Being gay linked to genes of mothers.

BEING gay could be linked to a twist in the genetic programme mothers pass on to their sons, it has been claimed.

Normally, a random process shuts down one of the two X sex chromosomes in every woman's cells.

But scientists found that in the case of mothers of gay men, the process was not random. One X chromosome was far more likely to be shut down than the other.

Only 4% of 103 women without gay sons showed this effect, compared with 14% of those with at least one gay son, New Scientist magazine reported.

Sven Bocklandt, from the University of California at Los Angeles, who carried out the study, suspects that the deactivation of certain genes women pass on to their sons may be behind the gay link.

While women have two X chromosomes, men have a paired X and Y. The X is inherited from their mother, and the Y from their father.

Like all other chromosomes, the X and Y sex chromosomes consists of strands of DNA along which are sited genes -- regions of DNA that provide the coded instructions for making proteins.

It is possible that affected mothers may not be resetting their own ``I like males'' programme, Bocklandt believes. They might be passing on genes that help them find men sexually attractive to their sons.

Ian Craig, from the Institute of Psychiatry in London is not convinced.

``I'm not absolutely persuaded, but it's an interesting hypothesis, '' he said.