In biology, cleavage refers to the division of cells in the early development of an embryo following fertilization). During cleavage, the zygote undergoes a series of mitotic divisions, dividing the large volume of egg cytoplasm into numerous smaller, nucleated cells called blastomeres. The types of cleavage are determined by the amount and distribution of yolk in the egg, and the cytoplasmic contents primarily determine the types of cleavage/14%3A_Embryonic_Development_and_its_Regulation/14.03%3A_Cleavage). There are three types of cleavage: holoblastic, meroblastic, and discoidal/14%3A_Embryonic_Development_and_its_Regulation/14.03%3A_Cleavage).

• Holoblastic Cleavage: In eggs that contain no or only moderate amounts of yolk, cytokinesis divides the cells completely. This type of cleavage is found in mammals and frogs/14%3A_Embryonic_Development_and_its_Regulation/14.03%3A_Cleavage).

• Meroblastic Cleavage: In eggs that contain a large amount of yolk, cytokinesis does not divide the egg completely. This type of cleavage is found in fish, reptiles, and some mammals/14%3A_Embryonic_Development_and_its_Regulation/14.03%3A_Cleavage).

• Discoidal Cleavage: In eggs that contain a large amount of yolk, cytokinesis occurs only in the cytoplasmic region of the egg, forming a disc of cells on top of the yolk. This type of cleavage is found in birds and reptiles/14%3A_Embryonic_Development_and_its_Regulation/14.03%3A_Cleavage).

Cleavage can also be classified based on the potency of blastomeres, which determines their developmental fate. There are two types of cleavage based on the potency of blastomeres:

• Determinate Cleavage: Also known as mosaic cleavage, this type of cleavage results in the developmental fate of the cells being set early in the embryo development. Each blastomere produced by early embryonic cleavage does not have the capacity to develop into a complete embryo. This type of cleavage is found in most protostomes).

• Indeterminate Cleavage: This type of cleavage is based on the potency of blastomeres where the blastomeres are qualitatively equal, and each can develop into an entire embryo when isolated. This type of cleavage is found in deuterostomes).

Cleavage is an essential process in the development of an organism. It provides a stockpile of cells out of which the embryo will be constructed, and it establishes a normal relationship between the nucleus and the volume of cytoplasm it regulates/14%3A_Embryonic_Development_and_its_Regulation/14.03%3A_Cleavage).