Partitioning of the cytoplasm during cleavage can result in segregation of specialized cytoplasmic components that will have profound effects on development. Cleavage segregates them and localized proteins into different cells. You can imagine, then, how important the pattern of cleavage is for establishment of an orderly array of functional entities in the embryo. If it is important to the embryo, it is important for you to understand and appreciate differences in cleavage patterns among different groups of organisms. Study the cleavage patterns carefully in your text.
Fertilization is a mitogenic stimulus that triggers the zygote to re-enter the cell cycle.
The shortening of the S-phase is accomplished by the simultaneous activation of multiple units of DNA replication. Further investigation of these genes and the proteins they encode should lead to an understanding of the molecular basis for the altered cleavage cell cyle. At the end of cleavage, the somatic cell cycle is established. The important consequences of this transition during development will be discussed in detail later. They have observed thick, short bundles of radially-arranged microtubules emanating from the contractile ring.