Sexual dimorphism: Neural circuit switches in the Drosophila brain.

The sex-determining genes Double Sex and Fruitless are expressed in sexually differentiated neurons of the Drosophila brain. A tiny cluster of neurons, aDN cells, serves as a key circuit switch with sexually dimorphic properties: those of female flies respond to visual signals in males, while those of male flies respond to smell and humidity in females, supporting effective courtship and communal egg laying behaviors, respectively.