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

Explain major divisions of the hypophysis, Q. What are the major divisions ...

Q. What are the major divisions of the hypophysis? What are their functions? The hypophysis is divided into two portions- the anterior hypophysis or adenohypophysis and the pos

Define requirements of sodium during pregnancy period, Define requirements ...

Define requirements of Sodium during pregnancy period? As you know, sodium plays a role in fluid balance. Sodium metabolism is altered during pregnancy under the stimulus of a

Functions of cerebrum, Functions of cerebrum The forebrain is otherw...

Functions of cerebrum The forebrain is otherwise called as ‘cerebrum'. It is highest centre for controlling several functions in the body, The most interesting aspect

Respiration, how respiration takes place in mammls and reptiles

how respiration takes place in mammls and reptiles

Why is cartilage more flexible than bone, Why is the cartilage more flexibl...

Why is the cartilage more flexible than bone? in general, why does cartilage take longer to repair than bone?

Unconventional feed resources and anti-nutritional factors, Unconventional ...

Unconventional Feed Resources and Anti-Nutritional Factors With increasing ruminant population, there is a need to identify and introduce new and lesser-known food and feed cro

Anti-diuretic hormone, who discovered it? and what is it''s physiologic fun...

who discovered it? and what is it''s physiologic functions?

Packaging for instruments and cassettes, Packaging for instruments and cass...

Packaging for instruments and cassettes Packaging used for instruments and cassettes prior to sterilization includes wrap, paper pouches, plastic pouches, combination paper/pl

What is oligosaccharides , Oligosaccharides are short chains of m...

Oligosaccharides are short chains of monosaccharides linked together by glycosidic bonds. In case of oligosaccharides  linked to proteins (glycoproteins)  or lipids (glycolipids) o

What is master gland, Which of the below is usually referred to as "master ...

Which of the below is usually referred to as "master gland" because it regulates so many body activities? Is it: a) Pituitary gland b) Thyroid gland c) Adrenal gland d

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