Does homosexuality affect the gene pool

Is homosexuality in the genes?

It's been 26 years since the US scientist Dean Hamer claimed to have discovered the so-called "gay gene": At that time, the geneticist had associated a specific section of the X chromosome with homosexuality and thus in science how caused some public excitement too.

So is the propensity for same-sex sexual behavior primarily innate? Or are there various environmental factors (from hormones in the womb to upbringing to chance encounters) that make people feel more attracted to their own gender and live homosexual relationships?

Since Hamer's study more than a quarter of a century ago, numerous other studies have been carried out on possible genetic factors influencing homosexuality. On the one hand, it showed that the "gay gene" could not be confirmed. On the other hand, the studies indicated that genetic factors can only explain part of sexual behavior.

The largest study by far

An international research team led by the US geneticist Andrea Ganna (Broad Institute) has carried out by far the largest genetic study on the subject in recent years. In this so-called genome-wide association study (GWAS), the genomes of around 500,000 people were scanned to see whether any connections could be found between their sexual behavior and hundreds of thousands of different DNA segments.

Most of the genetic information of the study participants came from the UK Biobank; to a lesser extent, it was volunteers who had consented to an examination of their genetic makeup as part of a research project by the US company 23andMe and who had also answered questionnaires on sexual behavior.

In total, the researchers found only five markers in the genome that could be associated with homosexual behavior. But the connections were very small, and two of the markers were only found in men: One of the gene segments contains sequences that code for olfactory receptors, another plays a role in hair loss.

Behavior not "readable"

Overall, however, the researchers come to the conclusion that sexual behavior is an extremely complex trait and that both genetic and environmental factors contribute to it. Genetic factors would explain eight to 25 percent of the variation in sexual behavior. This in turn means that one cannot read from a person's DNA whether a person shows heterosexual, homosexual or bisexual behavior.

The one in the journal Science The published study is also noteworthy for other reasons: On the one hand, the researchers consulted with representatives of the LGBT community (lesbian, gay, bisexual and transgender) prior to publication in order to prevent misinterpretations. For example, this led the study to emphasize a difference between sexual behavior and sexual identity.

On the other hand, the scientists have prepared their research results on the website geneticsexbehavior.info in an exemplary manner for the interested public. (Klaus Taschwer, August 29, 2019)

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