Study of gay brothers supports claims that male homosexuality may be genetic

Male figure created by some human chromosome. Digital illustration.ILLINOIS, United States, Thursday November 20, 2014 – A new study of nearly 800 gay brothers has reawakened the argument over the existence of a “gay gene” and bolstered evidence that genes play a role in the likelihood of men being homosexual.

While some scientists believe that several genes may affect sexual orientation, those participating in the most recent study said their results lend weight to previous evidence implicating genes on the X chromosome.

Chromosome X is one of two human sex chromosomes and is present in both men and women. The other is chromosome Y, which is present only in men.

The researchers also found evidence of influence from a gene or genes on a different chromosome, but the study did not identify which of hundreds of genes located in either place might be involved.

According to Dr Alan Sanders, lead author of the National Institutes of Health-funded study, 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.

Dr Sanders is a behavioural geneticist at North Shore University Health System Research Institute in Evanston, Illinois.

In the study, which was published Monday by the journal Psychological Medicine, the researchers said they found potential links to male homosexuality in a portion of chromosome X and on chromosome 8, based on an analysis of genetic material in blood or saliva samples from participants.

The scientists also noted that animal research suggested that a gene that may contribute to some sexual behaviour is located in one region of chromosome X – one of the same regions cited in the new study.

Dr Chad Zawitz, a Chicago physician who participated in the study, called the research “a giant step forward” toward answering scientific questions about homosexuality and helping reduce the stigma gays often face.

Being gay “is sort of like having certain eye colour or skin colour — it’s just who you are,” Zawitz said.

“Most heterosexuals I know didn’t choose to be heterosexual. It’s puzzling to me why people don’t understand.”

Experts not involved in the study were less enthusiastic and more sceptical.

Dr Robert Green, a medical geneticist at Harvard Medical School, called the new study “intriguing but not in any way conclusive.”

Neil Risch, a genetics expert at the University of California, San Francisco, went further, saying the data was statistically too weak to demonstrate any genetic link. Risch was involved in a smaller study that found no link between male homosexuality and chromosome X.

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