Qazi Rhaman, a King’s College London psychologist, said that genes are thought account for up to 40 per cent of a person’s sexual orientation is governed by genes, and that it is likely that many genes are involved.
This would make developing a genetic test incredibly difficult.
He said: ‘There is no real risk of anyone finding a 'genetic test' for sexual orientation based on these or any of the scientific findings about the genetics of sexuality from the past 20 years.
‘The reason is that there is no gay gene. You are not going to be able to develop a test to find them all.’
Dr Rhaman, who has written a book about sexual orientation, added that all psychological traits involve genetics and people should not be afraid about link homosexuality to genes.
Richard Lane, of gay rights organisation, Stonewall, said that while studies into the origins of homosexuality have yet to produce convincing evidence, they do to point to a biological root.
He said: ‘The thing that’s consistent across all of them is that they all point to sexual orientation being something fundamental to a person rather than the lifestyle choice some opponents of equality repeatedly suggest.’
Other studies suggests that conditions in the womb also influence sexual orientation.
For instance, the more older male siblings a man has, the greater chance he will be gay.
Scientists say the phenomenon cannot be explained by the youngest boy being babied and mollycoddled or other differences in the way they are brought up.
It is thought that carrying a male baby in the womb triggers an immune response in the mother, creating antibodies that attack part of the unborn child's brain linked to sexual orientation.
This response gets stronger the more boys a woman carries, raising the odds of homosexuality.
Exposure to hormones in the womb is also likely to be important and some argue that upbringing plays a role in sexuality.