Define cleavage patterns

Cleavage results in a blastula, a ball of cells with a central cavity called the blastocoel. Below are two diagrams of blastulas. On the left is a sea urchin blastula, and on the right is a frog blastula.

Cleavage patterns are quite diverse, and there are about as many ways to divide up the cytoplasm of an animal egg during cleavage as there are phyla of animals.



The pattern of cleavage is influenced by the amount of yolk in the egg. In eggs with less yolk, cleavages are equal, and the resulting blastomeres are of similar size (a). If the yolk is localized, such as in frog eggs, then cleavages are unequal - the cells derived from the yolky region (the vegetal pole) are larger than those derived from the region without yolk (the animal pole) (b).