28 January 2005
Male Sexual Orientation Genes Identified
by Kate Melville 
A study appearing in the journal Human Genetics has identified several areas of DNA that appear to influence whether a man is heterosexual or gay. University of Illinois at Chicago researcher Brian Mustanski found stretches of DNA that appeared to be linked to sexual orientation on three different chromosomes in the nucleus of cells of the human male. "There is no one 'gay' gene," said Mustanski. "Sexual orientation is a complex trait, so it's not surprising that we found several DNA regions involved in its expression. Our best guess is that multiple genes, potentially interacting with environmental influences, explain differences in sexual orientation."
The genomes of 456 men from 146 families with two or more gay brothers were analyzed. While earlier studies had focused solely on the X chromosome, one of the two sex chromosomes, the present study examined all 22 pairs of non-sex chromosomes in addition to the X chromosome. The other sex chromosome, called Y, was not explored. Identical stretches of DNA on three chromosomes - chromosomes 7, 8 and 10 - were found to be shared in about 60 percent of the gay brothers in the study, compared to about 50 percent expected by chance. The region on chromosome 10 correlated with sexual orientation only if it was inherited from the mother. "Our study helps to establish that genes play an important role in determining whether a man is gay or heterosexual," said Mustanski.
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