Same-sex attraction is affected by a mix of genetic and environmental influences, but there is no such thing as a single "gay gene", according to a major study.
Published by the American Association for the Advancement of Science in Science, the study analysed DNA from more than 470,000 people from the United States and the United Kingdom.
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It found five specific genetic variants associated with same-sex attraction. Although variations of these genes cannot accurately predict whether a person is gay, they do influence sexual behaviour.
"We established that the underlying genetic architecture is highly complex. There is certainly no single genetic determinant (sometimes referred to as the 'gay gene' in the media)," the study says.
Overall, genetics account for only between 8 percent and 25 percent of same-sex attraction. Genetic variations had a greater effect on male same-sex behaviour than women.
Previous studies have come to similar conclusions, but this is the largest study of its kind.
Ben Neale, the director of genetics with the Stanley Center for Psychiatric Research at the Broad Institute of MIT and Harvard, said that showed attraction was affected by both genetics and environmental influences.
"This is a natural and normal part of variation in our species. That should also support the position that we shouldn't try and develop gay cures. That's not in anyone's interest," said Neale, who was involved in the study.
"It's effectively impossible to predict an individual's sexual behaviour from their genome. Genetics is less than half of this story for sexual behaviour, but it's still a very important contributing factor."
GLAAD - the world's largest advocacy group for LGBTQ people - said the results reinforced there was no "conclusive degree to which nature or nurture influence how a gay or lesbian person behaves".
Some limitations to the studies were that all participants with at least one same-sex attraction were put in the same group and participants were mostly European or American.