Biology, asked by ayeshapervaiz3pe6ikb, 1 year ago

what role does grey Crescent play in the development of the embryo of frog

Answers

Answered by bharatDadhich
8
The frog egg is a huge cell; its volume is over 1.6 million times larger than a normal frog cell. During embryonic development, the egg will be converted into a tadpole containing millions of cells but containing the same amount of organic matter.The upper hemisphere of the egg — the animal pole — is dark.The lower hemisphere — the vegetal pole — is light.When deposited in the water and ready for fertilization, the haploid egg is at metaphase ofmeiosis II
FertilizationEntrance of the sperm initiates a sequence of events:Meiosis II is completed.The cytoplasm of the egg rotates about 30 degrees relative to the poles.In some amphibians (includingXenopus), this is revealed by the appearance of a light-colored band, thegray crescent.The gray crescent forms opposite the point where the sperm entered.It foretells the future pattern of the animal: its dorsal (D) and ventral (V) surfaces; its anterior (A) and posterior (P); its left and right sides.The haploid sperm and egg nuclei fuse to form thediploid zygote nucleus.CleavageThe zygote nucleus undergoes a series of mitoses, with the resulting daughter nuclei becoming partitioned off, by cytokinesis, in separate, and ever-smaller, cells.The first cleavage occurs shortly after the zygote nucleus forms.A furrow appears that runs longitudinally through the poles of the egg, passing through the point at which the sperm entered and bisecting the gray crescent.This divides the egg into two halves forming the 2-cell stage

The second cleavage forms the 4-cell stage. The cleavage furrow again runs through the poles but at right angles to the first furrow.

The furrow in the third cleavage runs horizontally but in a plane closer to the animal than to the vegetal pole. It produces the 8-cell stage.

The next few cleavages also proceed in synchrony, producing a 16-cell and then a 32-cell embryo.

However, as cleavage continues, the cells in the animal pole begin dividing more rapidly than those in the vegetal pole and thus become smaller and more numerous.

By the next day, continued cleavage has produced a hollow ball of thousands of cells called the blastula. A fluid-filled cavity, the blastocoel, forms within it.

During this entire processthere has been no growth of the embryo. In fact, because the cells of the blastula are so small, the blastula looks just like the original egg to the unaided eye.Not until the blastula contains some 4,000 cells is there any transcription of zygote genes. All of the activities up to now have been run by gene products (mRNA and proteins) deposited by the mother when she formed the egg.
GastrulationThe start of gastrulation is marked by the pushing inward ("invagination") of cells in the region of the embryo once occupied by the middle of the gray crescent. This produces:an opening (the blastopore) that will be the future anusa cluster of cells that develops into the Spemann organizer (named after one of the German embryologists who discovered its remarkable inductive properties).As gastrulation continues, three distinct "germ layers" are formed:ectodermmesodermendodermEach of these will have special roles to play in building the complete animal. Some are listed in the table.Germ-layer origin of various body tissuesEctodermMesodermEndodermskinnotochordinner lining of gut, liver, pancreasbrainmusclesinner lining of lungsspinal cordbloodinner lining of bladderall other neuronsbonethyroid and parathyroid glandssense receptorssex organsthymus

Answered by Nyaberiduke
2

Answer:

The grey crescent after being formed after the sperm enters the egg, they transform into spemann's organizer.

Explanation:

This acts like a call center from where signals of communication are sent to signal the beginning of development.

This is the part that enables and activates development through activating other parts responsible for development to begin development.

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