A genetic analysis of gay siblings supports the idea that genes on the X chromosome contribute to male homosexuality. Dean Hamer finally feels vindicated. But several subsequent studies called his finding into question.
Now the largest independent replication effort so far, looking at pairs of gay brothers, fingers the same region on the X. But not everyone finds the results convincing.
And the kind of DNA analysis used, known as a genetic linkage study, has largely been superseded by other techniques. Due to the limitations of this approach, the new work also fails to provide what behavioral geneticists really crave: Few scientists have ventured into this line of research.
Studies comparing identical and fraternal twins suggest there is some heritable component to homosexuality, but no one believes that a single gene or
Chromosome 8 homosexuality and christianity can make a person gay.
Any genetic predispositions probably interact with environmental factors that influence development of a sexual orientation. Several genomic studies have suggested regions that might influence sexual orientation, but they have relied on small numbers of participants and have been challenged repeatedly. InHamer, then at the U.
National Institutes of Health NIH in Bethesda, Maryland, published the first of these studies, suggesting that a specific stretch of the X chromosome called Xq28 holds a gene or genes that predispose a man to being gay. The finding made some evolutionary sense.
An X-linked gene for homosexuality has long been proposed as a way to explain how the trait persists in the population even though gay men tend to have fewer offspring: Many researchers were skeptical that an analysis of only 38 pairs of gay brothers was reliable, and several other groups failed to replicate the results. The paper Chromosome 8 homosexuality and christianity ignited social debate: Some speculated that a genetic test for homosexuality would lead to more discrimination, while others attacked the premise that being gay has a biological basis.
Michael Bailey, a psychologist at Northwestern University in Evanston, Illinois, wanted to put questions about Xq28 to rest. When Bailey and his colleagues analyzed the DNA of the pairs of brothers they had recruited, they were
Chromosome 8 homosexuality and christianity to see linkages on both Xq28 and a region of chromosome 8, which Hamer had also previously suggested held genes related to sexuality.
The work, published online today in Psychological Medicinetook longer to come to light than many expected.
After more than 7 years chipping away at the analysis between other projects, Bailey and psychiatrist Alan Sanders of NorthShore University HealthSystem Research Institute in Evanston, who led the investigation, began to discuss their findings at meetings. But it would be nearly 2 more years to publication, and Sanders acknowledges that at least one journal rejected the work.
In the meantime, the genetic linkage technique has largely been replaced with genome-wide association GWA studies. A linkage study identifies only broad regions containing dozens or even hundreds of genes, whereas GWA studies often allow the association of a specific gene with a certain trait in the population.
The paper little to clear up question about Xq28, he says.
Risch collaborated on a study that found no linkage at that region and says that more recent evidence casts further doubt. He also says the two linkages reported in the new work "Chromosome 8 homosexuality and christianity" not statistically significant. Sanders admits that although the strongest linkage he identified on chromosome 8, using an isolated genetic marker, clears the threshold for significance, the Xq28 linkage does not.
But he says both cases are bolstered by also less-than-significant data from neighboring markers, which appear to be shared at higher rates between pairs of brothers.
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How many live mosquitoes can fit into a syringe? Science 16 November VolIssue Another stretch of DNA on chromosome 8 also played a role in male that genes linked to homosexuality in men may have survived evolution.
Eight major studies of identical twins in Australia, the US and Scandinavia during before, one on the X chromosome and one on chromosome 8 Jews and Christians want to believe that homosexuality is environmental.