SCIENTISTS in the US have discovered what they believe could be part of the genetic roots of being gay. Researchers from North-western University, in Illinois, studied the DNA of 400 pairsof identical twins and foundthat two chromosomes were in-volved whether the men were gayor not.

A region of X chromosome - inherited from the mother - called "Xq28" had an impact on sexual orientation, as did DNA from chromosome 8. The exact way in which these genes affect sexual orientation remains unclear.

Professor Michael Bailey, who led the study, said last week: "Sexual orientation has nothing to do with choice. We found evidence for two sets [of genes] that affect whether a man is gay or straight. But it is not completely determinative - there are certainly other environmental factors involved."

Professor Bailey's colleague, Dr Alan Sanders, insisted that their research could not be used to formulate a pre-natal test to identify sexual orientation.

"When people say there's a gay gene, it's an oversimplification," Dr Sanders said. "There's more than one gene, and genetics is not the whole story."