The gene encodes the Fruitless protein. Male and female flies carry different versions of the fruitless protein, as a result of sex-specific splicing of the mRNA. The male form of Fruitless is critical for the male courtship ritual and males' preference for mating with females, as previous studies have shown.
Now, Barry J. Dickson and Ebru Demir of the Institute of Molecular Biotechnology of the Austrian Academy of Sciences show just how intimately fruitless is linked to these stereotypically male behaviors. They discovered that female flies with the male version of fruitless behave like males, directing at other females a sexual display nearly identical to their male counterparts.
Female flies with the male version of the protein also make amorous advances toward male flies that express female pheromones. In these cases, "we have been able to reverse the sex roles during Drosophila courtship," Dickson and Demir say.
Dickson and Demir created male-spliced versions of fruitless in female flies and female-spliced versions in male flies. Males with the female version of fruitless "barely court at all" when paired with virgin female flies in an observation chamber, according to the researchers.
Males with the female fruitless splice form were also more likely to court other males than flies with the male form, suggesting that male-specific fruitless splicing "not only promotes male-female courtship, it also inhibits male-male courtship," the researchers say.
Dickson and Demir refer to fruitless as a behavioral "switch gene" that is both necessary and sufficient to produce a particular behavior. Switch genes that trigger the development of a particular ana