Question

Cleavage is

• A. meiosis of zygote into blastomeres
• B. mitosis of the zygote into blastomere
• C. reductional division of zygote
• D. reductional division of the embryo

Answer 1

The correct option is B mitosis of the zygote into blastomere

Mitosis is a cellular process of duplication or replication, in which a mother cell is divided into two identical daughter cells. The cleavage starts soon after the fertilization and ends shortly after the stage (blastula) when the embryo achieves a new balance between nucleus and cytoplasm. Cleavage is a special type of mitosis (equational division) where the size of the cell decreases and the number of cells increases. These rapid mitotic divisions convert the single-celled zygote into a multicellular structure called a blastula. Cells of the cleavage stage are called blastomeres. Cleavage in a fertilized egg of a human starts in the fallopian tube forming 2, 4, 8, 16 daughter blastomeres. Embryo with 8-16 blastomeres is known as morula. The embryo keeps on multiplying by mitotic division and forms a cavity within the cell mass. The cavity is called blastocoel and the embryo is termed the blastocyst in this stage. The transition from fertilization to cleavage is caused by the activation of the mitosis promoting factor (MPF).

Meiosis is a form of cell division, which occurs in germ cells. It’s a type of reductional division where the number of chromosomes is reduced to half in a germ cell before sexual reproduction.
Figure: Development of the embryo