images/uesc_01_img0038.jpg]]

[[Image: Developing frog.jpg|thumb|Figure 12 Image details:
[[Image: Mature develop frog.jpg|thumb|Image details: Wikipedia (2009) TYPICAL FROG Primary source:[http://en.wikipedia.org/wiki/File:Red-eyed_Tree_Frog_-_Litoria_chloris_edit1.jpg]].jpg]]

===Delamination===

Delamination indicates a mass separating a group of cellular matter from other cellular groups. It has been illustrated that the division of notochord, mesoderm and endoderm tissues from each other to form distinct cellular masses is completed by the progression of delamination, subsequent to these materials moving to the inside throughout gastrulation. During the developing gastrula, the germ layers are all recognized. These distinct segments of the embryo develop from these germ tissue layers.

===Polarity and Rotation===

Throughout fertilisation to the beginning of gastrulation, the frog’s egg continues in the original location in relation to its polarity. Subsequent to gastrulation its polarity begins to differentiate. This progression is linked with migration of materials within the gastrula and can be responsible for the alterations of the centre of gravity.

===Closing of Blastopore===

Subsequent to the formation of the gastrula, the blastopore is visible as a tiny round circular filled cavity containing the yolk plug. As it continues to reduce in dimension, it represented as a pear-shaped outline through the mutual approach of its lateral lips. Through it final progression these fuse entirely to produce a longitudinal groove, the streak which continue dorsally and ventrally in a small aperture. The inferior aperture closes, resulting in a depression called the anal pit. The superior region remains open for some period and begins to as the neural groove is laid down.

===Post Gastrulation or Organogenesis===

Throughout the duration of pre-gastrulation, all tissues for different organs vanish from the surface of blastula and migrate inside to take their final arrangement in the embryo structure where organs are developed from their potential regions. Consequently organogenesis transfers an embryo into free larva structure.

----

==Germ-layer origin of various body tissues==
[[Image: Development Models of Frog.jpg|thumb|right|Figure 13 Image details:Vertebrate Structure and Development.jpg]]

Ectoderm will give raise to structures such as skin, brain, spinal cord, neurons and sense receptors.
Mesoderm will give raise to structrues such as notochord, muscles, blood, bone and sex organs.
Endoderm will give raise to sturctures such as inner lining of gut, liver, pancreas, lungs and bladder, thyroid and parathyroid glands and thymus.

== Structures derived from Germ-layers of frog species ==

[[Image:Development of Frog Layers.jpg|thumb|left|Figure 14 Primary source[http://www.bio.miami.edu/~cmallery/150/physiol/sf19x11b.jpg]Image details:J,Nassif 2009.jpg]]

[[Image:Development of frog layers.jpg|thumb|left|Figure 15 Primary source [http://www.bio.miami.edu/~cmallery/150/physiol/sf19x11b.jpg]Image details:J,Nassif 2009.jpg]]

'''Ectoderm '''

''Establishes the epidermal segments and its derivatives, to the frog’s nervous system. The ectoderm also contributes to :''

1. The olfactory and auditory epithelium.

2. The retina and lens of the eye.

3. Sensory organs.

4. The epithelial lining of the oral cavity and the anus.

5. The pineal and pituitary body.

'''Mesoderm'''

''Mesoderm originates:''

1. Connective tissue.

2. Muscles, except the notochord.

3. Blood vessels.

4. Lymphatics.

5. The peritoneum and the urinary and reproductive system.

6. The dermis, parts of the eye excluding lens, cornea, and conjunctiva.

'''Endoderm'''

''From the endoderm arises:''

1. The epithelial lining to the gut and oesophagus, stomach, intestine, bile duct.

2. The hepatic cells of the liver, respiratory tract, larynx, trachea and lungs.

3. The lining of the urinary bladder, pancreas thyroid and thymus.

[The two figures reveal the development of structures deriving from the celluar components of the embryology of the frog].[Structures derived from Germ-layers of frog species ]

==Life cycle of a frog==

'''Fertilization-egg''':

The female lays eggs in the spring. A group of fertilized eggs is called spawn;

'''7-10 days''':

Fertilized egg feed on remaining yolk which is in its gut. Their gills, mouth and tail have poorly developed. Begin to swim and feed on algae;

'''10-30 days(4 weeks):'''

A layer of skin grows over gills. Teeth begin to appear. A coiled gut start to develop. This is aid in digestion;

'''30-60 days(6-9 weeks):'''

Legs being to grow and head is more distinct. Start to eat insects. Arms begin to grow;

'''60-80 days(12 weeks):'''

Resemble a frog. Still have remaining tail;

'''80-140 days(20 weeks):'''

Fully developed, spend most of time out of water. Majority of frog live between 4-15 years.

==Timeline of frog development==

Development of egg and embryo at temperature 18 degree celsius.

'''0 hours''' - fertilization of the egg

'''1 hours''' - formation of the gray crescent due to pigment migration

'''3.5 hours''' - early cleavage

'''4.5 hours''' - blastula stage(coeloblastula with eccentric blastocoel

'''26 hours''' - gastrulation

'''26 hours''' -'' early'' - crescent shaped dorsal lip

'''34 hours''' - ''middle''- semicircular blastoporal lip

'''42 hours''' - ''late'' - circular blastoporal lip

'''50 hours''' - neurulation

'''50 hours''' - ''early'' - medullary plate

'''62 hours''' -'' middle''- neural folds converging

'''67 hours''' - ''late'' - neural tube formed and ciliation of embryo

'''84 hours''' - tail bud stage(early organogeny)

'''96 hours''' - muscular response to tactile stimulation

'''118 hours''' - early heart beat, development of gill buds

'''140 hours''' - hatching and gill circulation

'''162 hours''' - mouth opens and cornea becomes transparent

'''192 hours''' - tail fin circulation established

'''216 hours''' - degeneration of external gills, formation of operculum, development of embryonic teeth

'''240 hours''' - opercular fold over brachial chamber except for spiracle and internal gills

'''255 hours''' - prolonged larval stage with refinement of organs

'''270 hours''' - development of hindlimbs, internal development of forelimbs in opercular cavity

'''275 hours''' - projection of forelimbs through operculum, left side first

'''280 hours''' - absorption of the tail and reduction in size of the gut

'''284 hours''' - metamorphosis complete, emergence from water as miniature, air breathing frog

==Stages of frog embryology==
--[[User:S8600021|Mark Hill]] 08:40, 9 October 2009 (EST) [[Talk:2009_Group_Project_5#Constructive_Criticism_of_Coordinator|see my comment on images]]

The rate of development of the egg and embryo will depend upon the temperature at which they are kept. The approximate schedule of development at 23 degree celsius is provided below.

{| border='1px'
|+ Table 1: Stages of frog development
!Stage !!Time since fertilisation (hours)!!Stage Characteristic !!Embryo characteristic !!Image of frog stage
|-
|1
|0.00-1.30
|fertilization of the egg, post fertilization
|animal hemisphere, gray crescent and vegetal hemisphere are present
|[[File:Stage01ventral.jpg|100px]]
|-
|2
|1.30-2.00
|splits into two cells
|appearance of first cleavage furrow
|[[File:Stage02ventral.jpg|100px]]
|-
|3
|2.00-2.15
|becomes four cells
|appearance of second cleavage furrow
|[[File:Stage03dorsolat.jpg|100px]]
|-
|4
|2.15-2.45
|becomes eight cells
|appearance of third cleavage furrow
|[[File:Stage04dorsolat.jpg|100px]]
|-
|5
|2.45-3.00
|becomes sixteen cells
|appearance of fourth cleavage furrow
|[[File:Stage05dorsal.jpg|100px]]
|-
|6
|3.00-3.30
|becomes thirty-two cells
|appearance of fifth cleavage furrow
|[[File:Stage06animal.jpg|100px]]
|-
|6.5
|3.30-4.00
|blastula stage
|Three dorsal folds become visible as a result of endoderm invagination. Pole cells no longer visible on surface
|[[File:Stage065dorsal.jpg|100px]]
|-
|7
|4.00-5.00
|Gastrulation stage
|two primary germ layers. epiblast and endoderm
|[[File:Stage07ventral.jpg|100px]]
|-
|8
|5.00-7.00
|neurulation
|medullary plate, neural folds and neural tube
|[[File:Stage08animal.jpg|100px]]
|-
|9
|7.00-9.00
|germ layer
|complete lip involution encircling yolk
|[[File:Stage09veg.jpg|100px]]
|-
|10
|9.00-11.00
|early gastrula
|two primary germ layers
|[[File:Stage10veg.jpg|100px]]
|-
|10.5
|11.00-11.45
|gastrula
|two germ layers
|[[File:Stage105vegb.jpg|100px]]
|-
|11
|11.45-12.30
|medulla plate
|Yolk sac protrudes dorsally, labium moves to midline on ventral side
|[[File:Stage11veg.jpg|100px]]
|-
|11.5
|12.30-13.15
|continuation of medulla plate
|start closing the plate
|[[File:Stage115veg.jpg|100px]]
|-
|12
|13.15-14.15
|early neurula
|thickened ectoderm give rise to CNS
|[[File:Stage12veg.jpg|100px]]
|-
|12.5
|14.15-14.45
|neural folds
|expansion of cavity
|[[File:Stage125postdors.jpg|100px]]
|-
|13
|14.45-16.15
|neural folds
|continue expanding cavity
|[[File:Stage13postdors.jpg|100px]]
|-
|14
|16.15-17.30
|neural folds
|continuation of cavity
|[[File:Stage14postdors.jpg|100px]]
|-
|15
|17.30-18.15
|tail bud stage
|early organogeny
|[[File:Stage15postdors.jpg|100px]]
|-
|16
|18.15-18.45
|tail bud stage
|posterior ventral view
|[[File:Stage16ant.jpg|100px]]
|-
|17
|18.45-19.45
|tail bud stage
|anterior view
|[[File:Stage17ant.jpg|100px]]
|-
|19
|20.45-21.45
|neural fold close complete
|dorsal view
|[[File:Stage19dorsal.jpg|100px]]
|-
|20
|21.45-22.30
|early tail bud
|anterior view
|[[File:Stage20dorsal.jpg|100px]]
|-
|21
|22.30-24.00
|termination of neural crest
|progress to next stage
|[[File:Stage21ant.jpg|100px]]
|-
|22
|24.00-24.45
|prolonged development
|elongation
|[[File:Stage22lat.jpg|100px]]
|-
|23
|24.45-26.15
|elongation of embryo
|later view
|[[File:Stage23lat.jpg|100px]]
|-
|24
|26.15-27.30
|continuation of elongation of embryo
|dorsal view
|[[File:Stage24latsmall.jpg|50px]]
|-
|25
|27.30-29.30
|organs development
|embryo elongates and develops dorsal thickening
|[[File:Stage25dorsal.jpg|50px]]
|-
|26
|29.30-31.15
|elongation
|dorsally forms neural and brain cavity
|[[File:Stage26lat.jpg|50px]]
|-
|27
|31.15-32.30
|elongation of embryo
|dorsal view
|[[File:Stage27lat.jpg|50px]]
|-
|28
|32.30-35.00
|further development
|lateral view
|[[File:Stage28lat.jpg|50px]]
|-
|29-30
|35.00-37.30
|tail bud
|growth
|[[File:Stage29-30lat.jpg|50px]]
|-
|31
|37.30-40.00
|prolonged development
|bud development
|[[File:Stage31lat.jpg|50px]]
|-
|32
|40.00-44.30
|early muscular development
|elongation
|[[File:Stage32lat.jpg|50px]]
|-
|33-34
|44.30-50.00
|muscular movement
|apparatus for locomotion
|[[File:Stage33-34lat.jpg|50px]]
|-
|35-36
|50.00-53.30
|muscular movement
|apparatus for locomotion
|[[File:Stage35-36lat.jpg|50px]]
|-
|37-38
|53.30-56.30
|heart beat
|develops apparatus
|[[File:Stage37-38lat.jpg|50px]]
|-
|39
|56.30-66.00
|mouth opens
|cornea transparent
|[[File:Stage39latsmall.jpg|50px]]
|-
|40
|66.00-76.00
|gill circulation
|hatching
|[[File:Stage40lat.jpg|50px]]
|-
|41
|76.00-80.00
|tail, fin circulation
|circulation
|[[File:Stage41lat.jpg|50px]]
|-
|42
|80.00-86.00
|internal gills, operculum
|opercular fold, teeth
|[[File:Stage42lat.jpg|50px]]
|-
|43
|86.00-98.00
|operculum complete
|operculum closed on right
|[[File:Stage43lat.jpg|50px]]
|-
|46
|98.00-106.00
|metamorphosis
|emergence from water as miniature, operculum complete|
|[[File:Stage46lat.jpg|50px]]
|-
|}

==Abnormalities of frog==

Abnormalities of frog could be caused by multiple factors. These include change in climate, predators, parasites, bacteria, fungi, viruses or pollution and contaminants such as pesticides, metals and fertilizer.[http://www.fws.gov/contaminants/documents/frogsrefup_septoct_2006.pdf]

The Abnormalities are further classified into different categories. These categories are:

===1. Infectious Diseases:===

'''Perkinsus Symptoms-''' caused by perkinsus-like protozoan organism. Symptoms include swollen viscera that leads to a bloated body and and infected swollen heart

'''Ichthyophonus symptoms-''' cause by parasitic genus, where symptoms include a swollen tail resorption site that matches the surrounding skin in color and translucency.

[[Image:Abnormalities of Frog species.jpg|thumb|left|Figure A Image details[waterwatchadelaide.net.au].jpg]]

===2. Surficial Abnormalities:===

Surficial abnormalities as the one that are visible on the surface of the skin. This includes abnormal pigmentation, , subcutaneous hemorrhaging, wounds due to trauma or from a predator
Edema is a fluid-filled swelling under skin whihc is also a surficial abnormality.

===3. Skeletal Abnormalities:===

This is further classified into three more categories:

'''a. Skeletal Malformations-'''

* Microcephaly (small head or blunt snout)
*Scoliosis (Curved spine in lateral direction)
*Shrunken Limb (Micromelia)
*Amelia (Completely missing limb with no stump)

'''b. Skeletal Abnormalities of Unclear Etiology-'''

This condition arises when a frog has ectromelia (missing limb), brachydactyly (missing digits) or other such condition with no visible trauma or external damage, then this will be classified as the Skeletal abnormality of unclear etiology.

'''c. Skeletal Injuries-'''

Any limb missing or broken due to trauma or other related reason which shows clear evidence of it is classified as skeletal injury

===4. Eye Abnormalities:===

Most common includes-

'''i. Anophthalmia:''' Skin covers the eye socket as there is no eye

'''ii. Abnormal Iris Coloration:''' Reduced pigment in either one eye or both resulting in two different colours of the iris at times

'''iii. Abnormal size or shape:''' Both eyes either deviating from each other or size of pupil or iris is different than the other eye

[http://www.fws.gov/contaminants/Amphibian/pdfs/AbnormalitySOP_woutpics_Jan08.pdf ]

==Genetics==

There are a wide variety of species that differ from each other when it comes to genetics and their functioning.

'''TAXONOMY:''' '''Phylum''' ''Chordata'' / '''Sub Phylum''' ''Vertebrata'' / '''Class''' ''Amphibia'' / '''Order''' ''Anura''

Their are more than two dozen different families of frogs, where suborders are:

'''1. ARCHAEBATRACHIA-''' most primitive frogs

'''2. MESOBATRACHIA-''' linked between the Archaebatrachia and Neobatrachia

'''3. NEOBATRACHIA-''' most modern frogs

{| border='4px'
|+ '''General Info:'''
! !!
|-
| '''Number of frogs' species'''
| 5280
|-
| '''Smallest frog genome size:'''
| 0.95pg, Ornate burrowing frog
|-
| '''Largest frog genome size:'''
| 13.40pg, Ornate horned frog
|-
| '''Mean of frogs' genome'''
| 4.68pg ± 0.13
|-
|}

[http://www.genomesize.com]

*Majority of frogs have only 22 to 26 chromosomes and polyploid is very common where they are almost bisexual.

*Polyploid Amphibians reduce their total cell number such that they acheive the same body size as diploids. One of the most unsual forms of polypoidy in amphibians is the water frog ''Rana esculenta'' from Europe and Western Asia.

* The species with larger genomes have more genes for e.g. the frog genus ''Xenopus'' includes 16 species, with genome sizes ranging from 3.5 x 10^9 bp to 1.6 x 10^10 bp. These differences have arisen by numerous events of polyploidization within the past 40 million years or so. The ancestral chromosome number for the genus seems to have been 18, but there are species with 36, 72 and 105 chromosomes [http://www.xenbase.org/common/]

{| border='4px'
|+ '''Difference within two families'''
! '''SPECIES''' !! ''X.LAEVIS'' !! ''X.TROPICALIS''
|-
| '''PLOIDY'''
| Allotetraploid
| Diploid
|-
| '''NO. OF CHROMOSOMES'''
| 36 chromosomes
| 20 chromosomes
|-
| '''GENOME SIZE'''
| 3.1 x 10^9 bp
| 1.7 x 10^9 bp
|-
| '''EGG SIZE'''
| 1-1.3 mm
| 0.7-0.8 mm
|-
| '''GENERATION TIME'''
| 1-2 years
| 4 months
|-
|}
[http://www.xenbase.org/common/]

===Genome Sequencing===

Since Frog has a huge family with many different species, only few main species that are used widely for the purposes of experiments have their genome sequenced.

''Xenopus tropicalis'' has one of the smallest genomes among amphibians and has the shortest generation time- four to six months and the only diploid genome among the 14 Xenopus species. This means it has no more than two copies of most genes, whereas the other species of Xenopus have four copies of most genes (pseudotetraploid). US Department of Energy's Joint Genome Institute (JGI) in Walnut Creek, California, initiated the X. tropicalis Genome Project, finding 1,700 million base pairs.
[http://www.genome.gov/Pages/Research/Sequencing/BACLibrary/xenopusTropicalis.pdf]

===Xenopus oocytes===

* The oocytes provide an important expression system for molecular biology.

* By injecting DNA or mRNA into the oocyte or developing embryo, scientists can study the protein products in a controlled system. This allows rapid functional expression of manipulated DNAs (or mRNA). This is particularly useful in electrophysiology, where the ease of recording from the oocyte makes expression of membrane channels attractive.

* One challenge of oocyte work is eliminating native proteins that might confound results, such as membrane channels native to the oocyte.

* Translation of proteins can be blocked or splicing of pre-mRNA can be modified by injection of Morpholino antisense oligos into the oocyte (for distribution throughout the embryo) or early embryo (for distribution only into daughter cells of the injected cell).
[http://www.staff.unibe.ch/sigel/xenopus.html]

===Xenopus Laevis===

* ''Xenopus Laevis'' is an important model organism in developmental biology. X. laevis is tetraploid and reaches sexual maturity in 1 to 2 years. What makes it important in developmental biology is its large and easily manipulable embryo.

* Extracts from the eggs of X. laevis frogs are also commonly used for biochemical studies of DNA replication and repair, as these extracts fully support DNA replication and other related processes in a cell-free environment which allows easier manipulation.

* The Human chorionic gonadotropin hormone (hCG) is present in the urine of the pregnant women in large quantities only. This hormone in the urine induces X.laevis oocyte production which formed the basis of first well-documented method of pregnancy testing X. laevis is also notable for its use as the first well-documented method of pregnancy testing when it was discovered. Today, commercially available HCG is injected into Xenopus males and females to induce mating behavior and breed these frogs in captivity at any time of the year.

===Gene cluster===

* The alpha and beta globin genes are closely linked in small cluster of frogs compared to human and chicken

* The similarity of architecture of two clusters found in X.laevis supports the tetraploid origin

* The two loci encoding the muscle specific creatine kinase isoenzymes and have large differences in developmental profile, therefore suggesting that duplicate loci that have not undergone silencing are not simply redundant copies but have acquired specialization.

* Contains twice number of genes for proteins i.e. haemoglobin and sarcomeric actin serum albumin compared with other species

----

==Current Embrology Research==

Currently, a number of fields have benefited from the development of frog embrology. These include cloning, verification of messenger RNA, and Cell cycle.

===Cloning===
[[Image:Robert Briggs.jpg|thumb|left|Figure 16 Image details:Robert Briggs.jpg]]

In 1952, Robert Briggs and Thomas J King cloned northern leopard frogs using a method of nuclear transfer. Briggs and King's experiment was similar to that envisioned - and piloted using salamanders - by Hans Spemann in his 1938 proposal for a 'fantastical experiment'. Later, John Gurdon extended this work and showed that nuclei from differentiated cells could support development, although less well than those from early embryos. [http://genome.wellcome.ac.uk/doc_WTD020799.html]

Lemaitre et a. (2005) from MRC Cancer Cell Unit, Cambridge, U.K. worked on experiments that demonstrated that importance of serial nuclear transplantation for the sucessful cloning of frogs. He demonstrated that exposure of somatic-cell nuclei (erythrocyte nuclei) and sperm nuclei to an extract of mitotic cell extract reorganizes the chromatin into shorter loops and allows replication at much shorter intervals along the DNA. This increases the efficiency of DNA replication in mammalian cell-free systems.

===Transgenesis techniques for functional genomics in Xenopus===

Transgenesis in Xenopus is made possible due to large embryos, a reliable fate map, ease of microinjection, ease of dissection/micromanipulation and existence of the neuroendocrine reflex of background adaptation as a model for activation/inact.

Recently, Hajime Ogino and Haruki Ochi from Nura Institute of Science and Technology in Japan focused on the genomic resources and principles of the transgenesis techniques in Xenopus, and discusses their applications to genome wide network analysis, with emphasis on the use of bioinformatics tools. This is will to understand the gene regulatory networks that control vertebrate development. [http://www.ingentaconnect.com/content/bsc/dgd/2009/00000051/00000004/art00001%3Bjsessionid=4ah96rms73gcu.alexandra]

Xenopus used to be a problem in earlier days when it came to transgenesis. Current methods involves isolated sperm nuclei from Xenopus testis that are microinjected into unfertilized eggs. The generated transgenic tadpoles contain 5-35 copies of the integrated plasmid that are expressed in all cells. If desired, expression of the transgene can be directed to the appropriate tissue and at the appropriate time by using specific promoters, mostly the Xenopus POMC gene promoter (isolated from a Xenopus genomic DNA library) to specifically direct expression of green fluorescent protein (GFP) at high levels to the intermediate pituitary cells, which can either be over expressed or inhibited.[http://molanphys.ruhosting.nl/transgenesis.htm]

[[File:Transgenesis.JPG]]

===Verification of messenger RNA===

While the existence and role of messenger RNA (mRNA) was known in bacteria, in the 1960s it was still debated whether it also existed in vertebrates. Taking haemoglobin mRNA from immature red blood cells and injecting it into a Xenopus oocyte, John Gurdon showed that the haemoglobin protein was indeed produced. Producing proteins in Xenopus oocytes has proved to be extremely useful in cell biology, in particular for the study of receptor proteins.[http://genome.wellcome.ac.uk/doc_WTD020799.html]

===Cell Cycle===

As they develop outside the mother, frog eggs are well stocked with the proteins needed to drive the development of the embryo. Studies of these processes has shed considerable light on the processes involved in cell division - termed the cell cycle. [http://genome.wellcome.ac.uk/doc_WTD020799.html]

===Limb development in Xenopus Laevis===

[[Image: Frog Limb development.jpg|thumb|right|Image details:Primary source:[http://images.google.com.au/imgres?imgurl=http://www.sciencedaily.com/images/2006/06/060616130718.jpg&imgrefurl=http://www.sciencedaily.com/releases/2006/06/060616130718.htm&usg=__xliPsPAvheUBME_kjv_q7auiFbo=&h=333&w=300&sz=11&hl=en&start=2&um=1&tbnid=y_ntJtmkRSK7WM:&tbnh=119&tbnw=107&prev=/images%3Fq%3DLimb%2Bdevelopment%2Bin%2BXenopus%2BLaevis%26ndsp%3D18%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

Donald D. Brown (2005),Department of Embryology, Carnegie Institution of Washington demonstrated factors related to limb development of Xenopus Laevis. Thyroid hormone (TH) is found to be required for limb development in this frog. Specific cell types in the growing limb were targeted for expression of a dominant negative form of the TH receptor by sperm-mediated transgenesis. Limb muscle development, the innervation of muscle from the spinal cord, and cartilage growth can be inhibited without affecting patterning of the limb or differentiation of other cell types. Remodeling of the skin occurs late in metamorphosis after the limb has formed. The coordination of these independent programs is affected in part by the control that TH exerts over DNA replication in all cell types of the limb. [http://www.pnas.org/content/102/35/12455.full]

----

== Glossary ==

[[Image: Frog species.jpg|thumb|left|Image details:Primary source:www.olympus.co.jp/.../080925/large/p02L.jpg].jpg]]

*'''Amphibian:'''

''Relating to or characteristic of animals of the class amphibia.Amphibians are found in the taxonomic class of amphibia, amphibians are capable of both occupying and successfully living in both land and aquatic communities.amphibian''

*'''Augmentation:'''

''Enlargement/Increase in cellular size.''

*'''Autolysis:'''

''breakdown of a part or whole cell or tissue by self-produced enzymes''

*'''Blastomeres:'''

''The undifferentiated cells formed by cleavage of the fertilised ovum. This includes cells in the cleavage, morula, and blastula stages of the embryo''

*'''Carnivorous:'''
''
Flesh-eating; subsisting on animals as food.''

*'''Cleavage:'''

''he repeated division of a fertilised ovum ''

* '''Cleft:'''

''an opening, fissure, or V-shaped indentation made by or as if by splitting''

*'''Chordate:'''

''Members of a diverse phylum of animals that, as embryos, possess a (1) notochord; (2) a dorsal, hollow nerve cord, (3) pharyngeal gill slits; and (4) a post-anal tail''

''The act or state of splitting or dividing of a cell, particularly during the telophase of (animal) cell division.''

*'''Cytoplasm:'''

''The cytoplasm (of both eukaryotes and prokaryotes) is where the functions for cell expansion, growth, metabolism, and replication are carried out''

* '''Epiboly:'''
''The expansion of one cell sheet over other cells, as takes place during gastrulation''

*'''Fertilization:'''

''A process in sexual reproduction that involves the union of male (sperm) and female (ovum) gametes (each with a single, haploid set of chromosomes) to produce a diploid zygote.''

*'''Gamete:'''
''A reproductive cell (male (sperm) or female (egg)) that has only half the usual number of chromosomes''

*'''Gametogenesis:'''

''process leading to the production of gametes. The development and maturation of sex cells through meiosis.Another name for meiosis where a diploid cell is divided into two haploid cells with half the chromosome content of the diploid parent cell.''

*'''Herbivorous:'''

''eating plants; of or pertaining to the herbivora.''

*'''Holoblastic:'''

''The complete division of an isolecithal or microlecithal egg into blastomeres''

*'''Invagination:'''

''One of the methods by which the various germinal layers of the ovum are differentiated.''

*'''Isoenzymes:'''

''Isozymes (also known as isoenzymes) are enzymes that differ in amino acid sequence but catalyze the same chemical reaction.''

*'''Mesentery:'''

'' membranous fold attaching various organs to the body wall.''

*'''Metamorphosis:'''

''A change in the form and often habits of an animal after the embryonic stage during normal development.''

*'''Neuroendocrine:'''

''Neuroendocrine [IPA nʊəroʊˈɛndəkrɪn] cells are cells that release a hormone into the circulating blood in response to a neural stimulus.''

*'''Organogenesis:'''

''The part of embryonic development where the body's main organs develop.''

*'''Peritoneum:'''

''The smooth serous membrane which lines the cavity of the abdomen, or the whole body cavity when there is no diaphragm, and, turning back, surrounds the viscera, forming a closed, or nearly closed, sac.''

*'''Perivitelline space:'''

''The perivitelline space is the space between the zona pellucida and the plasma membrane (sometimes called the vitelline membrane) in a fertilized ovum.''

*'''Polyploidy:'''

''Cells with three or more sets of chromosomes.''

*'''Pronucleus:'''

''the nucleus of the ovum or sperm after fertilization but before they fuse to form the nucleus of the zygote ''

*'''Protoplasm:'''

''The fluid living content of the cell that consists of two major divisions, the cytoplasm and the nucleoplasm (cell nucleus). It is composed mainly of nucleic acids, proteins, lipids, carbohydrates, and inorganic salts''

*'''Segmentation:'''

''division of some metazoan bodies (such as annelida and Arthropoda) into repeated parts, segments. Segmentation can be homomeric (more or less the same) or heteromeric(different from each other).''

*'''Terrestrial:'''

''Of or on the ground, of the habitat of a plant, on land as opposed to in water, or on the ground as opposed to on another plant.''

*'''Transgenesis:'''

''Transgenesis is the process of introducing an exogenous gene - called a transgene - into a living organism so that the organism will exhibit a new property and transmit that property to its offspring.''

*'''Yolk:'''

''nutritive material of an ovum stored for the nutrition of an embryo''

*'''Zygote:'''

''The cell from which an organism develops, that results from the fertilization of the egg by the sperm.''

''Primary Resource "Biology- Online Dictionary''[http://www.biology-online.org/dictionary/Main_Page]

== References - Frog Embryology: ==

[[Image:Frog Research.jpg|thumb|left|Image details:[http://images.google.com.au/imgres?imgurl=http://www.odt.co.nz/files/story/2008/09/university_of_otago_zoology_senior_lecturer_phil_b_3343259744.jpg&imgrefurl=http://www.odt.co.nz/on-campus/university-otago/21670/dunedin-frog-man-wins-zoo-award&usg=__JvJJU5QfOnIwY2bk4xo64UXuJRs=&h=600&w=404&sz=22&hl=en&start=14&um=1&tbnid=AbsP89yWcUiilM:&tbnh=135&tbnw=91&prev=/images%3Fq%3Dfrog%2Bresearch%26hl%3Den%26um%3D1].jpg]]

1. Savage, J. M. (2002). The Amphibians and Reptiles of Costa Rica. University of Chicago Press, Chicago [http://www.springerlink.com/content/vv015277w1746llw/]

2. Ford, L.S.; D.C. Cannatella (1993). "The major clades of frogs". Herpetological Monographs 7: 94–117 [http://digimorph.org/specimens/Xenopus_laevis/]

3. Tyler, M. J. (1994). Australian Frogs A Natural History. Reed Books [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.gracilenta.html]

4. Cogger, H.G.; R.G. Zweifel, and D. Kirschner (2004). Encyclopedia of Reptiles & Amphibians Second Edition. Fog City Press [http://en.wikipedia.org/wiki/Microhylidae]

5. Beltz, Ellin (2005). Frogs: Inside their Remarkable World. Firefly Books [http://unjobs.org/authors/ellin-beltz]

6. Tyler, M. J. (1994). Australian Frogs A Natural History. Reed Books [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

7. Moury JD, Hanken J (1995) Early cranial neural crest migration in the direct-developing frog, Eleutherodactylus coqui. Acta
Anatomica (Basel) 153, 243-253.

8.Raynaud A (1985) Development of limbs and embryonic limb reduction. In Biology of the Reptilia (ed. Gans C, Billett F), pp.
59-148. New York: John Wiley.[http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=9309]

9. Hanken J (1986) Developmental evidence for amphibian origins. In Evolutionary Biology (ed. Hecht MK, Wallace B, Prance GT), 20, pp. 389-417. New York: Plenum Press. [Hanken J (1986) Developmental evidence for amphibian origins. In Evolutionary Biology (ed. Hecht MK, Wallace B, Prance GT), 20, pp. 389-417. New York: Plenum Press.]

10. Elinson RP (1990) Direct development in frogs : wiping the recapitulationist slate clean. Seminars in Developmental Biology
1, 263-270.

11. Beebee, T. J. C. 1996. Ecology and Conservation of Amphibians. Chapman and Hall. London. [http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V5X-3SVHMKH-1X&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=1021245355&_rerunOrigin=google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=825868e10cd178d16a8a0e5ad14dc5ef]

12. Lehtinen, R. M. 2002. The use of screw pines (Pandanus spp.) by amphibians and reptiles in Madagascar. Herpetological Bulletin 2002:20–25.

13. Parris, K. M. and M. A. McCarthy. 1999. What influences the structure of frog assemblages at forest streams. Australian Journal of Ecology 24:495–502. CrossRef

14. Zug, G. R. 1993. Herpetology: An Introductory Biology of Amphibians and Reptiles. Academic Press. San Diego, CA.

15. Slack,J.M.W., Darlington,B.G., Heath,J.K. and Godsave,S.F. (1987)Mesoderm induction in early Xenopus embryos by heparin-binding growth factors. Nature, 326, 197-200.

16. Melton,D.A. (1990) Activins are expressed early in Xenopus embryogenesis and can induce axial mesoderm and anterior structures. Cell, 63, 485-493.

17. Harland,R.M. and Misher,L. (1988) Stability of RNA in developing Xenopus embryos and identification of a destabilizing sequence in TFIIIA RNA. Development, 102, 837-852.

18. Cunliffe,V. and Smith,J.C. (1992) Ectopic mesoderm formation in Xenopus embryos caused by widespread expression of a Brachyury homologue. Nature, 358, 427-430.

19. Kinoshita,K., Bessho,T. and Asashima,M. (1993) Competence prepattern in the animal hemisphere of the 8-cell-stage Xenopus embryo. Devel. Biol., 160, 276-284.

20. LaBonne,C., Burke,B. and Whitman,M. (1995) Role of MAP kinase in mesoderm induction and axial patterning in Xenopus development. Development, 121, 1475-1486.

21. Green,J.B.A., New,H.V. and Smith,J.C. (1992) Responses of embryonic Xenopus cells to activin and FGF are separated by multiple dose thresholds and correspond to distinct axes of the mesoderm. Cell, 71, 731-739.

22. Grainger R., Blumberg B., Harland R., Amemiya C., Importance of Xenopus Tropicalis to biomedical and biological research, Benaroya Research Institute, Virginia Mason Research Center [http://www.genome.gov/Pages/Research/Sequencing/BACLibrary/xenopusTropicalis.pdf ]

23. Gregory, T.R. (2005). Animal Genome Size Database. [http://www.genomesize.com]

24. U.S Fish and Wildlife Services, ABNORMALITY CLASSIFICATION SOP, [http://www.fws.gov/contaminants/Amphibian/pdfs/AbnormalitySOP_woutpics_Jan08.pdf ]

25. Donald D. Brown*, Liquan Cai*, Biswajit Das*, Nicholas Marsh-Armstrong‡, Alexander M. Schreiber*, and Rejeanne Juste*(2005), Thyroid hormone controls multiple independent programs required for limb development in Xenopus laevis metamorphosis [http://www.pnas.org/content/102/35/12455.full]

26. Ogino, Hajime; Ochi, Haruki, Resources and transgenesis techniques for functional genomics in Xenopus, Development Growth & Differentiation, Volume 51, Number 4, May 2009 , pp. 387-401(15) [http://www.ingentaconnect.com/content/bsc/dgd/2009/00000051/00000004/art00001%3Bjsessionid=4ah96rms73gcu.alexandra]

27. Giles Newton (2004) Why the frog? The Human Genome, [http://genome.wellcome.ac.uk/doc_WTD020799.html]

28. Xenbase, [http://www.xenbase.org/common/]

29. Donders Center for Neuroscience & Nijmegen Center for Molecular Life Sciences (NCMLS), Beyond the genome (Xenopus transgenesis for functional genomics),Faculty of Science, Radboud University [http://molanphys.ruhosting.nl/transgenesis.htm]

== External Links ==
[[Image:Frog links.jpg|thumb|left|Image details:[http://images.google.com.au/imgres?imgurl=http://2.bp.blogspot.com/_o93AaY0GzH4/SjY_ZYv0PII/AAAAAAAAAgk/skruNc2yN78/s400/computer%2Bfrog.jpg&imgrefurl=http://hellaheaven-ana.blogspot.com/2009/06/talking-frog-contemporary-fairy-tale.html&usg=__oxji1TGLV2Fi7xe0dnlmuYk8gDo=&h=288&w=288&sz=16&hl=en&start=2&um=1&tbnid=ywZd4zpdxC5plM:&tbnh=115&tbnw=115&prev=/images%3Fq%3Dfrog%2Bon%2Bcomputer%26hl%3Den%26um%3D1].jpg]]

1. Frog embryology [http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/F/FrogEmbryology.html Frog Embryology]

2. Frog cellular materials [http://www.xenbase.org/xenbase/original/cell/cell.html xenbase]

3. The zoology of frog species [http://worms.zoology.wisc.edu/frogs/mainmenu.html zoology frogs]

4. Frog cycle [http://www.bioethics.gov/images/sc_images/frog_dev.gif bioethics frog] Just a little cycle of FROG'S life cycle

5. Frog Embryology [http://embryology.med.unsw.edu.au/OtherEmb/Frog.htm UNSW Embryology]

6. Frog Research [http://apps.carleton.edu/campus/library/now/exhibits/wallcharts/frog/ carleton library exhibit]

{{Template:Projects09}}
[[Category:Frog]]

2009 Group Project 5

2009-10-14T22:34:51Z

Z3258567: /* Growth and development of the Frog */

== The Embryology of Frogs ==

== The Frog ==

[[Image: Frog species .jpg|thumb|left|Image details: Wikipedia (2009) Frog species[http://en.wikipedia.org/wiki/Frog#Uses_in_agriculture_and_research].jpg]]

Frogs are scientifically identified by the structure of their long posterior limbs, a petite framework, webbed fingers and feet, budged eyes and the lack of a tail. The majority of frog species are extensively recognized as outstanding jumpers, due to their long, dominant legs, which are adaptations to progress jumping performance during activities. The Frog is one of the most frequently studied species in experimental embryology and most anatomical sciences. ''The Frog is a practically effective model for human embryological development given that the Frog:''

- Comprises of genes which can be effectively manipulated.

- Comprises of similar homogeny with humans species.

- Reproduces a large quantity of offspring in a short period of time.

- Are small species which can be simply sustained.

- Are not extremely luxurious and expensive.

== The History of the uses in agriculture and research ==

[[Image: Frog experiments .jpg|thumb|right|Image details: Scans of chemically cleared and dyed preserved deformed frogs and toads [http://www.sat.qc.ca/upload/residence/frog-04.jpg].jpg]]

There are numerous types of frog species that have been manipulated in many developmental experiments. The frog was traditionally used by countless of the early embryology investigators and presently there are several diverse molecular mechanisms regarding progression of the frog. Theses include:

'''1.''' Food source; frog legs are a delicacy and are eaten in European countries and in many parts of South American regions.

'''2.''' Frogs have the finest biochemical dissection of phenomena that take place in the egg and oocyte. Frogs are the evolutionarily closest to mammals, commonly used as a vertebrate model.

'''3.''' Frogs lay thousands of outsized eggs, from which cell extracts can be readily prepared that is capable of recapitulating most molecular phenomena in a test tube.

'''4.''' Frogs have been commonly used as a laboratory system for a very long period, and have an extensive history of producing crucial observations in countless fields of biology.

'''5.''' Frogs have a important historical connection to the study of epigenetics (John Gurdon-vertebrate cloning and reprogramming) which has been mostly performed on frog species.

'''6.''' Frogs also have very strong evidence of pattern formation and early development, as the embryos are large in size and experimentally manipulative.

'''7.''' Recent research into the biochemistry of chromatin and epigenetics has been performed with frog species and mammalian cultured cells.

'''8.''' The biggest weakness of the Frog model system is the difficulty of performing genetic experiments and analysis, as frogs are allotetraploid, meaning they take approximately a year to fully develop to sexual maturity, and the genome has not been completely sequenced. Nevertheless, biochemical manipulations of cell extracts, such as immunodepletions and application of heterologous DNAs and nuclei can avoid the need for genetic exploitation.

----

== Growth and development of the Frog ==

[[Image: Mature develop frog.jpg|thumb|Image details: Wikipedia (2009) Red Eyed Tree Frog Figure 1 Primary source:[http://en.wikipedia.org/wiki/File:Red-eyed_Tree_Frog_-_Litoria_chloris_edit1].jpg]]

* The frog is a well recognised species, abundant predominantly in ponds, swamps, though various species may also exist in damp or shady environments distant from moist habitats.

* Eggs of specific frogs are easily obtained and may be examined in from the beginning of fertilization onwards. The phases of embryonic development differs in various chordates, yet the typical phases are basically apparent in all frog species. The differences are associated principally to the amount of yolk particles present in an egg.

* The yolk particles offer nourishment of the developing embryo. The process of frog development will be discussed from the phases of gametogenesis to the adult stage.

----

== The Egg ==
[[Image:Development of Poles in frog Fertilization.jpg|thumb|left|Figure 4 Image details:J,Nassif 2009.jpg]]

- The embryology of a frog egg is a vast cell; its dimensions are approximately 1.4-1.6 million times larger than a typical aquatic species egg cell. Throughout the frog’s embryonic maturation period, the egg will be transformed into a tadpole encompassing millions of cells but still remains with its constant volume of genetic material, the vast prodction of cell have been illusttrated in the figure on the right revealing the production of eggs from female frogs. [http://en.wikipedia.org/wiki/Microhylidae]

- The early embryonic frog structure consists of three main segments the superior hemisphere known as the animal pole which is usually visible as a grey coloured area. The innermost layer appears to be between the outer two sections known as the gray crescent represented in black. Inferiorly, represents the vegetal pole typically lighter than the superior compartment illustrated in gold.

VIDEO RESOURCE: [http://www.youtube.com/watch?v=GO5YN_t1fqw&feature=related]

[[Image:Early Development of Frogs.jpg|thumb|left|Figure 3 Image details:J,Nassif 2009.jpg]]

==History of frog embryology use ==

*'''1851''' - ''Henby Nelson''(MD): He identified a remarkable fact through the frog embryo. Henby observed the first cleavage of the yolk, in the egg of the frog. And cleaved structure corresponds in line of direction to the longitudinal axis of the body of the embryo of the frog species.

[[Image:Wilhelm Roux.jpg|thumb|right|Wilhelm Roux[http://images.google.com.au/imgres?imgurl=http://www.todayinsci.com/R/Roux_Wilhelm/RouxWilhelmThm.jpg&imgrefurl=http://www.todayinsci.com/6/6_09.htm&usg=__qRLTEMTHdZpAHxiNX12hWjcm9tA=&h=125&w=100&sz=4&hl=en&start=2&um=1&tbnid=LIKIwZTqCpk7MM:&tbnh=90&tbnw=72&prev=/images%3Fq%3DWilhelm%2BRoux%26gbv%3D2%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

*'''1888''' - ''Wilhelm Roux'': Wilhelm Roux attempted to solve the above observation by damaging one cell of a two-cell frog embryo with a hot needle. The cell stayed in place. However, it did not develop further. Its partner developed into a left or right half-embryo;

*'''1907''' - ''John Hopkins'' hospital: In order to identify the cellular source of neuronal fibres. Scientist placed small portions of frog embryo spinal cords in lymph on a microscope slide and was able to observe clear cut neuronal sprouting.

*'''1951''' - ''Robert Briggs'': Robert Briggs was able to clone a frog embryo by substituting the nucleus of an unfertilized frog egg cell with the nucleus of a frog embryo cell. This process is known as nuclear transplant, has formed the basis for all cloning.

*'''1952''' - ''Robert Briggs and T.J. King'': Robert Briggs and T.J. King used frog for test experiment. Because the size of the eggs in the frogs are enormous compared with those of mammals, which make them easier to manipulate.

*'''1976'''- Using the technique that had been successful in cloning frog embryos, the doctor transferred the nucleus of one cells into a donated egg cell. As an embryo began to develop, it was implanted into the uterus of a young woman.

*'''1997''' - ''Wilmut and Campbell'': Utilizing the cloning technique from frog embryo, Drs. Wilmut and Campbell tried the starvation technique on embryo cells to produce Megan and Morag, the world's first cloned sheep and, until now, the most famous sheep in history.

*'''2000''' - ''Tokyo University'': Scientists at Tokyo University have grown artificial eyeballs. Scientists formed them in tadpoles by using frog embryo cells.

*'''2001''' - ''Advanced Cell Technology'': Scientists from Advanced Cell Technology announced production of a human embryo clone. This is significant as its parthenogenesis has been artificially induced in frogs.

[[Image:John Gurdon .jpg|thumb|right|John Gurdon [http://images.google.com.au/imgres?imgurl=http://www.pnas.org/site/misc/images/gurdon.jpg&imgrefurl=http://www.pnas.org/site/misc/classics4.shtml&usg=__1p-GA1PdOYsxKL-cznMb3RHCm98=&h=526&w=400&sz=223&hl=en&start=1&um=1&tbnid=9k4lhuLssiWCAM:&tbnh=132&tbnw=100&prev=/images%3Fq%3DJohn%2BGurdon%26gbv%3D2%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

*'''2002''' - ''John Gurdon'': John Gurdon from Wellcome Cancer Research Institute in Cambridge experimented on cloned frog embryo.

== Gametogenesis ==

* The sexual reproduction occurs through the fusion of either mature reproductive cells or germ cells known as gametes, which include the sperm from the male frog and ova from female frog species so as to form a single cell, the fertilized zygote. The gametes are typically developed in parents of different sexes . [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

* Males gametes is a spermatozoon , the female frog gamete is an ovum. Each gamete is formed by a process, recognised as maturation or gametogenesis in gonads. The typical male frog gonads are testies in male, while the female gonads are ovaries. The synthesis of both gonads is associated with the process of fertilization. [http://en.wikipedia.org/wiki/Microhylidae]

* The zygote changes into a mature frog through the process of embryology and metamorphosis. Gametogenesis is a in progression which frog gametes are established from germ cells. Initial germ cells are called primordial germ cells, which can be recognised extremely early in the life of frog species.

----

== The Egg & Fertilization ==

[[Image:Fertilized and Unfertilised Eggs.jpg|thumb|left|Figure 6 Image details:J,Nassif 2009.jpg]]

[[Image:Egg Development.jpg|thumb|left|Figure 7 Image details:J,Nassif 2009.jpg]]

- This occurs once the sperm cell has inserted, following the insertion of the sperm cells meiosis II is completed, there is a 30 degree position change of the cytoplasm, gray crescent allows this change to be visible in some amphibians, the gray crescent is able what determines the expect ted outline of how the frog will form. The sperm cell joins with the nuclei of the egg which forms the diploid zygote nucleus. --Sando Rashed 10:09, 24 September 2009 (EST)

- The early phases in the development of the egg is visible, but must be studied in tadpoles throughout maturation. In embryonic tadpoles of about 10 millimetres in length, soon after the opening of the oral cavity, a pair of longitudinal ridge-like thickenings of peritoneum becomes apparent along the posterior surface of the body cavity situated near to the mesentery and along the inner boundaries of the kidneys. Genital ridges are established in all tadpoles of this age, sex is not distinct until a later period. The development of the egg is illustrated in the figure on the left revealing the structure of a developed egg and a mature of egg.

[[Image:Fertilisation life cyle.jpg|thumb|Figure 8 Image details:Derived from primary source:[http://en.wikipedia.org/wiki/Frog]]]

== Maturation of the Egg ==

- The eggs have currently accomplished their full size, and develop from the exterior of the ovaries like a small shot, but they still have to pass through the course of maturation before they are prepared to be fertilised. This progression of maturation relates to the nucleus almost completely.

- The nucleus component, containing the nuclear fluid that excludes through the nuclear membrane into the substance of the egg, a great segment of the nuclear reticulum vanishes and becomes degraded into separate globules known as nucleoli, but a extremely small division remains in the midpoint as a slender intricately thread recognised as the nuclear skets.
Relative to the egg getting discharged from the ovary, the follicles shatter allowing the eggs to fall into the abdominal cavity of the frog species, the egg then passes forwards, directly by the contraction of the muscular wall, somewhat by the movement of the cilia of the peritoneum, to the apex of the oviduct, which positioned at the anterior compartment of the body cavity opposite to the roots of the respiratory organs.

- The terminal part of the oviduct establishes a thin-walled pouch capable of great swelling, inside which the eggs gathers in large numbers. In conclusion, the eggs are migrated out through the cloaca into water which the albuminous investments of the eggs rapidly augment to form the gelatinous mass of the frogs spawn.

== Maturation phases ==

'''1. Nuclear skein''', moves from the midpoint of the egg to its outer surface, which it reaches opposite the midpoint of the black pole. The skein, subsequently an unevenly twisted thread, now presumes the specific arrangement of a nuclear spindle, for instance may be visible in the nucleus of an epithelial or additional cell instantly prior to division of the cell occurs.[http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

'''2. The first Polar Body,''' regarding the instance the egg is laid, but prior to its fertilistion, the egg develops a considerably flattened appearance at its upper or black pole, a definite sum of fluid being exuded among the egg and the vitelline membrane. The nuclear spindle currently separate into two identical segments, one of which remains with the egg, and the supplementary is extruded as the first polar body, a small ovoidal white globule, which is situated on the surface of the egg surrounding the exuded peri-vitellline fluid.

'''3. The Second Polar Body''', half of the nuclear spindle that stay behind then splits into two equivalent divisions, one of which remains inside the egg as the female pronucleus, whereas the other segment is extruded as the second polar body, a small white globule extremely related to the first polar body, and like this positioned in the perivitelline fluid on the superior portion of the egg.

'''4. Fertilisation of the egg''', includes the synthesis of the spermatozoon with to egg, specifically, synthesis of the nuclei of these two bodies. The spermatozoa, subsequent to being shed over the seed by the male, distribute vigorously by means of their extended tails, break through the gelatinous investment of the female eggs, bore their way through the vitelline membrane and so go through into the eggs themselves, which they penetrate relative to the superior or black hemispheres.
* Subsequently, an hour following the spermatozoon has entered; a progression may be visible projecting within from the exterior segement of the egg, with a liquid spot in the mid point. This liquid centre is the nucleus of the spermatozoon, and is said to be the male pronucleus, it break through beyond into the female egg, transporting the specialised pigment into it, so that it appears bounded by a pigmented capsule linked with the exterior of the egg by a pigmented stalk.

* By this instance, the second polar body has been established and extruded, and the female pronucleus is merely the only component of the primary egg nucleus still present. Both the male and female pronuceli, which are at initially distance separate to each other, merge and after having enlarged significantly in size then fuse mutually about two and half hours after fertilisation has originated to produce the segmentation nucleus.
* The segmentation nucleus is a huge sphere-shaped vesicle embedded in delicately granular protoplasm, and bounded by a distinct capsule of pigment, its arrangement by the synthesis of the male and female pronuclei completes the action of fertilisation. Specifically female pronucleus may be observe as an imperfect nucleus, and consequently result in the course of fertilisation. The nucleus of the spermatozoon or male pronucleus, replaces the component of the egg- nucleus which has been misplaced as the polar bodies.

'''5. Segmentation of the Egg''', the initial phase of growth consist in constant separation of the egg, whereby it becomes transformed from the unicellular state, which is everlasting only in the lowest species, to muliticelluar state charactertics of all higher species. To these early processes of growth the names segmentation is specified. Shorty subsequent to the competition of fertilisation and arrangement of the segmentation nucleus this later misplaces its sphere-shaped appearance and develops to be spindle-shaped, the yolk granules at the equivalent instance showing a tendency to develop into lines distributing outwards from the distal segment of the spindle.
* The nucleus now split into two halves, which shift away from one another, the yolk granules are likely to combined themselves around the two nuclei, and a slender vertical plate of delicately granular substance is left, dividing the egg.[http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

* Superiorly the eggs depression now becomes visible, initially as a small cavity and then develops as a groove, which almost immediately extends all round, and speedily deepening, splits the egg into two entirely separate halves along a plane equivalent with the vertical plane.

* Shorty after, the two nuclei soon separate again into two, and therefore a second cleft is created in the same state as before, its additionally in the vertical plane, however in a plane at 90 degrees to the initial one, and on its finishing point the egg comprises of four accurately similar segments, each containing a nucleus. The third cleft is horizontal in shape, but not equal, lying closer to the superior than the lower pole, it segregates each of the four cells into, an superior smaller and a inferior larger pole

----

== Cleavage ==

[[Image: Frog Cleavage development.jpg|thumb|left|Figure 8.1 Image details:[http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/F/FrogEmbryology.html].jpg]]

* The egg of the frog is scientifically identified as’ telolecithal’ meaning there is a outsized amount of yolk concentrated at a single pole, in contrast to the concentration of cytoplasm and the site of the nucleus. The cleavage phases are holoblastic, therefore the total and after the second cleavage they are asymmetrical .The initial cleavage stage appears about two and half to three hours after fertilization. It commences as a minor depression in close proximity to the centre of the animal hemisphere. It appears as if some interior force is pushing the surface the egg towards the centre. This small upturned fold steadily continues in the form of a channel until it surrounds the egg. This groove is shallow in the commencement, but develop into deeper eventually separating the fertilized egg into two halves recognised as the blastomeres. [The figure on the left symbolise the development and growth of the frog embryo during cleavage].

* Internally the separation is mitotic, consequently each daughter cell contains a nucleus resulting from the copulation nucleus of the fertilised egg. This cleavage is vertical, the two cells are indistinguishable in respect of cytoplasm, pigment and yolk. The subsequent cleavage appears about an hour after the first. The channel of this cleavage begins at the centre of the animal hemisphere, is at right angles to the first and is vertical. This divides the egg into four blastomeres. The fourth blastomere so produced are not qualitatively equal, since of these only two contain the material from the gray crescent. The cleavage begins about thirty minutes after the second is completed or four hours after fertilisation. the cleavage plane of the third furrow is horizontal and slightly above the equator. Thus the four upper cells are a little smaller than the four lower cells. The smaller blastomeres are called micromeres and the larger blastomeres are called macromeres. The fourth cleavages follow 20 minutes after the third and tend to be vertical. This is usually a double furrow.

* The cleavage rate is accelerated with each of the early divisions and since the blastomeres are of unequal size and have varying amounts of cytoplasm and yolk, synchronous cleavage is lost and there is an obvious overlapping of the division. The upper most cells divide more rapidly than the lowermost cells. From this point onwards perfect symmetry in cleavage and in blastomere is very rare, although the embryo developed perfectly. The fifth cleavage is also doubled, appearing first in the upper hemisphere and then in the lower.

* The cleavage thus far follows the rule that each cleavage plane comes in at right angles to the previous one. The subsequent divisions become so irregular that it is previous one. The subsequent division become so irregular that it is impossible to trace out any plan or procedure. The segmentation continues more rapidly in the pigmented regions, since at that place the protoplasm is most dense, whereas, yolk which is very abundant in the vegetal side delays cell division. The multicelluar embryo at this stage is called morula by some biologists.

----

== Gastrulation ==

[[Image:FROG GASTRULATION .jpg|thumb|left|Figure Image details:[http://www.google.com.au/imgres?imgurl=http://bio1903.nicerweb.com/Locked/media/ch47/47_12FrogGastrulation.jpg&imgrefurl=http://bio1903.nicerweb.com/Locked/media/ch47/gastrulation-frog.html&h=540&w=480&sz=46&tbnid=N78sHjELreGGSM:&tbnh=132&tbnw=117&prev=/images%3Fq%3Dfrog%2B-%2Bgastrulation&hl=en&usg=__4VK9FYLft0W-4lBe6p5EtQAMiaI=&ei=qPy5SurtMJvE6wON8JmdAg&sa=X&oi=image_result&resnum=4&ct=image].jpg]]

''The phase of Blastulation is followed by the unique developmental progression of gastrulation. The process of frog gastrulation involves the following processes.''

'''1. Epiboly Phase'''

The pigmented cellular materials of blastula have the propensity to overgrow the yolk cells within the developing content. This course which is known as epiboly commences gradually in the final blastula and rapidly accelerates with advancing gastrulation development. The cellular matter within the animal pole reproduces and matures on all sides except in area surrounding the dorsal lip of the blastopore has been established.

'''2. Convergence'''

Scientists suggested that the unfolding was thought to result in spreading of the superficial cells over a substrate with suitable absorption properties. Consequently epiboly and convergence are an outcome to this spreading tendency, which is actually increased by a reduction in surface tension of the distributing cells.

'''3. Rotation'''

The epiboly phase is maintained until the region of the dorsal lip has migrated and is a to some extent greater than 90 degrees and the region of the white blastopore is reduced to small circular rings. This section will be positioned away from the developing vegetal pole. Laterally the complete developing gastrula has been rotated to a horizontal axis, allowing it to lie at right angles to the original median plane of the egg. Therefore, the course of rotation is such that the dorsal lip is practically pushed backwards in one direction as rapid or quicker than epiboly moves it forward in the other. The outcome will be that the blastopore produced at roughly the vegetal pole is posterior, and the dorsal and ventral lips are essentially dorsal and ventral. This in addition allows the eggs to form the antero-ventral side of the potential embryo whilst the area marked by the grey crescent is to develop the dorsal segment.

'''4. Invagination'''

Visible is a small fissure- like invagination which is apparent in the middle between the equator and the vegetal segment. The most superior or dorsal border of the cleft produce the dorsal lip of the blastopore. This imput move back and forth on the dorsal plane near the dorsal lip and migrates around the boundaries of the blastocoel in company with the extension of the lateral lips. This adapted invagination is maintained until the blastocoel cavity has been almost abolished; excluding the slender opening separating epiblasts from the hypoblast, the new segment formed is known as the archenteron cavity.

'''5. Involution'''

- Additional to previous course of action a distinct involution also occurs at the blastoporal borders. This is mainly dynamic at the median dorsal lip and gradually more less as it shifts across either side until it reaches the ventral lip where it constant.Throughout this progression, cells positioned beside the superior boundaries of the blastoporal lip migrate over the lip to the interior portion of the lip. These cells are remained within the embryo along the internal edge of the blastopore. This indicates the root of archenteron is composed of involuted cells and beyond this the external layer known as the ectoderm. The base and lateral sides are enclosed mainly of endodermal cellular material, which have been established from larger yolk cells, situated in the vegetal pole of the blastula.

- In the final phases of the gastrula development, the cells contributing to the floor of the archenteron, thin out significantly where they surround the blastocoel.
The hemispherical shaped dorsal lip of blastopore which become visible at the commencement of the gastruation stage carry on to augment, initially becoming semicircular, then transform into a horse shoe shaped and then finally forming into circular band. The band is the accomplished by the blastopore. Various yolk cells of vegetal pole present in the section are crowed into the blastoporal cavity where they form a gathering identified as a yolk plug. Blastopore rapidly reduces in size while the archenteron is still developing and becomes completely formed in the final stage; the yolk plug appears as only a small oval on the gastrula.

==Growth and Modification of Frog Species==

'''1. Changes in habits and habitats:'''

'''a)''' In frogs, metamorphosis is related with to the modifications and adaptations as a frog changes environmental habitats from an aquatic to a terrestrial mode. Metamorphosis has modified the adaption of frogs as this alteration it began during the aquatic adaptations in the surface of water to breathe air. Subsequently, it continues the terrestrial surroundings, therefore the frog species become abundant in vegetation area allowing the frog to transform in to amphibious species.

'''b)''' The transition during metamorphosis is linked with a change in food chain. The tadpoles being the embryonic origin of frogs are herbivorous, feeding on algae and green matter, which they collect by the adapted feature such as their teeth surrounding their mouths. Adult frogs, alternatively, are classified as carnivorous feeding on insects and worms. Occasionally, they also consume larger prey, for instance smaller frogs species and even little birds and rodents which they dominant and ingest.

[[Image:Development of frog from sperm to mature structure.jpg|thumb|left|Figure 9 Image details:J,Nassif 2009.jpg]]

'''2. Changes in Morphology'''

These include the decrease or complete absence of specific organs or structures which are essential during development of early frog embryology, but not critical in the mature frog species. The significant alterations of this nature include the following developmental structures.

'''a)''' The long tail of the tadpole alongside the fin folds is absorbed again during metamorphosis and becomes absent at the final stage of the metamorphosis.

'''b) '''The developing gills are resorted, the gill clefts are congested and the branchial cavities start to become absent. The reabsorbtion of gills also takes place by autolysis.

'''c)''' The teeth of the perioral disc additionally the homey lining of the jaws are shed.

'''d)''' The lateral line sense organs within the skin of tadpoles vanish throughout metamorphosis.

'''e)''' The cloacal tube begins to condensed and reduced.

'''f)''' Various blood vessels, together with parts of the aortic arches, are reduced during mature development.

(The figure on the left represents the transformation from a tadpole to a developing structure.)[http://science.jrank.org/pages/2862/Frogs-Adult-morphology.html]

'''3. Progressive or constructive changes'''

This process comprises of the development of specific organs which mature into functional systems only during metamorphosis.

'''a)''' During development the limbs continue to augment in size and differentiation. The forelimbs, which in the tadpole mature under the opercular membrane, which then break through to the exterior. Simultaneously there is a increase in the length and strength of the hind limbs, joints develop in them and the toes become visible.

'''b)''' The middle ear becomes apparent in relation with the first pharyngeal pouch. The tympanic membrane matures. It is bounded by circular tympanic cartilage which allows the frog to retain air.

'''c)''' The visual organs bulge up on the dorsal surface of the head developing the nictitating membrane.

'''d)''' There is augmentation of the tongue and the formation of thevomerina teeth.

[[Image: Growth model.jpg|thumb|Figure 10 Image details:J,Nassif2009:]]

'''4. Remodelling of some structures'''

Systematic organs which operate both in the early embryonic larva and the mature adult change their differentiation during metamorphosis so as to meet the requirements of the adult mode of life and due to the habitat adaptations. The figure on the right illustrates structures developing from specic germ cell layers.

'''a)''' The skin of the embryonic tadpole is lined with a double-layered epidermis. The number of layers of cells in the epidermis augments throughout metamorphosis. Superficial surface layers become cornified. Multicellular mucous and serous glands originate in the skin. The pigmentation of the skin continuously changes, new patterns and colour start to form.

'''b)''' There is a lengthening of the mouth gap as a result of rotation of the quadrate cartilage and the true jaws become functional.

'''c)''' The tongue rapidly progresses and becomes larger and more muscular.

'''d)''' The eyes become more specialised.

'''e)''' In early tadpoles, the GIT is extremely long and wound up into a spiral folds. The intestine become greatly lengthened in herbivorous species due to the vegetables food chain.[http://en.wikipedia.org/wiki/Frog]

'''5. Development of the reproductive system'''

(The figure below represents the reproductive and development cycle of a frog as it transform from egg to frog specie.)

In tadpoles, right after the mouth is being formed, two indentation like thickenings of peritoneum begin to appear near the body cavity (dorsal surface), which is nearest to the mesentery which is near the developing kidneys. These appear in all tadpoles.

These indentations appear here because of a change in the endothelial cells, everywhere else they are usually flat looking cells but they undergo a change and in this particular area become somewhat cuboidal/columnar.

Later on the indentations become more obvious due to the epithelial cells replicating numerously to form a thick layer. The posterior two thirds of the indentation for the female is the ovary and for the male it is the testis. The third that is left differentiates and becomes fat for the body.

[[Image: Mature frog life cyle.jpg|thumb|200px|left|Figure 11 Image details:Derived from primary source:http://www.scienceclarified.com/images/uesc_01_img0038.jpg]]

[[Image: Developing frog.jpg|thumb|Figure 12 Image details:
[[Image: Mature develop frog.jpg|thumb|Image details: Wikipedia (2009) TYPICAL FROG Primary source:[http://en.wikipedia.org/wiki/File:Red-eyed_Tree_Frog_-_Litoria_chloris_edit1.jpg]].jpg]]

===Delamination===

Delamination indicates a mass separating a group of cellular matter from other cellular groups. It has been illustrated that the division of notochord, mesoderm and endoderm tissues from each other to form distinct cellular masses is completed by the progression of delamination, subsequent to these materials moving to the inside throughout gastrulation. During the developing gastrula, the germ layers are all recognized. These distinct segments of the embryo develop from these germ tissue layers.

===Polarity and Rotation===

Throughout fertilisation to the beginning of gastrulation, the frog’s egg continues in the original location in relation to its polarity. Subsequent to gastrulation its polarity begins to differentiate. This progression is linked with migration of materials within the gastrula and can be responsible for the alterations of the centre of gravity.

===Closing of Blastopore===

Subsequent to the formation of the gastrula, the blastopore is visible as a tiny round circular filled cavity containing the yolk plug. As it continues to reduce in dimension, it represented as a pear-shaped outline through the mutual approach of its lateral lips. Through it final progression these fuse entirely to produce a longitudinal groove, the streak which continue dorsally and ventrally in a small aperture. The inferior aperture closes, resulting in a depression called the anal pit. The superior region remains open for some period and begins to as the neural groove is laid down.

===Post Gastrulation or Organogenesis===

Throughout the duration of pre-gastrulation, all tissues for different organs vanish from the surface of blastula and migrate inside to take their final arrangement in the embryo structure where organs are developed from their potential regions. Consequently organogenesis transfers an embryo into free larva structure.

----

==Germ-layer origin of various body tissues==
[[Image: Development Models of Frog.jpg|thumb|right|Figure 13 Image details:Vertebrate Structure and Development.jpg]]

Ectoderm will give raise to structures such as skin, brain, spinal cord, neurons and sense receptors.
Mesoderm will give raise to structrues such as notochord, muscles, blood, bone and sex organs.
Endoderm will give raise to sturctures such as inner lining of gut, liver, pancreas, lungs and bladder, thyroid and parathyroid glands and thymus.

== Structures derived from Germ-layers of frog species ==

[[Image:Development of Frog Layers.jpg|thumb|left|Figure 14 Primary source[http://www.bio.miami.edu/~cmallery/150/physiol/sf19x11b.jpg]Image details:J,Nassif 2009.jpg]]

[[Image:Development of frog layers.jpg|thumb|left|Figure 15 Primary source [http://www.bio.miami.edu/~cmallery/150/physiol/sf19x11b.jpg]Image details:J,Nassif 2009.jpg]]

'''Ectoderm '''

''Establishes the epidermal segments and its derivatives, to the frog’s nervous system. The ectoderm also contributes to :''

1. The olfactory and auditory epithelium.

2. The retina and lens of the eye.

3. Sensory organs.

4. The epithelial lining of the oral cavity and the anus.

5. The pineal and pituitary body.

'''Mesoderm'''

''Mesoderm originates:''

1. Connective tissue.

2. Muscles, except the notochord.

3. Blood vessels.

4. Lymphatics.

5. The peritoneum and the urinary and reproductive system.

6. The dermis, parts of the eye excluding lens, cornea, and conjunctiva.

'''Endoderm'''

''From the endoderm arises:''

1. The epithelial lining to the gut and oesophagus, stomach, intestine, bile duct.

2. The hepatic cells of the liver, respiratory tract, larynx, trachea and lungs.

3. The lining of the urinary bladder, pancreas thyroid and thymus.

[The two figures reveal the development of structures deriving from the celluar components of the embryology of the frog].[Structures derived from Germ-layers of frog species ]

==Life cycle of a frog==

'''Fertilization-egg''':

The female lays eggs in the spring. A group of fertilized eggs is called spawn;

'''7-10 days''':

Fertilized egg feed on remaining yolk which is in its gut. Their gills, mouth and tail have poorly developed. Begin to swim and feed on algae;

'''10-30 days(4 weeks):'''

A layer of skin grows over gills. Teeth begin to appear. A coiled gut start to develop. This is aid in digestion;

'''30-60 days(6-9 weeks):'''

Legs being to grow and head is more distinct. Start to eat insects. Arms begin to grow;

'''60-80 days(12 weeks):'''

Resemble a frog. Still have remaining tail;

'''80-140 days(20 weeks):'''

Fully developed, spend most of time out of water. Majority of frog live between 4-15 years.

==Timeline of frog development==

Development of egg and embryo at temperature 18 degree celsius.

'''0 hours''' - fertilization of the egg

'''1 hours''' - formation of the gray crescent due to pigment migration

'''3.5 hours''' - early cleavage

'''4.5 hours''' - blastula stage(coeloblastula with eccentric blastocoel

'''26 hours''' - gastrulation

'''26 hours''' -'' early'' - crescent shaped dorsal lip

'''34 hours''' - ''middle''- semicircular blastoporal lip

'''42 hours''' - ''late'' - circular blastoporal lip

'''50 hours''' - neurulation

'''50 hours''' - ''early'' - medullary plate

'''62 hours''' -'' middle''- neural folds converging

'''67 hours''' - ''late'' - neural tube formed and ciliation of embryo

'''84 hours''' - tail bud stage(early organogeny)

'''96 hours''' - muscular response to tactile stimulation

'''118 hours''' - early heart beat, development of gill buds

'''140 hours''' - hatching and gill circulation

'''162 hours''' - mouth opens and cornea becomes transparent

'''192 hours''' - tail fin circulation established

'''216 hours''' - degeneration of external gills, formation of operculum, development of embryonic teeth

'''240 hours''' - opercular fold over brachial chamber except for spiracle and internal gills

'''255 hours''' - prolonged larval stage with refinement of organs

'''270 hours''' - development of hindlimbs, internal development of forelimbs in opercular cavity

'''275 hours''' - projection of forelimbs through operculum, left side first

'''280 hours''' - absorption of the tail and reduction in size of the gut

'''284 hours''' - metamorphosis complete, emergence from water as miniature, air breathing frog

==Stages of frog embryology==
--[[User:S8600021|Mark Hill]] 08:40, 9 October 2009 (EST) [[Talk:2009_Group_Project_5#Constructive_Criticism_of_Coordinator|see my comment on images]]

The rate of development of the egg and embryo will depend upon the temperature at which they are kept. The approximate schedule of development at 23 degree celsius is provided below.

{| border='1px'
|+ Table 1: Stages of frog development
!Stage !!Time since fertilisation (hours)!!Stage Characteristic !!Embryo characteristic !!Image of frog stage
|-
|1
|0.00-1.30
|fertilization of the egg, post fertilization
|animal hemisphere, gray crescent and vegetal hemisphere are present
|[[File:Stage01ventral.jpg|100px]]
|-
|2
|1.30-2.00
|splits into two cells
|appearance of first cleavage furrow
|[[File:Stage02ventral.jpg|100px]]
|-
|3
|2.00-2.15
|becomes four cells
|appearance of second cleavage furrow
|[[File:Stage03dorsolat.jpg|100px]]
|-
|4
|2.15-2.45
|becomes eight cells
|appearance of third cleavage furrow
|[[File:Stage04dorsolat.jpg|100px]]
|-
|5
|2.45-3.00
|becomes sixteen cells
|appearance of fourth cleavage furrow
|[[File:Stage05dorsal.jpg|100px]]
|-
|6
|3.00-3.30
|becomes thirty-two cells
|appearance of fifth cleavage furrow
|[[File:Stage06animal.jpg|100px]]
|-
|6.5
|3.30-4.00
|blastula stage
|Three dorsal folds become visible as a result of endoderm invagination. Pole cells no longer visible on surface
|[[File:Stage065dorsal.jpg|100px]]
|-
|7
|4.00-5.00
|Gastrulation stage
|two primary germ layers. epiblast and endoderm
|[[File:Stage07ventral.jpg|100px]]
|-
|8
|5.00-7.00
|neurulation
|medullary plate, neural folds and neural tube
|[[File:Stage08animal.jpg|100px]]
|-
|9
|7.00-9.00
|germ layer
|complete lip involution encircling yolk
|[[File:Stage09veg.jpg|100px]]
|-
|10
|9.00-11.00
|early gastrula
|two primary germ layers
|[[File:Stage10veg.jpg|100px]]
|-
|10.5
|11.00-11.45
|gastrula
|two germ layers
|[[File:Stage105vegb.jpg|100px]]
|-
|11
|11.45-12.30
|medulla plate
|Yolk sac protrudes dorsally, labium moves to midline on ventral side
|[[File:Stage11veg.jpg|100px]]
|-
|11.5
|12.30-13.15
|continuation of medulla plate
|start closing the plate
|[[File:Stage115veg.jpg|100px]]
|-
|12
|13.15-14.15
|early neurula
|thickened ectoderm give rise to CNS
|[[File:Stage12veg.jpg|100px]]
|-
|12.5
|14.15-14.45
|neural folds
|expansion of cavity
|[[File:Stage125postdors.jpg|100px]]
|-
|13
|14.45-16.15
|neural folds
|continue expanding cavity
|[[File:Stage13postdors.jpg|100px]]
|-
|14
|16.15-17.30
|neural folds
|continuation of cavity
|[[File:Stage14postdors.jpg|100px]]
|-
|15
|17.30-18.15
|tail bud stage
|early organogeny
|[[File:Stage15postdors.jpg|100px]]
|-
|16
|18.15-18.45
|tail bud stage
|posterior ventral view
|[[File:Stage16ant.jpg|100px]]
|-
|17
|18.45-19.45
|tail bud stage
|anterior view
|[[File:Stage17ant.jpg|100px]]
|-
|19
|20.45-21.45
|neural fold close complete
|dorsal view
|[[File:Stage19dorsal.jpg|100px]]
|-
|20
|21.45-22.30
|early tail bud
|anterior view
|[[File:Stage20dorsal.jpg|100px]]
|-
|21
|22.30-24.00
|termination of neural crest
|progress to next stage
|[[File:Stage21ant.jpg|100px]]
|-
|22
|24.00-24.45
|prolonged development
|elongation
|[[File:Stage22lat.jpg|100px]]
|-
|23
|24.45-26.15
|elongation of embryo
|later view
|[[File:Stage23lat.jpg|100px]]
|-
|24
|26.15-27.30
|continuation of elongation of embryo
|dorsal view
|[[File:Stage24latsmall.jpg|50px]]
|-
|25
|27.30-29.30
|organs development
|embryo elongates and develops dorsal thickening
|[[File:Stage25dorsal.jpg|50px]]
|-
|26
|29.30-31.15
|elongation
|dorsally forms neural and brain cavity
|[[File:Stage26lat.jpg|50px]]
|-
|27
|31.15-32.30
|elongation of embryo
|dorsal view
|[[File:Stage27lat.jpg|50px]]
|-
|28
|32.30-35.00
|further development
|lateral view
|[[File:Stage28lat.jpg|50px]]
|-
|29-30
|35.00-37.30
|tail bud
|growth
|[[File:Stage29-30lat.jpg|50px]]
|-
|31
|37.30-40.00
|prolonged development
|bud development
|[[File:Stage31lat.jpg|50px]]
|-
|32
|40.00-44.30
|early muscular development
|elongation
|[[File:Stage32lat.jpg|50px]]
|-
|33-34
|44.30-50.00
|muscular movement
|apparatus for locomotion
|[[File:Stage33-34lat.jpg|50px]]
|-
|35-36
|50.00-53.30
|muscular movement
|apparatus for locomotion
|[[File:Stage35-36lat.jpg|50px]]
|-
|37-38
|53.30-56.30
|heart beat
|develops apparatus
|[[File:Stage37-38lat.jpg|50px]]
|-
|39
|56.30-66.00
|mouth opens
|cornea transparent
|[[File:Stage39latsmall.jpg|50px]]
|-
|40
|66.00-76.00
|gill circulation
|hatching
|[[File:Stage40lat.jpg|50px]]
|-
|41
|76.00-80.00
|tail, fin circulation
|circulation
|[[File:Stage41lat.jpg|50px]]
|-
|42
|80.00-86.00
|internal gills, operculum
|opercular fold, teeth
|[[File:Stage42lat.jpg|50px]]
|-
|43
|86.00-98.00
|operculum complete
|operculum closed on right
|[[File:Stage43lat.jpg|50px]]
|-
|46
|98.00-106.00
|metamorphosis
|emergence from water as miniature, operculum complete|
|[[File:Stage46lat.jpg|50px]]
|-
|}

==Abnormalities of frog==

Abnormalities of frog could be caused by multiple factors. These include change in climate, predators, parasites, bacteria, fungi, viruses or pollution and contaminants such as pesticides, metals and fertilizer.[http://www.fws.gov/contaminants/documents/frogsrefup_septoct_2006.pdf]

The Abnormalities are further classified into different categories. These categories are:

===1. Infectious Diseases:===

'''Perkinsus Symptoms-''' caused by perkinsus-like protozoan organism. Symptoms include swollen viscera that leads to a bloated body and and infected swollen heart

'''Ichthyophonus symptoms-''' cause by parasitic genus, where symptoms include a swollen tail resorption site that matches the surrounding skin in color and translucency.

[[Image:Abnormalities of Frog species.jpg|thumb|left|Figure A Image details[waterwatchadelaide.net.au].jpg]]

===2. Surficial Abnormalities:===

Surficial abnormalities as the one that are visible on the surface of the skin. This includes abnormal pigmentation, , subcutaneous hemorrhaging, wounds due to trauma or from a predator
Edema is a fluid-filled swelling under skin whihc is also a surficial abnormality.

===3. Skeletal Abnormalities:===

This is further classified into three more categories:

'''a. Skeletal Malformations-'''

* Microcephaly (small head or blunt snout)
*Scoliosis (Curved spine in lateral direction)
*Shrunken Limb (Micromelia)
*Amelia (Completely missing limb with no stump)

'''b. Skeletal Abnormalities of Unclear Etiology-'''

This condition arises when a frog has ectromelia (missing limb), brachydactyly (missing digits) or other such condition with no visible trauma or external damage, then this will be classified as the Skeletal abnormality of unclear etiology.

'''c. Skeletal Injuries-'''

Any limb missing or broken due to trauma or other related reason which shows clear evidence of it is classified as skeletal injury

===4. Eye Abnormalities:===

Most common includes-

'''i. Anophthalmia:''' Skin covers the eye socket as there is no eye

'''ii. Abnormal Iris Coloration:''' Reduced pigment in either one eye or both resulting in two different colours of the iris at times

'''iii. Abnormal size or shape:''' Both eyes either deviating from each other or size of pupil or iris is different than the other eye

[http://www.fws.gov/contaminants/Amphibian/pdfs/AbnormalitySOP_woutpics_Jan08.pdf ]

==Genetics==

There are a wide variety of species that differ from each other when it comes to genetics and their functioning.

'''TAXONOMY:''' '''Phylum''' ''Chordata'' / '''Sub Phylum''' ''Vertebrata'' / '''Class''' ''Amphibia'' / '''Order''' ''Anura''

Their are more than two dozen different families of frogs, where suborders are:

'''1. ARCHAEBATRACHIA-''' most primitive frogs

'''2. MESOBATRACHIA-''' linked between the Archaebatrachia and Neobatrachia

'''3. NEOBATRACHIA-''' most modern frogs

{| border='4px'
|+ '''General Info:'''
! !!
|-
| '''Number of frogs' species'''
| 5280
|-
| '''Smallest frog genome size:'''
| 0.95pg, Ornate burrowing frog
|-
| '''Largest frog genome size:'''
| 13.40pg, Ornate horned frog
|-
| '''Mean of frogs' genome'''
| 4.68pg ± 0.13
|-
|}

[http://www.genomesize.com]

*Majority of frogs have only 22 to 26 chromosomes and polyploid is very common where they are almost bisexual.

*Polyploid Amphibians reduce their total cell number such that they acheive the same body size as diploids. One of the most unsual forms of polypoidy in amphibians is the water frog ''Rana esculenta'' from Europe and Western Asia.

* The species with larger genomes have more genes for e.g. the frog genus ''Xenopus'' includes 16 species, with genome sizes ranging from 3.5 x 10^9 bp to 1.6 x 10^10 bp. These differences have arisen by numerous events of polyploidization within the past 40 million years or so. The ancestral chromosome number for the genus seems to have been 18, but there are species with 36, 72 and 105 chromosomes [http://www.xenbase.org/common/]

{| border='4px'
|+ '''Difference within two families'''
! '''SPECIES''' !! ''X.LAEVIS'' !! ''X.TROPICALIS''
|-
| '''PLOIDY'''
| Allotetraploid
| Diploid
|-
| '''NO. OF CHROMOSOMES'''
| 36 chromosomes
| 20 chromosomes
|-
| '''GENOME SIZE'''
| 3.1 x 10^9 bp
| 1.7 x 10^9 bp
|-
| '''EGG SIZE'''
| 1-1.3 mm
| 0.7-0.8 mm
|-
| '''GENERATION TIME'''
| 1-2 years
| 4 months
|-
|}
[http://www.xenbase.org/common/]

===Genome Sequencing===

Since Frog has a huge family with many different species, only few main species that are used widely for the purposes of experiments have their genome sequenced.

''Xenopus tropicalis'' has one of the smallest genomes among amphibians and has the shortest generation time- four to six months and the only diploid genome among the 14 Xenopus species. This means it has no more than two copies of most genes, whereas the other species of Xenopus have four copies of most genes (pseudotetraploid). US Department of Energy's Joint Genome Institute (JGI) in Walnut Creek, California, initiated the X. tropicalis Genome Project, finding 1,700 million base pairs.
[http://www.genome.gov/Pages/Research/Sequencing/BACLibrary/xenopusTropicalis.pdf]

===Xenopus oocytes===

* The oocytes provide an important expression system for molecular biology.

* By injecting DNA or mRNA into the oocyte or developing embryo, scientists can study the protein products in a controlled system. This allows rapid functional expression of manipulated DNAs (or mRNA). This is particularly useful in electrophysiology, where the ease of recording from the oocyte makes expression of membrane channels attractive.

* One challenge of oocyte work is eliminating native proteins that might confound results, such as membrane channels native to the oocyte.

* Translation of proteins can be blocked or splicing of pre-mRNA can be modified by injection of Morpholino antisense oligos into the oocyte (for distribution throughout the embryo) or early embryo (for distribution only into daughter cells of the injected cell).
[http://www.staff.unibe.ch/sigel/xenopus.html]

===Xenopus Laevis===

* ''Xenopus Laevis'' is an important model organism in developmental biology. X. laevis is tetraploid and reaches sexual maturity in 1 to 2 years. What makes it important in developmental biology is its large and easily manipulable embryo.

* Extracts from the eggs of X. laevis frogs are also commonly used for biochemical studies of DNA replication and repair, as these extracts fully support DNA replication and other related processes in a cell-free environment which allows easier manipulation.

* The Human chorionic gonadotropin hormone (hCG) is present in the urine of the pregnant women in large quantities only. This hormone in the urine induces X.laevis oocyte production which formed the basis of first well-documented method of pregnancy testing X. laevis is also notable for its use as the first well-documented method of pregnancy testing when it was discovered. Today, commercially available HCG is injected into Xenopus males and females to induce mating behavior and breed these frogs in captivity at any time of the year.

===Gene cluster===

* The alpha and beta globin genes are closely linked in small cluster of frogs compared to human and chicken

* The similarity of architecture of two clusters found in X.laevis supports the tetraploid origin

* The two loci encoding the muscle specific creatine kinase isoenzymes and have large differences in developmental profile, therefore suggesting that duplicate loci that have not undergone silencing are not simply redundant copies but have acquired specialization.

* Contains twice number of genes for proteins i.e. haemoglobin and sarcomeric actin serum albumin compared with other species

----

==Current Embrology Research==

Currently, a number of fields have benefited from the development of frog embrology. These include cloning, verification of messenger RNA, and Cell cycle.

===Cloning===
[[Image:Robert Briggs.jpg|thumb|left|Figure 16 Image details:Robert Briggs.jpg]]

In 1952, Robert Briggs and Thomas J King cloned northern leopard frogs using a method of nuclear transfer. Briggs and King's experiment was similar to that envisioned - and piloted using salamanders - by Hans Spemann in his 1938 proposal for a 'fantastical experiment'. Later, John Gurdon extended this work and showed that nuclei from differentiated cells could support development, although less well than those from early embryos. [http://genome.wellcome.ac.uk/doc_WTD020799.html]

Lemaitre et a. (2005) from MRC Cancer Cell Unit, Cambridge, U.K. worked on experiments that demonstrated that importance of serial nuclear transplantation for the sucessful cloning of frogs. He demonstrated that exposure of somatic-cell nuclei (erythrocyte nuclei) and sperm nuclei to an extract of mitotic cell extract reorganizes the chromatin into shorter loops and allows replication at much shorter intervals along the DNA. This increases the efficiency of DNA replication in mammalian cell-free systems.

===Transgenesis techniques for functional genomics in Xenopus===

Transgenesis in Xenopus is made possible due to large embryos, a reliable fate map, ease of microinjection, ease of dissection/micromanipulation and existence of the neuroendocrine reflex of background adaptation as a model for activation/inact.

Recently, Hajime Ogino and Haruki Ochi from Nura Institute of Science and Technology in Japan focused on the genomic resources and principles of the transgenesis techniques in Xenopus, and discusses their applications to genome wide network analysis, with emphasis on the use of bioinformatics tools. This is will to understand the gene regulatory networks that control vertebrate development. [http://www.ingentaconnect.com/content/bsc/dgd/2009/00000051/00000004/art00001%3Bjsessionid=4ah96rms73gcu.alexandra]

Xenopus used to be a problem in earlier days when it came to transgenesis. Current methods involves isolated sperm nuclei from Xenopus testis that are microinjected into unfertilized eggs. The generated transgenic tadpoles contain 5-35 copies of the integrated plasmid that are expressed in all cells. If desired, expression of the transgene can be directed to the appropriate tissue and at the appropriate time by using specific promoters, mostly the Xenopus POMC gene promoter (isolated from a Xenopus genomic DNA library) to specifically direct expression of green fluorescent protein (GFP) at high levels to the intermediate pituitary cells, which can either be over expressed or inhibited.[http://molanphys.ruhosting.nl/transgenesis.htm]

[[File:Transgenesis.JPG]]

===Verification of messenger RNA===

While the existence and role of messenger RNA (mRNA) was known in bacteria, in the 1960s it was still debated whether it also existed in vertebrates. Taking haemoglobin mRNA from immature red blood cells and injecting it into a Xenopus oocyte, John Gurdon showed that the haemoglobin protein was indeed produced. Producing proteins in Xenopus oocytes has proved to be extremely useful in cell biology, in particular for the study of receptor proteins.[http://genome.wellcome.ac.uk/doc_WTD020799.html]

===Cell Cycle===

As they develop outside the mother, frog eggs are well stocked with the proteins needed to drive the development of the embryo. Studies of these processes has shed considerable light on the processes involved in cell division - termed the cell cycle. [http://genome.wellcome.ac.uk/doc_WTD020799.html]

===Limb development in Xenopus Laevis===

[[Image: Frog Limb development.jpg|thumb|right|Image details:Primary source:[http://images.google.com.au/imgres?imgurl=http://www.sciencedaily.com/images/2006/06/060616130718.jpg&imgrefurl=http://www.sciencedaily.com/releases/2006/06/060616130718.htm&usg=__xliPsPAvheUBME_kjv_q7auiFbo=&h=333&w=300&sz=11&hl=en&start=2&um=1&tbnid=y_ntJtmkRSK7WM:&tbnh=119&tbnw=107&prev=/images%3Fq%3DLimb%2Bdevelopment%2Bin%2BXenopus%2BLaevis%26ndsp%3D18%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

Donald D. Brown (2005),Department of Embryology, Carnegie Institution of Washington demonstrated factors related to limb development of Xenopus Laevis. Thyroid hormone (TH) is found to be required for limb development in this frog. Specific cell types in the growing limb were targeted for expression of a dominant negative form of the TH receptor by sperm-mediated transgenesis. Limb muscle development, the innervation of muscle from the spinal cord, and cartilage growth can be inhibited without affecting patterning of the limb or differentiation of other cell types. Remodeling of the skin occurs late in metamorphosis after the limb has formed. The coordination of these independent programs is affected in part by the control that TH exerts over DNA replication in all cell types of the limb. [http://www.pnas.org/content/102/35/12455.full]

----

== Glossary ==

[[Image: Frog species.jpg|thumb|left|Image details:Primary source:www.olympus.co.jp/.../080925/large/p02L.jpg].jpg]]

*'''Amphibian:'''

''Relating to or characteristic of animals of the class amphibia.Amphibians are found in the taxonomic class of amphibia, amphibians are capable of both occupying and successfully living in both land and aquatic communities.amphibian''

*'''Augmentation:'''

''Enlargement/Increase in cellular size.''

*'''Autolysis:'''

''breakdown of a part or whole cell or tissue by self-produced enzymes''

*'''Blastomeres:'''

''The undifferentiated cells formed by cleavage of the fertilised ovum. This includes cells in the cleavage, morula, and blastula stages of the embryo''

*'''Carnivorous:'''
''
Flesh-eating; subsisting on animals as food.''

*'''Cleavage:'''

''he repeated division of a fertilised ovum ''

* '''Cleft:'''

''an opening, fissure, or V-shaped indentation made by or as if by splitting''

*'''Chordate:'''

''Members of a diverse phylum of animals that, as embryos, possess a (1) notochord; (2) a dorsal, hollow nerve cord, (3) pharyngeal gill slits; and (4) a post-anal tail''

''The act or state of splitting or dividing of a cell, particularly during the telophase of (animal) cell division.''

*'''Cytoplasm:'''

''The cytoplasm (of both eukaryotes and prokaryotes) is where the functions for cell expansion, growth, metabolism, and replication are carried out''

* '''Epiboly:'''
''The expansion of one cell sheet over other cells, as takes place during gastrulation''

*'''Fertilization:'''

''A process in sexual reproduction that involves the union of male (sperm) and female (ovum) gametes (each with a single, haploid set of chromosomes) to produce a diploid zygote.''

*'''Gamete:'''
''A reproductive cell (male (sperm) or female (egg)) that has only half the usual number of chromosomes''

*'''Gametogenesis:'''

''process leading to the production of gametes. The development and maturation of sex cells through meiosis.Another name for meiosis where a diploid cell is divided into two haploid cells with half the chromosome content of the diploid parent cell.''

*'''Herbivorous:'''

''eating plants; of or pertaining to the herbivora.''

*'''Holoblastic:'''

''The complete division of an isolecithal or microlecithal egg into blastomeres''

*'''Invagination:'''

''One of the methods by which the various germinal layers of the ovum are differentiated.''

*'''Isoenzymes:'''

''Isozymes (also known as isoenzymes) are enzymes that differ in amino acid sequence but catalyze the same chemical reaction.''

*'''Mesentery:'''

'' membranous fold attaching various organs to the body wall.''

*'''Metamorphosis:'''

''A change in the form and often habits of an animal after the embryonic stage during normal development.''

*'''Neuroendocrine:'''

''Neuroendocrine [IPA nʊəroʊˈɛndəkrɪn] cells are cells that release a hormone into the circulating blood in response to a neural stimulus.''

*'''Organogenesis:'''

''The part of embryonic development where the body's main organs develop.''

*'''Peritoneum:'''

''The smooth serous membrane which lines the cavity of the abdomen, or the whole body cavity when there is no diaphragm, and, turning back, surrounds the viscera, forming a closed, or nearly closed, sac.''

*'''Perivitelline space:'''

''The perivitelline space is the space between the zona pellucida and the plasma membrane (sometimes called the vitelline membrane) in a fertilized ovum.''

*'''Polyploidy:'''

''Cells with three or more sets of chromosomes.''

*'''Pronucleus:'''

''the nucleus of the ovum or sperm after fertilization but before they fuse to form the nucleus of the zygote ''

*'''Protoplasm:'''

''The fluid living content of the cell that consists of two major divisions, the cytoplasm and the nucleoplasm (cell nucleus). It is composed mainly of nucleic acids, proteins, lipids, carbohydrates, and inorganic salts''

*'''Segmentation:'''

''division of some metazoan bodies (such as annelida and Arthropoda) into repeated parts, segments. Segmentation can be homomeric (more or less the same) or heteromeric(different from each other).''

*'''Terrestrial:'''

''Of or on the ground, of the habitat of a plant, on land as opposed to in water, or on the ground as opposed to on another plant.''

*'''Transgenesis:'''

''Transgenesis is the process of introducing an exogenous gene - called a transgene - into a living organism so that the organism will exhibit a new property and transmit that property to its offspring.''

*'''Yolk:'''

''nutritive material of an ovum stored for the nutrition of an embryo''

*'''Zygote:'''

''The cell from which an organism develops, that results from the fertilization of the egg by the sperm.''

''Primary Resource "Biology- Online Dictionary''[http://www.biology-online.org/dictionary/Main_Page]

== References - Frog Embryology: ==

[[Image:Frog Research.jpg|thumb|left|Image details:[http://images.google.com.au/imgres?imgurl=http://www.odt.co.nz/files/story/2008/09/university_of_otago_zoology_senior_lecturer_phil_b_3343259744.jpg&imgrefurl=http://www.odt.co.nz/on-campus/university-otago/21670/dunedin-frog-man-wins-zoo-award&usg=__JvJJU5QfOnIwY2bk4xo64UXuJRs=&h=600&w=404&sz=22&hl=en&start=14&um=1&tbnid=AbsP89yWcUiilM:&tbnh=135&tbnw=91&prev=/images%3Fq%3Dfrog%2Bresearch%26hl%3Den%26um%3D1].jpg]]

1. Savage, J. M. (2002). The Amphibians and Reptiles of Costa Rica. University of Chicago Press, Chicago [http://www.springerlink.com/content/vv015277w1746llw/]

2. Ford, L.S.; D.C. Cannatella (1993). "The major clades of frogs". Herpetological Monographs 7: 94–117 [http://digimorph.org/specimens/Xenopus_laevis/]

3. Tyler, M. J. (1994). Australian Frogs A Natural History. Reed Books [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.gracilenta.html]

4. Cogger, H.G.; R.G. Zweifel, and D. Kirschner (2004). Encyclopedia of Reptiles & Amphibians Second Edition. Fog City Press [http://en.wikipedia.org/wiki/Microhylidae]

5. Beltz, Ellin (2005). Frogs: Inside their Remarkable World. Firefly Books [http://unjobs.org/authors/ellin-beltz]

6. Tyler, M. J. (1994). Australian Frogs A Natural History. Reed Books [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

7. Moury JD, Hanken J (1995) Early cranial neural crest migration in the direct-developing frog, Eleutherodactylus coqui. Acta
Anatomica (Basel) 153, 243-253.

8.Raynaud A (1985) Development of limbs and embryonic limb reduction. In Biology of the Reptilia (ed. Gans C, Billett F), pp.
59-148. New York: John Wiley.[http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=9309]

9. Hanken J (1986) Developmental evidence for amphibian origins. In Evolutionary Biology (ed. Hecht MK, Wallace B, Prance GT), 20, pp. 389-417. New York: Plenum Press. [Hanken J (1986) Developmental evidence for amphibian origins. In Evolutionary Biology (ed. Hecht MK, Wallace B, Prance GT), 20, pp. 389-417. New York: Plenum Press.]

10. Elinson RP (1990) Direct development in frogs : wiping the recapitulationist slate clean. Seminars in Developmental Biology
1, 263-270.

11. Beebee, T. J. C. 1996. Ecology and Conservation of Amphibians. Chapman and Hall. London. [http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V5X-3SVHMKH-1X&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=1021245355&_rerunOrigin=google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=825868e10cd178d16a8a0e5ad14dc5ef]

12. Lehtinen, R. M. 2002. The use of screw pines (Pandanus spp.) by amphibians and reptiles in Madagascar. Herpetological Bulletin 2002:20–25.

13. Parris, K. M. and M. A. McCarthy. 1999. What influences the structure of frog assemblages at forest streams. Australian Journal of Ecology 24:495–502. CrossRef

14. Zug, G. R. 1993. Herpetology: An Introductory Biology of Amphibians and Reptiles. Academic Press. San Diego, CA.

15. Slack,J.M.W., Darlington,B.G., Heath,J.K. and Godsave,S.F. (1987)Mesoderm induction in early Xenopus embryos by heparin-binding growth factors. Nature, 326, 197-200.

16. Melton,D.A. (1990) Activins are expressed early in Xenopus embryogenesis and can induce axial mesoderm and anterior structures. Cell, 63, 485-493.

17. Harland,R.M. and Misher,L. (1988) Stability of RNA in developing Xenopus embryos and identification of a destabilizing sequence in TFIIIA RNA. Development, 102, 837-852.

18. Cunliffe,V. and Smith,J.C. (1992) Ectopic mesoderm formation in Xenopus embryos caused by widespread expression of a Brachyury homologue. Nature, 358, 427-430.

19. Kinoshita,K., Bessho,T. and Asashima,M. (1993) Competence prepattern in the animal hemisphere of the 8-cell-stage Xenopus embryo. Devel. Biol., 160, 276-284.

20. LaBonne,C., Burke,B. and Whitman,M. (1995) Role of MAP kinase in mesoderm induction and axial patterning in Xenopus development. Development, 121, 1475-1486.

21. Green,J.B.A., New,H.V. and Smith,J.C. (1992) Responses of embryonic Xenopus cells to activin and FGF are separated by multiple dose thresholds and correspond to distinct axes of the mesoderm. Cell, 71, 731-739.

22. Grainger R., Blumberg B., Harland R., Amemiya C., Importance of Xenopus Tropicalis to biomedical and biological research, Benaroya Research Institute, Virginia Mason Research Center [http://www.genome.gov/Pages/Research/Sequencing/BACLibrary/xenopusTropicalis.pdf ]

23. Gregory, T.R. (2005). Animal Genome Size Database. [http://www.genomesize.com]

24. U.S Fish and Wildlife Services, ABNORMALITY CLASSIFICATION SOP, [http://www.fws.gov/contaminants/Amphibian/pdfs/AbnormalitySOP_woutpics_Jan08.pdf ]

25. Donald D. Brown*, Liquan Cai*, Biswajit Das*, Nicholas Marsh-Armstrong‡, Alexander M. Schreiber*, and Rejeanne Juste*(2005), Thyroid hormone controls multiple independent programs required for limb development in Xenopus laevis metamorphosis [http://www.pnas.org/content/102/35/12455.full]

26. Ogino, Hajime; Ochi, Haruki, Resources and transgenesis techniques for functional genomics in Xenopus, Development Growth & Differentiation, Volume 51, Number 4, May 2009 , pp. 387-401(15) [http://www.ingentaconnect.com/content/bsc/dgd/2009/00000051/00000004/art00001%3Bjsessionid=4ah96rms73gcu.alexandra]

27. Giles Newton (2004) Why the frog? The Human Genome, [http://genome.wellcome.ac.uk/doc_WTD020799.html]

28. Xenbase, [http://www.xenbase.org/common/]

29. Donders Center for Neuroscience & Nijmegen Center for Molecular Life Sciences (NCMLS), Beyond the genome (Xenopus transgenesis for functional genomics),Faculty of Science, Radboud University [http://molanphys.ruhosting.nl/transgenesis.htm]

== External Links ==
[[Image:Frog links.jpg|thumb|left|Image details:[http://images.google.com.au/imgres?imgurl=http://2.bp.blogspot.com/_o93AaY0GzH4/SjY_ZYv0PII/AAAAAAAAAgk/skruNc2yN78/s400/computer%2Bfrog.jpg&imgrefurl=http://hellaheaven-ana.blogspot.com/2009/06/talking-frog-contemporary-fairy-tale.html&usg=__oxji1TGLV2Fi7xe0dnlmuYk8gDo=&h=288&w=288&sz=16&hl=en&start=2&um=1&tbnid=ywZd4zpdxC5plM:&tbnh=115&tbnw=115&prev=/images%3Fq%3Dfrog%2Bon%2Bcomputer%26hl%3Den%26um%3D1].jpg]]

1. Frog embryology [http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/F/FrogEmbryology.html Frog Embryology]

2. Frog cellular materials [http://www.xenbase.org/xenbase/original/cell/cell.html xenbase]

3. The zoology of frog species [http://worms.zoology.wisc.edu/frogs/mainmenu.html zoology frogs]

4. Frog cycle [http://www.bioethics.gov/images/sc_images/frog_dev.gif bioethics frog] Just a little cycle of FROG'S life cycle

5. Frog Embryology [http://embryology.med.unsw.edu.au/OtherEmb/Frog.htm UNSW Embryology]

6. Frog Research [http://apps.carleton.edu/campus/library/now/exhibits/wallcharts/frog/ carleton library exhibit]

{{Template:Projects09}}
[[Category:Frog]]

Talk:2009 Group Project 5

2009-10-12T13:08:40Z

Z3258567: /* Group Project Updates */

== Group Project Updates ==
--[[User:Z3258567|Sando Rashed]] 00:08, 13 October 2009 (EST) i got rid of a few more individual signatures
--[[User:Z3126345|Gang Liu]] 14:42, 8 October 2009 (EST)Hi group, one of the peer comments is to delete individual signature, so i got rid of all the signatures on the page.

--[[User:S8600021|Mark Hill]] 10:08, 10 October 2009 (EST) The [[2009_Group_Project_5#Stages_of_frog_embryology|stage images]] you have begun to add to your project are from [http://www.xenbase.org/anatomy/alldev.do? Xenbase - stages] it is incorrect to give UNSW Embryology as the source as my page just provides links to this external site. "Digitized images and developmental data from Nieuwkoop and Faber (1994) Normal Table of Xenopus laevis (Daudin). Garland Publishing Inc, New York ISBN 0-8153-1896-0." you will need to get permission to use these images in your project.

--[[User:Z3126345|Gang Liu]] 22:22, 11 October 2009 (EST)Thank you Dr Hill. I've just realised. Yes, i will try to get permission from authors.

== Project Updates ==
--[[User:Z3283499|Antonio Lee]] 10:57, 2 October 2009 (EST) Hi everyone, I will be working with you during the Lab10 Tutorial and here is the news link and PDF of the manuscript for your group exercise. I encourage you to read the paper before the tutorial. Also, please indicate next to the questions below (using either your initials or student number) which one of the four questions you wish to address.
:'''Group 5 :''' [http://www.sciencedaily.com/releases/2009/09/090918111056.htm '''Human Induced Pluripotent Stem Cells Retain Some Gene Expression Of Donor Cells'''] in Science Daily Published online 19 September 2009 [[Media:ANAT2341_Lab10_2009_Group 5 Reading.pdf|Manuscript (PDF): Transcriptional Signature and Memory Retention of Human-Induced Pluripotent Stem Cells]]

----

:'''Question 1. What is the background to the existing problem / disease condition? (z3295026)- JOE NASSIF'''
''

The discovery of neural stem cells, has lead to the exposure that a single cellular factor can be carried out to re-program and stimulate a human cellular component into a pluripotent form, allow the cell to have the ability to distinguish any category of cellular material in the human body. The ability of this process will allow the identification of common cellular material and what is not common for instance abnormal tumour cell or cancer cells, this process of iPSCs is an advantage in recognising normal and abnormal cellular matter extrinistically as the stem cell will recognise what it going to develop into, through signalling and programming. These stem cells are extremely useful in therapeutic uses, muscular dystrophies and replacement of cell into the specific regions of the human body needed to be replaced or repaired.

An arrangement of four particular factors was experimented to generate iPSCs, using knowledge involving viral vectors including viruses with the possibility to influence the transcriptional configuration of the cellular material, at times inducing the cell death process and trying to destroy cancerous material in specific regions of the body.

The mouse and human genetics in relations to iPSCs have revealed to be comparable to embryonic stem cells in relation to the cellular behaviour, gene expression and their potential to make a distinction between different types of cells.

Sequentially in regard to the advantage of reprogramming specific genetic materials, it is necessary to model processes to encourage pluripotency in the alterations of the genome, and it structures. By reprogramming neural cellular materials with the human body and creating iPSCs from human neural stem cells lacking the presence of specific viruses, the scientists developed new understanding of the function of iPSCs.'' --[[User:Z3295026|Joe Nassif]] 13:33, 8 October 2009 (EST)

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:Question 2. What approach / method did the research team take to tackle / improve the problem? (z3255007)- Sadaf Masood

''Introduction of Viral-free, integration free reprogramming approach, where pluripotent factors Oct4 and Nanog were cloned and transferred into human fetal neural progenitor cells under high frequency, which when expressed itself, became human iPSCs. This is also considered a safe approach in clinical terms as virus will not be affecting the genome.''

:Question 3. What was the breakthrough / major advancement OR failure / drawback? and why might this be of significance?(z3126345) Gary Liu

while both mouse and human iPSCs have been shown to be similar to embryonic stem cells in terms of cell behavior, gene expression and their potential to differentiate into different types of cells, researchers had not achieved a comprehensive analysis to compare iPSCs and embryonic stem cells.

"One reason is that previous methodologies used to derive iPSCs weren't 'footprint free,'" Muotri explained. "Viruses could integrate into the genome of the cell, possibly affecting or disrupting genes."

"In order to take full advantage of reprogramming, it is essential to develop methods to induce pluripotency in the absence of permanent changes in the genome," added Fred H. Gage, PhD, a professor in the Laboratory for Genetics at the Salk Institute and the Vi and John Adler Chair for Research on Age-Related Neurodegenerative Diseases.

:Question 4. What are the next steps in moving forward? What are the next or new hurdles to overcome? --[[User:Z3258567|Sando Rashed]] 14:15, 8 October 2009 (EST)
they have been able to find out that there is a safe way to create induced pluripotent stem cells, but what they are able to research now is that do these cells they have created have a issue with there memories is it affected by using a viral free method.

==Constructive Criticism of Coordinator==
--[[User:S8600021|Mark Hill]] 08:07, 8 October 2009 (EST) The following comments are general in nature in no specific order, as it would be inappropriate to suggest specific changes and then assess the final project. Comments will be added during this week and you still have one week before final submission.

* [[:File:Fertilized_and_Unfertilised_Eggs.jpg]] [[:File:Egg_Development.jpg]] what is the original source that these images are based upon? There is no description on the image page when it opens of what the images are showing.
* Some figure legend titles could be tidier.
* There is no list of changes that have been made in response to peer review process.
* The [[2009_Group_Project_5#Stages_of_frog_embryology|stage images]] you have begun to add to your project are from [http://www.xenbase.org/anatomy/alldev.do? Xenbase - stages] it is incorrect to give UNSW Embryology as the source as my page just provides links to this external site. "Digitized images and developmental data from Nieuwkoop and Faber (1994) Normal Table of Xenopus laevis (Daudin). Garland Publishing Inc, New York ISBN 0-8153-1896-0." you will need to get permission to use these images in your project.

==Constructive Criticism of Peers==

--[[User:Z3218657|Sally Clarke]] 10:12, 1 October 2009 (EST)
Great Assignments guys

- Great use of images

- It jumps straight into the information which can be either a good and bad thing depending on what you are trying to achieve, maybe add in an introductory section which leads the reader on to the next bits of information

- is the anatomy section of the Frog Necessary - remember what we are studying here!!!

- The staging section is good except that you only link to the images - would you be able to have thumbnails of each of them in the table - it would help the information

- Wiki Pages??? Maybe not

- Try to make your information a little more succinct as you repeat information in the timeline and staging sections and remember formatting - history section etc.

- Include the information on why this model is used - advantages and disadvantages of this model maybe

- Current research is good but you should probably include some info on the genome - or a link to find out information about it

Overall its a great project!

--[[User:Z3223194|Bronwyn Lewis-Jones]] 09:06, 1 October 2009 (EST) This is a great assignment. Congratulations. Well set out and good use of applicable images. I think the most important change to make is to include an introduction which gives the reader a brief understanding about the frog (the anatomy section does a good job of this but maybe include a few sentences in an intro) and why it is used in embryology research. Also you could be more specific with your image labels (e.g. "Typical Frog" - why not give us it's biological name if possible). I think you could also cut back on some unnecessary information in the timing/staging section(s). Also it might be a good idea to remove the signatures to allow the reader to focus on the information. Hope you find this helpful. :)

--[[User:Z3218146|Julianna Lam]] 01:39, 1 October 2009 (EST) great work guys.

- history section is lacking information

- the maturation phases are too detailed and i dont think that much detail is required.

- staging and timeline is excellent. it could look better if there were more pictures added into the staging part.

- the glossary is very helpful

--[[User:Z3254857|Begum Sonmez]] 22:49, 30 September 2009 (EST)
Hello Group 5. I'd like to start off by saying that the effort you all have put into you page is impressive. The first thing I noticed was the background information on the frog such as the embryology, growth and development, anatomy, and the egg of the frog. I found this extra information informative, interesting, and due to the lack of text,easy-to-read and engaging. The video under 'The Egg' depicting Early cleavage was an interesting video. I like how it wasn't placed under timeline or stages. The reason is because timeline and stages already has enough images, and this short and simple video provides an introduction to development.

*You all might have noticed there is a problem with the formatting of the History section (the text needs to be 'pulled down' below the image 'Early Development of Frogs'. The same problem is found under the sections 'Abnormalities of the Frog', and 'Current Research'.
*I think the sentence strucutre, and punctuation of the History section should be looked at. For example, '1851 - Henby Nelson(MD): He identified a remarkable fact through frog embryo. Henby observed the first cleavage of the yolk, in the egg of the frog. And corresponds in its line of direction to the longitudinal axis of the body of the embryo of those animals;' should read:
'1851 - Henby Nelson(MD): He identified a remarkable fact through '''the''' frog embryo. Henby observed the first cleavage of the yolk in the egg of the frog. And ('''what? The Yolk?''') corresponds in its line of direction to the longitudinal axis of the body of the embryo of those animals ('''of what animals?'''). This is just something small that should be worked on just to make more sense, but the amount of text you included is good.
*Under Gametogenesis, the sentence 'Gametogenesis is a progression which frog gametes are established from cells, called germ cells.' should read 'Gametogenesis is a progression '''in''' which frog gametes are established from '''germ cells'''.' Again, this is just a small amendment, but it will still be effective.
*Good pictures under 'Egg and Fertilisation' and under 'Gastrulation'.
*Under Gastrulation, the sentence 'In frogs, metamorphosis is related with to the modifications and adaptations as a frog changes environmental habitats from an aquatic to a terrestrial mode.' should read 'In frogs, metamorphosis is related '''with or to''' the modifications and adaptations '''occuring or taking place''' as a frog changes environmental habitats from an aquatic to a terrestrial mode.'
*Too much unnecessary text under 'Maturation phases'. Try condensing the text under '4. Fertilisation of the egg' and '5.Segmentation of the Egg'.
*There is a good amount of information under the 'Structures derived from Germ-layers of frog species' section. It can be improved by listing (in dot form or numbering) the structures instead of including them all in a paragraph. I really liked this section. To the artist of the drawings: great work. I found them really helpful and relevant.
*Under 'Current Research', try to include dates for 'Transgenesis techniques for functional genomics in Xenopus' and 'Verification of messenger RNA'. Also, is there a specific example of a current research under the sub-heading 'Cell Cycle'. This would be more resourceful for the reader.
*The glossary was helpful.
Overall, well done on your efforts Group 5. The pictures are a great asset to this page.

--[[User:Z3252231|Angama Yaquobi]] 22:01, 30 September 2009 (EST)
Congratulation all the team members of group 5, the page looks amazing. Very well researched. So far one of the best looking
page with alot of informative content.Great images used throughout the entire page especially in the section of the growth and modification of frog species.However i suggest few changes can make the page look even better

* Lack of information in the section of history.

* There is too much information in the maturation phase which can be concised to make it much more easy for the readers to acquire the important information.

* For the section of current research more information is needed to give readers a more in-depth knowledge of the current research done on the model.

Overall well researched page. Well done guys. cheers.

--[[User:Z3186093|Jenny Guy]] 19:01, 30 September 2009 (EST)

Improvements:
* The frog...is a specific breed of frog used? Or are many types used for embryological research? This should be stated in the introduction. The image youve used from wiki is fine except its a "typical frog"...what is this? are you forming your page based on this frog?
* I dont believe the anatomy of the frog needs to be stated. We're researching the embryology, and yes this is going to be different to the human, so state the differences that cause embryology problems. Obviously we're going to be different but if you want to state that the frog only has 3 chambers, state that heart research wouldnt use a frog model since its not similar.
* Need to do some formatting - history heading is misplaced, i almost missed it.
* There is a hell of a lot of information to digest for the fertilisation. Would it be possible to cut some of this down? Select the best parts?
* Stages is very plain. Enough said.
* The image of the frog abnormalities...is it in the wrong spot? Shouldn't it be put close to the skeletal abnormalities paragraph - and refer to the image, and not the infectious diseases section.
* In genetics, can you explain why frogs have different numbers of chromosomes. Does this mean that some breeds of frogs can mate because they would have ill adapting chromosomes? How does the chromosomes it does have relate to human chromosomes??
* i got very confused with the subtypes of families of frogs...is the embryological research affected with modern or primative frogs?
* Has the genome been sequenced? Apparently so? Some of the english here needs to be editted. Grammar isnt good, some sentences dont make too much sense.
* Have you listed "links to related resources/research laboratories?" like Mark asked for in the marking criteria?? nope.

--[[User:Z3218792|Gabriela Pinget]] 14:36, 30 September 2009 (EST) Hello! Nice page! Mind if I criticise?

- I like the use of the anatomy of the frog to better orientate the reader. Although it is slightly superflous, it does not contain too much information to look out of place,so it looks good

-Maybe in the intro you should add a little info on why it is a model for embryological studies i.e. its advantages over the others

- I like the clear structure of the history section. It makes it very easy to read and understand.Although, the poor grammar makes it a little hard to understand (e.g. you may want to re-word what you wrote for 1976, it reads as though a woman was impregnated with a frog)

-perhaps there is a little too much detail on the growth and development of the frog. It's a little overwhelming- also quite a bit of repetition in this section

--[[User:Z3217015|Mitchell Mathieson]] 09:32, 25 September 2009 (EST) I think the looks good. However, the information is very spread out all over the place, and there is a bit of irrelevant information, such as the anatomy of the frog. There also seems to be repeated information in the stages and timelines; such as having tables and text to say the same thing. There was a heavy emphasis on the stages of development (it pretty much takes up 3/4 of the page) which probably could have been done more succinctly. The formatting needs a bit of fine tuning (heading separated from their text, and gaps everywhere), but in general it is good; the information is quite useful and well written.

--[[User:Z3224449|Elide Newton]] 14:57, 26 September 2009 (EST)HELLO GROUP 5: Well done on your assignment. my one piece of advice on your assignment is all about improving the flow and purpose of your assignment. Firstly There needs to be a introduction to the frog. why the frog is used as a model for embryology? By understanding the stages of development and timeline of the frog we can study the frog as a model. Why it is a good model and our understanding can be linked to why is has been used in the past and why it is being used currently in the future. hopefully this introduction clarifies the purpose of your information, and gives an outline to what you will cover in the assignment. also there is lots of unimportant information in regards to this assignment which is clouding your purpose of timeline, stages, genetics, past, present and future research. with this introduction paragraph, stating what topics you will cover and how these fit into using the frog as a model for embryology, hopefully it will flow better. all the best!

--[[User:Z3126328|Jin Lee]] 16:32, 26 September 2009 (EST) congulatulation Group5. The assignment looks good however, if you can make some additions it will be even better. Here is my suggestions: firstly the reference needs to be looked after. secondly some of sections are irrelevant(I found the 'anatomy of the frog' is irrelevant) and too much general information about the frog. May be better to focus on the assignment cirteria. For the history section, information is lacking(it's too brief) may be trying to add some more details about the each scietists...eg. in 1976, please mention which doctor you are reffering to. For the current research section, some more information needs. Overall, the assignment is visually well represented but may be concentrate on the main sections like timeline, stages, genetics, history and current research.

--[[User:Z3187802|Vishnnu Shanmugam]] 21:37, 26 September 2009 (EST)Great work frog group. The assignment you have put together is informative and well organized. One of the best features of the project is how clicking on the image takes you to another page with detailed and thorough explanations of the image. It is also good to see that you have added extra sections such as “abnormalities of the frog” and “the egg”. I note that too many groups are only interested in the headings specified in the marking criteria and have not done any extra work. The glossary is also a nice touch. Ways of improving the assignment:

- The background section introducing the frog needs to have information on why the frog model is useful. Include information on spawning, maintenance of specimens, genetic attributes and genetic similarities with humans.

- Although the addition of extra sections is good, it needs to be relevant to embryology. The anatomy of the frog section concentrates on the anatomy of the adult frog which is irrelevant for this project.

- The assignment should contain links to research laboratories and researchers as specified by the marking criteria. The external links do not do this.

- Remove the signature and time stamping at different sections of the assignment. The group project is collective effort, and the final presentation should not look like it has been split up. Do not worry about your contributions as these are logged and available for viewing under the “my contributions link”

- Some links in the text transfer you to Wikipedia pages on the frog....these should not be used as a source of information in academic projects.

- The assignment needs to be properly referenced as there are no references made in the actual text. see www.lc.unsw.edu.au/onlib/ref_apa.html for help with APA referencing

Overall a good project, some changes and additions are necessary to make it outstanding.

--[[User:Z3252340|Emily Wong]] 11:06, 27 September 2009 (EST) Firstly, Great work group 5. This project is very informative, well structured but a little unorganized. There is an extremely large amount of text presented. Perhaps a few more pictures or diagrams to negate some of the written work would be a way to improve the project. The work is well referenced with an extensive reference list. There is a lot of information on content that is not required. A way to improve your project would be to summarise a lot of this unnecessary information and maybe try and place it under one of the content headings. It appeared that a lot of this information was about stages or time points so maybe you could include this information in one of those sections.

--[[User:Z3217686|Thomas Dangerfield]] 14:25, 28 September 2009 (EST)Hey guys! Nice job! Plenty of information present, it just seems to jumble around a lot. Definitely needs an introduction, and possibly the first available section could be moved to after the anatomy of the frog. I don't mind the basic anatomy of the frog by the way, as it provides a little background to what the reader is going to end up with at the end of the development stage. Also the images could have a caption about what is actually happening in the image or what the images are trying to describe. There also seems to be a whole of a lot of information and plenty of images on the development and growth of the frog, but comparatively little on the genetics section. Chromosome maps can be very handy and comparisons with the human genome can help establish a picture of what you are trying to say. Just some organization and possible sifting of information would do the assignment nicely! Still, a very nice job on the frog guys!

--[[User:Z3185685|Sumaiya Rahman]] 17:16, 28 September 2009 (EST) Hey guys! Wow congrats on the assignment. I actually like the extra topics on the page. It makes it interesting and gives a lot of background knowledge to the reader. As mentioned, i am not sure why you have put in your signature stamps, this is not necessary. A lot of good images have been used but maybe instead of using figure 1, figure 2 etc. under the images; you could write what the image actually shows. I think this is what we were told to do? The links to the images in each stage are really good and help convey the information. The other thing that would help improve your page would be the addition of a glossary. Well done overall!

--[[User:Z3215682|Carly Mooney]] 11:56, 29 September 2009 (EST)
I think this was the assignment that looked the most professional. I liked the additional anatomy of the frog section, Few suggestions:
*a proper paragraphed introduction
*perhaps either in introduction of the history of the model needs a small explanation of why you use the frog as a model.
*remove the signatures, it is distracting and looks like it wasn't a group effort
*some sections were well referenced and others not, this needs to be unified.
*I think some of the sections with single images can afford to have those images enlarged slightly.
Overall this assignment looks the most unified of them all so congrats.

--[[User:Z3220040|Joanne Raffel]] 16:41, 29 September 2009 (EST) Well researched page. I would recommend including an introduction, which would make a better transition into the next section, also the growth and development, the egg and the anatomy section could have been condensed into one section. I thought there was too many main headings, I would recommend including subheadings, otherwise the information seems disjointed. I also got very confused reading through the page as I wasnt sure which heading was apart of another or whether it was something completely new. The history section was well formatted, however more information would have been appreciated as there didnt seem to be much of the actual history, more of a timeline of the frog. I thought the gametogenesis section was irrelevent. I also didnt need to know who wrote what section, this is a group assessment. Some of your headings could have been phrased more appropriately and clearer. The egg and fertilisation section would have been more impressive with subheadings rather than continuous main headings, whereby allowing the information to flow, also some of the information wasnt introduced in each section, it was just assumed. The maturation section would be better formatted in a table rather than a chunk of text. Cleavage, gastrulation, growth and modification, germ layer origin and structures derived from germ layer would be better as one section rather than multiple. The life cycle was extremly short and lacked information. The timeline was well formatted however I would have liked pictures. The staging section was organised clearly, however I would have liked to have seem part of the image rather than having to see it via the link. The abnormalities and genetics section would have been clearly as paragraphs with more information describing what is occuring rather than listing it, pictures would also be appreciated if possible. The current research section covered a number of topics however each section was very short. The glossary was appreciated however some of the words werent necessary (i.e. aquatic). Overall a very good page with some interesting images.

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--[[User:S8600021|Mark Hill]] 01:50, 8 September 2009 (EST) Still coming along, you have a lot of interesting pieces of information and some fair images. But how do the images relate to the text and where is the linkage? It is always easier to paste a whole lot of text information without interpreting what it actually means. Some of the information is good, tough some text also looks to be sourced without referencing. Overall the page lacks an integrated feel and structure.

--[[User:S8600021|Mark Hill]] 08:45, 21 August 2009 (EST) This is a good start. It is important that the project page content/structure reflects what all members of the group have in mind. There should be a list of relevant references now on this discussion pages.

== Background Reading ==

--[[User:Z3255007|Sadaf Masood]] 21:44, 8 September 2009 (EST) This link is for you Gary
http://www.xenbase.org/xenbase/original/atlas/NF/NF1-10.html

--[[User:Z3126345|Gang Liu]] 15:18, 23 September 2009 (EST) hi could anyone tell me how to upload pictures on the main page. i'm trying to upload pictures from this link http://www.xenbase.org/xenbase/original/atlas/NF/NF1-10.html, into the last column of stages of frog embryo table. cheers!

Hey guys!!

I have only met one person in the group..and that was today in the lecture (3/08/09)

Still missing out on the third person here!

Lets decide on the animal guys before the lab!!!!

Cheers!

--[[User:Z3126345|Gang Liu]] 15:22, 16 August 2009 (EST)Hi all, I'm Gary and i've just enrolled into this subject mid-week last week. Will try to catch up with the group assignment and individual homework.

--[[User:Z3126345|Gang Liu]] 14:54, 19 August 2009 (EST)Hi group, since we are dividing the assessment. I would like to work on sections such as "The egg", "Fertilization", "Cleavage", "Gastrulation", and "Hand-drawing diagram". Thank you.

--[[User:Z3126345|Gang Liu]] 12:56, 20 August 2009 (EST)Hi all, Joe is working on the first six subheadings. And i'm happy to take whatever subheadings the rest of the group is not working on. Thank you.

--[[User:Z3126345|Gang Liu]] 14:07, 20 August 2009 (EST)Hi all, after this week's group dicussion in the lab, we split the tasks as the following:
*Joe is responsible for subheadings such as egg, fertilization, cleavage, gastrulation, differentiation and growth;
*Gary is responsible for subheadings such as anatomy of frog, timeline and stage(introduction), and abnormalities;
*Sando is responsible for subheadings such as reproduction(male and female)+random subheading;
*Sadaf is responsible for subheadings such as current research, genetics and glossary.

--[[User:Z3126345|Gang Liu]] 17:26, 23 August 2009 (EST)Hi all, should we mention ''Xenopus'', part of frog family? --[[User:Z3126345|Gang Liu]] 09:29, 27 August 2009 (EST)Please ignore this line

--[[User:Z3126345|Gang Liu]] 18:00, 26 August 2009 (EST)Joe, thank you for updating our group page. Will upload my contents as soon as possible.

Hey guys, i need the list of words for the glossary or do u want me to pick them out myself?
thanks!--[[User:Z3255007|Sadaf Masood]] 10:47, 27 August 2009 (EST)

--[[User:Z3126345|Gang Liu]] 11:24, 27 August 2009 (EST)Hi, sadaf, will upload my glossary by tomorrow. Thanks.

--[[User:Z3126345|Gang Liu]] 11:30, 27 August 2009 (EST)Hi group, i just realised there is no one doing history part. Is there anyone would like to take this part? Or else, i'll work on it. Let us know.

http://books.google.com.au/books?id=OeAf7ChZD8QC&printsec=frontcover&dq=frog+embryology&lr=#v=onepage&q=&f=false

sick website

http://www.youddl.com/

EGG:

http://www.youtube.com/watch?v=GO5YN_t1fqw
--[[User:Z3258567|Sando Rashed]] 18:17, 23 September 2009 (EST) as late as im posting this i havent had time this past week to upload my notes but im putting them up now

--[[User:Z3258567|Sando Rashed]] 18:18, 23 September 2009 (EST)Gastrulation of a frog embryology
An invagination of cells that is found in the area of the embryo where it occupies the middle of the gray crescent, this is the beginning of gastrulation.
This beginning is what creates the blastopore which in the future will become the anus, and a group of cells that would later on produce the notochord which will eventually become the backbone (also known as the speeman organizer). Stimulates the ectoderm to form neural tissue (rather than it forming skin), so it begins the staging of the neural folds, which eventually the tips of the folds will form the neural tube which will become the spinal chord and the brain.
During gastrulation three layers start forming, these layers are known as the ectoderm, endoderm and the mesoderm.
Layer Forms out of it

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Ectoderm which may form the Brain, skin, spinal chord

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Mesoderm which may form the Notochord, muscles, brain

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Endoderm which may form the Inner lining of lings, bladder, thymus forms here.

--[[User:Z3258567|Sando Rashed]] 22:24, 23 September 2009 (EST)Cleavage = the repeated division of a fertilised ovum
When the zygote nucleus forms the first cleavage forms, this nucleus undergoes a number of mitosis processes, a wrinkle forms down longitudinally passing the poles of the eggs where the sperm enters. This is how the egg is split up into two halves and this process is what forms the 2-cell stage.
The process of the second cleavage is the process that allows the 4-cell stage to occur, the wrinkle runs through the poles at right angles instead of running through it longitudinally.
The 8 stage cell is formed during the third cleavage it cuts across horizontally but it cuts through closer to the animal poles rather than the vegetal poles.
As cleavages continually occur a 16 and 32 cell embryo are formed, and as these cleavages continuously occur the cells closer to the animal poles divide more rapidly and in more numbers compared to the vegetal pole. Eventually with all these cells continuously forming the blastula forms and a blastoseal which is a fluid filled cavity forms within it (no growth of the embryo has formed).
--[[User:Z3258567|Sando Rashed]] 23:06, 23 September 2009 (EST)Anatomy of a Frog
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The anatomy of a frog has many specialized features that are unique to the frog to help them live in their environment, they have long sticky tongues that help with them to grab food, they have specialized bones in the legs to help them jump.
When under water frogs are able to breathe through their skin, the oxygen is able to diffuse straight into the blood through the pores on the skin; they also have lungs that allow them to breathe on land.
In frogs they have 3 valves instead of the 4 valves in humans, they have one ventricle and two atria’s, the spiral valve does not allow blood with oxygen to mix with blood that has no oxygen.
Frogs are able to listen to sounds that have a low pitch through their skin as well as hearing sounds with a high pitch through their ears.

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The Egg

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The egg of a frog is approximately 1.6 million times larger than a normal frog cell. While all the embryological development is occurring through time it will eventually become a tadpole.
The egg can be divided into three different regions, the top part of the egg is known as the animal pole, the bottom half of the egg is known as the vegetal pole and a segment between the animal and vegetal pole is known as the gray crescent.--[[User:Z3258567|Sando Rashed]] 10:09, 24 September 2009 (EST)

Fertilization
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This occurs once the sperm cell has inserted, following the insertion of the sperm cells meiosis II is completed, there is a 30 degree position change of the cytoplasm, gray crescent allows this change to be visible in some amphibians, the gray crescent is able what determines the expect ted outline of how the frog will form. The sperm cell joins with the nuclei of the egg which forms the diploid zygote nucleus. --[[User:Z3258567|Sando Rashed]] 10:09, 24 September 2009 (EST)

2009 Group Project 5

2009-10-12T13:07:59Z

Z3258567: /* The History of the uses in agriculture and research */

== The Embryology of Frogs ==

== The Frog ==

[[Image: Frog species .jpg|thumb|left|Image details: Wikipedia (2009) Frog species[http://en.wikipedia.org/wiki/Frog#Uses_in_agriculture_and_research].jpg]]

Frogs are scientifically identified by the structure of their long posterior limbs, a petite framework, webbed fingers and feet, budged eyes and the lack of a tail. The majority of frog species are extensively recognized as outstanding jumpers, due to their long, dominant legs, which are adaptations to progress jumping performance during activities. The Frog is one of the most frequently studied species in experimental embryology and most anatomical sciences. The Frog is a practically effective model for human embryological development given that the Frog:

* Comprises of genes which can be effectively manipulated

* Comprises of similar homogeny with humans species

* Reproduces a large quantity of offspring in a short period of time

* Are small species which can be simply sustained

* Are not extremely luxurious and expensive

== The History of the uses in agriculture and research ==

Frog species are reared commercially for a variety purposes. Specific species of frogs are used as:

* Food source; frog legs are a delicacy and are eaten in European countries and in many parts of South American regions.

* Dead frogs are commonly consume for dissections in universities to contrast the organs and systems. This practice has turn down in current years with the growing in concerns about animal welfare.

* Frogs have achieved to be significant models of organisms throughout the history of science as their small bodies are able to be experimented upon.

* Frogs are used in cloning research and other embryonic experiments since frogs are amongst the closest living relatives of man to lack egg shells characteristic of most other vertebrates, and therefore make possible observations of early maturation.

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== Growth and development of the Frog ==

[[Image: Mature develop frog.jpg|thumb|Image details: Wikipedia (2009) TYPICAL FROG Figure 1 Primary source:[http://en.wikipedia.org/wiki/File:Red-eyed_Tree_Frog_-_Litoria_chloris_edit1].jpg]]

* The frog is a well recognised species, abundant predominantly in ponds, swamps, though various species may also exist in damp or shady environments distant from moist habitats.

* Eggs of specific frogs are easily obtained and may be examined in from the beginning of fertilization onwards. The phases of embryonic development differs in various chordates, yet the typical phases are basically apparent in all frog species. The differences are associated principally to the amount of yolk particles present in an egg.

* The yolk particles offer nourishment of the developing embryo. The process of frog development will be discussed from the phases of gametogenesis to the adult stage.

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== The Egg ==
[[Image:Development of Poles in frog Fertilization.jpg|thumb|left|Figure 4 Image details:J,Nassif 2009.jpg]]

* The embryology of a frog egg is a vast cell; its dimensions are approximately 1.4-1.6 million times larger than a typical aquatic species egg cell. Throughout the frog’s embryonic maturation period, the egg will be transformed into a tadpole encompassing millions of cells but still remains with its constant volume of genetic material, the vast prodction of cell have been illusttrated in the figure on the right revealing the production of eggs from female frogs. [http://en.wikipedia.org/wiki/Microhylidae]

* The early embryonic frog structure consists of three main segments the superior hemisphere known as the animal pole which is usually visible as a grey coloured area. The innermost layer appears to be between the outer two sections known as the gray crescent represented in black. Inferiorly, represents the vegetal pole typically lighter than the superior compartment illustrated in gold.

VIDEO RESOURCE: [http://www.youtube.com/watch?v=GO5YN_t1fqw&feature=related]

[[Image:Early Development of Frogs.jpg|thumb|left|Figure 3 Image details:J,Nassif 2009.jpg]]

==History of frog embryology use ==

*'''1851''' - ''Henby Nelson''(MD): He identified a remarkable fact through the frog embryo. Henby observed the first cleavage of the yolk, in the egg of the frog. And cleaved structure corresponds in line of direction to the longitudinal axis of the body of the embryo of the frog species.

[[Image:Wilhelm Roux.jpg|thumb|right|Wilhelm Roux[http://images.google.com.au/imgres?imgurl=http://www.todayinsci.com/R/Roux_Wilhelm/RouxWilhelmThm.jpg&imgrefurl=http://www.todayinsci.com/6/6_09.htm&usg=__qRLTEMTHdZpAHxiNX12hWjcm9tA=&h=125&w=100&sz=4&hl=en&start=2&um=1&tbnid=LIKIwZTqCpk7MM:&tbnh=90&tbnw=72&prev=/images%3Fq%3DWilhelm%2BRoux%26gbv%3D2%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

*'''1888''' - ''Wilhelm Roux'': Wilhelm Roux attempted to solve the above observation by damaging one cell of a two-cell frog embryo with a hot needle. The cell stayed in place. However, it did not develop further. Its partner developed into a left or right half-embryo;

*'''1907''' - ''John Hopkins'' hospital: In order to identify the cellular source of neuronal fibres. Scientist placed small portions of frog embryo spinal cords in lymph on a microscope slide and was able to observe clear cut neuronal sprouting.

*'''1951''' - ''Robert Briggs'': Robert Briggs was able to clone a frog embryo by substituting the nucleus of an unfertilized frog egg cell with the nucleus of a frog embryo cell. This process is known as nuclear transplant, has formed the basis for all cloning.

*'''1952''' - ''Robert Briggs and T.J. King'': Robert Briggs and T.J. King used frog for test experiment. Because the size of the eggs in the frogs are enormous compared with those of mammals, which make them easier to manipulate.

*'''1976'''- Using the technique that had been successful in cloning frog embryos, the doctor transferred the nucleus of one cells into a donated egg cell. As an embryo began to develop, it was implanted into the uterus of a young woman.

*'''1997''' - ''Wilmut and Campbell'': Utilizing the cloning technique from frog embryo, Drs. Wilmut and Campbell tried the starvation technique on embryo cells to produce Megan and Morag, the world's first cloned sheep and, until now, the most famous sheep in history.

*'''2000''' - ''Tokyo University'': Scientists at Tokyo University have grown artificial eyeballs. Scientists formed them in tadpoles by using frog embryo cells.

*'''2001''' - ''Advanced Cell Technology'': Scientists from Advanced Cell Technology announced production of a human embryo clone. This is significant as its parthenogenesis has been artificially induced in frogs.

[[Image:John Gurdon .jpg|thumb|right|John Gurdon [http://images.google.com.au/imgres?imgurl=http://www.pnas.org/site/misc/images/gurdon.jpg&imgrefurl=http://www.pnas.org/site/misc/classics4.shtml&usg=__1p-GA1PdOYsxKL-cznMb3RHCm98=&h=526&w=400&sz=223&hl=en&start=1&um=1&tbnid=9k4lhuLssiWCAM:&tbnh=132&tbnw=100&prev=/images%3Fq%3DJohn%2BGurdon%26gbv%3D2%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

*'''2002''' - ''John Gurdon'': John Gurdon from Wellcome Cancer Research Institute in Cambridge experimented on cloned frog embryo.

== Gametogenesis ==

* The sexual reproduction occurs through the fusion of either mature reproductive cells or germ cells known as gametes, which include the sperm from the male frog and ova from female frog species so as to form a single cell, the fertilized zygote. The gametes are typically developed in parents of different sexes . [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

* Males gametes is a spermatozoon , the female frog gamete is an ovum. Each gamete is formed by a process, recognised as maturation or gametogenesis in gonads. The typical male frog gonads are testies in male, while the female gonads are ovaries. The synthesis of both gonads is associated with the process of fertilization. [http://en.wikipedia.org/wiki/Microhylidae]

* The zygote changes into a mature frog through the process of embryology and metamorphosis. Gametogenesis is a in progression which frog gametes are established from germ cells. Initial germ cells are called primordial germ cells, which can be recognised extremely early in the life of frog species.

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== The Egg & Fertilization ==

[[Image:Fertilized and Unfertilised Eggs.jpg|thumb|left|Figure 6 Image details:J,Nassif 2009.jpg]]

[[Image:Egg Development.jpg|thumb|left|Figure 7 Image details:J,Nassif 2009.jpg]]

* This occurs once the sperm cell has inserted, following the insertion of the sperm cells meiosis II is completed, there is a 30 degree position change of the cytoplasm, gray crescent allows this change to be visible in some amphibians, the gray crescent is able what determines the expect ted outline of how the frog will form. The sperm cell joins with the nuclei of the egg which forms the diploid zygote nucleus. --Sando Rashed 10:09, 24 September 2009 (EST)

* The early phases in the development of the egg is visible, but must be studied in tadpoles throughout maturation. In embryonic tadpoles of about 10 millimetres in length, soon after the opening of the oral cavity, a pair of longitudinal ridge-like thickenings of peritoneum becomes apparent along the posterior surface of the body cavity situated near to the mesentery and along the inner boundaries of the kidneys. Genital ridges are established in all tadpoles of this age, sex is not distinct until a later period. The development of the egg is illustrated in the figure on the left revealing the structure of a developed egg and a mature of egg.

[[Image:Fertilisation life cyle.jpg|thumb|Figure 8 Image details:Derived from primary source:[http://en.wikipedia.org/wiki/Frog]]]

== Maturation of the Egg ==

* The eggs have currently accomplished their full size, and develop from the exterior of the ovaries like a small shot, but they still have to pass through the course of maturation before they are prepared to be fertilised. This progression of maturation relates to the nucleus almost completely.

* The nucleus component, containing the nuclear fluid that excludes through the nuclear membrane into the substance of the egg, a great segment of the nuclear reticulum vanishes and becomes degraded into separate globules known as nucleoli, but a extremely small division remains in the midpoint as a slender intricately thread recognised as the nuclear skets.
Relative to the egg getting discharged from the ovary, the follicles shatter allowing the eggs to fall into the abdominal cavity of the frog species, the egg then passes forwards, directly by the contraction of the muscular wall, somewhat by the movement of the cilia of the peritoneum, to the apex of the oviduct, which positioned at the anterior compartment of the body cavity opposite to the roots of the respiratory organs.

* The terminal part of the oviduct establishes a thin-walled pouch capable of great swelling, inside which the eggs gathers in large numbers. In conclusion, the eggs are migrated out through the cloaca into water which the albuminous investments of the eggs rapidly augment to form the gelatinous mass of the frogs spawn.

== Maturation phases ==

'''1. Nuclear skein''', moves from the midpoint of the egg to its outer surface, which it reaches opposite the midpoint of the black pole. The skein, subsequently an unevenly twisted thread, now presumes the specific arrangement of a nuclear spindle, for instance may be visible in the nucleus of an epithelial or additional cell instantly prior to division of the cell occurs.[http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

'''2. The first Polar Body,''' regarding the instance the egg is laid, but prior to its fertilistion, the egg develops a considerably flattened appearance at its upper or black pole, a definite sum of fluid being exuded among the egg and the vitelline membrane. The nuclear spindle currently separate into two identical segments, one of which remains with the egg, and the supplementary is extruded as the first polar body, a small ovoidal white globule, which is situated on the surface of the egg surrounding the exuded peri-vitellline fluid.

'''3. The Second Polar Body''', half of the nuclear spindle that stay behind then splits into two equivalent divisions, one of which remains inside the egg as the female pronucleus, whereas the other segment is extruded as the second polar body, a small white globule extremely related to the first polar body, and like this positioned in the perivitelline fluid on the superior portion of the egg.

'''4. Fertilisation of the egg''', includes the synthesis of the spermatozoon with to egg, specifically, synthesis of the nuclei of these two bodies. The spermatozoa, subsequent to being shed over the seed by the male, distribute vigorously by means of their extended tails, break through the gelatinous investment of the female eggs, bore their way through the vitelline membrane and so go through into the eggs themselves, which they penetrate relative to the superior or black hemispheres.
* Subsequently, an hour following the spermatozoon has entered; a progression may be visible projecting within from the exterior segement of the egg, with a liquid spot in the mid point. This liquid centre is the nucleus of the spermatozoon, and is said to be the male pronucleus, it break through beyond into the female egg, transporting the specialised pigment into it, so that it appears bounded by a pigmented capsule linked with the exterior of the egg by a pigmented stalk.
* By this instance, the second polar body has been established and extruded, and the female pronucleus is merely the only component of the primary egg nucleus still present. Both the male and female pronuceli, which are at initially distance separate to each other, merge and after having enlarged significantly in size then fuse mutually about two and half hours after fertilisation has originated to produce the segmentation nucleus.
* The segmentation nucleus is a huge sphere-shaped vesicle embedded in delicately granular protoplasm, and bounded by a distinct capsule of pigment, its arrangement by the synthesis of the male and female pronuclei completes the action of fertilisation. Specifically female pronucleus may be observe as an imperfect nucleus, and consequently result in the course of fertilisation. The nucleus of the spermatozoon or male pronucleus, replaces the component of the egg- nucleus which has been misplaced as the polar bodies.

'''5. Segmentation of the Egg''', the initial phase of growth consist in constant separation of the egg, whereby it becomes transformed from the unicellular state, which is everlasting only in the lowest species, to muliticelluar state charactertics of all higher species. To these early processes of growth the names segmentation is specified. Shorty subsequent to the competition of fertilisation and arrangement of the segmentation nucleus this later misplaces its sphere-shaped appearance and develops to be spindle-shaped, the yolk granules at the equivalent instance showing a tendency to develop into lines distributing outwards from the distal segment of the spindle.
* The nucleus now split into two halves, which shift away from one another, the yolk granules are likely to combined themselves around the two nuclei, and a slender vertical plate of delicately granular substance is left, dividing the egg.[http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

* Superiorly the eggs depression now becomes visible, initially as a small cavity and then develops as a groove, which almost immediately extends all round, and speedily deepening, splits the egg into two entirely separate halves along a plane equivalent with the vertical plane.

* Shorty after, the two nuclei soon separate again into two, and therefore a second cleft is created in the same state as before, its additionally in the vertical plane, however in a plane at 90 degrees to the initial one, and on its finishing point the egg comprises of four accurately similar segments, each containing a nucleus. The third cleft is horizontal in shape, but not equal, lying closer to the superior than the lower pole, it segregates each of the four cells into, an superior smaller and a inferior larger pole

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== Cleavage ==

[[Image: Frog Cleavage development.jpg|thumb|left|Figure 8.1 Image details:[http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/F/FrogEmbryology.html].jpg]]

* The egg of the frog is scientifically identified as’ telolecithal’ meaning there is a outsized amount of yolk concentrated at a single pole, in contrast to the concentration of cytoplasm and the site of the nucleus. The cleavage phases are holoblastic, therefore the total and after the second cleavage they are asymmetrical .The initial cleavage stage appears about two and half to three hours after fertilization. It commences as a minor depression in close proximity to the centre of the animal hemisphere. It appears as if some interior force is pushing the surface the egg towards the centre. This small upturned fold steadily continues in the form of a channel until it surrounds the egg. This groove is shallow in the commencement, but develop into deeper eventually separating the fertilized egg into two halves recognised as the blastomeres. [The figure on the left symbolise the development and growth of the frog embryo during cleavage].

* Internally the separation is mitotic, consequently each daughter cell contains a nucleus resulting from the copulation nucleus of the fertilised egg. This cleavage is vertical, the two cells are indistinguishable in respect of cytoplasm, pigment and yolk. The subsequent cleavage appears about an hour after the first. The channel of this cleavage begins at the centre of the animal hemisphere, is at right angles to the first and is vertical. This divides the egg into four blastomeres. The fourth blastomere so produced are not qualitatively equal, since of these only two contain the material from the gray crescent. The cleavage begins about thirty minutes after the second is completed or four hours after fertilisation. the cleavage plane of the third furrow is horizontal and slightly above the equator. Thus the four upper cells are a little smaller than the four lower cells. The smaller blastomeres are called micromeres and the larger blastomeres are called macromeres. The fourth cleavages follow 20 minutes after the third and tend to be vertical. This is usually a double furrow.

* The cleavage rate is accelerated with each of the early divisions and since the blastomeres are of unequal size and have varying amounts of cytoplasm and yolk, synchronous cleavage is lost and there is an obvious overlapping of the division. The upper most cells divide more rapidly than the lowermost cells. From this point onwards perfect symmetry in cleavage and in blastomere is very rare, although the embryo developed perfectly. The fifth cleavage is also doubled, appearing first in the upper hemisphere and then in the lower.

* The cleavage thus far follows the rule that each cleavage plane comes in at right angles to the previous one. The subsequent divisions become so irregular that it is previous one. The subsequent division become so irregular that it is impossible to trace out any plan or procedure. The segmentation continues more rapidly in the pigmented regions, since at that place the protoplasm is most dense, whereas, yolk which is very abundant in the vegetal side delays cell division. The multicelluar embryo at this stage is called morula by some biologists.

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== Gastrulation ==

[[Image:FROG GASTRULATION .jpg|thumb|left|Figure Image details:[http://www.google.com.au/imgres?imgurl=http://bio1903.nicerweb.com/Locked/media/ch47/47_12FrogGastrulation.jpg&imgrefurl=http://bio1903.nicerweb.com/Locked/media/ch47/gastrulation-frog.html&h=540&w=480&sz=46&tbnid=N78sHjELreGGSM:&tbnh=132&tbnw=117&prev=/images%3Fq%3Dfrog%2B-%2Bgastrulation&hl=en&usg=__4VK9FYLft0W-4lBe6p5EtQAMiaI=&ei=qPy5SurtMJvE6wON8JmdAg&sa=X&oi=image_result&resnum=4&ct=image].jpg]]

''The phase of Blastulation is followed by the unique developmental progression of gastrulation. The process of frog gastrulation involves the following processes.''

'''1. Epiboly Phase'''

The pigmented cellular materials of blastula have the propensity to overgrow the yolk cells within the developing content. This course which is known as epiboly commences gradually in the final blastula and rapidly accelerates with advancing gastrulation development. The cellular matter within the animal pole reproduces and matures on all sides except in area surrounding the dorsal lip of the blastopore has been established.

'''2. Convergence'''

Scientists suggested that the unfolding was thought to result in spreading of the superficial cells over a substrate with suitable absorption properties. Consequently epiboly and convergence are an outcome to this spreading tendency, which is actually increased by a reduction in surface tension of the distributing cells.

'''3. Rotation'''

The epiboly phase is maintained until the region of the dorsal lip has migrated and is a to some extent greater than 90 degrees and the region of the white blastopore is reduced to small circular rings. This section will be positioned away from the developing vegetal pole. Laterally the complete developing gastrula has been rotated to a horizontal axis, allowing it to lie at right angles to the original median plane of the egg. Therefore, the course of rotation is such that the dorsal lip is practically pushed backwards in one direction as rapid or quicker than epiboly moves it forward in the other. The outcome will be that the blastopore produced at roughly the vegetal pole is posterior, and the dorsal and ventral lips are essentially dorsal and ventral. This in addition allows the eggs to form the antero-ventral side of the potential embryo whilst the area marked by the grey crescent is to develop the dorsal segment.

'''4. Invagination'''

Visible is a small fissure- like invagination which is apparent in the middle between the equator and the vegetal segment. The most superior or dorsal border of the cleft produce the dorsal lip of the blastopore. This imput move back and forth on the dorsal plane near the dorsal lip and migrates around the boundaries of the blastocoel in company with the extension of the lateral lips. This adapted invagination is maintained until the blastocoel cavity has been almost abolished; excluding the slender opening separating epiblasts from the hypoblast, the new segment formed is known as the archenteron cavity.

'''5. Involution'''

Additional to previous course of action a distinct involution also occurs at the blastoporal borders. This is mainly dynamic at the median dorsal lip and gradually more less as it shifts across either side until it reaches the ventral lip where it constant.Throughout this progression, cells positioned beside the superior boundaries of the blastoporal lip migrate over the lip to the interior portion of the lip. These cells are remained within the embryo along the internal edge of the blastopore. This indicates the root of archenteron is composed of involuted cells and beyond this the external layer known as the ectoderm. The base and lateral sides are enclosed mainly of endodermal cellular material, which have been established from larger yolk cells, situated in the vegetal pole of the blastula. In the final phases of the gastrula development, the cells contributing to the floor of the archenteron, thin out significantly where they surround the blastocoel.
The hemispherical shaped dorsal lip of blastopore which become visible at the commencement of the gastruation stage carry on to augment, initially becoming semicircular, then transform into a horse shoe shaped and then finally forming into circular band. The band is the accomplished by the blastopore. Various yolk cells of vegetal pole present in the section are crowed into the blastoporal cavity where they form a gathering identified as a yolk plug. Blastopore rapidly reduces in size while the archenteron is still developing and becomes completely formed in the final stage; the yolk plug appears as only a small oval on the gastrula.

==Growth and Modification of Frog Species==

'''1. Changes in habits and habitats:'''

'''a)''' In frogs, metamorphosis is related with to the modifications and adaptations as a frog changes environmental habitats from an aquatic to a terrestrial mode. Metamorphosis has modified the adaption of frogs as this alteration it began during the aquatic adaptations in the surface of water to breathe air. Subsequently, it continues the terrestrial surroundings, therefore the frog species become abundant in vegetation area allowing the frog to transform in to amphibious species.

'''b)''' The transition during metamorphosis is linked with a change in food chain. The tadpoles being the embryonic origin of frogs are herbivorous, feeding on algae and green matter, which they collect by the adapted feature such as their teeth surrounding their mouths. Adult frogs, alternatively, are classified as carnivorous feeding on insects and worms. Occasionally, they also consume larger prey, for instance smaller frogs species and even little birds and rodents which they dominant and ingest.

[[Image:Development of frog from sperm to mature structure.jpg|thumb|left|Figure 9 Image details:J,Nassif 2009.jpg]]

'''2. Changes in Morphology'''

These include the decrease or complete absence of specific organs or structures which are essential during development of early frog embryology, but not critical in the mature frog species. The significant alterations of this nature include the following developmental structures.

'''a)''' The long tail of the tadpole alongside the fin folds is absorbed again during metamorphosis and becomes absent at the final stage of the metamorphosis.

'''b) '''The developing gills are resorted, the gill clefts are congested and the branchial cavities start to become absent. The reabsorbtion of gills also takes place by autolysis.

'''c)''' The teeth of the perioral disc additionally the homey lining of the jaws are shed.

'''d)''' The lateral line sense organs within the skin of tadpoles vanish throughout metamorphosis.

'''e)''' The cloacal tube begins to condensed and reduced.

'''f)''' Various blood vessels, together with parts of the aortic arches, are reduced during mature development.

(The figure on the left represents the transformation from a tadpole to a developing structure.)[http://science.jrank.org/pages/2862/Frogs-Adult-morphology.html]

'''3. Progressive or constructive changes'''

This process comprises of the development of specific organs which mature into functional systems only during metamorphosis.

'''a)''' During development the limbs continue to augment in size and differentiation. The forelimbs, which in the tadpole mature under the opercular membrane, which then break through to the exterior. Simultaneously there is a increase in the length and strength of the hind limbs, joints develop in them and the toes become visible.

'''b)''' The middle ear becomes apparent in relation with the first pharyngeal pouch. The tympanic membrane matures. It is bounded by circular tympanic cartilage which allows the frog to retain air.

'''c)''' The visual organs bulge up on the dorsal surface of the head developing the nictitating membrane.

'''d)''' There is augmentation of the tongue and the formation of thevomerina teeth.

[[Image: Growth model.jpg|thumb|Figure 10 Image details:J,Nassif2009:]]

'''4. Remodelling of some structures'''

Systematic organs which operate both in the early embryonic larva and the mature adult change their differentiation during metamorphosis so as to meet the requirements of the adult mode of life and due to the habitat adaptations. The figure on the right illustrates structures developing from specic germ cell layers.

'''a)''' The skin of the embryonic tadpole is lined with a double-layered epidermis. The number of layers of cells in the epidermis augments throughout metamorphosis. Superficial surface layers become cornified. Multicellular mucous and serous glands originate in the skin. The pigmentation of the skin continuously changes, new patterns and colour start to form.

'''b)''' There is a lengthening of the mouth gap as a result of rotation of the quadrate cartilage and the true jaws become functional.

'''c)''' The tongue rapidly progresses and becomes larger and more muscular.

'''d)''' The eyes become more specialised.

'''e)''' In early tadpoles, the GIT is extremely long and wound up into a spiral folds. The intestine become greatly lengthened in herbivorous species due to the vegetables food chain.[http://en.wikipedia.org/wiki/Frog]

'''5. Development of the reproductive system'''

(The figure below represents the reproductive and development cycle of a frog as it transform from egg to frog specie.)

In tadpoles, right after the mouth is being formed, two indentation like thickenings of peritoneum begin to appear near the body cavity (dorsal surface), which is nearest to the mesentery which is near the developing kidneys. These appear in all tadpoles.

These indentations appear here because of a change in the endothelial cells, everywhere else they are usually flat looking cells but they undergo a change and in this particular area become somewhat cuboidal/columnar.

Later on the indentations become more obvious due to the epithelial cells replicating numerously to form a thick layer. The posterior two thirds of the indentation for the female is the ovary and for the male it is the testis. The third that is left differentiates and becomes fat for the body.

[[Image: Mature frog life cyle.jpg|thumb|200px|left|Figure 11 Image details:Derived from primary source:http://www.scienceclarified.com/images/uesc_01_img0038.jpg]]

[[Image: Developing frog.jpg|thumb|Figure 12 Image details:
[[Image: Mature develop frog.jpg|thumb|Image details: Wikipedia (2009) TYPICAL FROG Primary source:[http://en.wikipedia.org/wiki/File:Red-eyed_Tree_Frog_-_Litoria_chloris_edit1.jpg]].jpg]]

===Delamination===

Delamination indicates a mass separating a group of cellular matter from other cellular groups. It has been illustrated that the division of notochord, mesoderm and endoderm tissues from each other to form distinct cellular masses is completed by the progression of delamination, subsequent to these materials moving to the inside throughout gastrulation. During the developing gastrula, the germ layers are all recognized. These distinct segments of the embryo develop from these germ tissue layers.

===Polarity and Rotation===

Throughout fertilisation to the beginning of gastrulation, the frog’s egg continues in the original location in relation to its polarity. Subsequent to gastrulation its polarity begins to differentiate. This progression is linked with migration of materials within the gastrula and can be responsible for the alterations of the centre of gravity.

===Closing of Blastopore===

Subsequent to the formation of the gastrula, the blastopore is visible as a tiny round circular filled cavity containing the yolk plug. As it continues to reduce in dimension, it represented as a pear-shaped outline through the mutual approach of its lateral lips. Through it final progression these fuse entirely to produce a longitudinal groove, the streak which continue dorsally and ventrally in a small aperture. The inferior aperture closes, resulting in a depression called the anal pit. The superior region remains open for some period and begins to as the neural groove is laid down.

===Post Gastrulation or Organogenesis===

Throughout the duration of pre-gastrulation, all tissues for different organs vanish from the surface of blastula and migrate inside to take their final arrangement in the embryo structure where organs are developed from their potential regions. Consequently organogenesis transfers an embryo into free larva structure.

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==Germ-layer origin of various body tissues==
[[Image: Development Models of Frog.jpg|thumb|right|Figure 13 Image details:Vertebrate Structure and Development.jpg]]

Ectoderm will give raise to structures such as skin, brain, spinal cord, neurons and sense receptors.
Mesoderm will give raise to structrues such as notochord, muscles, blood, bone and sex organs.
Endoderm will give raise to sturctures such as inner lining of gut, liver, pancreas, lungs and bladder, thyroid and parathyroid glands and thymus.

== Structures derived from Germ-layers of frog species ==

[[Image:Development of Frog Layers.jpg|thumb|left|Figure 14 Primary source[http://www.bio.miami.edu/~cmallery/150/physiol/sf19x11b.jpg]Image details:J,Nassif 2009.jpg]]

[[Image:Development of frog layers.jpg|thumb|left|Figure 15 Primary source [http://www.bio.miami.edu/~cmallery/150/physiol/sf19x11b.jpg]Image details:J,Nassif 2009.jpg]]

'''Ectoderm '''

''Establishes the epidermal segments and its derivatives, to the frog’s nervous system. The ectoderm also contributes to :"

1. The olfactory and auditory epithelium.

2. The retina and lens of the eye.

3. Sensory organs.

4. The epithelial lining of the oral cavity and the anus.

5. The pineal and pituitary body.

'''Mesoderm'''

''Mesoderm originates:''

1. Connective tissue.

2. Muscles, except the notochord.

3. Blood vessels.

4. Lymphatics.

5. The peritoneum and the urinary and reproductive system.

6. The dermis, parts of the eye excluding lens, cornea, and conjunctiva.

'''Endoderm'''

''From the endoderm arises:''

1. The epithelial lining to the gut and oesophagus, stomach, intestine, bile duct.

2. The hepatic cells of the liver, respiratory tract, larynx, trachea and lungs.

3. The lining of the urinary bladder, pancreas thyroid and thymus.

[The two figures reveal the development of structures deriving from the celluar components of the embryology of the frog].[Structures derived from Germ-layers of frog species ]

==Life cycle of a frog==

'''Fertilization-egg''':

The female lays eggs in the spring. A group of fertilized eggs is called spawn;

'''7-10 days''':

Fertilized egg feed on remaining yolk which is in its gut. Their gills, mouth and tail have poorly developed. Begin to swim and feed on algae;

'''10-30 days(4 weeks):'''

A layer of skin grows over gills. Teeth begin to appear. A coiled gut start to develop. This is aid in digestion;

'''30-60 days(6-9 weeks):'''

Legs being to grow and head is more distinct. Start to eat insects. Arms begin to grow;

'''60-80 days(12 weeks):'''

Resemble a frog. Still have remaining tail;

'''80-140 days(20 weeks):'''

Fully developed, spend most of time out of water. Majority of frog live between 4-15 years.

==Timeline of frog development==

Development of egg and embryo at temperature 18 degree celsius.

'''0 hours''' - fertilization of the egg

'''1 hours''' - formation of the gray crescent due to pigment migration

'''3.5 hours''' - early cleavage

'''4.5 hours''' - blastula stage(coeloblastula with eccentric blastocoel

'''26 hours''' - gastrulation

'''26 hours''' -'' early'' - crescent shaped dorsal lip

'''34 hours''' - ''middle''- semicircular blastoporal lip

'''42 hours''' - ''late'' - circular blastoporal lip

'''50 hours''' - neurulation

'''50 hours''' - ''early'' - medullary plate

'''62 hours''' -'' middle''- neural folds converging

'''67 hours''' - ''late'' - neural tube formed and ciliation of embryo

'''84 hours''' - tail bud stage(early organogeny)

'''96 hours''' - muscular response to tactile stimulation

'''118 hours''' - early heart beat, development of gill buds

'''140 hours''' - hatching and gill circulation

'''162 hours''' - mouth opens and cornea becomes transparent

'''192 hours''' - tail fin circulation established

'''216 hours''' - degeneration of external gills, formation of operculum, development of embryonic teeth

'''240 hours''' - opercular fold over brachial chamber except for spiracle and internal gills

'''255 hours''' - prolonged larval stage with refinement of organs

'''270 hours''' - development of hindlimbs, internal development of forelimbs in opercular cavity

'''275 hours''' - projection of forelimbs through operculum, left side first

'''280 hours''' - absorption of the tail and reduction in size of the gut

'''284 hours''' - metamorphosis complete, emergence from water as miniature, air breathing frog

==Stages of frog embryology==
--[[User:S8600021|Mark Hill]] 08:40, 9 October 2009 (EST) [[Talk:2009_Group_Project_5#Constructive_Criticism_of_Coordinator|see my comment on images]]

The rate of development of the egg and embryo will depend upon the temperature at which they are kept. The approximate schedule of development at 23 degree celsius is provided below.

{| border='1px'
|+ Table 1: Stages of frog development
!Stage !!Time since fertilisation (hours)!!Stage Characteristic !!Embryo characteristic !!Image of frog stage
|-
|1
|0.00-1.30
|fertilization of the egg, post fertilization
|animal hemisphere, gray crescent and vegetal hemisphere are present
|[[File:Stage01animal.jpg|200px]]

|-
|2
|1.30-2.00
|splits into two cells
|appearance of first cleavage furrow
|[[File:Stage02ventral.jpg|200px]]
|-
|3
|2.00-2.15
|becomes four cells
|appearance of second cleavage furrow
|[[File:Stage03animal.jpg|200px]]
|-
|4
|2.15-2.45
|becomes eight cells
|appearance of third cleavage furrow
|[[File:Stage04dorsolat.jpg|200px]]
|-
|5
|2.45-3.00
|becomes sixteen cells
|appearance of fourth cleavage furrow
|[[File:Stage05dorsal.jpg|200px]]
|-
|6
|3.00-3.30
|becomes thirty-two cells
|appearance of fifth cleavage furrow
|[[File:Stage06animal.jpg|200px]]
|-
|6.5
|3.30-4.00
|blastula stage
|Three dorsal folds become visible as a result of endoderm invagination. Pole cells no longer visible on surface
|[[File:Stage065dorsal.jpg|200px]]
|-
|7
|4.00-5.00
|Gastrulation stage
|two primary germ layers. epiblast and endoderm
|[[File:Stage07dorsal.jpg|200px]]
|-
|8
|5.00-7.00
|neurulation
|medullary plate, neural folds and neural tube
|[[File:Stage08dorsal.jpg|200px]]
|-
|9
|7.00-9.00
|germ layer
|complete lip involution encircling yolk
|[[File:Stage09veg.jpg|200px]]
|-
|10
|9.00-11.00
|early gastrula
|two primary germ layers
|[[File:Stage10veg.jpg|200px]]
|-
|10.5
|11.00-11.45
|gastrula
|two germ layers
|[[File:Stage105vega.jpg|200px]]
|-
|11
|11.45-12.30
|medulla plate
|Yolk sac protrudes dorsally, labium moves to midline on ventral side
|[[File:Stage11veg.jpg|200px]]
|-
|11.5
|12.30-13.15
|continuation of medulla plate
|start closing the plate
|[[File:Stage115veg.jpg|200px]]
|-
|12
|13.15-14.15
|early neurula
|thickened ectoderm give rise to CNS
|[[File:Stage12veg.jpg|200px]]
|-
|12.5
|14.15-14.45
|neural folds
|expansion of cavity
|[[File:Stage125postdors.jpg|200px]]
|-
|13
|14.45-16.15
|neural folds
|continue expanding cavity
|[[File:Stage13postdors.jpg|200px]]
|-
|14
|16.15-17.30
|neural folds
|continuation of cavity
|[[File:Stage14postdors.jpg|200px]]
|-
|15
|17.30-18.15
|tail bud stage
|early organogeny
|[[File:Stage15postdors.jpg|200px]]
|-
|16
|18.15-18.45
|tail bud stage
|posterior ventral view
|[[File:Stage16ant.jpg|200px]]
|-
|17
|18.45-19.45
|tail bud stage
|anterior view
|[[File:Stage17ant.jpg|200px]]
|-
|18
|19.45-20.45
|close neural fold
|anterior view
|[[File:Stage19dorsal.jpg|200px]]
|-
|19
|20.45-21.45
|neural fold close complete
|dorsal view
|[[File:Stage19ant.jpg|200px]]
|-
|20
|21.45-22.30
|early tail bud
|anterior view
|[http://www.xenbase.org/xenbase/original/atlas/NF/stage20ant.jpg stage 20]
|-
|21
|22.30-24.00
|termination of neural crest
|progress to next stage
|[http://www.xenbase.org/xenbase/original/atlas/NF/stage21ant.jpg stage 21]
|-
|22
|24.00-24.45
|prolonged development
|elongation
|[http://www.xenbase.org/xenbase/original/atlas/NF/stage22dorsal.jpg stage 22]
|-
|23
|24.45-26.15
|elongation of embryo
|later view
|[http://www.xenbase.org/xenbase/original/atlas/NF/stage23dorsal.jpg stage 23]
|-
|24
|26.15-27.30
|continuation of elongation of embryo
|dorsal view
|[http://www.xenbase.org/xenbase/original/atlas/NF/stage24dorsal.jpg stage 24]
|-
|25
|27.30-29.30
|organs development
|embryo elongates and develops dorsal thickening
|[http://www.xenbase.org/xenbase/original/atlas/NF/stage25dorsal.jpg stage 25]
|-
|26
|29.30-31.15
|elongation
|dorsally forms neural and brain cavity
|[http://www.xenbase.org/xenbase/original/atlas/NF/stage26dorsal.jpg stage 26]
|-
|27
|31.15-32.30
|elongation of embryo
|dorsal view
|[http://www.xenbase.org/xenbase/original/atlas/NF/stage27dorsal.jpg stage 27]
|-
|28
|32.30-35.00
|further development
|lateral view
|[http://www.xenbase.org/xenbase/original/atlas/NF/stage28dorsal.jpg stage 28]
|-
|29-30
|35.00-37.30
|tail bud
|growth
|[http://www.xenbase.org/xenbase/original/atlas/NF/stage29-30lat.jpg stage 29-30]
|-
|31
|37.30-40.00
|prolonged development
|bud development
|[http://www.xenbase.org/xenbase/original/atlas/NF/stage31lat.jpg stage 31]
|-
|32
|40.00-44.30
|early muscular development
|elongation
|[http://www.xenbase.org/xenbase/original/atlas/NF/stage32lat.jpg stage 32]
|-
|33-34
|44.30-50.00
|muscular movement
|apparatus for locomotion
|[http://www.xenbase.org/xenbase/original/atlas/NF/stage33-34lat.jpg stage 33-34]
|-
|35-36
|50.00-53.30
|muscular movement
|apparatus for locomotion
|[http://www.xenbase.org/xenbase/original/atlas/NF/stage35-36lat.jpg stage35-36]
|-
|37-38
|53.30-56.30
|heart beat
|develops apparatus
|[http://www.xenbase.org/xenbase/original/atlas/NF/stage37-38lat.jpg stage 37-38]
|-
|39
|56.30-66.00
|mouth opens
|cornea transparent
|[http://www.xenbase.org/xenbase/original/atlas/NF/stage39latsmall.jpg stage 39]
|-
|40
|66.00-76.00
|gill circulation
|hatching
|[http://www.xenbase.org/xenbase/original/atlas/NF/stage40lat.jpg stage 40]
|-
|41
|76.00-80.00
|tail, fin circulation
|circulation
|[http://www.xenbase.org/xenbase/original/atlas/NF/stage41lat.jpg stage 41]
|-
|42
|80.00-86.00
|internal gills, operculum
|opercular fold, teeth
|[http://www.xenbase.org/xenbase/original/atlas/NF/stage42lat.jpg stage 42]
|-
|43
|86.00-98.00
|operculum complete
|operculum closed on right
|[http://www.xenbase.org/xenbase/original/atlas/NF/stage43lat.jpg stage 43]
|-
|46
|98.00-106.00
|metamorphosis
|emergence from water as miniature, operculum complete
|[http://www.xenbase.org/xenbase/original/atlas/NF/stage46lat.jpg stage 46]
|-
|}

==Abnormalities of frog==

Abnormalities of frog could be caused by multiple factors. These include change in climate, predators, parasites, bacteria, fungi, viruses or pollution and contaminants such as pesticides, metals and fertilizer.[http://www.fws.gov/contaminants/documents/frogsrefup_septoct_2006.pdf]

The Abnormalities are further classified into different categories. These categories are:

===1. Infectious Diseases:===

'''Perkinsus Symptoms-''' caused by perkinsus-like protozoan organism. Symptoms include swollen viscera that leads to a bloated body and and infected swollen heart

'''Ichthyophonus symptoms-''' cause by parasitic genus, where symptoms include a swollen tail resorption site that matches the surrounding skin in color and translucency.

[[Image:Abnormalities of Frog species.jpg|thumb|left|Figure A Image details[waterwatchadelaide.net.au].jpg]]

===2. Surficial Abnormalities:===

Surficial abnormalities as the one that are visible on the surface of the skin. This includes abnormal pigmentation, , subcutaneous hemorrhaging, wounds due to trauma or from a predator
Edema is a fluid-filled swelling under skin whihc is also a surficial abnormality.

===3. Skeletal Abnormalities:===

This is further classified into three more categories:

'''a. Skeletal Malformations-'''

* Microcephaly (small head or blunt snout)
*Scoliosis (Curved spine in lateral direction)
*Shrunken Limb (Micromelia)
*Amelia (Completely missing limb with no stump)

'''b. Skeletal Abnormalities of Unclear Etiology-'''

This condition arises when a frog has ectromelia (missing limb), brachydactyly (missing digits) or other such condition with no visible trauma or external damage, then this will be classified as the Skeletal abnormality of unclear etiology.

'''c. Skeletal Injuries-'''

Any limb missing or broken due to trauma or other related reason which shows clear evidence of it is classified as skeletal injury

===4. Eye Abnormalities:===

Most common includes-

'''i. Anophthalmia:''' Skin covers the eye socket as there is no eye

'''ii. Abnormal Iris Coloration:''' Reduced pigment in either one eye or both resulting in two different colours of the iris at times

'''iii. Abnormal size or shape:''' Both eyes either deviating from each other or size of pupil or iris is different than the other eye

[http://www.fws.gov/contaminants/Amphibian/pdfs/AbnormalitySOP_woutpics_Jan08.pdf ]

==Genetics==

There are a wide variety of species that differ from each other when it comes to genetics and their functioning.

'''TAXONOMY:''' '''Phylum''' ''Chordata'' / '''Sub Phylum''' ''Vertebrata'' / '''Class''' ''Amphibia'' / '''Order''' ''Anura''

Their are more than two dozen different families of frogs, where suborders are:

'''1. ARCHAEBATRACHIA-''' most primitive frogs

'''2. MESOBATRACHIA-''' linked between the Archaebatrachia and Neobatrachia

'''3. NEOBATRACHIA-''' most modern frogs

{| border='4px'
|+ '''General Info:'''
! !!
|-
| '''Number of frogs' species'''
| 5280
|-
| '''Smallest frog genome size:'''
| 0.95pg, Ornate burrowing frog
|-
| '''Largest frog genome size:'''
| 13.40pg, Ornate horned frog
|-
| '''Mean of frogs' genome'''
| 4.68pg ± 0.13
|-
|}

[http://www.genomesize.com]

*Majority of frogs have only 22 to 26 chromosomes and polyploid is very common where they are almost bisexual.

*Polyploid Amphibians reduce their total cell number such that they acheive the same body size as diploids. One of the most unsual forms of polypoidy in amphibians is the water frog ''Rana esculenta'' from Europe and Western Asia.

* The species with larger genomes have more genes for e.g. the frog genus ''Xenopus'' includes 16 species, with genome sizes ranging from 3.5 x 10^9 bp to 1.6 x 10^10 bp. These differences have arisen by numerous events of polyploidization within the past 40 million years or so. The ancestral chromosome number for the genus seems to have been 18, but there are species with 36, 72 and 105 chromosomes [http://www.xenbase.org/common/]

{| border='4px'
|+ '''Difference within two families'''
! '''SPECIES''' !! ''X.LAEVIS'' !! ''X.TROPICALIS''
|-
| '''PLOIDY'''
| Allotetraploid
| Diploid
|-
| '''NO. OF CHROMOSOMES'''
| 36 chromosomes
| 20 chromosomes
|-
| '''GENOME SIZE'''
| 3.1 x 10^9 bp
| 1.7 x 10^9 bp
|-
| '''EGG SIZE'''
| 1-1.3 mm
| 0.7-0.8 mm
|-
| '''GENERATION TIME'''
| 1-2 years
| 4 months
|-
|}
[http://www.xenbase.org/common/]

===Genome Sequencing===

Since Frog has a huge family with many different species, only few main species that are used widely for the purposes of experiments have their genome sequenced.

''Xenopus tropicalis'' has one of the smallest genomes among amphibians and has the shortest generation time- four to six months and the only diploid genome among the 14 Xenopus species. This means it has no more than two copies of most genes, whereas the other species of Xenopus have four copies of most genes (pseudotetraploid). US Department of Energy's Joint Genome Institute (JGI) in Walnut Creek, California, initiated the X. tropicalis Genome Project, finding 1,700 million base pairs.
[http://www.genome.gov/Pages/Research/Sequencing/BACLibrary/xenopusTropicalis.pdf]

===Xenopus oocytes===

* The oocytes provide an important expression system for molecular biology.

* By injecting DNA or mRNA into the oocyte or developing embryo, scientists can study the protein products in a controlled system. This allows rapid functional expression of manipulated DNAs (or mRNA). This is particularly useful in electrophysiology, where the ease of recording from the oocyte makes expression of membrane channels attractive.

* One challenge of oocyte work is eliminating native proteins that might confound results, such as membrane channels native to the oocyte.

* Translation of proteins can be blocked or splicing of pre-mRNA can be modified by injection of Morpholino antisense oligos into the oocyte (for distribution throughout the embryo) or early embryo (for distribution only into daughter cells of the injected cell).
[http://www.staff.unibe.ch/sigel/xenopus.html]

===Xenopus Laevis===

* ''Xenopus Laevis'' is an important model organism in developmental biology. X. laevis is tetraploid and reaches sexual maturity in 1 to 2 years. What makes it important in developmental biology is its large and easily manipulable embryo.

* Extracts from the eggs of X. laevis frogs are also commonly used for biochemical studies of DNA replication and repair, as these extracts fully support DNA replication and other related processes in a cell-free environment which allows easier manipulation.

* The Human chorionic gonadotropin hormone (hCG) is present in the urine of the pregnant women in large quantities only. This hormone in the urine induces X.laevis oocyte production which formed the basis of first well-documented method of pregnancy testing X. laevis is also notable for its use as the first well-documented method of pregnancy testing when it was discovered. Today, commercially available HCG is injected into Xenopus males and females to induce mating behavior and breed these frogs in captivity at any time of the year.

===Gene cluster===

* The alpha and beta globin genes are closely linked in small cluster of frogs compared to human and chicken

* The similarity of architecture of two clusters found in X.laevis supports the tetraploid origin

* The two loci encoding the muscle specific creatine kinase isoenzymes and have large differences in developmental profile, therefore suggesting that duplicate loci that have not undergone silencing are not simply redundant copies but have acquired specialization.

* Contains twice number of genes for proteins i.e. haemoglobin and sarcomeric actin serum albumin compared with other species

----

==Current Embrology Research==

Currently, a number of fields have benefited from the development of frog embrology. These include cloning, verification of messenger RNA, and Cell cycle.

===Cloning===
[[Image:Robert Briggs.jpg|thumb|left|Figure 16 Image details:Robert Briggs.jpg]]

In 1952, Robert Briggs and Thomas J King cloned northern leopard frogs using a method of nuclear transfer. Briggs and King's experiment was similar to that envisioned - and piloted using salamanders - by Hans Spemann in his 1938 proposal for a 'fantastical experiment'. Later, John Gurdon extended this work and showed that nuclei from differentiated cells could support development, although less well than those from early embryos. [http://genome.wellcome.ac.uk/doc_WTD020799.html]

Lemaitre et a. (2005) from MRC Cancer Cell Unit, Cambridge, U.K. worked on experiments that demonstrated that importance of serial nuclear transplantation for the sucessful cloning of frogs. He demonstrated that exposure of somatic-cell nuclei (erythrocyte nuclei) and sperm nuclei to an extract of mitotic cell extract reorganizes the chromatin into shorter loops and allows replication at much shorter intervals along the DNA. This increases the efficiency of DNA replication in mammalian cell-free systems.

===Transgenesis techniques for functional genomics in Xenopus===

Transgenesis in Xenopus is made possible due to large embryos, a reliable fate map, ease of microinjection, ease of dissection/micromanipulation and existence of the neuroendocrine reflex of background adaptation as a model for activation/inact.

Recently, Hajime Ogino and Haruki Ochi from Nura Institute of Science and Technology in Japan focused on the genomic resources and principles of the transgenesis techniques in Xenopus, and discusses their applications to genome wide network analysis, with emphasis on the use of bioinformatics tools. This is will to understand the gene regulatory networks that control vertebrate development. [http://www.ingentaconnect.com/content/bsc/dgd/2009/00000051/00000004/art00001%3Bjsessionid=4ah96rms73gcu.alexandra]

Xenopus used to be a problem in earlier days when it came to transgenesis. Current methods involves isolated sperm nuclei from Xenopus testis that are microinjected into unfertilized eggs. The generated transgenic tadpoles contain 5-35 copies of the integrated plasmid that are expressed in all cells. If desired, expression of the transgene can be directed to the appropriate tissue and at the appropriate time by using specific promoters, mostly the Xenopus POMC gene promoter (isolated from a Xenopus genomic DNA library) to specifically direct expression of green fluorescent protein (GFP) at high levels to the intermediate pituitary cells, which can either be over expressed or inhibited.[http://molanphys.ruhosting.nl/transgenesis.htm]

[[File:Transgenesis.JPG]]

===Verification of messenger RNA===

While the existence and role of messenger RNA (mRNA) was known in bacteria, in the 1960s it was still debated whether it also existed in vertebrates. Taking haemoglobin mRNA from immature red blood cells and injecting it into a Xenopus oocyte, John Gurdon showed that the haemoglobin protein was indeed produced. Producing proteins in Xenopus oocytes has proved to be extremely useful in cell biology, in particular for the study of receptor proteins.[http://genome.wellcome.ac.uk/doc_WTD020799.html]

===Cell Cycle===

As they develop outside the mother, frog eggs are well stocked with the proteins needed to drive the development of the embryo. Studies of these processes has shed considerable light on the processes involved in cell division - termed the cell cycle. [http://genome.wellcome.ac.uk/doc_WTD020799.html]

===Limb development in Xenopus Laevis===

[[Image: Frog Limb development.jpg|thumb|right|Image details:Primary source:[http://images.google.com.au/imgres?imgurl=http://www.sciencedaily.com/images/2006/06/060616130718.jpg&imgrefurl=http://www.sciencedaily.com/releases/2006/06/060616130718.htm&usg=__xliPsPAvheUBME_kjv_q7auiFbo=&h=333&w=300&sz=11&hl=en&start=2&um=1&tbnid=y_ntJtmkRSK7WM:&tbnh=119&tbnw=107&prev=/images%3Fq%3DLimb%2Bdevelopment%2Bin%2BXenopus%2BLaevis%26ndsp%3D18%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

Donald D. Brown (2005),Department of Embryology, Carnegie Institution of Washington demonstrated factors related to limb development of Xenopus Laevis. Thyroid hormone (TH) is found to be required for limb development in this frog. Specific cell types in the growing limb were targeted for expression of a dominant negative form of the TH receptor by sperm-mediated transgenesis. Limb muscle development, the innervation of muscle from the spinal cord, and cartilage growth can be inhibited without affecting patterning of the limb or differentiation of other cell types. Remodeling of the skin occurs late in metamorphosis after the limb has formed. The coordination of these independent programs is affected in part by the control that TH exerts over DNA replication in all cell types of the limb. [http://www.pnas.org/content/102/35/12455.full]

----

== Glossary ==

[[Image: Frog species.jpg|thumb|left|Image details:Primary source:www.olympus.co.jp/.../080925/large/p02L.jpg].jpg]]

*'''Amphibian:'''

''Relating to or characteristic of animals of the class amphibia.Amphibians are found in the taxonomic class of amphibia, amphibians are capable of both occupying and successfully living in both land and aquatic communities.amphibian''

*'''Augmentation:'''

''Enlargement/Increase in cellular size.''

*'''Autolysis:'''

''breakdown of a part or whole cell or tissue by self-produced enzymes''

*'''Blastomeres:'''

''The undifferentiated cells formed by cleavage of the fertilised ovum. This includes cells in the cleavage, morula, and blastula stages of the embryo''

*'''Carnivorous:'''
''
Flesh-eating; subsisting on animals as food.''

*'''Cleavage:'''

''he repeated division of a fertilised ovum ''

* '''Cleft:'''

''an opening, fissure, or V-shaped indentation made by or as if by splitting''

*'''Chordate:'''

''Members of a diverse phylum of animals that, as embryos, possess a (1) notochord; (2) a dorsal, hollow nerve cord, (3) pharyngeal gill slits; and (4) a post-anal tail''

''The act or state of splitting or dividing of a cell, particularly during the telophase of (animal) cell division.''

*'''Cytoplasm:'''

''The cytoplasm (of both eukaryotes and prokaryotes) is where the functions for cell expansion, growth, metabolism, and replication are carried out''

* '''Epiboly:'''
''The expansion of one cell sheet over other cells, as takes place during gastrulation''

*'''Fertilization:'''

''A process in sexual reproduction that involves the union of male (sperm) and female (ovum) gametes (each with a single, haploid set of chromosomes) to produce a diploid zygote.''

*'''Gamete:'''
''A reproductive cell (male (sperm) or female (egg)) that has only half the usual number of chromosomes''

*'''Gametogenesis:'''

''process leading to the production of gametes. The development and maturation of sex cells through meiosis.Another name for meiosis where a diploid cell is divided into two haploid cells with half the chromosome content of the diploid parent cell.''

*'''Herbivorous:'''

''eating plants; of or pertaining to the herbivora.''

*'''Holoblastic:'''

''The complete division of an isolecithal or microlecithal egg into blastomeres''

*'''Invagination:'''

''One of the methods by which the various germinal layers of the ovum are differentiated.''

*'''Isoenzymes:'''

''Isozymes (also known as isoenzymes) are enzymes that differ in amino acid sequence but catalyze the same chemical reaction.''

*'''Mesentery:'''

'' membranous fold attaching various organs to the body wall.''

*'''Metamorphosis:'''

''A change in the form and often habits of an animal after the embryonic stage during normal development.''

*'''Neuroendocrine:'''

''Neuroendocrine [IPA nʊəroʊˈɛndəkrɪn] cells are cells that release a hormone into the circulating blood in response to a neural stimulus.''

*'''Organogenesis:'''

''The part of embryonic development where the body's main organs develop.''

*'''Peritoneum:'''

''The smooth serous membrane which lines the cavity of the abdomen, or the whole body cavity when there is no diaphragm, and, turning back, surrounds the viscera, forming a closed, or nearly closed, sac.''

*'''Perivitelline space:'''

''The perivitelline space is the space between the zona pellucida and the plasma membrane (sometimes called the vitelline membrane) in a fertilized ovum.''

*'''Polyploidy:'''

''Cells with three or more sets of chromosomes.''

*'''Pronucleus:'''

''the nucleus of the ovum or sperm after fertilization but before they fuse to form the nucleus of the zygote ''

*'''Protoplasm:'''

''The fluid living content of the cell that consists of two major divisions, the cytoplasm and the nucleoplasm (cell nucleus). It is composed mainly of nucleic acids, proteins, lipids, carbohydrates, and inorganic salts''

*'''Segmentation:'''

''division of some metazoan bodies (such as annelida and Arthropoda) into repeated parts, segments. Segmentation can be homomeric (more or less the same) or heteromeric(different from each other).''

*'''Terrestrial:'''

''Of or on the ground, of the habitat of a plant, on land as opposed to in water, or on the ground as opposed to on another plant.''

*'''Transgenesis:'''

''Transgenesis is the process of introducing an exogenous gene - called a transgene - into a living organism so that the organism will exhibit a new property and transmit that property to its offspring.''

*'''Yolk:'''

''nutritive material of an ovum stored for the nutrition of an embryo''

*'''Zygote:'''

''The cell from which an organism develops, that results from the fertilization of the egg by the sperm.''

''Primary Resource "Biology- Online Dictionary''[http://www.biology-online.org/dictionary/Main_Page]

== References - Frog Embryology: ==

[[Image:Frog Research.jpg|thumb|left|Image details:[http://images.google.com.au/imgres?imgurl=http://www.odt.co.nz/files/story/2008/09/university_of_otago_zoology_senior_lecturer_phil_b_3343259744.jpg&imgrefurl=http://www.odt.co.nz/on-campus/university-otago/21670/dunedin-frog-man-wins-zoo-award&usg=__JvJJU5QfOnIwY2bk4xo64UXuJRs=&h=600&w=404&sz=22&hl=en&start=14&um=1&tbnid=AbsP89yWcUiilM:&tbnh=135&tbnw=91&prev=/images%3Fq%3Dfrog%2Bresearch%26hl%3Den%26um%3D1].jpg]]

1. Savage, J. M. (2002). The Amphibians and Reptiles of Costa Rica. University of Chicago Press, Chicago [http://www.springerlink.com/content/vv015277w1746llw/]

2. Ford, L.S.; D.C. Cannatella (1993). "The major clades of frogs". Herpetological Monographs 7: 94–117 [http://digimorph.org/specimens/Xenopus_laevis/]

3. Tyler, M. J. (1994). Australian Frogs A Natural History. Reed Books [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.gracilenta.html]

4. Cogger, H.G.; R.G. Zweifel, and D. Kirschner (2004). Encyclopedia of Reptiles & Amphibians Second Edition. Fog City Press [http://en.wikipedia.org/wiki/Microhylidae]

5. Beltz, Ellin (2005). Frogs: Inside their Remarkable World. Firefly Books [http://unjobs.org/authors/ellin-beltz]

6. Tyler, M. J. (1994). Australian Frogs A Natural History. Reed Books [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

7. Moury JD, Hanken J (1995) Early cranial neural crest migration in the direct-developing frog, Eleutherodactylus coqui. Acta
Anatomica (Basel) 153, 243-253.

8.Raynaud A (1985) Development of limbs and embryonic limb reduction. In Biology of the Reptilia (ed. Gans C, Billett F), pp.
59-148. New York: John Wiley.[http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=9309]

9. Hanken J (1986) Developmental evidence for amphibian origins. In Evolutionary Biology (ed. Hecht MK, Wallace B, Prance GT), 20, pp. 389-417. New York: Plenum Press. [Hanken J (1986) Developmental evidence for amphibian origins. In Evolutionary Biology (ed. Hecht MK, Wallace B, Prance GT), 20, pp. 389-417. New York: Plenum Press.]

10. Elinson RP (1990) Direct development in frogs : wiping the recapitulationist slate clean. Seminars in Developmental Biology
1, 263-270.

11. Beebee, T. J. C. 1996. Ecology and Conservation of Amphibians. Chapman and Hall. London. [http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V5X-3SVHMKH-1X&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=1021245355&_rerunOrigin=google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=825868e10cd178d16a8a0e5ad14dc5ef]

12. Lehtinen, R. M. 2002. The use of screw pines (Pandanus spp.) by amphibians and reptiles in Madagascar. Herpetological Bulletin 2002:20–25.

13. Parris, K. M. and M. A. McCarthy. 1999. What influences the structure of frog assemblages at forest streams. Australian Journal of Ecology 24:495–502. CrossRef

14. Zug, G. R. 1993. Herpetology: An Introductory Biology of Amphibians and Reptiles. Academic Press. San Diego, CA.

15. Slack,J.M.W., Darlington,B.G., Heath,J.K. and Godsave,S.F. (1987)Mesoderm induction in early Xenopus embryos by heparin-binding growth factors. Nature, 326, 197-200.

16. Melton,D.A. (1990) Activins are expressed early in Xenopus embryogenesis and can induce axial mesoderm and anterior structures. Cell, 63, 485-493.

17. Harland,R.M. and Misher,L. (1988) Stability of RNA in developing Xenopus embryos and identification of a destabilizing sequence in TFIIIA RNA. Development, 102, 837-852.

18. Cunliffe,V. and Smith,J.C. (1992) Ectopic mesoderm formation in Xenopus embryos caused by widespread expression of a Brachyury homologue. Nature, 358, 427-430.

19. Kinoshita,K., Bessho,T. and Asashima,M. (1993) Competence prepattern in the animal hemisphere of the 8-cell-stage Xenopus embryo. Devel. Biol., 160, 276-284.

20. LaBonne,C., Burke,B. and Whitman,M. (1995) Role of MAP kinase in mesoderm induction and axial patterning in Xenopus development. Development, 121, 1475-1486.

21. Green,J.B.A., New,H.V. and Smith,J.C. (1992) Responses of embryonic Xenopus cells to activin and FGF are separated by multiple dose thresholds and correspond to distinct axes of the mesoderm. Cell, 71, 731-739.

22. Grainger R., Blumberg B., Harland R., Amemiya C., Importance of Xenopus Tropicalis to biomedical and biological research, Benaroya Research Institute, Virginia Mason Research Center [http://www.genome.gov/Pages/Research/Sequencing/BACLibrary/xenopusTropicalis.pdf ]

23. Gregory, T.R. (2005). Animal Genome Size Database. [http://www.genomesize.com]

24. U.S Fish and Wildlife Services, ABNORMALITY CLASSIFICATION SOP, [http://www.fws.gov/contaminants/Amphibian/pdfs/AbnormalitySOP_woutpics_Jan08.pdf ]

25. Donald D. Brown*, Liquan Cai*, Biswajit Das*, Nicholas Marsh-Armstrong‡, Alexander M. Schreiber*, and Rejeanne Juste*(2005), Thyroid hormone controls multiple independent programs required for limb development in Xenopus laevis metamorphosis [http://www.pnas.org/content/102/35/12455.full]

26. Ogino, Hajime; Ochi, Haruki, Resources and transgenesis techniques for functional genomics in Xenopus, Development Growth & Differentiation, Volume 51, Number 4, May 2009 , pp. 387-401(15) [http://www.ingentaconnect.com/content/bsc/dgd/2009/00000051/00000004/art00001%3Bjsessionid=4ah96rms73gcu.alexandra]

27. Giles Newton (2004) Why the frog? The Human Genome, [http://genome.wellcome.ac.uk/doc_WTD020799.html]

28. Xenbase, [http://www.xenbase.org/common/]

29. Donders Center for Neuroscience & Nijmegen Center for Molecular Life Sciences (NCMLS), Beyond the genome (Xenopus transgenesis for functional genomics),Faculty of Science, Radboud University [http://molanphys.ruhosting.nl/transgenesis.htm]

== External Links ==
[[Image:Frog links.jpg|thumb|left|Image details:[http://images.google.com.au/imgres?imgurl=http://2.bp.blogspot.com/_o93AaY0GzH4/SjY_ZYv0PII/AAAAAAAAAgk/skruNc2yN78/s400/computer%2Bfrog.jpg&imgrefurl=http://hellaheaven-ana.blogspot.com/2009/06/talking-frog-contemporary-fairy-tale.html&usg=__oxji1TGLV2Fi7xe0dnlmuYk8gDo=&h=288&w=288&sz=16&hl=en&start=2&um=1&tbnid=ywZd4zpdxC5plM:&tbnh=115&tbnw=115&prev=/images%3Fq%3Dfrog%2Bon%2Bcomputer%26hl%3Den%26um%3D1].jpg]]

1. Frog embryology [http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/F/FrogEmbryology.html Frog Embryology]

2. Frog cellular materials [http://www.xenbase.org/xenbase/original/cell/cell.html xenbase]

3. The zoology of frog species [http://worms.zoology.wisc.edu/frogs/mainmenu.html zoology frogs]

4. Frog cycle [http://www.bioethics.gov/images/sc_images/frog_dev.gif bioethics frog] Just a little cycle of FROG'S life cycle

5. Frog Embryology [http://embryology.med.unsw.edu.au/OtherEmb/Frog.htm UNSW Embryology]

6. Frog Research [http://apps.carleton.edu/campus/library/now/exhibits/wallcharts/frog/ carleton library exhibit]

{{Template:Projects09}}
[[Category:Frog]]

2009 Group Project 5

2009-10-12T13:07:40Z

Z3258567: /* The Frog */

== The Embryology of Frogs ==

== The Frog ==

[[Image: Frog species .jpg|thumb|left|Image details: Wikipedia (2009) Frog species[http://en.wikipedia.org/wiki/Frog#Uses_in_agriculture_and_research].jpg]]

Frogs are scientifically identified by the structure of their long posterior limbs, a petite framework, webbed fingers and feet, budged eyes and the lack of a tail. The majority of frog species are extensively recognized as outstanding jumpers, due to their long, dominant legs, which are adaptations to progress jumping performance during activities. The Frog is one of the most frequently studied species in experimental embryology and most anatomical sciences. The Frog is a practically effective model for human embryological development given that the Frog:

* Comprises of genes which can be effectively manipulated

* Comprises of similar homogeny with humans species

* Reproduces a large quantity of offspring in a short period of time

* Are small species which can be simply sustained

* Are not extremely luxurious and expensive

== The History of the uses in agriculture and research ==

Frog species are reared commercially for a variety purposes. Specific species of frogs are used as:

* Food source; frog legs are a delicacy and are eaten in European countries and in many parts of South American regions.

* Dead frogs are commonly consume for dissections in universities to contrast the organs and systems. This practice has turn down in current years with the growing in concerns about animal welfare.

* Frogs have achieved to be significant models of organisms throughout the history of science as their small bodies are able to be experimented upon.

* Frogs are used in cloning research and other embryonic experiments since frogs are amongst the closest living relatives of man to lack egg shells characteristic of most other vertebrates, and therefore make possible observations of early maturation.

--[[User:Z3295026|Joe Nassif]] 20:51, 12 October 2009 (EST)

----

== Growth and development of the Frog ==

[[Image: Mature develop frog.jpg|thumb|Image details: Wikipedia (2009) TYPICAL FROG Figure 1 Primary source:[http://en.wikipedia.org/wiki/File:Red-eyed_Tree_Frog_-_Litoria_chloris_edit1].jpg]]

* The frog is a well recognised species, abundant predominantly in ponds, swamps, though various species may also exist in damp or shady environments distant from moist habitats.

* Eggs of specific frogs are easily obtained and may be examined in from the beginning of fertilization onwards. The phases of embryonic development differs in various chordates, yet the typical phases are basically apparent in all frog species. The differences are associated principally to the amount of yolk particles present in an egg.

* The yolk particles offer nourishment of the developing embryo. The process of frog development will be discussed from the phases of gametogenesis to the adult stage.

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== The Egg ==
[[Image:Development of Poles in frog Fertilization.jpg|thumb|left|Figure 4 Image details:J,Nassif 2009.jpg]]

* The embryology of a frog egg is a vast cell; its dimensions are approximately 1.4-1.6 million times larger than a typical aquatic species egg cell. Throughout the frog’s embryonic maturation period, the egg will be transformed into a tadpole encompassing millions of cells but still remains with its constant volume of genetic material, the vast prodction of cell have been illusttrated in the figure on the right revealing the production of eggs from female frogs. [http://en.wikipedia.org/wiki/Microhylidae]

* The early embryonic frog structure consists of three main segments the superior hemisphere known as the animal pole which is usually visible as a grey coloured area. The innermost layer appears to be between the outer two sections known as the gray crescent represented in black. Inferiorly, represents the vegetal pole typically lighter than the superior compartment illustrated in gold.

VIDEO RESOURCE: [http://www.youtube.com/watch?v=GO5YN_t1fqw&feature=related]

[[Image:Early Development of Frogs.jpg|thumb|left|Figure 3 Image details:J,Nassif 2009.jpg]]

==History of frog embryology use ==

*'''1851''' - ''Henby Nelson''(MD): He identified a remarkable fact through the frog embryo. Henby observed the first cleavage of the yolk, in the egg of the frog. And cleaved structure corresponds in line of direction to the longitudinal axis of the body of the embryo of the frog species.

[[Image:Wilhelm Roux.jpg|thumb|right|Wilhelm Roux[http://images.google.com.au/imgres?imgurl=http://www.todayinsci.com/R/Roux_Wilhelm/RouxWilhelmThm.jpg&imgrefurl=http://www.todayinsci.com/6/6_09.htm&usg=__qRLTEMTHdZpAHxiNX12hWjcm9tA=&h=125&w=100&sz=4&hl=en&start=2&um=1&tbnid=LIKIwZTqCpk7MM:&tbnh=90&tbnw=72&prev=/images%3Fq%3DWilhelm%2BRoux%26gbv%3D2%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

*'''1888''' - ''Wilhelm Roux'': Wilhelm Roux attempted to solve the above observation by damaging one cell of a two-cell frog embryo with a hot needle. The cell stayed in place. However, it did not develop further. Its partner developed into a left or right half-embryo;

*'''1907''' - ''John Hopkins'' hospital: In order to identify the cellular source of neuronal fibres. Scientist placed small portions of frog embryo spinal cords in lymph on a microscope slide and was able to observe clear cut neuronal sprouting.

*'''1951''' - ''Robert Briggs'': Robert Briggs was able to clone a frog embryo by substituting the nucleus of an unfertilized frog egg cell with the nucleus of a frog embryo cell. This process is known as nuclear transplant, has formed the basis for all cloning.

*'''1952''' - ''Robert Briggs and T.J. King'': Robert Briggs and T.J. King used frog for test experiment. Because the size of the eggs in the frogs are enormous compared with those of mammals, which make them easier to manipulate.

*'''1976'''- Using the technique that had been successful in cloning frog embryos, the doctor transferred the nucleus of one cells into a donated egg cell. As an embryo began to develop, it was implanted into the uterus of a young woman.

*'''1997''' - ''Wilmut and Campbell'': Utilizing the cloning technique from frog embryo, Drs. Wilmut and Campbell tried the starvation technique on embryo cells to produce Megan and Morag, the world's first cloned sheep and, until now, the most famous sheep in history.

*'''2000''' - ''Tokyo University'': Scientists at Tokyo University have grown artificial eyeballs. Scientists formed them in tadpoles by using frog embryo cells.

*'''2001''' - ''Advanced Cell Technology'': Scientists from Advanced Cell Technology announced production of a human embryo clone. This is significant as its parthenogenesis has been artificially induced in frogs.

[[Image:John Gurdon .jpg|thumb|right|John Gurdon [http://images.google.com.au/imgres?imgurl=http://www.pnas.org/site/misc/images/gurdon.jpg&imgrefurl=http://www.pnas.org/site/misc/classics4.shtml&usg=__1p-GA1PdOYsxKL-cznMb3RHCm98=&h=526&w=400&sz=223&hl=en&start=1&um=1&tbnid=9k4lhuLssiWCAM:&tbnh=132&tbnw=100&prev=/images%3Fq%3DJohn%2BGurdon%26gbv%3D2%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

*'''2002''' - ''John Gurdon'': John Gurdon from Wellcome Cancer Research Institute in Cambridge experimented on cloned frog embryo.

== Gametogenesis ==

* The sexual reproduction occurs through the fusion of either mature reproductive cells or germ cells known as gametes, which include the sperm from the male frog and ova from female frog species so as to form a single cell, the fertilized zygote. The gametes are typically developed in parents of different sexes . [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

* Males gametes is a spermatozoon , the female frog gamete is an ovum. Each gamete is formed by a process, recognised as maturation or gametogenesis in gonads. The typical male frog gonads are testies in male, while the female gonads are ovaries. The synthesis of both gonads is associated with the process of fertilization. [http://en.wikipedia.org/wiki/Microhylidae]

* The zygote changes into a mature frog through the process of embryology and metamorphosis. Gametogenesis is a in progression which frog gametes are established from germ cells. Initial germ cells are called primordial germ cells, which can be recognised extremely early in the life of frog species.

----

== The Egg & Fertilization ==

[[Image:Fertilized and Unfertilised Eggs.jpg|thumb|left|Figure 6 Image details:J,Nassif 2009.jpg]]

[[Image:Egg Development.jpg|thumb|left|Figure 7 Image details:J,Nassif 2009.jpg]]

* This occurs once the sperm cell has inserted, following the insertion of the sperm cells meiosis II is completed, there is a 30 degree position change of the cytoplasm, gray crescent allows this change to be visible in some amphibians, the gray crescent is able what determines the expect ted outline of how the frog will form. The sperm cell joins with the nuclei of the egg which forms the diploid zygote nucleus. --Sando Rashed 10:09, 24 September 2009 (EST)

* The early phases in the development of the egg is visible, but must be studied in tadpoles throughout maturation. In embryonic tadpoles of about 10 millimetres in length, soon after the opening of the oral cavity, a pair of longitudinal ridge-like thickenings of peritoneum becomes apparent along the posterior surface of the body cavity situated near to the mesentery and along the inner boundaries of the kidneys. Genital ridges are established in all tadpoles of this age, sex is not distinct until a later period. The development of the egg is illustrated in the figure on the left revealing the structure of a developed egg and a mature of egg.

[[Image:Fertilisation life cyle.jpg|thumb|Figure 8 Image details:Derived from primary source:[http://en.wikipedia.org/wiki/Frog]]]

== Maturation of the Egg ==

* The eggs have currently accomplished their full size, and develop from the exterior of the ovaries like a small shot, but they still have to pass through the course of maturation before they are prepared to be fertilised. This progression of maturation relates to the nucleus almost completely.

* The nucleus component, containing the nuclear fluid that excludes through the nuclear membrane into the substance of the egg, a great segment of the nuclear reticulum vanishes and becomes degraded into separate globules known as nucleoli, but a extremely small division remains in the midpoint as a slender intricately thread recognised as the nuclear skets.
Relative to the egg getting discharged from the ovary, the follicles shatter allowing the eggs to fall into the abdominal cavity of the frog species, the egg then passes forwards, directly by the contraction of the muscular wall, somewhat by the movement of the cilia of the peritoneum, to the apex of the oviduct, which positioned at the anterior compartment of the body cavity opposite to the roots of the respiratory organs.

* The terminal part of the oviduct establishes a thin-walled pouch capable of great swelling, inside which the eggs gathers in large numbers. In conclusion, the eggs are migrated out through the cloaca into water which the albuminous investments of the eggs rapidly augment to form the gelatinous mass of the frogs spawn.

== Maturation phases ==

'''1. Nuclear skein''', moves from the midpoint of the egg to its outer surface, which it reaches opposite the midpoint of the black pole. The skein, subsequently an unevenly twisted thread, now presumes the specific arrangement of a nuclear spindle, for instance may be visible in the nucleus of an epithelial or additional cell instantly prior to division of the cell occurs.[http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

'''2. The first Polar Body,''' regarding the instance the egg is laid, but prior to its fertilistion, the egg develops a considerably flattened appearance at its upper or black pole, a definite sum of fluid being exuded among the egg and the vitelline membrane. The nuclear spindle currently separate into two identical segments, one of which remains with the egg, and the supplementary is extruded as the first polar body, a small ovoidal white globule, which is situated on the surface of the egg surrounding the exuded peri-vitellline fluid.

'''3. The Second Polar Body''', half of the nuclear spindle that stay behind then splits into two equivalent divisions, one of which remains inside the egg as the female pronucleus, whereas the other segment is extruded as the second polar body, a small white globule extremely related to the first polar body, and like this positioned in the perivitelline fluid on the superior portion of the egg.

'''4. Fertilisation of the egg''', includes the synthesis of the spermatozoon with to egg, specifically, synthesis of the nuclei of these two bodies. The spermatozoa, subsequent to being shed over the seed by the male, distribute vigorously by means of their extended tails, break through the gelatinous investment of the female eggs, bore their way through the vitelline membrane and so go through into the eggs themselves, which they penetrate relative to the superior or black hemispheres.
* Subsequently, an hour following the spermatozoon has entered; a progression may be visible projecting within from the exterior segement of the egg, with a liquid spot in the mid point. This liquid centre is the nucleus of the spermatozoon, and is said to be the male pronucleus, it break through beyond into the female egg, transporting the specialised pigment into it, so that it appears bounded by a pigmented capsule linked with the exterior of the egg by a pigmented stalk.
* By this instance, the second polar body has been established and extruded, and the female pronucleus is merely the only component of the primary egg nucleus still present. Both the male and female pronuceli, which are at initially distance separate to each other, merge and after having enlarged significantly in size then fuse mutually about two and half hours after fertilisation has originated to produce the segmentation nucleus.
* The segmentation nucleus is a huge sphere-shaped vesicle embedded in delicately granular protoplasm, and bounded by a distinct capsule of pigment, its arrangement by the synthesis of the male and female pronuclei completes the action of fertilisation. Specifically female pronucleus may be observe as an imperfect nucleus, and consequently result in the course of fertilisation. The nucleus of the spermatozoon or male pronucleus, replaces the component of the egg- nucleus which has been misplaced as the polar bodies.

'''5. Segmentation of the Egg''', the initial phase of growth consist in constant separation of the egg, whereby it becomes transformed from the unicellular state, which is everlasting only in the lowest species, to muliticelluar state charactertics of all higher species. To these early processes of growth the names segmentation is specified. Shorty subsequent to the competition of fertilisation and arrangement of the segmentation nucleus this later misplaces its sphere-shaped appearance and develops to be spindle-shaped, the yolk granules at the equivalent instance showing a tendency to develop into lines distributing outwards from the distal segment of the spindle.
* The nucleus now split into two halves, which shift away from one another, the yolk granules are likely to combined themselves around the two nuclei, and a slender vertical plate of delicately granular substance is left, dividing the egg.[http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

* Superiorly the eggs depression now becomes visible, initially as a small cavity and then develops as a groove, which almost immediately extends all round, and speedily deepening, splits the egg into two entirely separate halves along a plane equivalent with the vertical plane.

* Shorty after, the two nuclei soon separate again into two, and therefore a second cleft is created in the same state as before, its additionally in the vertical plane, however in a plane at 90 degrees to the initial one, and on its finishing point the egg comprises of four accurately similar segments, each containing a nucleus. The third cleft is horizontal in shape, but not equal, lying closer to the superior than the lower pole, it segregates each of the four cells into, an superior smaller and a inferior larger pole

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== Cleavage ==

[[Image: Frog Cleavage development.jpg|thumb|left|Figure 8.1 Image details:[http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/F/FrogEmbryology.html].jpg]]

* The egg of the frog is scientifically identified as’ telolecithal’ meaning there is a outsized amount of yolk concentrated at a single pole, in contrast to the concentration of cytoplasm and the site of the nucleus. The cleavage phases are holoblastic, therefore the total and after the second cleavage they are asymmetrical .The initial cleavage stage appears about two and half to three hours after fertilization. It commences as a minor depression in close proximity to the centre of the animal hemisphere. It appears as if some interior force is pushing the surface the egg towards the centre. This small upturned fold steadily continues in the form of a channel until it surrounds the egg. This groove is shallow in the commencement, but develop into deeper eventually separating the fertilized egg into two halves recognised as the blastomeres. [The figure on the left symbolise the development and growth of the frog embryo during cleavage].

* Internally the separation is mitotic, consequently each daughter cell contains a nucleus resulting from the copulation nucleus of the fertilised egg. This cleavage is vertical, the two cells are indistinguishable in respect of cytoplasm, pigment and yolk. The subsequent cleavage appears about an hour after the first. The channel of this cleavage begins at the centre of the animal hemisphere, is at right angles to the first and is vertical. This divides the egg into four blastomeres. The fourth blastomere so produced are not qualitatively equal, since of these only two contain the material from the gray crescent. The cleavage begins about thirty minutes after the second is completed or four hours after fertilisation. the cleavage plane of the third furrow is horizontal and slightly above the equator. Thus the four upper cells are a little smaller than the four lower cells. The smaller blastomeres are called micromeres and the larger blastomeres are called macromeres. The fourth cleavages follow 20 minutes after the third and tend to be vertical. This is usually a double furrow.

* The cleavage rate is accelerated with each of the early divisions and since the blastomeres are of unequal size and have varying amounts of cytoplasm and yolk, synchronous cleavage is lost and there is an obvious overlapping of the division. The upper most cells divide more rapidly than the lowermost cells. From this point onwards perfect symmetry in cleavage and in blastomere is very rare, although the embryo developed perfectly. The fifth cleavage is also doubled, appearing first in the upper hemisphere and then in the lower.

* The cleavage thus far follows the rule that each cleavage plane comes in at right angles to the previous one. The subsequent divisions become so irregular that it is previous one. The subsequent division become so irregular that it is impossible to trace out any plan or procedure. The segmentation continues more rapidly in the pigmented regions, since at that place the protoplasm is most dense, whereas, yolk which is very abundant in the vegetal side delays cell division. The multicelluar embryo at this stage is called morula by some biologists.

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== Gastrulation ==

[[Image:FROG GASTRULATION .jpg|thumb|left|Figure Image details:[http://www.google.com.au/imgres?imgurl=http://bio1903.nicerweb.com/Locked/media/ch47/47_12FrogGastrulation.jpg&imgrefurl=http://bio1903.nicerweb.com/Locked/media/ch47/gastrulation-frog.html&h=540&w=480&sz=46&tbnid=N78sHjELreGGSM:&tbnh=132&tbnw=117&prev=/images%3Fq%3Dfrog%2B-%2Bgastrulation&hl=en&usg=__4VK9FYLft0W-4lBe6p5EtQAMiaI=&ei=qPy5SurtMJvE6wON8JmdAg&sa=X&oi=image_result&resnum=4&ct=image].jpg]]

''The phase of Blastulation is followed by the unique developmental progression of gastrulation. The process of frog gastrulation involves the following processes.''

'''1. Epiboly Phase'''

The pigmented cellular materials of blastula have the propensity to overgrow the yolk cells within the developing content. This course which is known as epiboly commences gradually in the final blastula and rapidly accelerates with advancing gastrulation development. The cellular matter within the animal pole reproduces and matures on all sides except in area surrounding the dorsal lip of the blastopore has been established.

'''2. Convergence'''

Scientists suggested that the unfolding was thought to result in spreading of the superficial cells over a substrate with suitable absorption properties. Consequently epiboly and convergence are an outcome to this spreading tendency, which is actually increased by a reduction in surface tension of the distributing cells.

'''3. Rotation'''

The epiboly phase is maintained until the region of the dorsal lip has migrated and is a to some extent greater than 90 degrees and the region of the white blastopore is reduced to small circular rings. This section will be positioned away from the developing vegetal pole. Laterally the complete developing gastrula has been rotated to a horizontal axis, allowing it to lie at right angles to the original median plane of the egg. Therefore, the course of rotation is such that the dorsal lip is practically pushed backwards in one direction as rapid or quicker than epiboly moves it forward in the other. The outcome will be that the blastopore produced at roughly the vegetal pole is posterior, and the dorsal and ventral lips are essentially dorsal and ventral. This in addition allows the eggs to form the antero-ventral side of the potential embryo whilst the area marked by the grey crescent is to develop the dorsal segment.

'''4. Invagination'''

Visible is a small fissure- like invagination which is apparent in the middle between the equator and the vegetal segment. The most superior or dorsal border of the cleft produce the dorsal lip of the blastopore. This imput move back and forth on the dorsal plane near the dorsal lip and migrates around the boundaries of the blastocoel in company with the extension of the lateral lips. This adapted invagination is maintained until the blastocoel cavity has been almost abolished; excluding the slender opening separating epiblasts from the hypoblast, the new segment formed is known as the archenteron cavity.

'''5. Involution'''

Additional to previous course of action a distinct involution also occurs at the blastoporal borders. This is mainly dynamic at the median dorsal lip and gradually more less as it shifts across either side until it reaches the ventral lip where it constant.Throughout this progression, cells positioned beside the superior boundaries of the blastoporal lip migrate over the lip to the interior portion of the lip. These cells are remained within the embryo along the internal edge of the blastopore. This indicates the root of archenteron is composed of involuted cells and beyond this the external layer known as the ectoderm. The base and lateral sides are enclosed mainly of endodermal cellular material, which have been established from larger yolk cells, situated in the vegetal pole of the blastula. In the final phases of the gastrula development, the cells contributing to the floor of the archenteron, thin out significantly where they surround the blastocoel.
The hemispherical shaped dorsal lip of blastopore which become visible at the commencement of the gastruation stage carry on to augment, initially becoming semicircular, then transform into a horse shoe shaped and then finally forming into circular band. The band is the accomplished by the blastopore. Various yolk cells of vegetal pole present in the section are crowed into the blastoporal cavity where they form a gathering identified as a yolk plug. Blastopore rapidly reduces in size while the archenteron is still developing and becomes completely formed in the final stage; the yolk plug appears as only a small oval on the gastrula.

==Growth and Modification of Frog Species==

'''1. Changes in habits and habitats:'''

'''a)''' In frogs, metamorphosis is related with to the modifications and adaptations as a frog changes environmental habitats from an aquatic to a terrestrial mode. Metamorphosis has modified the adaption of frogs as this alteration it began during the aquatic adaptations in the surface of water to breathe air. Subsequently, it continues the terrestrial surroundings, therefore the frog species become abundant in vegetation area allowing the frog to transform in to amphibious species.

'''b)''' The transition during metamorphosis is linked with a change in food chain. The tadpoles being the embryonic origin of frogs are herbivorous, feeding on algae and green matter, which they collect by the adapted feature such as their teeth surrounding their mouths. Adult frogs, alternatively, are classified as carnivorous feeding on insects and worms. Occasionally, they also consume larger prey, for instance smaller frogs species and even little birds and rodents which they dominant and ingest.

[[Image:Development of frog from sperm to mature structure.jpg|thumb|left|Figure 9 Image details:J,Nassif 2009.jpg]]

'''2. Changes in Morphology'''

These include the decrease or complete absence of specific organs or structures which are essential during development of early frog embryology, but not critical in the mature frog species. The significant alterations of this nature include the following developmental structures.

'''a)''' The long tail of the tadpole alongside the fin folds is absorbed again during metamorphosis and becomes absent at the final stage of the metamorphosis.

'''b) '''The developing gills are resorted, the gill clefts are congested and the branchial cavities start to become absent. The reabsorbtion of gills also takes place by autolysis.

'''c)''' The teeth of the perioral disc additionally the homey lining of the jaws are shed.

'''d)''' The lateral line sense organs within the skin of tadpoles vanish throughout metamorphosis.

'''e)''' The cloacal tube begins to condensed and reduced.

'''f)''' Various blood vessels, together with parts of the aortic arches, are reduced during mature development.

(The figure on the left represents the transformation from a tadpole to a developing structure.)[http://science.jrank.org/pages/2862/Frogs-Adult-morphology.html]

'''3. Progressive or constructive changes'''

This process comprises of the development of specific organs which mature into functional systems only during metamorphosis.

'''a)''' During development the limbs continue to augment in size and differentiation. The forelimbs, which in the tadpole mature under the opercular membrane, which then break through to the exterior. Simultaneously there is a increase in the length and strength of the hind limbs, joints develop in them and the toes become visible.

'''b)''' The middle ear becomes apparent in relation with the first pharyngeal pouch. The tympanic membrane matures. It is bounded by circular tympanic cartilage which allows the frog to retain air.

'''c)''' The visual organs bulge up on the dorsal surface of the head developing the nictitating membrane.

'''d)''' There is augmentation of the tongue and the formation of thevomerina teeth.

[[Image: Growth model.jpg|thumb|Figure 10 Image details:J,Nassif2009:]]

'''4. Remodelling of some structures'''

Systematic organs which operate both in the early embryonic larva and the mature adult change their differentiation during metamorphosis so as to meet the requirements of the adult mode of life and due to the habitat adaptations. The figure on the right illustrates structures developing from specic germ cell layers.

'''a)''' The skin of the embryonic tadpole is lined with a double-layered epidermis. The number of layers of cells in the epidermis augments throughout metamorphosis. Superficial surface layers become cornified. Multicellular mucous and serous glands originate in the skin. The pigmentation of the skin continuously changes, new patterns and colour start to form.

'''b)''' There is a lengthening of the mouth gap as a result of rotation of the quadrate cartilage and the true jaws become functional.

'''c)''' The tongue rapidly progresses and becomes larger and more muscular.

'''d)''' The eyes become more specialised.

'''e)''' In early tadpoles, the GIT is extremely long and wound up into a spiral folds. The intestine become greatly lengthened in herbivorous species due to the vegetables food chain.[http://en.wikipedia.org/wiki/Frog]

'''5. Development of the reproductive system'''

(The figure below represents the reproductive and development cycle of a frog as it transform from egg to frog specie.)

In tadpoles, right after the mouth is being formed, two indentation like thickenings of peritoneum begin to appear near the body cavity (dorsal surface), which is nearest to the mesentery which is near the developing kidneys. These appear in all tadpoles.

These indentations appear here because of a change in the endothelial cells, everywhere else they are usually flat looking cells but they undergo a change and in this particular area become somewhat cuboidal/columnar.

Later on the indentations become more obvious due to the epithelial cells replicating numerously to form a thick layer. The posterior two thirds of the indentation for the female is the ovary and for the male it is the testis. The third that is left differentiates and becomes fat for the body.

[[Image: Mature frog life cyle.jpg|thumb|200px|left|Figure 11 Image details:Derived from primary source:http://www.scienceclarified.com/images/uesc_01_img0038.jpg]]

[[Image: Developing frog.jpg|thumb|Figure 12 Image details:
[[Image: Mature develop frog.jpg|thumb|Image details: Wikipedia (2009) TYPICAL FROG Primary source:[http://en.wikipedia.org/wiki/File:Red-eyed_Tree_Frog_-_Litoria_chloris_edit1.jpg]].jpg]]

===Delamination===

Delamination indicates a mass separating a group of cellular matter from other cellular groups. It has been illustrated that the division of notochord, mesoderm and endoderm tissues from each other to form distinct cellular masses is completed by the progression of delamination, subsequent to these materials moving to the inside throughout gastrulation. During the developing gastrula, the germ layers are all recognized. These distinct segments of the embryo develop from these germ tissue layers.

===Polarity and Rotation===

Throughout fertilisation to the beginning of gastrulation, the frog’s egg continues in the original location in relation to its polarity. Subsequent to gastrulation its polarity begins to differentiate. This progression is linked with migration of materials within the gastrula and can be responsible for the alterations of the centre of gravity.

===Closing of Blastopore===

Subsequent to the formation of the gastrula, the blastopore is visible as a tiny round circular filled cavity containing the yolk plug. As it continues to reduce in dimension, it represented as a pear-shaped outline through the mutual approach of its lateral lips. Through it final progression these fuse entirely to produce a longitudinal groove, the streak which continue dorsally and ventrally in a small aperture. The inferior aperture closes, resulting in a depression called the anal pit. The superior region remains open for some period and begins to as the neural groove is laid down.

===Post Gastrulation or Organogenesis===

Throughout the duration of pre-gastrulation, all tissues for different organs vanish from the surface of blastula and migrate inside to take their final arrangement in the embryo structure where organs are developed from their potential regions. Consequently organogenesis transfers an embryo into free larva structure.

----

==Germ-layer origin of various body tissues==
[[Image: Development Models of Frog.jpg|thumb|right|Figure 13 Image details:Vertebrate Structure and Development.jpg]]

Ectoderm will give raise to structures such as skin, brain, spinal cord, neurons and sense receptors.
Mesoderm will give raise to structrues such as notochord, muscles, blood, bone and sex organs.
Endoderm will give raise to sturctures such as inner lining of gut, liver, pancreas, lungs and bladder, thyroid and parathyroid glands and thymus.

== Structures derived from Germ-layers of frog species ==

[[Image:Development of Frog Layers.jpg|thumb|left|Figure 14 Primary source[http://www.bio.miami.edu/~cmallery/150/physiol/sf19x11b.jpg]Image details:J,Nassif 2009.jpg]]

[[Image:Development of frog layers.jpg|thumb|left|Figure 15 Primary source [http://www.bio.miami.edu/~cmallery/150/physiol/sf19x11b.jpg]Image details:J,Nassif 2009.jpg]]

'''Ectoderm '''

''Establishes the epidermal segments and its derivatives, to the frog’s nervous system. The ectoderm also contributes to :"

1. The olfactory and auditory epithelium.

2. The retina and lens of the eye.

3. Sensory organs.

4. The epithelial lining of the oral cavity and the anus.

5. The pineal and pituitary body.

'''Mesoderm'''

''Mesoderm originates:''

1. Connective tissue.

2. Muscles, except the notochord.

3. Blood vessels.

4. Lymphatics.

5. The peritoneum and the urinary and reproductive system.

6. The dermis, parts of the eye excluding lens, cornea, and conjunctiva.

'''Endoderm'''

''From the endoderm arises:''

1. The epithelial lining to the gut and oesophagus, stomach, intestine, bile duct.

2. The hepatic cells of the liver, respiratory tract, larynx, trachea and lungs.

3. The lining of the urinary bladder, pancreas thyroid and thymus.

[The two figures reveal the development of structures deriving from the celluar components of the embryology of the frog].[Structures derived from Germ-layers of frog species ]

==Life cycle of a frog==

'''Fertilization-egg''':

The female lays eggs in the spring. A group of fertilized eggs is called spawn;

'''7-10 days''':

Fertilized egg feed on remaining yolk which is in its gut. Their gills, mouth and tail have poorly developed. Begin to swim and feed on algae;

'''10-30 days(4 weeks):'''

A layer of skin grows over gills. Teeth begin to appear. A coiled gut start to develop. This is aid in digestion;

'''30-60 days(6-9 weeks):'''

Legs being to grow and head is more distinct. Start to eat insects. Arms begin to grow;

'''60-80 days(12 weeks):'''

Resemble a frog. Still have remaining tail;

'''80-140 days(20 weeks):'''

Fully developed, spend most of time out of water. Majority of frog live between 4-15 years.

==Timeline of frog development==

Development of egg and embryo at temperature 18 degree celsius.

'''0 hours''' - fertilization of the egg

'''1 hours''' - formation of the gray crescent due to pigment migration

'''3.5 hours''' - early cleavage

'''4.5 hours''' - blastula stage(coeloblastula with eccentric blastocoel

'''26 hours''' - gastrulation

'''26 hours''' -'' early'' - crescent shaped dorsal lip

'''34 hours''' - ''middle''- semicircular blastoporal lip

'''42 hours''' - ''late'' - circular blastoporal lip

'''50 hours''' - neurulation

'''50 hours''' - ''early'' - medullary plate

'''62 hours''' -'' middle''- neural folds converging

'''67 hours''' - ''late'' - neural tube formed and ciliation of embryo

'''84 hours''' - tail bud stage(early organogeny)

'''96 hours''' - muscular response to tactile stimulation

'''118 hours''' - early heart beat, development of gill buds

'''140 hours''' - hatching and gill circulation

'''162 hours''' - mouth opens and cornea becomes transparent

'''192 hours''' - tail fin circulation established

'''216 hours''' - degeneration of external gills, formation of operculum, development of embryonic teeth

'''240 hours''' - opercular fold over brachial chamber except for spiracle and internal gills

'''255 hours''' - prolonged larval stage with refinement of organs

'''270 hours''' - development of hindlimbs, internal development of forelimbs in opercular cavity

'''275 hours''' - projection of forelimbs through operculum, left side first

'''280 hours''' - absorption of the tail and reduction in size of the gut

'''284 hours''' - metamorphosis complete, emergence from water as miniature, air breathing frog

==Stages of frog embryology==
--[[User:S8600021|Mark Hill]] 08:40, 9 October 2009 (EST) [[Talk:2009_Group_Project_5#Constructive_Criticism_of_Coordinator|see my comment on images]]

The rate of development of the egg and embryo will depend upon the temperature at which they are kept. The approximate schedule of development at 23 degree celsius is provided below.

{| border='1px'
|+ Table 1: Stages of frog development
!Stage !!Time since fertilisation (hours)!!Stage Characteristic !!Embryo characteristic !!Image of frog stage
|-
|1
|0.00-1.30
|fertilization of the egg, post fertilization
|animal hemisphere, gray crescent and vegetal hemisphere are present
|[[File:Stage01animal.jpg|200px]]

|-
|2
|1.30-2.00
|splits into two cells
|appearance of first cleavage furrow
|[[File:Stage02ventral.jpg|200px]]
|-
|3
|2.00-2.15
|becomes four cells
|appearance of second cleavage furrow
|[[File:Stage03animal.jpg|200px]]
|-
|4
|2.15-2.45
|becomes eight cells
|appearance of third cleavage furrow
|[[File:Stage04dorsolat.jpg|200px]]
|-
|5
|2.45-3.00
|becomes sixteen cells
|appearance of fourth cleavage furrow
|[[File:Stage05dorsal.jpg|200px]]
|-
|6
|3.00-3.30
|becomes thirty-two cells
|appearance of fifth cleavage furrow
|[[File:Stage06animal.jpg|200px]]
|-
|6.5
|3.30-4.00
|blastula stage
|Three dorsal folds become visible as a result of endoderm invagination. Pole cells no longer visible on surface
|[[File:Stage065dorsal.jpg|200px]]
|-
|7
|4.00-5.00
|Gastrulation stage
|two primary germ layers. epiblast and endoderm
|[[File:Stage07dorsal.jpg|200px]]
|-
|8
|5.00-7.00
|neurulation
|medullary plate, neural folds and neural tube
|[[File:Stage08dorsal.jpg|200px]]
|-
|9
|7.00-9.00
|germ layer
|complete lip involution encircling yolk
|[[File:Stage09veg.jpg|200px]]
|-
|10
|9.00-11.00
|early gastrula
|two primary germ layers
|[[File:Stage10veg.jpg|200px]]
|-
|10.5
|11.00-11.45
|gastrula
|two germ layers
|[[File:Stage105vega.jpg|200px]]
|-
|11
|11.45-12.30
|medulla plate
|Yolk sac protrudes dorsally, labium moves to midline on ventral side
|[[File:Stage11veg.jpg|200px]]
|-
|11.5
|12.30-13.15
|continuation of medulla plate
|start closing the plate
|[[File:Stage115veg.jpg|200px]]
|-
|12
|13.15-14.15
|early neurula
|thickened ectoderm give rise to CNS
|[[File:Stage12veg.jpg|200px]]
|-
|12.5
|14.15-14.45
|neural folds
|expansion of cavity
|[[File:Stage125postdors.jpg|200px]]
|-
|13
|14.45-16.15
|neural folds
|continue expanding cavity
|[[File:Stage13postdors.jpg|200px]]
|-
|14
|16.15-17.30
|neural folds
|continuation of cavity
|[[File:Stage14postdors.jpg|200px]]
|-
|15
|17.30-18.15
|tail bud stage
|early organogeny
|[[File:Stage15postdors.jpg|200px]]
|-
|16
|18.15-18.45
|tail bud stage
|posterior ventral view
|[[File:Stage16ant.jpg|200px]]
|-
|17
|18.45-19.45
|tail bud stage
|anterior view
|[[File:Stage17ant.jpg|200px]]
|-
|18
|19.45-20.45
|close neural fold
|anterior view
|[[File:Stage19dorsal.jpg|200px]]
|-
|19
|20.45-21.45
|neural fold close complete
|dorsal view
|[[File:Stage19ant.jpg|200px]]
|-
|20
|21.45-22.30
|early tail bud
|anterior view
|[http://www.xenbase.org/xenbase/original/atlas/NF/stage20ant.jpg stage 20]
|-
|21
|22.30-24.00
|termination of neural crest
|progress to next stage
|[http://www.xenbase.org/xenbase/original/atlas/NF/stage21ant.jpg stage 21]
|-
|22
|24.00-24.45
|prolonged development
|elongation
|[http://www.xenbase.org/xenbase/original/atlas/NF/stage22dorsal.jpg stage 22]
|-
|23
|24.45-26.15
|elongation of embryo
|later view
|[http://www.xenbase.org/xenbase/original/atlas/NF/stage23dorsal.jpg stage 23]
|-
|24
|26.15-27.30
|continuation of elongation of embryo
|dorsal view
|[http://www.xenbase.org/xenbase/original/atlas/NF/stage24dorsal.jpg stage 24]
|-
|25
|27.30-29.30
|organs development
|embryo elongates and develops dorsal thickening
|[http://www.xenbase.org/xenbase/original/atlas/NF/stage25dorsal.jpg stage 25]
|-
|26
|29.30-31.15
|elongation
|dorsally forms neural and brain cavity
|[http://www.xenbase.org/xenbase/original/atlas/NF/stage26dorsal.jpg stage 26]
|-
|27
|31.15-32.30
|elongation of embryo
|dorsal view
|[http://www.xenbase.org/xenbase/original/atlas/NF/stage27dorsal.jpg stage 27]
|-
|28
|32.30-35.00
|further development
|lateral view
|[http://www.xenbase.org/xenbase/original/atlas/NF/stage28dorsal.jpg stage 28]
|-
|29-30
|35.00-37.30
|tail bud
|growth
|[http://www.xenbase.org/xenbase/original/atlas/NF/stage29-30lat.jpg stage 29-30]
|-
|31
|37.30-40.00
|prolonged development
|bud development
|[http://www.xenbase.org/xenbase/original/atlas/NF/stage31lat.jpg stage 31]
|-
|32
|40.00-44.30
|early muscular development
|elongation
|[http://www.xenbase.org/xenbase/original/atlas/NF/stage32lat.jpg stage 32]
|-
|33-34
|44.30-50.00
|muscular movement
|apparatus for locomotion
|[http://www.xenbase.org/xenbase/original/atlas/NF/stage33-34lat.jpg stage 33-34]
|-
|35-36
|50.00-53.30
|muscular movement
|apparatus for locomotion
|[http://www.xenbase.org/xenbase/original/atlas/NF/stage35-36lat.jpg stage35-36]
|-
|37-38
|53.30-56.30
|heart beat
|develops apparatus
|[http://www.xenbase.org/xenbase/original/atlas/NF/stage37-38lat.jpg stage 37-38]
|-
|39
|56.30-66.00
|mouth opens
|cornea transparent
|[http://www.xenbase.org/xenbase/original/atlas/NF/stage39latsmall.jpg stage 39]
|-
|40
|66.00-76.00
|gill circulation
|hatching
|[http://www.xenbase.org/xenbase/original/atlas/NF/stage40lat.jpg stage 40]
|-
|41
|76.00-80.00
|tail, fin circulation
|circulation
|[http://www.xenbase.org/xenbase/original/atlas/NF/stage41lat.jpg stage 41]
|-
|42
|80.00-86.00
|internal gills, operculum
|opercular fold, teeth
|[http://www.xenbase.org/xenbase/original/atlas/NF/stage42lat.jpg stage 42]
|-
|43
|86.00-98.00
|operculum complete
|operculum closed on right
|[http://www.xenbase.org/xenbase/original/atlas/NF/stage43lat.jpg stage 43]
|-
|46
|98.00-106.00
|metamorphosis
|emergence from water as miniature, operculum complete
|[http://www.xenbase.org/xenbase/original/atlas/NF/stage46lat.jpg stage 46]
|-
|}

==Abnormalities of frog==

Abnormalities of frog could be caused by multiple factors. These include change in climate, predators, parasites, bacteria, fungi, viruses or pollution and contaminants such as pesticides, metals and fertilizer.[http://www.fws.gov/contaminants/documents/frogsrefup_septoct_2006.pdf]

The Abnormalities are further classified into different categories. These categories are:

===1. Infectious Diseases:===

'''Perkinsus Symptoms-''' caused by perkinsus-like protozoan organism. Symptoms include swollen viscera that leads to a bloated body and and infected swollen heart

'''Ichthyophonus symptoms-''' cause by parasitic genus, where symptoms include a swollen tail resorption site that matches the surrounding skin in color and translucency.

[[Image:Abnormalities of Frog species.jpg|thumb|left|Figure A Image details[waterwatchadelaide.net.au].jpg]]

===2. Surficial Abnormalities:===

Surficial abnormalities as the one that are visible on the surface of the skin. This includes abnormal pigmentation, , subcutaneous hemorrhaging, wounds due to trauma or from a predator
Edema is a fluid-filled swelling under skin whihc is also a surficial abnormality.

===3. Skeletal Abnormalities:===

This is further classified into three more categories:

'''a. Skeletal Malformations-'''

* Microcephaly (small head or blunt snout)
*Scoliosis (Curved spine in lateral direction)
*Shrunken Limb (Micromelia)
*Amelia (Completely missing limb with no stump)

'''b. Skeletal Abnormalities of Unclear Etiology-'''

This condition arises when a frog has ectromelia (missing limb), brachydactyly (missing digits) or other such condition with no visible trauma or external damage, then this will be classified as the Skeletal abnormality of unclear etiology.

'''c. Skeletal Injuries-'''

Any limb missing or broken due to trauma or other related reason which shows clear evidence of it is classified as skeletal injury

===4. Eye Abnormalities:===

Most common includes-

'''i. Anophthalmia:''' Skin covers the eye socket as there is no eye

'''ii. Abnormal Iris Coloration:''' Reduced pigment in either one eye or both resulting in two different colours of the iris at times

'''iii. Abnormal size or shape:''' Both eyes either deviating from each other or size of pupil or iris is different than the other eye

[http://www.fws.gov/contaminants/Amphibian/pdfs/AbnormalitySOP_woutpics_Jan08.pdf ]

==Genetics==

There are a wide variety of species that differ from each other when it comes to genetics and their functioning.

'''TAXONOMY:''' '''Phylum''' ''Chordata'' / '''Sub Phylum''' ''Vertebrata'' / '''Class''' ''Amphibia'' / '''Order''' ''Anura''

Their are more than two dozen different families of frogs, where suborders are:

'''1. ARCHAEBATRACHIA-''' most primitive frogs

'''2. MESOBATRACHIA-''' linked between the Archaebatrachia and Neobatrachia

'''3. NEOBATRACHIA-''' most modern frogs

{| border='4px'
|+ '''General Info:'''
! !!
|-
| '''Number of frogs' species'''
| 5280
|-
| '''Smallest frog genome size:'''
| 0.95pg, Ornate burrowing frog
|-
| '''Largest frog genome size:'''
| 13.40pg, Ornate horned frog
|-
| '''Mean of frogs' genome'''
| 4.68pg ± 0.13
|-
|}

[http://www.genomesize.com]

*Majority of frogs have only 22 to 26 chromosomes and polyploid is very common where they are almost bisexual.

*Polyploid Amphibians reduce their total cell number such that they acheive the same body size as diploids. One of the most unsual forms of polypoidy in amphibians is the water frog ''Rana esculenta'' from Europe and Western Asia.

* The species with larger genomes have more genes for e.g. the frog genus ''Xenopus'' includes 16 species, with genome sizes ranging from 3.5 x 10^9 bp to 1.6 x 10^10 bp. These differences have arisen by numerous events of polyploidization within the past 40 million years or so. The ancestral chromosome number for the genus seems to have been 18, but there are species with 36, 72 and 105 chromosomes [http://www.xenbase.org/common/]

{| border='4px'
|+ '''Difference within two families'''
! '''SPECIES''' !! ''X.LAEVIS'' !! ''X.TROPICALIS''
|-
| '''PLOIDY'''
| Allotetraploid
| Diploid
|-
| '''NO. OF CHROMOSOMES'''
| 36 chromosomes
| 20 chromosomes
|-
| '''GENOME SIZE'''
| 3.1 x 10^9 bp
| 1.7 x 10^9 bp
|-
| '''EGG SIZE'''
| 1-1.3 mm
| 0.7-0.8 mm
|-
| '''GENERATION TIME'''
| 1-2 years
| 4 months
|-
|}
[http://www.xenbase.org/common/]

===Genome Sequencing===

Since Frog has a huge family with many different species, only few main species that are used widely for the purposes of experiments have their genome sequenced.

''Xenopus tropicalis'' has one of the smallest genomes among amphibians and has the shortest generation time- four to six months and the only diploid genome among the 14 Xenopus species. This means it has no more than two copies of most genes, whereas the other species of Xenopus have four copies of most genes (pseudotetraploid). US Department of Energy's Joint Genome Institute (JGI) in Walnut Creek, California, initiated the X. tropicalis Genome Project, finding 1,700 million base pairs.
[http://www.genome.gov/Pages/Research/Sequencing/BACLibrary/xenopusTropicalis.pdf]

===Xenopus oocytes===

* The oocytes provide an important expression system for molecular biology.

* By injecting DNA or mRNA into the oocyte or developing embryo, scientists can study the protein products in a controlled system. This allows rapid functional expression of manipulated DNAs (or mRNA). This is particularly useful in electrophysiology, where the ease of recording from the oocyte makes expression of membrane channels attractive.

* One challenge of oocyte work is eliminating native proteins that might confound results, such as membrane channels native to the oocyte.

* Translation of proteins can be blocked or splicing of pre-mRNA can be modified by injection of Morpholino antisense oligos into the oocyte (for distribution throughout the embryo) or early embryo (for distribution only into daughter cells of the injected cell).
[http://www.staff.unibe.ch/sigel/xenopus.html]

===Xenopus Laevis===

* ''Xenopus Laevis'' is an important model organism in developmental biology. X. laevis is tetraploid and reaches sexual maturity in 1 to 2 years. What makes it important in developmental biology is its large and easily manipulable embryo.

* Extracts from the eggs of X. laevis frogs are also commonly used for biochemical studies of DNA replication and repair, as these extracts fully support DNA replication and other related processes in a cell-free environment which allows easier manipulation.

* The Human chorionic gonadotropin hormone (hCG) is present in the urine of the pregnant women in large quantities only. This hormone in the urine induces X.laevis oocyte production which formed the basis of first well-documented method of pregnancy testing X. laevis is also notable for its use as the first well-documented method of pregnancy testing when it was discovered. Today, commercially available HCG is injected into Xenopus males and females to induce mating behavior and breed these frogs in captivity at any time of the year.

===Gene cluster===

* The alpha and beta globin genes are closely linked in small cluster of frogs compared to human and chicken

* The similarity of architecture of two clusters found in X.laevis supports the tetraploid origin

* The two loci encoding the muscle specific creatine kinase isoenzymes and have large differences in developmental profile, therefore suggesting that duplicate loci that have not undergone silencing are not simply redundant copies but have acquired specialization.

* Contains twice number of genes for proteins i.e. haemoglobin and sarcomeric actin serum albumin compared with other species

----

==Current Embrology Research==

Currently, a number of fields have benefited from the development of frog embrology. These include cloning, verification of messenger RNA, and Cell cycle.

===Cloning===
[[Image:Robert Briggs.jpg|thumb|left|Figure 16 Image details:Robert Briggs.jpg]]

In 1952, Robert Briggs and Thomas J King cloned northern leopard frogs using a method of nuclear transfer. Briggs and King's experiment was similar to that envisioned - and piloted using salamanders - by Hans Spemann in his 1938 proposal for a 'fantastical experiment'. Later, John Gurdon extended this work and showed that nuclei from differentiated cells could support development, although less well than those from early embryos. [http://genome.wellcome.ac.uk/doc_WTD020799.html]

Lemaitre et a. (2005) from MRC Cancer Cell Unit, Cambridge, U.K. worked on experiments that demonstrated that importance of serial nuclear transplantation for the sucessful cloning of frogs. He demonstrated that exposure of somatic-cell nuclei (erythrocyte nuclei) and sperm nuclei to an extract of mitotic cell extract reorganizes the chromatin into shorter loops and allows replication at much shorter intervals along the DNA. This increases the efficiency of DNA replication in mammalian cell-free systems.

===Transgenesis techniques for functional genomics in Xenopus===

Transgenesis in Xenopus is made possible due to large embryos, a reliable fate map, ease of microinjection, ease of dissection/micromanipulation and existence of the neuroendocrine reflex of background adaptation as a model for activation/inact.

Recently, Hajime Ogino and Haruki Ochi from Nura Institute of Science and Technology in Japan focused on the genomic resources and principles of the transgenesis techniques in Xenopus, and discusses their applications to genome wide network analysis, with emphasis on the use of bioinformatics tools. This is will to understand the gene regulatory networks that control vertebrate development. [http://www.ingentaconnect.com/content/bsc/dgd/2009/00000051/00000004/art00001%3Bjsessionid=4ah96rms73gcu.alexandra]

Xenopus used to be a problem in earlier days when it came to transgenesis. Current methods involves isolated sperm nuclei from Xenopus testis that are microinjected into unfertilized eggs. The generated transgenic tadpoles contain 5-35 copies of the integrated plasmid that are expressed in all cells. If desired, expression of the transgene can be directed to the appropriate tissue and at the appropriate time by using specific promoters, mostly the Xenopus POMC gene promoter (isolated from a Xenopus genomic DNA library) to specifically direct expression of green fluorescent protein (GFP) at high levels to the intermediate pituitary cells, which can either be over expressed or inhibited.[http://molanphys.ruhosting.nl/transgenesis.htm]

[[File:Transgenesis.JPG]]

===Verification of messenger RNA===

While the existence and role of messenger RNA (mRNA) was known in bacteria, in the 1960s it was still debated whether it also existed in vertebrates. Taking haemoglobin mRNA from immature red blood cells and injecting it into a Xenopus oocyte, John Gurdon showed that the haemoglobin protein was indeed produced. Producing proteins in Xenopus oocytes has proved to be extremely useful in cell biology, in particular for the study of receptor proteins.[http://genome.wellcome.ac.uk/doc_WTD020799.html]

===Cell Cycle===

As they develop outside the mother, frog eggs are well stocked with the proteins needed to drive the development of the embryo. Studies of these processes has shed considerable light on the processes involved in cell division - termed the cell cycle. [http://genome.wellcome.ac.uk/doc_WTD020799.html]

===Limb development in Xenopus Laevis===

[[Image: Frog Limb development.jpg|thumb|right|Image details:Primary source:[http://images.google.com.au/imgres?imgurl=http://www.sciencedaily.com/images/2006/06/060616130718.jpg&imgrefurl=http://www.sciencedaily.com/releases/2006/06/060616130718.htm&usg=__xliPsPAvheUBME_kjv_q7auiFbo=&h=333&w=300&sz=11&hl=en&start=2&um=1&tbnid=y_ntJtmkRSK7WM:&tbnh=119&tbnw=107&prev=/images%3Fq%3DLimb%2Bdevelopment%2Bin%2BXenopus%2BLaevis%26ndsp%3D18%26hl%3Den%26sa%3DN%26um%3D1].jpg]]

Donald D. Brown (2005),Department of Embryology, Carnegie Institution of Washington demonstrated factors related to limb development of Xenopus Laevis. Thyroid hormone (TH) is found to be required for limb development in this frog. Specific cell types in the growing limb were targeted for expression of a dominant negative form of the TH receptor by sperm-mediated transgenesis. Limb muscle development, the innervation of muscle from the spinal cord, and cartilage growth can be inhibited without affecting patterning of the limb or differentiation of other cell types. Remodeling of the skin occurs late in metamorphosis after the limb has formed. The coordination of these independent programs is affected in part by the control that TH exerts over DNA replication in all cell types of the limb. [http://www.pnas.org/content/102/35/12455.full]

----

== Glossary ==

[[Image: Frog species.jpg|thumb|left|Image details:Primary source:www.olympus.co.jp/.../080925/large/p02L.jpg].jpg]]

*'''Amphibian:'''

''Relating to or characteristic of animals of the class amphibia.Amphibians are found in the taxonomic class of amphibia, amphibians are capable of both occupying and successfully living in both land and aquatic communities.amphibian''

*'''Augmentation:'''

''Enlargement/Increase in cellular size.''

*'''Autolysis:'''

''breakdown of a part or whole cell or tissue by self-produced enzymes''

*'''Blastomeres:'''

''The undifferentiated cells formed by cleavage of the fertilised ovum. This includes cells in the cleavage, morula, and blastula stages of the embryo''

*'''Carnivorous:'''
''
Flesh-eating; subsisting on animals as food.''

*'''Cleavage:'''

''he repeated division of a fertilised ovum ''

* '''Cleft:'''

''an opening, fissure, or V-shaped indentation made by or as if by splitting''

*'''Chordate:'''

''Members of a diverse phylum of animals that, as embryos, possess a (1) notochord; (2) a dorsal, hollow nerve cord, (3) pharyngeal gill slits; and (4) a post-anal tail''

''The act or state of splitting or dividing of a cell, particularly during the telophase of (animal) cell division.''

*'''Cytoplasm:'''

''The cytoplasm (of both eukaryotes and prokaryotes) is where the functions for cell expansion, growth, metabolism, and replication are carried out''

* '''Epiboly:'''
''The expansion of one cell sheet over other cells, as takes place during gastrulation''

*'''Fertilization:'''

''A process in sexual reproduction that involves the union of male (sperm) and female (ovum) gametes (each with a single, haploid set of chromosomes) to produce a diploid zygote.''

*'''Gamete:'''
''A reproductive cell (male (sperm) or female (egg)) that has only half the usual number of chromosomes''

*'''Gametogenesis:'''

''process leading to the production of gametes. The development and maturation of sex cells through meiosis.Another name for meiosis where a diploid cell is divided into two haploid cells with half the chromosome content of the diploid parent cell.''

*'''Herbivorous:'''

''eating plants; of or pertaining to the herbivora.''

*'''Holoblastic:'''

''The complete division of an isolecithal or microlecithal egg into blastomeres''

*'''Invagination:'''

''One of the methods by which the various germinal layers of the ovum are differentiated.''

*'''Isoenzymes:'''

''Isozymes (also known as isoenzymes) are enzymes that differ in amino acid sequence but catalyze the same chemical reaction.''

*'''Mesentery:'''

'' membranous fold attaching various organs to the body wall.''

*'''Metamorphosis:'''

''A change in the form and often habits of an animal after the embryonic stage during normal development.''

*'''Neuroendocrine:'''

''Neuroendocrine [IPA nʊəroʊˈɛndəkrɪn] cells are cells that release a hormone into the circulating blood in response to a neural stimulus.''

*'''Organogenesis:'''

''The part of embryonic development where the body's main organs develop.''

*'''Peritoneum:'''

''The smooth serous membrane which lines the cavity of the abdomen, or the whole body cavity when there is no diaphragm, and, turning back, surrounds the viscera, forming a closed, or nearly closed, sac.''

*'''Perivitelline space:'''

''The perivitelline space is the space between the zona pellucida and the plasma membrane (sometimes called the vitelline membrane) in a fertilized ovum.''

*'''Polyploidy:'''

''Cells with three or more sets of chromosomes.''

*'''Pronucleus:'''

''the nucleus of the ovum or sperm after fertilization but before they fuse to form the nucleus of the zygote ''

*'''Protoplasm:'''

''The fluid living content of the cell that consists of two major divisions, the cytoplasm and the nucleoplasm (cell nucleus). It is composed mainly of nucleic acids, proteins, lipids, carbohydrates, and inorganic salts''

*'''Segmentation:'''

''division of some metazoan bodies (such as annelida and Arthropoda) into repeated parts, segments. Segmentation can be homomeric (more or less the same) or heteromeric(different from each other).''

*'''Terrestrial:'''

''Of or on the ground, of the habitat of a plant, on land as opposed to in water, or on the ground as opposed to on another plant.''

*'''Transgenesis:'''

''Transgenesis is the process of introducing an exogenous gene - called a transgene - into a living organism so that the organism will exhibit a new property and transmit that property to its offspring.''

*'''Yolk:'''

''nutritive material of an ovum stored for the nutrition of an embryo''

*'''Zygote:'''

''The cell from which an organism develops, that results from the fertilization of the egg by the sperm.''

''Primary Resource "Biology- Online Dictionary''[http://www.biology-online.org/dictionary/Main_Page]

== References - Frog Embryology: ==

[[Image:Frog Research.jpg|thumb|left|Image details:[http://images.google.com.au/imgres?imgurl=http://www.odt.co.nz/files/story/2008/09/university_of_otago_zoology_senior_lecturer_phil_b_3343259744.jpg&imgrefurl=http://www.odt.co.nz/on-campus/university-otago/21670/dunedin-frog-man-wins-zoo-award&usg=__JvJJU5QfOnIwY2bk4xo64UXuJRs=&h=600&w=404&sz=22&hl=en&start=14&um=1&tbnid=AbsP89yWcUiilM:&tbnh=135&tbnw=91&prev=/images%3Fq%3Dfrog%2Bresearch%26hl%3Den%26um%3D1].jpg]]

1. Savage, J. M. (2002). The Amphibians and Reptiles of Costa Rica. University of Chicago Press, Chicago [http://www.springerlink.com/content/vv015277w1746llw/]

2. Ford, L.S.; D.C. Cannatella (1993). "The major clades of frogs". Herpetological Monographs 7: 94–117 [http://digimorph.org/specimens/Xenopus_laevis/]

3. Tyler, M. J. (1994). Australian Frogs A Natural History. Reed Books [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.gracilenta.html]

4. Cogger, H.G.; R.G. Zweifel, and D. Kirschner (2004). Encyclopedia of Reptiles & Amphibians Second Edition. Fog City Press [http://en.wikipedia.org/wiki/Microhylidae]

5. Beltz, Ellin (2005). Frogs: Inside their Remarkable World. Firefly Books [http://unjobs.org/authors/ellin-beltz]

6. Tyler, M. J. (1994). Australian Frogs A Natural History. Reed Books [http://www.s4space.com.au/ross%20alford/fomi%20cd/files.cd/l.ornatus.html]

7. Moury JD, Hanken J (1995) Early cranial neural crest migration in the direct-developing frog, Eleutherodactylus coqui. Acta
Anatomica (Basel) 153, 243-253.

8.Raynaud A (1985) Development of limbs and embryonic limb reduction. In Biology of the Reptilia (ed. Gans C, Billett F), pp.
59-148. New York: John Wiley.[http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=9309]

9. Hanken J (1986) Developmental evidence for amphibian origins. In Evolutionary Biology (ed. Hecht MK, Wallace B, Prance GT), 20, pp. 389-417. New York: Plenum Press. [Hanken J (1986) Developmental evidence for amphibian origins. In Evolutionary Biology (ed. Hecht MK, Wallace B, Prance GT), 20, pp. 389-417. New York: Plenum Press.]

10. Elinson RP (1990) Direct development in frogs : wiping the recapitulationist slate clean. Seminars in Developmental Biology
1, 263-270.

11. Beebee, T. J. C. 1996. Ecology and Conservation of Amphibians. Chapman and Hall. London. [http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V5X-3SVHMKH-1X&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=1021245355&_rerunOrigin=google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=825868e10cd178d16a8a0e5ad14dc5ef]

12. Lehtinen, R. M. 2002. The use of screw pines (Pandanus spp.) by amphibians and reptiles in Madagascar. Herpetological Bulletin 2002:20–25.

13. Parris, K. M. and M. A. McCarthy. 1999. What influences the structure of frog assemblages at forest streams. Australian Journal of Ecology 24:495–502. CrossRef

14. Zug, G. R. 1993. Herpetology: An Introductory Biology of Amphibians and Reptiles. Academic Press. San Diego, CA.

15. Slack,J.M.W., Darlington,B.G., Heath,J.K. and Godsave,S.F. (1987)Mesoderm induction in early Xenopus embryos by heparin-binding growth factors. Nature, 326, 197-200.

16. Melton,D.A. (1990) Activins are expressed early in Xenopus embryogenesis and can induce axial mesoderm and anterior structures. Cell, 63, 485-493.

17. Harland,R.M. and Misher,L. (1988) Stability of RNA in developing Xenopus embryos and identification of a destabilizing sequence in TFIIIA RNA. Development, 102, 837-852.

18. Cunliffe,V. and Smith,J.C. (1992) Ectopic mesoderm formation in Xenopus embryos caused by widespread expression of a Brachyury homologue. Nature, 358, 427-430.

19. Kinoshita,K., Bessho,T. and Asashima,M. (1993) Competence prepattern in the animal hemisphere of the 8-cell-stage Xenopus embryo. Devel. Biol., 160, 276-284.

20. LaBonne,C., Burke,B. and Whitman,M. (1995) Role of MAP kinase in mesoderm induction and axial patterning in Xenopus development. Development, 121, 1475-1486.

21. Green,J.B.A., New,H.V. and Smith,J.C. (1992) Responses of embryonic Xenopus cells to activin and FGF are separated by multiple dose thresholds and correspond to distinct axes of the mesoderm. Cell, 71, 731-739.

22. Grainger R., Blumberg B., Harland R., Amemiya C., Importance of Xenopus Tropicalis to biomedical and biological research, Benaroya Research Institute, Virginia Mason Research Center [http://www.genome.gov/Pages/Research/Sequencing/BACLibrary/xenopusTropicalis.pdf ]

23. Gregory, T.R. (2005). Animal Genome Size Database. [http://www.genomesize.com]

24. U.S Fish and Wildlife Services, ABNORMALITY CLASSIFICATION SOP, [http://www.fws.gov/contaminants/Amphibian/pdfs/AbnormalitySOP_woutpics_Jan08.pdf ]

25. Donald D. Brown*, Liquan Cai*, Biswajit Das*, Nicholas Marsh-Armstrong‡, Alexander M. Schreiber*, and Rejeanne Juste*(2005), Thyroid hormone controls multiple independent programs required for limb development in Xenopus laevis metamorphosis [http://www.pnas.org/content/102/35/12455.full]

26. Ogino, Hajime; Ochi, Haruki, Resources and transgenesis techniques for functional genomics in Xenopus, Development Growth & Differentiation, Volume 51, Number 4, May 2009 , pp. 387-401(15) [http://www.ingentaconnect.com/content/bsc/dgd/2009/00000051/00000004/art00001%3Bjsessionid=4ah96rms73gcu.alexandra]

27. Giles Newton (2004) Why the frog? The Human Genome, [http://genome.wellcome.ac.uk/doc_WTD020799.html]

28. Xenbase, [http://www.xenbase.org/common/]

29. Donders Center for Neuroscience & Nijmegen Center for Molecular Life Sciences (NCMLS), Beyond the genome (Xenopus transgenesis for functional genomics),Faculty of Science, Radboud University [http://molanphys.ruhosting.nl/transgenesis.htm]

== External Links ==
[[Image:Frog links.jpg|thumb|left|Image details:[http://images.google.com.au/imgres?imgurl=http://2.bp.blogspot.com/_o93AaY0GzH4/SjY_ZYv0PII/AAAAAAAAAgk/skruNc2yN78/s400/computer%2Bfrog.jpg&imgrefurl=http://hellaheaven-ana.blogspot.com/2009/06/talking-frog-contemporary-fairy-tale.html&usg=__oxji1TGLV2Fi7xe0dnlmuYk8gDo=&h=288&w=288&sz=16&hl=en&start=2&um=1&tbnid=ywZd4zpdxC5plM:&tbnh=115&tbnw=115&prev=/images%3Fq%3Dfrog%2Bon%2Bcomputer%26hl%3Den%26um%3D1].jpg]]

1. Frog embryology [http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/F/FrogEmbryology.html Frog Embryology]

2. Frog cellular materials [http://www.xenbase.org/xenbase/original/cell/cell.html xenbase]

3. The zoology of frog species [http://worms.zoology.wisc.edu/frogs/mainmenu.html zoology frogs]

4. Frog cycle [http://www.bioethics.gov/images/sc_images/frog_dev.gif bioethics frog] Just a little cycle of FROG'S life cycle

5. Frog Embryology [http://embryology.med.unsw.edu.au/OtherEmb/Frog.htm UNSW Embryology]

6. Frog Research [http://apps.carleton.edu/campus/library/now/exhibits/wallcharts/frog/ carleton library exhibit]

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[[Category:Frog]]