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

Explain stavudine, Explain Stavudine It can be given either in initial ...

Explain Stavudine It can be given either in initial combination therapy or after failure of regimens containing other NRTIs. Cross-resistance with zidovudine is frequent, ho

Structures shared by every chordate, Q What are the three structures shared...

Q What are the three structures shared by every chordate that characterize the group? All beings of the phylum Chordata have branchial clefts in the pharynx in some species pre

Phylum, detail study of coelenterata

detail study of coelenterata

Adrenal medulla, ADRENA L MEDULLA The adrenal medulla develops from th...

ADRENA L MEDULLA The adrenal medulla develops from the neuroectoderm of the embryo. Medulla consists of chromaffin cells or phaeochromocytes. These cells are connected wi

Transcription of eukaryotic protein coding genes, 1. The transcription and ...

1. The transcription and replication of DNA requires a multitude of protein complexes a. Describe the events that occur during the initiation of transcription of eukaryotic prot

What are instances of a carnivorous, Q What are instances of a carnivorous ...

Q What are instances of a carnivorous and an herbivorous reptile? Iguanas are herbivorous, Snakes are carnivorous. Q. Do beings of the class Reptilia perform gas exchange i

What are exocrine respective hormones and enzymes, What are the pancreatic ...

What are the pancreatic tissues involved respectively in the exocrine and endocrine secretions? What are their respective hormones and enzymes? The exocrine secretion of the pa

Is protein collagen has a high proportion of glycine, The protein collagen ...

The protein collagen has a high proportion (20% or more) of A. asparagine and glutamine B. proline and hydroxyproline C. glycine D. both A and B E. both A and C F

What are the final digestion products of protein, What are the final diges...

What are the final digestion products of (a) protein, (b) fat, (c) starch?   a) Proteins are digested to amino acids, b) fats are digested to fatty acids and glycerol,

Noise pollution, Sound is a main mean of communication and entertainment an...

Sound is a main mean of communication and entertainment and is also very effective alarm system for some animal. A loud and unwanted or unpleasant sound causes discomfort and is ca

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