Washington: In significant discovery, researchers in the US have found fresh evidence that the male sexual orientation is influenced by genes.
The genes on at least two chromosomes affected whether a man was gay or straight, they claimed.
Scientists tested the DNA of 400 gay men.
They found that a region of the X chromosome called 'Xq28' had some impact on men's sexual behaviour.
Another stretch of DNA on chromosome 8 also played a role in male sexual orientation.
"Sexual orientation has nothing to do with choice. We found evidence for two sets of genes that affect whether a man is gay or straight,” said Michael Bailey, a psychologist at Northwestern University in Illinois.
But it is not completely determinative as there are certainly other environmental factors involved, the study added.
While 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.
When people say there's a gay gene, it's an oversimplification. There's more than one gene, and genetics is not the whole story.
“Whatever gene contributes to sexual orientation, you can think of it as much as contributing to heterosexuality as much as you can think of it contributing to homosexuality. It contributes to a variation in the trait,” explained Bailey.