Types of cleavage, Biology

Assignment Help:

Types of Cleavage

a) Radial Type: If each of the blastomeres of upper tier lies exactly over the corresponding blastomeres of the lower tier the pattern of cleavage is radially symmetrical i.e. blastomeres are arranged along the radii of the sphere, e.g. echinoderms, Amphioxus, amphibians.

b) Spiral Type: The upper tier of blastomeres of 8-cell stage embryo may be shifted with respect to the lower tier so that radially symmetrical arrangement of blastomeres is distorted in various degrees. In such a case the blastomeres of the upper tier do not lie exactly over the corresponding blastomeres of the lower tier.

Instead, all the blastomeres of upper tier are shifted in the same direction with respect to all the blastomeres of the lower tier. This position results from the oblique position of mitotic spindle so that, from the start, two daughter blastomeres do not lie one above the other, e.g., annelids, molluscs, some helminths of order polycladida.


Related Discussions:- Types of cleavage

Cobalt (co) - micronutrients, Cobalt (Co) - Micronutrients The Co conc...

Cobalt (Co) - Micronutrients The Co concentration in the dry matter of plants grown in soil normally lies around 0.02 to 0.5 ppm. In soils the content varies from 1 to 40 ppm.

Biology, excretory organs of different animals from protozoa to mammals

excretory organs of different animals from protozoa to mammals

What is lyophobic, What is lyophobic If the affinity of the dispersed p...

What is lyophobic If the affinity of the dispersed phase to go into or to remain in colloidal dispersion is slight, the dispersed phase is said to be lyophobic (solvent repelli

Zoonoses disease-transmissible spongif orm encephalopathies, Transmissible ...

Transmissible spongif orm encephalopathies Transmissible spongiform encephalopathies (TSEs, also called Prion diseases) are fatal neurodegenerative diseases such as scrapie of

What are the muscle of the diaphragm, Would you expect the muscle fibers of...

Would you expect the muscle fibers of the tongue to be striated or smooth? What about the muscle of the diaphragm/ Explain your answer.

Requirements of various nutrients in constipation, Q. Requirements of vario...

Q. Requirements of various nutrients in constipation? The requirements of various nutrients are not altered in constipation. It is essentially a normal balanced diet (normal RD

Define rna synthesis , The general mechanism of RNA synthesis by these euk...

The general mechanism of RNA synthesis by these eukaryotic RNA polymerases is the same as for the prokaryotic enzyme that is: ?   The initiation  of RNA synthesis  by RNA polyme

What are the elements that constitute the stomata, What are the elements th...

What are the elements that constitute the stomata? The Stomata is made of a central opening the ostiole or slit delimited by two guard cells responsible for its closing or open

Corelation of st depressoin with coronary angiography, Q. Corelation of ST ...

Q. Corelation of ST Depressoin with Coronary Angiography? Various investigators considered 1 mm of horizontal or downsloping ST depression to denote a positive test and used fr

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