A University of California study has taken a small step in the nature versus nurture debate, suggesting homosexuality is a result of a mother’s genes.

According to study results published in New Scientist, variations in the genetic program that fetuses inherit from parents could determine sexual preference.

Women have two X chromosomes, while men have an X and a Y chromosome. Daughters are produced when two X chromosomes are passed on, one from each parent. Sons are created when an X chromosome is passed on from the mother, and a Y chromosome is passed on from the father.

Increased chemical markers then shut down the mother’s remaining X chromosome. This process, called X-inactivation, is random and either chromosome could be inactivated.

Researchers suggest homosexuals appear to receive one of the mother’s X chromosomes more often than the other. This X chromosome could be responsible for mothers finding men attractive, giving gay men female qualities.

Scott Bocklandt of the University of California, Los Angeles, compared blood and saliva samples from 97 mothers of gay men and 103 mothers of straight men.

The results revealed that 14 percent of women with at least one gay son appeared to show the same X chromosome was far more likely to be shut down than the other.

Only 4 percent of the women with no gay sons displayed this process. The figure increased to 23 percent among mothers with two or more gay sons.

Daughters do not appear to be affected by the X-inactivation process.

It was possible affected mothers might not be resetting their own I like males program when passing on their X chromosome, Bocklandt told a meeting of the American Society of Human Genetics in Toronto last week.

I’m not absolutely persuaded, but it’s an interesting hypothesis, Ian Craig of the Institute of psychiatry in London said. Until you’ve got some molecular way to test it, it’s just a nice idea.

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