No ‘gay gene’ can predict sexual orientation, study says

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All else being equal, the larger a study, the more confident we can be in the results.

Ganna and a world staff of scientists examined knowledge from greater than 470,000 individuals in the United States and the UK to see whether or not sure genetic markers of their DNA had been linked to their sexual conduct.

To obtain such a large sample, we used data that had been collected as part of much broader projects.

Researchers conducted analyses of data for 477,522 participants in surveys from the United Kingdom and USA, and then performed comparison testing among some 15,142 people in the U.S. and Sweden. Using a genome-wide association study (GWAS), the team analyzed people's self-reported sexual history and - for those who had previously had sex with a person of the same sex, gender, or orientation - compared it against millions of genetic markers across entire genomes to determine which of the four DNA bases (A, C, G, and T) were present at common locations. And the authors found that there was little overlap between the genetic influences behind whether someone had ever engaged in same-sex behaviour and the degree to which they had same-sex partners (i.e, having sex mostly or exclusively with the same sex).

The results also call into question the Kinsey Scale, a long-utilized rating scale of sexual attraction developed in part by sex researcher Alfred Kinsey, Ganna said. "Instead, the predisposition to same-sex sexual behavior appeared influenced by a complex mix of genetic and environmental influences".

Individually, each of these genes has only a very small effect, but their combined effect is substantial.

Then, by looking at the sexual behavior and relatedness of individuals, they estimated that about a third of the variation in same-sex behavior is explained by genetics.

Some of the genes that we could be sure about gave us clues about the biological underpinnings of sexual preference. Five of the genetic markers were "significantly" associated with same-sex behaviour, the researchers said, but even these are far from being predictive of a person's sexual preferences.

They note that some among these variants are linked to the biological pathways for sex hormones and olfaction, providing clues into mechanisms influencing same-sex behavior. They said the findings highlight the complexity of human traits such as sexuality.

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"The genetics suggest that it is an oversimplification to assume that the more someone is attracted to the same sex, the less they are attracted to the opposite sex", the authors wrote.

Second, we established that, on the genetic level, there is no single continuum from gay to straight.

The five specific genes related to same-sex desire cropped up in odd places, the researchers noted.

While we've known from previous twin and family studies that our sexual preferences are influenced by our genes, it's been hard for scientists to pinpoint whether any specific genetic markers could play a role.

Scientific findings are often complex, and it is easy for them to be misrepresented in the media.

"We showed that the genes that distinguish people who'd never had a same-sex partner from those who had are not the same as those that distinguish people with lower versus higher proportions of same-sex partners", Dr Zietsch said. Both of these interpretations are wrong.

For example, one was located in a stretch of DNA that contains several genes related to the sense of smell, Ganna said. There may be some proof of a correlation between left-handedness and same-sex attraction, and left-handedness has each genetic and environmental influences.

To answer further questions the public might have about the study, we created a website with answers to frequently asked questions, and an explanatory video. Earlier research, the researchers stated, weren't massive sufficient to disclose the delicate results of particular person genes.

Brendan Zietsch is ARC Future Fellow at The University of Queensland.

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