2009 Group Project 5
- 1 The Embryology of Frogs
- 2 Growth and development of the Frog
- 3 Anatomy of frog
- 4 The Egg
- 5 Gametogenesis
- 6 The Egg & Fertilization
- 7 Maturation of the Egg
- 8 Maturation phases
- 9 Cleavage
- 10 Gastrulation
- 11 Growth and Modification of Frog Species
- 12 Gastrulation
- 13 Germ-layer origin of various body tissues
- 14 Structures derived from Germ-layers of frog species
- 15 Timeline of development
- 16 Stages of frog embryology
- 17 Abnormalities of frog
- 18 Genetics
- 19 Current Embrology Research
- 20 Glossary
- 21 References - Frog Embryology:
- 22 ANAT2341 group projects
The Embryology of Frogs
Growth and development of the Frog
- 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. --Joe Nassif 17:29, 19 August 2009 (EST)
Anatomy of frog
- Frogs are classified in animal kingdom as amphibian. This is analysed base on their unique abilities to survive on dryland as well as underwater. In addition, frogs have a pair of lungs that allow them to breathe when on land. When underwater, frog can breathe through their skin. Oxygen in the water can pass through their porous skin and penetrate directly in blood.
- Frogs have a three-chambered heart with two atria and one ventricle. Unlike humans which possess a four-chambered heart with two atria and two ventricles. A valve with a frog's heart is called spiral valve, which directs the flow of blood to prevent oxgenated and deoxygenated blood from mixing.
- Frogs have developed highly specialised anatomical structures in order to adapt different living conditions. Such structures include their powerful hind limbs adapt for both swimming and leaping. The webs on the hind feet provide a large surface area for pushing aganist water. Also, frogs have a highly developed sense of hearing, which aid them to detect high-pictched sounds with their ears and low pictched sounds through their skins. Frogs have a keen sense of sight and smell. They can detect predators and prey using their large eyes that protrude from their head.--Gang Liu 10:26, 27 August 2009 (EST)
- 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 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.--Joe Nassif 17:29, 19 August 2009 (EST)
VIDEO RESOURCE: 
- 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 .
- 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.
- The zygote changes into a mature frog through the process of embryology and metamorphosis. Gametogenesis is a progression which frog gametes are established from cells, called germ cells. Initial germ cells are called primordial germ cells, which can be recognised extremely early in the life of frog species.--Joe Nassif 13:30, 27 August 2009 (EST)
The Egg & Fertilization
- 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.
--Joe Nassif 09:54, 2 September 2009 (EST)
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.
--Joe Nassif 09:54, 2 September 2009 (EST)
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.
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.
- 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
--Joe Nassif 09:54, 2 September 2009 (EST)
- 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.
- 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.--Joe Nassif 13:31, 27 August 2009 (EST)
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.
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.
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.
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.
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. --Joe Nassif 09:54, 2 September 2009 (EST)
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.
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.
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.
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.
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.
5. Development of the reproductive system
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.
--Joe Nassif 09:55, 2 September 2009 (EST)
The start of gastrulation is marked by the pushing inward of the cells in the region of embryo. This produces, first, an opening that will be the future anus. Second, a cluster of cells that develops into the Spemann organiser. As gastrulation continus, three different germ layers are formed. These are ectoderm, mesoderm and endoderm. --Gang Liu 18:27, 19 August 2009 (EST)
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.
--Joe Nassif 08:58, 2 September 2009 (EST)
Germ-layer origin of various body tissues
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.--Gang Liu 18:32, 19 August 2009 (EST)
Structures derived from Germ-layers of frog species
Establishes the epidermal segments and its derivatives, to the frog’s nervous system. The ectoderm also contributes to the olfactory and auditory epithelium additionally to the retina and lens of the eye, also other sensory organs. The epithelial lining of the oral cavity and the anus and the pineal and pituitary body are derived by the ectoderm.
Mesoderm originates the connective tissue and muscles, except the notochord, it also derives blood vessels, lymphatics, and to the peritoneum and the urinary and reproductive system. It also has a relationship with the dermis, parts of the eye excluding lens, cornea, and conjunctiva.
From the endoderm arises the epithelial lining to the gut and oesophagus, stomach, intestine, bile duct and the hepatic cells of the liver, respiratory tract, larynx, trachea and lungs, lining of the urinary bladder, pancreas thyroid and thymus.
--Joe Nassif 09:52, 2 September 2009 (EST)
Timeline of development
The female lays eggs in the spring. A group of fertilized eggs is called spawn;
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.--Gang Liu 11:19, 27 August 2009 (EST)
Stages of frog embryology
- ==Stages of frog development==
|1 Fertilization of the egg||0.00|
|2 Formation of the gray crescent due to pigment migration||0.00-1.00|
|3 Blastula stage||1.00-3.50||two cells||rotation||coeloblastula with eccentric blastocoel|
|4 Gastrulation||3.5-4.5||four cells||early-crescent-shaped dorsal lip;middle-semi-circular blastoporal lip;late-circular blastoporal lip|
|5 Neurulation||4.5-5.5||eight cells||early-medullary plate; middle-neural folds converging; late-neural tube formed and ciliation of embryo|
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 fertiliser.--Gang Liu 10:40, 27 August 2009 (EST)
7.Timeline -how long
8. Diagram (Hand-drawn)
9. Germ-layer origin of various body tissues
10.Developmental factors associated with specfic stages of growth
11. Staging - are there species specific staging, what occurs when
12.History of Model Use - when was it first used, what embryology research
There are a wide variety of species that differ from each other when it comes to genetics and their functioning. Therefore XENOPUS LAEVIS is chosen as it is widely used for the purposes of the experiments.
Diploid number of chromosomes in Xenopus frog: 36
Haploid number: 18
DNA content (C value)= 3.1 pg, lowest amongst amphibians
Chromosomes: Short chromosomes with small chromomeres
Class: Belongs to tetraploid class
Sequence Divergence: Less than 10% sequence divergence
Karyotype: 18 pairs of distinct chromosomes forming bivalenst in meiosis, independent disomic inheritance of duplicated genes, haploid 18 chromosome zygotes
Mutants: 40 recessive mutants: certain part of genetic info presented in non-duplicated form
Diploid or Allotertraploid: Functional diploid even though its genomes shows features of allotetraploid origin
- The alpha and beta globin genes are closely linked in smale cluster compared to human, 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.
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.
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.
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.--Gang Liu 18:51, 19 August 2009 (EST)
14. Current Embryology Research - research papers and findings
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
Living in or on water for all or a substantial part of the life span (generally restricted to fresh water or inland waters).
breakdown of a part or whole cell or tissue by self-produced enzymes
The undifferentiated cells formed by cleavage of the fertilised ovum. This includes cells in the cleavage, morula, and blastula stages of the embryo
Flesh-eating; subsisting on animals as food.
The act or state of splitting or dividing of a cell, particularly during the telophase of (animal) cell division.
The cytoplasm (of both eukaryotes and prokaryotes) is where the functions for cell expansion, growth, metabolism, and replication are carried out
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.
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.
eating plants; of or pertaining to the herbivora.
The complete division of an isolecithal or microlecithal egg into blastomeres
One of the methods by which the various germinal layers of the ovum are differentiated.
membranous fold attaching various organs to the body wall.
A change in the form and often habits of an animal after the embryonic stage during normal development.
The part of embryonic development where the body's main organs develop.
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.
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
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).
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.
Primary Resource "Biology- Online Dictionary
--Joe Nassif 09:53, 2 September 2009 (EST)
References - Frog Embryology:
--Mark Hill 16:24, 29 August 2009 (EST) I have fixed these references.
4. bioethics frog Just a little cycle of FROG'S life cycle