Question

During cleavage, what is true about embryo?

• A. Nucleocytoplasmic ratio remains unchanged
• B. Size does not increase
• C. There is less consumption of oxygen
• D. The division is like meiosis

Answer 1

Answer: (B)

Size does not increase

Shortly after fertilization, the zygote undergoes cleavage, a series of rapid mitotic divisions with no period of growth during each cell cycle. For this reason, although the cell number increases, the embryo does not increase in size. The zygote initially divides to form a 2-celled embryo. Then each of these cells undergoes mitosis and divides, bringing the number of cells to 4. Repeated divisions increase the number of cells, called as blastomeres, that make up the embryo. At about the 32-cell stage the embryo is a solid ball of blastomeres called as morula. Eventually, anywhere from 64 to several hundred blastomeres form the blastula, which is usually a hollow ball with a fluid-filled cavity, the blastocoel.

Thus, the correct option is (B).