An ovum (also called the egg) is a female reproductive cell or gamete. The egg contains the parents' genetic contribution; each child normally receives one-half of her/his genes from the mother and one-half from the father. The mother's contribution is packaged within the egg, which is present in the ovary until discharged in the middle of the menstrual cycle. The egg is then fertilized by the sperm, which carries the other half of the child's genes. This union of the sperm and ovum is referred to as a fertilized ovum (or zygote) for the first two weeks. After that it is know as an embryo.