What do the new ‘gay genes’ tell us about sexual orientation?

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Illustration of rainbow DNA (deoxyribonucleic acid) with defocus on background

Andy Coghlan writes at New Scientist:

Two gene variants have been found to be more common in gay men, adding to mounting evidence that sexual orientation is at least partly biologically determined. How does this change what we already knew?

Didn’t we already know there were “gay genes”?
We have known for decades that sexual orientation is partly heritable in men, thanks to studies of families in which some people are straight and some people are gay. In 1993, genetic variations in a region on the X chromosome  in men were linked to whether they were heterosexual or homosexual, and in 1995, a region on chromosome 8 was identified. Both findings were confirmed in a study of gay and straight brothers in 2014. However, these studies didn’t home in on any specific genes on this chromosome.

What’s new about the latest study?
For the first time, individual genes have been identified that may influence how sexual orientation develops in boys and men, both in the womb and during life. Alan Sanders at North Shore University, Illinois, and his team pinpointed these genes by comparing DNA from 1077 gay and 1231 straight men. They scanned the men’s entire genomes, looking for single-letter differences in their DNA sequences. This enabled them to home in on two genes whose variants seem to be linked to sexual orientation.

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