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A 1993 study proposed a genetic factor in gay male orientation could be found on the X chromosome, which males inherit from their mothers. That study, led by geneticist Dean Hamer at the National Institute, seemed consistent with other research.
The researchers, led by clinical neurologists George Rice and George Ebers at the University of Western Ontario, focused on just one part of the male chromosome, identified by a genetic signpost known as Xq28.
They chose that region of the genome because “the most compelling” scientific evidence so far had traced male sexual orientation to the Xq28 position, researchers said. “We were tasting a very specific hypothesis” said study coauthor Neil Risch at Stanford University.
Researchers began by placing ads in two Canadian news magazines seeking families with at least two gay brothers. They eventually found 48 families willing to provide blood samples for genetic analysis, including 46 with two gay brothers in each and two families with three gay brothers each.
The families with three gay brothers were each counted as having three gay sibling pairs, producing a total of 52 pairs of DNA samples. A gay interviewer affirmed the sexual orientation of the study subjects by questioning them at the time blood samples were drawn.
The scientisits then conducted a detailed molecular analysis, hunting for common gene forms near Xq28 that might have a significant bearing on sexual orientation. In the end, no such sequences were found.
Michael Bailey, associate professor of psychology at Northwestern University, who found strong evidence of genetic links to homosexuality in a 1991 study of identical twins, called the new study “certainly relevant, but not decisive.”
Levay, now an independent author in Los Angeles of book including “Queer Science,” said he remains convinced by other strands of evidence that genetics have a bearing on homosexuality.
“What this study throws into question is whether that includes this particular gene on the X chromosome,” he said. “Beyond that, it’s an open question.”
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