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

Structure of the cilia and flagella, Normal 0 false false f...

Normal 0 false false false EN-IN X-NONE X-NONE MicrosoftInternetExplorer4

Define briefly about the manganese toxicity, Define Briefly about the Manga...

Define Briefly about the Manganese Toxicity? Manganese is considered least toxic of the trace minerals through oral intake. However, some people may be at a risk to develop tox

Epidermis, EPIDERMIS - Ectodermal in origin. Outer part of skin. Mad...

EPIDERMIS - Ectodermal in origin. Outer part of skin. Made up of stratified epithelium. Branches of sensory nerves present. More branches on lips, tips of fingers. B

How do taenias obtain food and make gas exchange, How do taenias obtain foo...

How do taenias obtain food and make gas exchange? Tapeworms have hooks and sucking structures on their heads (scolex) that fixate the parasite in the gut wall; these structures

What are neurodegenerative diseases, What are neurodegenerative diseases an...

What are neurodegenerative diseases and how might they be treated? Neurodegenerative diseases that include Alzheimer's, Parkinson's, Huntington's, and amyotrophic lateral scler

Which mechanism is significant in death of erythrocytes, Of the following, ...

Of the following, which mechanisms are significant in the death of erythrocytes (pron: eh-rith-reh-sites) in human blood? Is it a) Phagocytosis (pron: fag-eh-seh-toe-sis) b)

Plant classfication, why obelia is considered to be of special interest in ...

why obelia is considered to be of special interest in zoology as an animal showing an intermediate grade of organisation

Dna replication in bacteria, The DNA replication is a biological procedure ...

The DNA replication is a biological procedure which happens in all living organisms and copies their DNA; it is the basis for biological inheritance. The process will starts when o

Importance of the brain evolved from fishes to reptiles, How has the import...

How has the importance of the brain evolved from fishes to reptiles? From the least to the most difficult brain structure, it is evident that the brain, from fishes to beings o

Homeostais, what is homeostasis and how does it happen

what is homeostasis and how does it happen

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