Page "XY sex-determination system" Paragraph 1

The XY sex-determination system is the sex-determination system found in humans, most other mammals, some insects ( Drosophila ) and some plants ( Ginkgo ).

In this system, females have two of the same kind of sex chromosome ( XX ), and are called the homogametic sex.

Males have two distinct sex chromosomes ( XY ), and are called the heterogametic sex.

However, an opposite scheme is found in birds.