In embryology, cleavage is the division of cells in the early embryo. The zygotes of many species undergo rapid cell cycles with no significant growth, producing a cluster of cells the same size as the original zygote. The different cells derived from cleavage are called blastomeres and form a compact mass called the morula. Cleavage ends with the formation of the blastula.
Depending mostly on the amount of yolk in the egg, the cleavage can be holoblastic (total or entire cleavage) or meroblastic (partial cleavage). The pole of the egg with the highest concentration of yolk is referred to as the vegetal pole while the opposite is referred to as the animal pole.
Cleavage differs from other forms of cell division in that it increases the number of cells without increasing the mass. This means that with each successive subdivision, the ratio of nuclear to cytoplasmic material increases.
Other articles related to "cleavage, embryo":
... There are several differences between the cleavagein placental mammals and the cleavagein other animals ... Cleavageis holoblastic and rotational ... At the eight-cell stage, the embryogoes through some changes ...
Famous quotes containing the word cleavage:
“Jesus abolished the very concept of guiltMhe denied any cleavage between God and man. He lived this unity of God and man as his glad tidings ... and not as a prerogative!”
—Friedrich Nietzsche (18441900)