(Agencies)
Updated: 2007-10-16 09:40

However, he added, "If we confirm that sexual orientation is an immutable characteristic, we are much more likely to get the courts to rule against discrimination."

There is less research on lesbians, Sanders said, although some studies suggest that male and female sexual orientation may have different genetic influences.

His new research is an attempt to duplicate and expand on a study published in 1993 involving 40 pairs of gay brothers. That hotly debated study, wrongly touted as locating "the gay gene," found that gay brothers shared genetic markers in a region on the X chromosome, which men inherit from their mothers.

That implies that any genes influencing sexual orientation lie somewhere in that region.

Previous attempts to duplicate those results failed. But Sanders said that with so many participants, his study has a better chance of finding the same markers and perhaps others on different chromosomes.

If these markers appear in gay brothers but not their straight brothers or parents, that would suggest a link to sexual orientation. The study is designed to find genetic markers, not to explain any genetic role in behavior.

And Sanders said even if he finds no evidence, that won't mean genetics play no role; it may simply mean that individual genes have a smaller effect.

Skeptics include Stanton Jones, a psychology professor and provost at Wheaton College in Wheaton, Ill. An evangelical Christian, Jones last month announced results of a study he co-authored that says it's possible for gays to "convert" — changing their sexual orientation without harm.

Jones said his results suggest biology plays only a minor role in sexual orientation, and that researchers seeking genetic clues generally have a pro-gay agenda that will produce biased results.

Sanders disputed that criticism.

"We do not have a predetermined point we are trying to prove," he said. "We are trying to pry some of nature's secrets loose with respect to a fundamental human trait."

Jones acknowledged that he's not a neutral observer. His study involved 98 gays "seeking help" from Exodus International, a Christian group that believes homosexuals can become straight through prayer and counseling. Exodus International funded Jones' study.

The group's president, Alan Chambers, said he is a former homosexual who went straight and believes homosexuality is morally wrong.

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