Patterns of cleavage, Biology


Patterns of cleavage depends upon amount of yolk & distribution of yolk.

These are following types -


In radial cleavage the cleavage furrow cut straight through the egg at right angle to another.]

It results blastomeres appear to be arranged radially. eg. Sponge & Coelenterata.


The cleavage furrow of first three division do not cut straight the axis of the egg.

It determine by radial symmetry in animal. eg. Ctenophora.


In this the mitotic spindle of the third cleavage in the four blatomeres are laid down obliquely and are arranged in a sort spiral.

It result four blastomeres of upper tier do not lie over the corresponding blatomeres of lower tier. eg. Annelids, moluscs, nemerteans.

Spiral cleavage is of two types -

(i) Dextral or Dextrotrophic - Blastomere rotate clockwise (i.e. right hand spiral). eg. Mollusca.

(ii) Sinistral or Levotrophic - The blastomere rotate anticlockwise (i.e. left hand coiling). eg. Flat worm, Round worm & Annelids.


In this two of the four blastomere are smaller than the other two and establish bilateral symmetry at the four cell stage. eg. Echinodermata & Chordata.

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Posted Date: 10/3/2012 8:55:53 AM | Location : United States

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