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

Primary producers - biotic components , Primary producers - Biotic Componen...

Primary producers - Biotic Components The major primary producers of aquatic ecosystems (freshwater and marine) are various species of algae. In terrestrial ecosystems the ma

Explain procedure for gram staining of bacterial cultures, Explain Procedur...

Explain Procedure for Gram Staining of Bacterial Cultures? Now carry out the exercise following the steps enumerated herewith. 1. Prepare bacterial smear on a clean, non-gre

Biosphere, The biosphere is composed of all living organism. This sphere in...

The biosphere is composed of all living organism. This sphere includes all the microorganism, plants and animals of earth. In fact biosphere involves interaction of living beings w

Nervous system - spinal nerves, SPINAL NERVES 31 Pairs. Mixed type. ...

SPINAL NERVES 31 Pairs. Mixed type. Total weight 150 gms. At the base of origin of spinal nerves gland of swammardon or calcarious ganglion is present. Composed of m

Can enhancers work in trans, Can enhancers work in trans? That is, can an e...

Can enhancers work in trans? That is, can an enhancer on one piece of DNA activate a promoter on another piece of DNA. Propose an experiment to test this. Be sure to discuss any ap

List the four phases of meiosis i, List the four phases of meiosis I, and b...

List the four phases of meiosis I, and briefly explain what occurs during each phase Prophase I: DNA coils into chromosomes, the nucleolus and nuclear envelope disappear, the m

Which are the eukaryotic, Which of the following are eukaryotic? Bacteria p...

Which of the following are eukaryotic? Bacteria protists fungi animals' archaea plants and animals only all of the choices are eukaryotic.

What dna and rna are polymers composed are called, DNA and RNA are polymers...

DNA and RNA are polymers composed of repeated units called?

Middle lamella, MIDDLE LAMELLA It is thin, amorphous, intercellular ...

MIDDLE LAMELLA It is thin, amorphous, intercellular matrix between 2 adjacent plant cell. The cells of plant tissue generally cemented together by an intercellular matrix

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