Animal Reproduction and Development
Fertilization and Early Embryonic Development
In fertilization, the sperm binds to the egg, allowing their membranes to fuse and the sperm to transfer its nucleus into the egg.
Cleavage, the Blastula Stage, and Gastrulation
A zygote undergoes rapid cell divisions (cleavage) to form a spherical ball of cells: the blastula; this will further develop into a blastocyst.