Birds show the ZZ-ZW system of sex determination. In this system, the female is heterogametic (ZW), and the male is homogametic (ZZ). During gametogenesis, half of the eggs have a Z chromosome and the other half will have a W chromosome. For males, all sperm contains a single Z chromosome. On fertilization of Z egg with Z sperm, a male with ZZ genotype is produced. When W egg fertilizes with Z sperm, a female with ZW genotype is produced. Snakes, butterflies, some amphibians, and some fishes also exhibit this type of sex determination.In humans, females have a pair of same sex chromosomes (X chromosomes) beside autosomes.Hence, females show homogametic, that is, the gametes formed by human females will be of the same type.Males are heterogametic. They have two different sex chromosomes designated as X and Y chromosomes besides the autosomes.Since the gamete produced by human males will have different sex chromosomes, so, in the case of humans, the male determines the sex of the offspring.