Target Exam

CUET

Subject

Biology

Chapter

Human Reproduction

Question:

What is a distinctive feature of cleavage in comparison to typical mitosis?

Options:

Cleavage involves the division of egg cytoplasm into increasingly larger cells.

Cleavage has a prolonged G1 and G2 phase for cell growth.

Cleavage involves rapid mitotic division without a growth phase between divisions.

Cleavage does not involve mitosis.

Correct Answer:

Cleavage involves rapid mitotic division without a growth phase between divisions.

Explanation:

The correct answer is Option (3) –Cleavage involves rapid mitotic division without a growth phase between divisions.

After fertilization, the development of a multicellular organism proceeds by a process called cleavage, a series of mitotic divisions whereby the enormous volume of egg cytoplasm is divided into numerous smaller, nucleated cells. These cleavage-stage cells are called blastomeres. The zygotic genome, transmitted by mitosis to all the new cells, does not function in early-cleavage embryos. Few, if any, mRNAs are made until relatively late in cleavage, and the embryo can divide properly even when chemicals are used experimentally to inhibit transcription. During cleavage, however, cytoplasmic volume does not increase. Rather, the enormous volume of zygote cytoplasm is divided into increasingly smaller cells. First the egg is divided in half, then quarters, then eighths, and so forth. This division of egg cytoplasm without increasing its volume is accomplished by abolishing the growth period between cell divisions (that is, the G1 and G2 phases of the cell cycle). Meanwhile, the cleavage of nuclei occurs at a rapid rate never seen again (not even in tumor cells).