K12 Comparative Embryology: Difference between revisions

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==Tissue Development==
==Tissue Development==

Revision as of 11:00, 14 October 2016

Embryology - 28 Mar 2024    Facebook link Pinterest link Twitter link  Expand to Translate  
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Introduction

Newborn.jpg
Mouse.jpg
Rat.jpg
Chick icon.jpg
Frog-icon.png
Zebrafish-icon.png
Fly-icon.png
C elegans.jpg
Sow and piglet.jpg
Rabbit.jpg
Dog-adult.jpg
Guineapig icon.jpg
Cowcalf.jpg
Echidna.jpg
Red-necked wallaby.jpg
Platypus.jpg
Bat icon.jpg
Lizard embryo 03.jpg
Grasshopper- female.jpg
Medaka.jpg
All human and animal embryos go through very similar stages of early development. See also Humans and Animal Embryology.


What are the key things in development that we share?

This page introduces a few of the concepts of comparative development shared with all animals.

Ernst Haeckel (1834 – 1919) "ontogeny recapitulates phylogeny" claimed that an individual organism's biological development (ontogeny), parallels and summarises its species evolutionary development (phylogeny). First a single-celled organism, then evolve into a fish, then an amphibian, then a reptile, then a bird, and finally reach a mammal.
Current developmental biology shows that animals follow similar developmental programs, but do not go through a "species change" during development.


Meiosis | Mitosis | Gastrulation | Body Plan | Limbs | Tissue Development | Organ Development


K12 Links: Start Here | Week 1 | Week 2 | Week 3 | Week 4 | Week 5 to 8 | Arms and Legs | Heart | Fetus | Brain Growth | Eyes and Ears | Animal Development Times | Humans and Animal Embryology | Comparative Embryology | Thalidomide
Teacher Note 
Mark Hill.jpg This is currently only a draft designed to help K12 students understand comparative embryology.

I am currently looking to simplify concepts and include images on this page. I am happy to receive feedback as too what you may like to be included here. I have also begun to add some simple exercises that can be used in class to help understand concepts in embryonic development and comparison. Note some of the links on this page leave the K12 notes section and may be beyond the level of your students, bookmark this page to easily return here.

This page can be printed using the menu from the list at the bottom of the page "Printable version" or Printable version.


Also look at the K12 Human and Other Animal Development that simply compares development times and embryo structures.

K12 Professional Development 2016 | K12 Professional Development 2014

Meiosis

In the male and female in all animals (and plants) that reproduce sexually to form an embryo, these very first cells form by meiosis.

Meiosis a reductive form of cell division that only occurs in the egg (oocyte) and sperm (spermatozoa) and allows new genetic combinations of offspring to be generated.

Meiosis has 2 key components:

  1. Genetic reorganisation - the genetic material (chromosomes) that you have from your mother and father are recombined.
  2. Genetic reductive - the chromosome number is halved and only fertilisation will allow the paired chromosomes that we all contain in all our cells.
Human idiogram.jpg

Meiosis in all mammals:

  • Female embryo XX - X chromosome from egg and X chromosome from sperm
  • Male embryo XY - X chromosome from egg and Y chromosome from sperm
  • Both male and female embryos - get the recombined 22 autosomes and the mother's mitochondrial DNA
<html5media height="200" width="300">File:Oocyte_Meiosis_01.mp4</html5media>

This movie shows the egg (oocyte) completing the first part of meiosis (meiosis I). The chromosomes are coloured blue, the cell membrane is green. The small structure on the left are chromosomes that will not be used in the embryo.

Mitosis

Mitosis is the type of normal cell division that allows growth and development of all animal embryos.

After the first cell has been formed by the egg (oocyte) and sperm (spermatozoa) fusing, every cell division in the embryo forms 2 genetically identical daughter cells. Every mitosis in all animal cells has the same features.


Mitosis has 2 key components:

  1. Chromosome duplication - has to occur before cell division can occur.
  2. Mitosis - a set of 5 standard phases dividing the nucleus (and the chromosomes it contains) before the cytoplasm divides.



Mitosis is a biological process that is the same (evolutionarily conserved) in all plants and animals.
<html5media height="300" width="300">File:Mitosis 11.mp4</html5media>

This movie shows a cell that has already begun mitosis separating the chromosomes in the nucleus then the cell cytoplasm. The chromosomes are white.

Gastrulation

Development of any animal requires the differentiation of different cell types and tissues from essentially the same initial cells. One of the first shared steps is the process of "gastrulation" (means gut formation). This forms the 3 cell layers that will form all the embryo, they are often described as the "germ layers" and this stage of development as the "gastrula". The same layers form the same structures in all these animals.


3 Germ Layers:

  1. Ectoderm - outer layer of skin (epidermis) and nervous system (central nervous system and peripheral nervous system).
  2. Mesoderm - bone, muscle, cartilage, blood (connective tissues)
  3. Endoderm - lining of the gut, lungs, endocrine organs.



Gastrulation is a process that occurs in nearly all animals and each germ layer contributes the same body components to all animal embryos.
germ cell layers

Body Plan

The next step in development of any animal requires the embryo body plan (axes) by a patterning process.

Body plan (axes)

  1. head and body
  2. left and right side
  3. front and back


Many signals used to establish this patterning have been identified and are shared (similar or the same) between different animals. Note that some of the signals used to establish the overall body plan can be reused later at other stages in embryo development and within the body organs and tissues.

Body plan genes and signaling pathways are similar for all animals.
animal body patterns

Different animal body plan axes.

Below is an example of what happens in a fly if these patterning signals get disrupted, putting legs from the body on the head where antenna should be located.

Fly wild-type head.jpg Fly antennapedia head.jpg
Normal fly head with antenna Abnormal fly head with legs for antenna

This fly mutation identified a common patterning gene family called Hox that establishes the head to tail axes in the embryo.

This complicated picture shows how different Hox genes are expressed at different embryo levels in different species (worms, flies, mouse and human).

Proposed Hox protein classification.jpg

Teacher Note 
Mark Hill.jpg The fly head picture is easy to explain, and you can also talk about the 1995 Nobel Prize for this discovery.

The Hox gene picture will be difficult for students to understand. Just understand that in all animal embryos, different Hox genes are expressed along the head to tail axis of the embryo and that this establishes an initial pattern in all embryos.

"Hox" is the acronym for "Homeobox", a large family of similar genes that control the formation of many body structures during early embryonic development.

Here is a page with University level student information on Homeobox

Limbs

Many different animals form limbs (arms and legs). During embryo development there are common signalling molecules and regions that form the initial limb structure. A similar process occurs for both the upper (arm) and low (leg) limb development.


The final limb structures formed can appear different, but the bones shows that they share a pattern of development.

Stage16-17-limbs01.jpg

Early human embryo upper and lower limbs.

Limb comparison cartoon 02.jpg

Upper limb bones of 4 different species. Each limb is significantly different in size and function, but all contain the same basic skeletal structures.

Limb bud geometry and patterning.jpg

Cartoon of the early limb showing regions that establish the developmental patterning.

Limbs even though animal arms, legs, flippers and wings appear externally different their skeletons show common features.

Tissue Development

All animal embryos have similar tissues (connective, muscle, nervous, and epithelial) that that develop in different regions of the embryo. The development of these tissues is different from embryo patterning and is separate for each tissue.


The developmental signals that control say a connective tissue, like bone, are the same for all bones throughout the body. These mechanisms are the same in other animals. Therefore bone development will go through similar stages in all animals bodies even though different bones are eventually formed.

Appendicular skeleton.jpg

The limb skeleton.

Teacher Note 
Mark Hill.jpg If the students have already done some biology they should understand these 4 main tissue types: connective, muscle, nervous, and epithelial. It is beyond the scope of this current page to go through these developmental molecular mechanisms.

Organ Development

Many animals have common organs used for digestion (stomach, liver, pancreas), breathing (lungs), waste (kidneys) and cardiovascular (heart).

The signalling mechanisms that are used to control their initial development and later internal patterning are the same in many different species embryos.

Teacher Note 
Mark Hill.jpg Organ development is difficult to explain easily to students. The diagram below shows how the mouse liver development is controlled by different genes. Most easily explained as, similar to what is seen in the human liver development.
Liver development signaling.jpg

Mouse liver development

  • E - means the embryonic day of development.
  • Red names - are the genes controlling specific development steps.
  • The other colours refer to developmental stages and features.

Animal Models

These shared signalling mechanisms allow us to use animal development to study both normal and abnormal human development.

Common animal "models" used include mouse (mammal), chicken (bird) and zebrafish (fish). Though very different species, current research shows that these embryos share common signalling mechanisms that form similar structures in different animals.

  • mouse - (mammal) good model for easy genetic manipulation.
  • chicken - (bird) develops in an egg so the earlier stages of development can be observed in the living embryo.
  • zebrafish - (fish) good model of vertebrate (backbone) animal development as the embryos are "see through" and can be observed while growing.


Zebrafish embryo development from the 1-cell stage to 85 hours post fertilisation.

<html5media height="300" width="948">File:zebrafish movie01.mp4</html5media>


Now looks at Human and Other Animal Development



Cite this page: Hill, M.A. (2024, March 28) Embryology K12 Comparative Embryology. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/K12_Comparative_Embryology

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© Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G