what is embryogenesis?

Embryogenesis is the process by which the embryo forms and develops. In mammals, the term refers chiefly to early stages of prenatal development, whereas the terms fetus and fetal development describe later stages.

Embryogenesis always starts with the fertilization of the ovum (or egg) by sperm. Once fertilized, the ovum is referred to as a zygote, a single cell embryo. The zygote undergoes rapid mitotic divisions with no significant growth (a process known as cleavage) and cellular differentiation, leading to development of a multicellular embryo.