Bilateral cleavage, Biology

Assignment Help:

Bilateral Cleavage

In some animals (for example tunicates and nematodes, although in different way), the arrangement of 4 blastomeres after second cleavage is almost radially symmetrical like in the radial kind of cleavage, but two of these are larger than to the other two blastomeres establishing a plane of bilateral symmetry in the developing embryo. During consequent cleavages the bilateral arrangement of blastomeres might be still more obvious. Further, relies on whether a particular cleavage furrow may divide the egg totally or partially, cleavage has been described as:

a) Holoblastic or complete: Each cleavage furrow divides the whole egg completely in the specific plane. It may be:

A) Equal holoblastic cleavage: It takes place in alecithal (eutherian mammals) or microlecithal (Amphioxus, echinoderms) eggs in which each cleavage furrow divides the egg so as to generate blastomeres of approximately equal size.

B) Unequal holoblastic cleavage: This occurs in mesolecithal and moderately telolecithal eggs (lower groups of bony fishes and amphibians), in which the yolk is mainly concentrated in the vegetal hemisphere. In these eggs the first and second cleavage divisions take place along Meridional planes generating 4 equal blastomeres. But, due to the yolk being concentrated in the vegetal region, the 3rd cleavage furrow is latitudinal above the equator and closer to the animal pole. The furrow divides each of the 4 blastomeres totally but not equally into a small and larger daughter blastomeres. Hence the third cleavage is, unequal holoblastic producing 4 small blastomeres (micromeres) in the animal region and 4 large blastomeres (macromeres) in the vegetal region. Subsequently the micromeres consisting of relatively less yolk divide at a very much faster rate as compared to the large yolky macromeres.


Related Discussions:- Bilateral cleavage

Blood clotting, BLOO D CLOTTING - It is a nature's device to check ...

BLOO D CLOTTING - It is a nature's device to check the excessive loss of blood from an injury. Bleeding time is 1-3 minutes. Clotting time is 2-6 minutes. Process of

What is photosynthesis , What is Photosynthesis ? Photosynthesis is t...

What is Photosynthesis ? Photosynthesis is the method by which plants trap radiant energy from the sun and convert the energy into a biochemical form. This biochemical energy

What is the molecular formula of glucose, Q. What is the molecular formula ...

Q. What is the molecular formula of glucose? How can its structural formula be explained? The molecular formula of glucose is C 6 H 12 O 6 . Structurally glucose is a hexago

Describe tranposition of great arteries intact ventricular, Describe tranpo...

Describe tranposition of great arteries with intact ventricular septum? Transposition of great arteries with intact ventricular septum (or small VSD): There is usually inadequa

What, what are mendal low

what are mendal low

Germplasm conservation - plant tissue and organ culture, Germplasm Conserva...

Germplasm Conservation - plant tissue and organ culture Totipotent plant cells and shoot tips can be freeze-preserved in liquid nitrogen (-196? C) for long periods, and wh

Define kingdom monera and protista?, Q. Which are the beings that constitut...

Q. Which are the beings that constitute the kingdom Monera? The kingdom Monera is the kingdom of the prokaryotes, archaebacteria and composed of bacteria. Q. Which are the

Do progeny shows all of the dominant phenotypes, Individuals of the followi...

Individuals of the following genotype are crossed: aa BB Cc Dd (crossed with) Aa Bb Cc Dd A) How many different phenotypes are possible for the progeny? B) What are the chanc

Why diabetics patient should have vegetables every day, Why Diabetics patie...

Why Diabetics patient should have Vegetables every day Diabetics should have vegetables every day. Fresh vegetables are to be preferred because they have less fats and salt. Da

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd