The fruitless gene (fru) is a Drosophila melanogaster gene that encodes several variants of a putative transcription factor protein. Normal fruitless function is required for proper development of several anatomical structures necessary for courtship, including motor neurons which innervate muscles needed for fly sexual behaviors. The gene does not have an obvious mammallian homolog, but appears to function in sex determination in species as distant as the mosquito Anopheles gambiae.fruitless serves as an example of how a gene or groups of genes may regulate the development and/or function of neurons involved in innate behavior. Research on fruitless has received attention in the popular press, since it provokes discussion on genetics of human sexual orientation, and behaviors such as gender-specific aggression.