The amount of yolk and its distribution are changed in the egg. This is affected

The correct answer is cleavage pattern.

Cleavage is the series of rapid mitotic cell divisions that a zygote undergoes after fertilization to become a multicellular embryo. The pattern and rate of cleavage are strongly influenced by the amount of yolk (lecithality) and its spatial distribution within the egg cytoplasm.

Yolk is a dense, inert material that provides nourishment to the developing embryo. Because it is viscous and metabolically inactive, yolk acts as a mechanical barrier to the mitotic spindle and the cleavage furrow. As a result, regions of the egg rich in yolk divide more slowly or do not divide completely, whereas regions with less yolk divide more rapidly.

Depending on the yolk distribution, two primary types of cleavage patterns are observed:
1. Holoblastic Cleavage (Complete Cleavage): Occurs in eggs with little to no yolk (isolecithal) or a moderate amount of yolk (mesolecithal). Here, the cleavage furrows pass completely through the egg, dividing it entirely into blastomeres.
2. Meroblastic Cleavage (Incomplete Cleavage): Occurs in eggs with a large amount of yolk (telolecithal or centrolecithal). The cleavage furrow cannot penetrate the dense yolk mass, restricting cell division to a small active region of cytoplasm (such as the blastodisc in bird eggs).

Therefore, the amount and distribution of yolk directly determine the specific cleavage pattern of the developing egg.