sex-determination system XY sex-determination system https://en.wikipedia.org/wiki/XY_sex-determination_system https://www.wikidata.org/wiki/Q1604486 The sex-determination system found in humans, most other mammals, some insects (Drosophila), some snakes, and some plants (Ginkgo). In this system, the sex of an individual is determined by a pair of sex chromosomes. Females typically have two of the same kind of sex chromosome (XX), and are called the homogametic sex. Males typically have two different kinds of sex chromosomes (XY), and are called the heterogametic sex.