In addition to 22 homologous pairs of autosomes, human females have a homologous pair of X chromosomes, whereas human males have an XY chromosome pair. Until now, we have only considered inheritance patterns among non-sex chromosomes, or autosomes.

The sex chromosomes are one pair of non-homologous chromosomes. In tropical clown fish, the dominant individual in a group becomes female while the others are male. Some species, such as some snails, practice sex change adults start out male, then become female. For example, temperature-dependent sex determination is relatively common,Īnd there are many other types of environmental sex determination. However, there are other sex determination systems in nature. In humans, as well as in many other animals and some plants, the sex of the individual is determined by sex chromosomes.