It could overturn the findings of a theory based on a 1993 study that found a genetic marker more common in gay men. Picture: AP

London - Scientists have ruled out the existence of a single so-called "gay gene".

The largest ever genetic study into sexuality found no evidence of DNA material that was entirely responsible for homosexuality.

It could overturn the findings of a theory based on a 1993 study that found a genetic marker more common in gay men.

Experts now say thousands of genes are involved in sexuality – and even then their influence may be no more than 25 percent.

The environment that people grow up in is likely to be more important than DNA. Researchers sequenced the genes of more than 470 000 people, principally taken from the UK Biobank genetic database and DNA testing website 23andMe. 

Dr Benjamin Neale, a co-author of the study from the Broad Institute in the US, said: "This study disproves the notion that there is a so-called gay gene and disproves the notion that sexual behaviour is a choice."

He added: "We also found that 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." 

The study found an individual’s genes have less influence on their sexuality than their height or educational ability. Dr Neale, a statistical geneticist, said the study was "reassuring" for those who fear that there might one day be attempts to edit DNA. 

He said: "The genetics are just too complicated and biology and the environment are both involved." Scientists combed database information for common genetic variations in people who had slept with someone of the same sex.

But they could not find the genetic marker inherited from a mother through the X chromosome that sparked the theory of a "gay gene" after being found by US geneticist Dean Hamer in 1993.

Dr Hamer himself said at the time that a single gene was too simple an explanation. And the new study, published in the journal Science, found only five genes with a significant link to being gay. Together, these explain one percent of someone’s sexuality, and thousands of further genes combined are needed to have a larger effect.

The study did find a potential genetic link between homosexuality and baldness in men, however, which might suggest sex hormones important in hair loss also affect sexuality.

Daily Mail