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For men, new research suggests that clues to sexual orientation may lie not just in the genes, but in the spaces between the DNA, where molecular marks instruct genes when to turn on and off and how strongly to express themselves.
At the 2015 meeting of the American Society of Human Genetics, UCLA molecular biologist Tuck C. Ngun reported that in studying the genetic material of 47 pairs of identical male twins, he has identified “epigenetic marks” in nine areas of the human genome that are strongly linked to male homosexuality.
In individuals, said Ngun, the presence of these distinct molecular marks can predict homosexuality with an accuracy of close to 70 percent.
Experts said the results — as yet unpublished in a peer-reviewed journal — offer preliminary new evidence that a man’s genetic inheritance is only one influence on his sexual orientation. Through the epigenome, the results suggest, some facet of life experience likely also primes a man for same-sex attraction.
Geneticists suggest that together, the human genome and its epigenome reflect the interaction of nature and nurture — both our fixed inheritance and our bodies’ flexible responses to the world — in making us who we are.
Ngun’s study of twins doesn’t reveal how or when a male takes on the epigenomic marks that distinguish him as homosexual. Many researchers believe that a person’s eventual sexual preferences are shaped in the uterus, by hormonal shifts during key stages of fetal brain development.
Read full, original post: Scientists find DNA differences between gay men and their straight twin brothers