A

David

Darling

cleavage (embryology)

In embryology, cleavage is a progressive series of cell divisions by which a fertilized egg is transformed into the earliest embryonic stage of the blastula. The egg is divided into blastomeres (smaller cells), each containing a diploid number of chromosomes. In mammals, the second division is generally at right-angles to the first and the third at right-angles to the previous two.