A change in temperature is all it takes for genetically-engineered male flies to switch from being heterosexual to homosexual. The change occurs within minutes and is reversible. This discovery will help scientists figure out how the brain may be involved in determining sexual orientation.
Some of the neurons affected are involved in sensing pheromones, which play an important role in fly courtship behavior, but their influence in human sexual behavior is still unknown. Dean Hamer of the NIH says scientists should now try to find the genes that determine sexuality in mammals, since homosexual behavior is widespread among animals, suggesting a strong genetic influence. Hamer's team has published two highly controversial studies suggesting there?s a "gay gene" on human chromosome X, although a different group failed to reproduce their results.
It has been previously suggested that some regions of the nervous system are connected to sexual orientation. Researcher Toshihiro Kitamoto genetically engineered flies especially to test the genetic theory of homosexuality. The mutation is temperature sensitive, meaning neurons carrying the mutation suddenly become inactive above 30
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