What is cleavage ? Write down its characteristics.

Explanation

Cleavage. It is rapid mitotic division of zygote to form multicellular hollow, spherical embryonic stage called as blastula.
Characteristics of cleavage.
1 It is rapid mitotic division of zygote to form multicellular structure blastula. 2. The resultant cells are called as blastomeres. 3. The blastomeres become smaller and smaller during cleavage as there is no growth during division so it is also known as fractionating division. 4. The nuclear cytoplasmic ratio goes on increasing as the cleavage progresses, because of DNA replication but no cytoplasmic synthesis. 5. Daughter cells are genetically similar to the parent cell. 6. Earlier divisions are synchronous, but later on it is lost. 7. `O_2` consumption is rapid during cleavage. 8. Mitotic divisions continue until the average cell size characteristics of an organism is achieved. 9. Number of division depend on the volume of egg and the typical somatic cells. 10. The speed and pattern of cleavage depends on cytoplasmic yolk content (deutoplasm) rather than nucleus. The yolk material tends to suppess the cleavage.