What do you mean by the term Cleavage in relation to mitotic divisions ?

The term cleavage or segmentation is applied to the early repeated mitotic divisions of the fertilized egg or zygote resulting in 2, 4, 8, 16 and, pre daughter cells called blastomeres.

The daughter cells do not separate but remain attached with one another forming embryonic stages. Several cleavage patterns are recognized. According to potentiality of early blastomeres, cleavages are two types.

(a) Determinate cleavage:

Early blastomers are not equipotential and thus future of each blastomere has been determined previously. So blastomeres produce a particular part of embryo.

(b) Inderminative cleavage:

Early blastomeres have equivalent potentialities and if separated each can give rise to complete embryo.

According to cleavage furrow cleavages are:

(a) Radial: The furrows line up in successive tiers.

(b) Spiral: Furrows are right angle to each other.

According to the amount of egg and plane a mode of division cleavage may be:

(a) Holoblastic: Complete or total and equal division of zygote producing all equal sized blastomeres.

(b) Meroblastic: This cleavage is incomplete or partial restricted to the animal pole, producing a germinal disc.

(c) Superficial: Division restricted to a superficial peripheral layer around the yolk.