A team of scientists led by Dean Hamer, an American Aids researcher, caused a furore in 1993 when it reported the results of a study purporting to find a genetic trait linked to homosexuality.
Dr Hamer, a scientist at the US National Cancer Institute in Washington, studied the family histories of gay men and used blood tests to find evidence of a gene inherited from mothers which he said could predispose males to homosexuality.
Dr Hamer, who is homosexual, said at the time: "Our research implies that being gay or straight relies to some extent on a genetic predisposition. We can only speculate on what the gene does. Once we have the gene, we'll be able to understand it."
However, several years of research aimed at isolating the gene proved fruitless. Now, a second team of scientists has cast doubt on the evidence published by Dr Hamer six years ago.
George Rice and George Ebers of the University of Western Ontario in Canada studied 148 families with two gay sons, 34 families with three gay sons and two families with four.
Dr Hamer investigated the family history of a smaller sample of 76 gay men and 40 pairs of gay brothers.
Dr Rice's group used sophisticated genetic tests to analyse the same region of the X chromosome - which men inherit only from their mothers - where Dr Hamer claimed to have found a genetic "marker" for homosexuality.
The Canadian group reports in the journal Science that it failed to find a link between this marker and homosexuality, which should have emerged because their study was bigger than Dr Hamer's.
"It is unclear why our results are so discrepant from Hamer's original study. Because our study was larger than that of Hamer, we certainly had adequate power to detect a genetic effect as large as was reported in that study," the Canadian scientists report.
"None the less, our data do not support the presence of a gene of large effect influencing sexual orientation."
The scientists said that they do not dismiss the possibility of another gay gene being present and recommended that studies should continue to try to find it.
The gay gene received a mixed reaction when it was announced. In the US, gay groups said that it showed homosexuality was a normal, biological condition, but gay groups in Britain expressed concern that it might be used by some people to abort foetuses found to be carrying the gene.Reuse content