When a sperm and egg combine, it is called

fertilization.

When a sperm and egg combine, the process is called fertilization. This occurs in the fallopian tube during sexual reproduction. The sperm, which carries the father's genetic material, penetrates the egg, which carries the mother's genetic material. This fusion of the sperm and egg forms a single cell called a zygote, which contains the complete set of chromosomes required to develop into a human being.