"The zygote is a single cell and contains the genetic blueprint to direct the next complex steps to become the embryo and fetus," says What to Expect Medical Review Board Member Aaron K.

After a sperm fertilizes an egg, the totipotent cell divides into a zygote. As division continues, some cells divide into the growing mass, distinguishing cells that form the embryo (epiblast) from ...

The fusion of sperm and egg gametes during human fertilization establishes a diploid zygote and initiates a series of cell divisions that result in a multicellular embryo. The blastocyst stage is ...