"Male sexual orientation influenced by genes, study shows"
A study of gay men in the US has found fresh evidence that male sexual orientation is influenced by genes. Scientists tested the DNA of 400 gay men and found that genes on at least two chromosomes affected whether a man was gay or straight
A region of the X chromosome called Xq28 had some impact on men's sexual behaviour – though scientists have no idea which of the many genes in the region are involved, nor how many lie elsewhere in the genome.
In follow-up work, he found that 33 out of 40 gay brothers inherited similar genetic markers on the Xq28 region of the X chromosome, suggesting key genes resided there.
Researchers have speculated in the past that genes linked to homosexuality in men may have survived evolution because they happened to make women who carried them more fertile. This may be the case for genes in the Xq28 region, as the X chromosome is passed down to men exclusively from their mothers.
The gene or genes in the Xq28 region that influence sexual orientation have a limited and variable impact. Not all of the gay men in Bailey's study inherited the same Xq28 region. The genes were neither sufficient, nor necessary, to make any of the men gay.
http://www.theguardian.com/science/2014/feb/14/genes-influence-male-sexual-orientation-studyWhile genes do contribute to sexual orientation, other multiple factors play a greater role, perhaps including the levels of hormones a baby is exposed to in the womb. "Sexual orientation has nothing to do with choice," said Bailey. "We found evidence for two sets [of genes] that affect whether a man is gay or straight. But it is not completely determinative; there are certainly other environmental factors involved."
"When people say there's a gay gene, it's an oversimplification," Sanders said. "There's more than one gene, and genetics is not the whole story.