According to a recent study, there's evidence that male sexual orientation is genetic. Researchers discovered that genes on at least two chromosomes influence whether a man is gay or straight. These genes are passed down exclusively from their mothers.

The study—which hasn't yet been published, was presented at the American Association for the Advancement of Science in Chicago. It tested the DNA of 400 gay men and found that a region of the X chromosome called Xq28 was the influence to men's sexual behavior. The X chromosome is inherited directly from mothers.

But scientists also found that those genes were neither sufficient necessary for gay men. Some did not inherit the Xq28 region.
Sexual orientation has nothing to do with choice. We found evidence for two sets [of genes] that affect whether a man is gay or straight. But it is not completely determinative; there are certainly other environmental factors involved.
Is genetics the whole story when it comes to sexuality?