Question

During cleavage, nucleocytoplasmic ratio (nucleus/cytoplasm)
A)Increases
B)Decreases
C)Remains same
D)None of the above

Answer 1

Hint: Cleavage is the division of cells in an embryo. The cells derived from cleavage are called blastomere. Blastula forms after the end of cleavage. The cleavage depends on the amount of the yolk present in the egg.

Complete answer:
To solve this question, we must know about the process of cleavage.
The process of cleavage follows fertilisation which is activated by cyclin-dependent kinase complexes. There is no significant overall growth and results in the formation of a cluster of cells whose size is similar to that of a zygote.

Types of cleavage-
1.Holoblastic- It takes place when the amount of yolk is less. It results in the total or complete cleavage of the fertilised egg.
2.Meroblastic- this type of cleavage takes place when the amount of yolk in the fertilised egg is more. It is also called partial or incomplete cleavage.
In cell division the number of cells a well as the nuclear mass increases. But in cleavage the nuclear mass and the number of cells increases nut the cytoplasmic mass remains the same. The cytoplasm is half in the daughter cells after successive divisions. Thus the ratio of nucleocytoplasmic mass fairly increases.

Hence, the correct answer is option (A)

Note: The placental mammals show low rate of cell division. The divisions are asynchronous. The transcription of the zygote takes place at two, four or eight cell stages. They show rotational and holoblastic cleavage.