They identified sequences of DNA related to sexual orientation in three separate chromosomes
"There is no one 'gay' gene," said Mustanski. "Sexual orientation is a complex trait, so it's not surprising that we found several DNA regions involved in its expression."
"Our best guess is that multiple genes, potentially interacting with environmental influences, explain differences in sexual orientation."
The researchers analyzed the genomes of 456 men from 146 families with two or more gay brothers.
In contrast to earlier studies which have focused exclusively on the X chromosome, the current study examined all 22 pairs of non-sex chromosomes as well as the X chromosome. The Y chromosome was not considered because it is believe to carry few genes.
Three identical DNA sequences were found on chromosomes 7, 8 and 10. About 60 percent of the gay brothers shared these sequences. This is 10 percent higher than would be expected by chance.
"Our study helps to establish that genes play an important role in determining whether a man is gay or heterosexual," said Mustanski. "The next steps will be to see if these findings can be confirmed and to identify the particular genes within these newly discovered chromosomal sequences that are linked to sexual orientation."