Y chromosome: Quick facts

9/10/03. By Giles Newton

The 'maleness' chromosome.

The chromosome

  • The Y chromosome is male specific, passing from father to son.
  • The chromosome sequence of 23 million base pairs of DNA was published in May 2003.
  • Approximately 1 in 1000 men carry two Y chromosomes (47, XYY). Most fertile XYY men eliminate one Y chromosome in their germline. Those that do retain all three chromosomes in their germline tend not to produce viable sperm.

The genes

  • The Y chromosome has only 78 protein-coding genes, encoding a mere 27 distinct proteins.
  • The SRY (sex-determining region Y) gene triggers development of the testes and, via hormones, 'maleness'.
  • SRY may have evolved from a gene found on the X chromosome, Sox3.
  • Loss or inactivation of the SRY gene can lead to XY females. If SRY transfers to the X chromosome, XX males can result.
  • Sex reversal can also commonly result from mutations on other chromosomes carrying genes in the sex-determining pathway downstream of SRY.
  • Some Y genes have close relatives on the X and play roles in both sexes; many have male-specific roles in sperm formation.
  • Several Y genes are found in multiple copies. There are as many as 40 copies of the TSPY gene, for example.
  • The presence of hairy ears has often been described as the only Y-specific trait. However, it is still not clear if it is due to a gene on the Y chromosome.

Further reading

Skaletsky H, et al. The male-specific region of the human Y chromosome is a mosaic of discrete sequence classes. Nature 2003 423, 825–837A. Abstract

Share |
Wellcome Trust, Gibbs Building, 215 Euston Road, London NW1 2BE, UK T:+44 (0)20 7611 8888