Then, the fertilized egg, or zygote, undergoes to form a massive ball of identical cells. finally, the cells become specialized in structure and function through the process of

Cell division, cell differentiation

Explanation:

Cell division is the phenomena in which a parent cell divides into two or more cells. Cellular differentiation is the phenomena in which a cell changes form from one cell type to another. In general, the cell changes to a more specialized type to perform a particular function in the body.  

After the fertilization of the egg with that of the sperm the diploid cell called as zygote is formed the zygote undergoes repeated number of cell division until a considerable mass of cell develops. The cells in the mas gets specialized by the process of differentiation so as perform different functions in the embryo or developing fetus.

the denominator has a very specific role.