Class 12 NEET Biology Human Reproduction Questions Part 1

(a) : Cleavage is a series of cell divisions by which a single fertilized egg cell is trans formed into a multicellular body, the blastula. Characteristically no growth occurs during cleavage, the shape of the embryo is unchanged except for the formation of central cavity (the blastocoel), and the ratio of nuclear material (DNA) to cytoplasm increases. The mode of cleavage is determined by the amount of yolk and its distribution. On this basis cleavage may be holoblastic and meroblastic.