Sex Chromosome

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. (From King & Stansfield, A Dictionary of Genetics, 4th ed)