¹ Source: wiktionary.com
Medical Definition of Sex chromosomes
1. The homologous chromosomes that are dissimilar in the heterogametic sex. There are the x chromosome, the y chromosome, and the w, z chromosomes (in animals in which the female is the heterogametic sex (the silkworm moth bombyx mori, for example). In such cases the w chromosome is the female-determining and the male is zz. (12 Dec 1998)