Y-chromosome - Definition and Overview

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.

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 (http://www.biology.ucsc.edu/people/barrylab/public_html/classes/old_animal_behavior/Sex_devo.htm)
• SRY: Sex determination (http://www.ncbi.nlm.nih.gov/books/bv.fcgi?call=bv.View..ShowSection&rid=gnd.section.156) from the National Center for Biotechnology Information