But geneticists have had only a handful of underpowered studies to address a complex, fraught, and often stigmatized area of human behavior. Now, the largest-ever study of the genetics of sexual orientation has revealed four genetic variants strongly associated with what the researchers call nonheterosexual behavior. Some geneticists are hailing the findings as a cautious but significant step in understanding the role of genes in sexuality. Others question the wisdom of asking the question in the first place. Andrea Ganna, a research fellow with the Broad Institute in Cambridge, Massachusetts, and Harvard Medical School in Boston, and colleagues examined data from hundreds of thousands of people who provided both DNA and behavioral information to two large genetic surveys, the UK Biobank study and the private genetics firm 23andMe. The researchers performed a genome-wide association study GWAS in which they looked for specific variations in DNA that were more common in people who reported at least one same-sex sexual experience.
Giant study links DNA variants to same-sex behavior
What do the new ‘gay genes’ tell us about sexual orientation? | New Scientist
This is the process where DNA expression is influenced by any number of external factors in the environment. And in the case of homosexuality, the researchers argue, the environment is the womb itself. Writing in The Quarterly Review of Biology , researchers William Rice, a professor at the University of California, Santa Barbara, and Urban Friberg, a professor at Uppsala University in Sweden, believe that homosexuality can be explained by the presence of epi-marks — temporary switches that control how our genes are expressed during gestation and after we're born. Specifically, the researchers discovered sex-specific epi-marks which, unlike most genetic switches, get passed down from father to daughter or mother to son. Most epi-marks don't normally pass between generations and are essentially "erased. Epigenetic mechanisms can be seen as an added layer of information that clings to our DNA.
What do the new ‘gay genes’ tell us about sexual orientation?
Few aspects of human biology are as complex—or politically fraught—as sexual orientation. Now, a new study claims to dispel the notion that a single gene or handful of genes make a person prone to same-sex behavior. The analysis, which examined the genomes of nearly half a million men and women, found that although genetics are certainly involved in who people choose to have sex with, there are no specific genetic predictors. Yet some researchers question whether the analysis, which looked at genes associated with sexual activity rather than attraction, can draw any real conclusions about sexual orientation. The handful of genetic studies conducted in the past few decades have looked at only a few hundred individuals at most—and almost exclusively men.
How do genes influence our sexuality? The question has long been fraught with controversy. An ambitious new study — the largest ever to analyze the genetics of same-sex sexual behavior — found that genetics does play a role, responsible for perhaps a third of the influence on whether someone has same-sex sex.