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“There will be men who have the form of gene that increases the chance of being gay, but they won’t be gay.”īecause many genes and other factors seem likely to play a role in sexual orientation, this may explain why some people are bisexual or see sexual orientation as a spectrum. “There are probably multiple genes involved, each with a fairly low effect,” he says. No, says Sanders, because many other factors play a role, including the environment. Grave’s disease is more common in gay than straight men, and some research suggests that gay men tend to be thinner – which might possibly be a result of thyroid overdrive.Īre all men who have the “gay” variants of these genes gay? For instance, TSHR function is disrupted in a genetic condition called Grave’s disease, which causes the thyroid gland to become over-active, accelerating metabolism and leading to weight-loss. The fact that TSHR seems to be involved in sexual orientation fits with evidence that thyroid function seems to be linked to sexuality. In this way, the gene plays an important role in controlling thyroid function. Called TSHR, it makes a type of receptor protein that recognises and binds to a hormone that stimulates the thyroid. This gene is found on chromosome 14 and is mainly active in the thyroid, but also the brain. “So this particular finding is a potential link between the neuroanatomy and molecular genetics of sexual orientation.
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“This is thought to be a crucial time for sexual differentiation in this part of the brain,” says LeVay. Other research has found that this gene, called SLITRK6, is active in the hypothalamus of male mice fetuses a few days before they are born. This was discovered by neuroscientist Simon LeVay, who says he is excited that the gene discovery seems to fit with what he found. Interestingly, this brain region contains the hypothalamus, which was identified in 1991 as differing in size between gay and straight men. One of the genes, which sits on chromosome 13, is active in a part of the brain called the diencephalon. What genes did they find and what do they do? This enabled them to home in on two genes whose variants seem to be linked to sexual orientation. They scanned the men’s entire genomes, looking for single-letter differences in their DNA sequences. Alan Sanders at North Shore University, Illinois, and his team pinpointed these genes by comparing DNA from 1077 gay and 1231 straight men. However, these studies didn’t home in on any specific genes on this chromosome.įor 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. Both findings were confirmed in a study of gay and straight brothers in 2014. 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. 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. Didn’t we already know there were “gay genes”?