What is effect of yolk on cleavage?

Yolk affects cleavage by influencing the type and pattern of cell division during early embryonic development. In species with a high yolk content, such as birds and reptiles, cleavage is often discoidal and meroblastic, meaning that only a portion of the zygote undergoes division due to the large yolk mass. In contrast, organisms with little to no yolk, like many mammals, exhibit holoblastic cleavage, where the entire zygote divides uniformly. The presence and distribution of yolk ultimately determine the cleavage pattern and subsequent developmental processes.