I imagine that by now everyone has heard about the creation of lesbian fruitflies:

"We have shown that a single gene in the fruit fly is sufficient to determine all aspects of the flies' sexual orientation and behavior," said the paper's lead author, Dr. Barry Dickson, senior scientist at the Institute of Molecular Biotechnology at the Austrian Academy of Sciences in Vienna. "It's very surprising.

"What it tells us is that instinctive behaviors can be specified by genetic programs, just like the morphologic development of an organ or a nose."

The results are certain to prove influential in debates about whether genes or environment determine who we are, how we act and, especially, our sexual orientation, although it is not clear now if there is a similar master sexual gene for humans.

Still, experts said they were both awed and shocked by the findings. "The results are so clean and compelling, the whole field of the genetic roots of behavior is moved forward tremendously by this work," said Dr. Michael Weiss, chairman of the department of biochemistry at Case Western Reserve University. "Hopefully this will take the discussion about sexual preferences out of the realm of morality and put it in the realm of science."

David Velleman has some interesting comments.

...studies also exclude the hypothesis that sexual orientation is fully determined by genetics. To begin with, virtually all research on sexual orientation relies on something like the "Kinsey scale", which measures orientation on a seven-point scale (0 to 6). The lay conception of homosexuality as an all-or-nothing trait has no basis in scientific observation. And the best-designed studies of identical twins have found that in over two-thirds of the pairs that include a homosexual twin (scoring 1 or higher on the Kinsey scale), the other twin is not homosexual. This finding decisively rules out the possibility that sexual orientation is genetically determined, though further statistical analysis shows that it is indeed significantly influenced by genetic inheritance.

In short, we aren't going to discover a "gay gene" -- not even a constellation of "gay genes" -- though we probably will discover genes that influence sexual preference.

This is either wrong or merely imprecisely phrased. The possibility of a "gay gene" has not been ruled out. It may be possible, for example, that holders of a "gay gene" are gay with 100% certainty, but those who do not possess it can still become gay with some nonzero probability. Then, you would have the sort of result produced in the study Velleman cites, where not all twins have the same sexual orientation.