Scientists in the United States have concluded there is no such thing as a single “gay gene” which predetermines someone’s sexuality.
The study, published in the influential journal Science, analysed half a million DNA profiles as part of research in Europe and the United States.
In the 1990s, shortly after DNA was first discovered, it was speculated that a single gene may define someone’s sexuality in the same someone’s hair or eye colour depends on their genes.
In 1993 a genetic study on 40 families claimed to have identified the Xq28 gene as defining sexual orientation.
But Ben Neale, a member of MIT and Harvard's Broad Institute, said: "We found that it's effectively impossible to predict an individual's sexual behavior from their genome.”
The LGBTQ advocacy group GLAAD said the study "provides even more evidence that that being gay or lesbian is a natural part of human life."
The researchers said sexual orientation does have a genetic component but the effect is mediated by a myriad of genes.
Mr Neale said: "There is no single gay gene but rather the contribution of many small genetic effects scattered across the genome.”
He said environmental factors in someone’s childhood also play a part in an individual’s sexuality.
The authors of the report - two of whom were gay - found five points in human chromosomes, called loci, which appear closely linked to sexuality.
One of the loci is associated with baldness in men.
Fah Sathirapongsasuti, a scientist with the company 23andMe, said: "Genetics definitely play a part, but nonetheless, it is possibly a minority part - and there is an unexplained environmental effect that one can never put a finger on exactly."
The study also challenged the Kinsey Scale, which described people as varying from exclusively heterosexual to exclusively homosexual.
The authors wrote: "The genetics suggest that it is an oversimplification to assume that the more someone is attracted to the same sex, the less they are attracted to the opposite sex.”
Much of the data came from the UK Biobank, which is comprised mainly of white people.