In a large study of more than 490,000 men and women in the United States, United Kingdom and Sweden, researchers discovered four genetic variants that occur more often in people who indicated on questionnaires that they had had same-sex sexual partners. Andrea Ganna, a geneticist at the Broad Institute of MIT and Harvard reported the results October 19 at the annual meeting of the American Society of Human Genetics. Two of the variants were specific to men’s sexual partner choice. The other two influence sex partner choice for both men and women.
Collectively, the DNA differences explained only 8 to 12 percent of the heritability of having same-sex partners. “There is no gay gene,” Ganna said, “but rather non-heterosexuality is influenced by many tiny-effect genetic factors.”
But that doesn’t mean that genes control sexual behavior or orientation. “Same-sex sexuality appears to be genetically influenced, but not genetically determined,” [psychologist Lisa] Diamond says.
[A] variant on chromosome 15 linked to men having sex with men is also associated with male pattern baldness. Another variant in the study is near the ORA51A gene on chromosome 11, which is involved in the ability to smell certain chemicals. That’s interesting because smell has been linked to attraction before, Ganna said. The researchers don’t yet know exactly which genes are involved in mate choice or exactly how they influence behavior.
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