Gershon, MD, professor of psychiatry and human genetics at the University of Chicago, says the study represents an important step forward in understanding how genes affect human sexual orientation. New Targets for Gay Gene ResearchĮlliot S.
If the findings hold up, then Mustanski says they could start to look for the individual genes within these regions linked to sexual orientation. Researchers say the next step is to verify these results in a different group of men to see if the same genetic regions are associated with sexual orientation. Using a similar approach, researchers were able to locate a few potential genetic neighborhoods that likely contribute to male sexual orientation. Rather than guessing that doctors live in a particular type of house and going to only the houses that meet that criteria, researchers in this scenario would knock on every door to ask the residents if a doctor lives on their street. Mustanski compares the study's approach to a search for doctors in a town of 40,000 people, a number that roughly corresponds to the number of human genes. The regions on chromosome 10 were only associated with male sexual orientation if they were inherited from the mother. The regions on chromosome 7 and 8 were associated with male sexual orientation regardless of whether the man got them from his mother or father. This is slightly more than the 50% expected by chance alone. These common genetic patterns were shared by 60% of the gay men in the study.
The genetic scans showed a clustering of the same genetic pattern among the gay men on three chromosomes - chromosomes 7, 8, and 10. In the study, researchers analyzed the genetic makeup of 456 men from 146 families with two or more gay brothers. The rest is thought to be due to environment and possibly other biologic but nongenetic causes. Previous studies in male twins have suggested that between 40%-60% of the variability in sexual orientation is due to genes. "It's going to be a combination of various genes acting together as well as possibly interacting with environmental influences." "Since sexual orientation is such a complex trait, we're never going to find any one gene that determines whether someone is gay or not," says Mustanski. Its goal was not to replicate those findings but to search for new genetic markers associated with male sexual orientation. Hamer is also senior author of the current study, which appears in the March issue of Human Genetics.īut researchers say this study takes a different approach. Other researchers are attempting to replicate and verify Hamer's findings. Since then, questions arose regarding the validity of those results. That study linked DNA markers on the X chromosome to male sexual orientation. Gay Gene DebateĪ heated debate over the existence of a "gay gene" emerged from a 1993 report published in the journal Science by then-NIH researcher Dean Hamer, PhD.
The findings show that identical stretches of DNA on three chromosomes were shared by about 60% of gay brothers in the study compared to the about 50% normally expected by chance. But this study examined genetic information on all chromosomes, including genes from the father. Genes on this chromosome are only passed to a son from his mother. Those previous studies looked only at the genes located on the X chromosome. "It builds on previous studies that have consistently found evidence of genetic influence on sexual orientation, but our study is the first to look at exactly where those genes are located," says researcher Brian Mustanski, PhD, a psychologist at the University of Illinois at Chicago. The results suggest that several genetic regions may influence homosexuality. Researchers say it's the first time the entire human genetic makeup has been scanned in search of possible genetic determinants of male sexual orientation. 28, 2005 - The genes a man gets from his mother and father may play an important role in determining whether he is gay or not, according to a new study likely to reignite the "gay gene" debate.