These different cytoplasmic environments result in the expression of different genes in different cells. Inherited traits then emerge, in an orderly fashion, in space and time by mechanisms controlling gene expression. Embryonic development involves cell division, differentiation, and morphogenesis. Cell division results in an increase in the number of cells. All the cells result from mitotic divisions beginning with the zygote.
Differentiation is the development of specialized cells that are organized into tissues and organs.
This differentiation is controlled by the cell's expression of different genes brought on by its contact with the environment. Morphogenesis includes the physical processes that give shape to the animal's body and organs. Fertilization forms the diploid zygote and triggers the onset of embryonic development. When the head of the sperm contacts the egg the enzymes are released from a vesicle via exocytosis. This allows the arcosomal process to elongate and penetrate the the jell coat of the egg.