Results of a five-year study of 409 independent pairs of homosexual brothers in 384 families find that genetics play a key role in male sexual orientation. Alan Sanders, M.D., a psychiatrist who studies behavioral genetics at NorthShore University HealthSystem Research Institute, was the principal investigator of the molecular genetics study that scanned the entire human genome to search for evidence of genetic links to variation in sexual orientation in men.

“We found two strong links in chromosome 8 and chromosome Xq28, which supports that this is not a one-gene, one-trait scenario,” said Dr. Sanders. “These genetic variations contribute to the development of the important psychological trait of male sexual orientation.

The new evidence “is not proof but it’s a pretty good indication” that genes on the two chromosomes have some influence over sexual orientation.”

Participants in the study were gay men with at least one living gay brother (full brothers, half brothers or fraternal twins). They were asked to provide DNA samples through blood or saliva and to complete a questionnaire about their sexual and personal history and that of immediate family members. The study was funded by the US National Institutes of Health from the National Institute for Child Health and Human Development.

“Understanding the origins of sexual orientation enables us to learn a great deal about sexual motivation, sexual identity, gender identity and sex differences,” Dr. Sanders added.

The full paper, “Genome-wide scan demonstrates significant linkage for male sexual orientation”, which is published in Psychological Medicine can be read free of charge for a limited time here.

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