In this study, the authors investigated genes controlling sexually dimorphic behavioural traits in mice. They identifed dimorphically expressed genes in the adult mouse hypothalamus and amygdala that were regulated in a sex-specific, spatially restricted manner by sex hormones. Targeted disruption of four of these genes individually resulted in deficits in sex-specific behavioural traits, such as male and female sexual behaviour. Thus, the neural circuits leading to these traits are goverened by separate genetic switches that act in response to sex hormones.