Abstract
The sex-determining region of the human Y chromosome contains a gene, ZFY , that encodes a zinc-finger protein. ZFY may prove to be the testis-determining factor. There is a closely related gene, ZFX , on the human X chromosome. In most species of placental mammals, we detect two ZFY -related loci: one on the Y chromosome and one on the X chromosome. However, there are four ZFY -homologous loci in mouse: Zfy-1 and Zfy-2 map to the sex-determining region of the mouse Y chromosome, Zfx is on the mouse X chromosome, and a fourth locus is autosomal.