I'm sure you guys have heard of HOX, the set of growth genes active during early development almost entirely responsible for determining the physical proportions of the body (body plan). HOX genes are physical switch genes regulating growth and physical development. There is clearly a genetic basis to certain aspects of behavior but is there anything a drastic as HOX genes? Are there behavioral switch genes? The answer remains debatable for humans, but the fru gene in Drosophila has been identified as one such gene. The fruitless (fru) gene is spliced sex-specifically in Drosophila giving rise to distinct male and female proteins. Male Drosophila preform an elaborate, innate mating ritual that shows almost no variation between individuals and is always directed towards females but when fru is mutated this mating ritual can is often disrupted even though physically the males show no mutations. Females never engage in courting behavior. Researchers created male Drosophila with forced female splicing of fru and found the males no longer showed courtship behavior; they were behaviorally female in mating. The males showed no significant differences in their anatomy. They then created female Drosophila with forced male splicing of fru and found the females displayed the male courtship behavior, performing the entire, elaborate male courtship ritual directed towards other females without changing their anatomy. These experiments demonstrate the sex-specific splicing of fru in Drosophila is both necissary and sufficent to confer mating behavior and sexual preference. These findings not only raise questions about the existence of behavior switch genes in other more complex animals, including humans but also about the basis of sexual orientation. Is it possible sexual orientation is controlled by a similar behavioral switch gene in humans? Behavioral switch genes are extremely hard to locate because our understanding of the biological basis of behavior is still so limited, however, the discovery of the fru gene's role in sexual orientation/mating preference in Drosophila may provide clues to the identification of related behavioral switch genes in other animals.
Here's the original paper: fruitless Splicing Specifies Male Courtship Behavior in Drosophila