XY sex-determination system

The XY sex-determination system is a well-known sex-determination system. It is found in human beings and other mammals. In the XY sex-determination system, females have two of the same kind of sex chromosome (XX), while males have two distinct sex chromosomes (XY). Some species (including humans) have a gene SRY on the Y chromosome that determines maleness; others (such as the fruit fly) use the presence of two X chromosomes to determine femaleness.

SRY is not the only male-determining gene in mammals, or even the most common: most non-primate mammals use a different Y-chromosome gene, UBE1, for this purpose. Also, two species of "mole voles", Ellobius tancrei and E. lutescens, have lost the Y chromosome entirely. In one species, both sexes have unpaired X chromosomes; in the other, both females and males have XX.

The XY sex determination system was first described independently by Dr. Nettie Stevens and Edmund Beecher Wilson in 1905.

See also

• chromosome, for information on abnormalities of the XY sex-determination system
• intersexual for information on variations in human sexual forms
• sexual differentiation, (human)
• testis-determining factor
• Barr body
• Y-chromosomal Adam

External links

• Sex Determination and Differentiation
• SRY: Sex determination from the National Center for Biotechnology Information