Question

Beginning of embryonic development in the egg is indicated by

• A. Cleavage
• B. Differentiation
• C. Polarity
• D. Organogenesis

Answer 1

The correct option is A Cleavage

Despite its simple appearance, the zygote is totipotent, that is, it gives rise to all the cell types of the new individual. Because the ovum is very large compared with the sperm, the bulk of the zygote cytoplasm and organelles comes from the ovum. However, the sperm and ovum usually contribute equal numbers of chromosomes.

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.