McKeown suspected that multiple genes shape behavior and that doublesex played a role. But experimenting with doublesex is difficult. When both copies of the gene are removed ?a powerful way to test gene function ?flies have the physical features of both sexes. As a result, these mutant females are not recognized by normal males and these mutant males are not recognized by normal females ?and none of the mutants can mate. So this makes it difficult for scientists to categorize their behavior as gender appropriate.
So McKeown raised flies missing one of two copies of doublesex, a process that didn't completely remove the gene's influence but drastically reduced it. The result: Flies' sexual equipment was intact, but, theoretically, their sexual behavior might be different. McKeown and graduate student Troy Shirangi also reduced the activity of the fruitless gene as well as one called "retained."
Shirangi and McKeown did, indeed, see a doublesex influence. Doublesex helped the males act macho during courting ?chasing females, shaking their wings to "sing" love songs, tapping or licking their intended mates. In females, doublesex worked together with the gene retained to make them more receptive to this wooing; Females with two good copies of the gene were more likely to listen to love songs and to copulate. Interestingly, reducing the activity of doublesex or retained also allowed females to court like males, even though they lack the male-behavior-inducing activity of fruitless.
By manipulating fruitless and retained in other experiments, McKeown and his team found critical interactions, or overlaps, in the "mind" and "body" pathways. Retained acts in both sexes,