A gamete that belongs to one of two distinguishable types: A heterogamete differs in shape and size ffrom the one with which it unites in fertilization:

A heterogamete is a mature reproductive cell produced by the heterogametic sex.

A gamete may fuse with another gamete of the opposite sex, to form a zygote (fertilized gamete). The male gametes are known as sperms and the female gametes as eggs.