US scientists study gay brothers
A large study of gay brothers adds to evidence that genes influence men's chances of being homosexual, but the results aren't strong enough to prove it.
Some scientists believe several genes might affect sexual orientation. Researchers who led the new study of nearly 800 gay brothers say their results bolster previous evidence pointing to genes on the X chromosome.
They also found evidence of influence from a gene or genes on a different chromosome. But the study doesn't identify which of hundreds of genes located in either place might be involved.