UK researchers have identified and characterized a master regulator of the sex determination process in the African malaria mosquito Anopheles gambiae. The team analysed the transcriptomes of male and female embryos and identified the gene Yob as a maleness-conferring Y chromosome-linked factor. Yob expression was observed from the onset of zygotic transcription throughout the life of males. The gene was found to encode a 56-amino-acid protein that controls the male-specific splicing of doublesex (dsx). Ectopic embryonic delivery of Yob mRNA was lethal for genetically female embryos, but had no effect on genetic males. By contrast, silencing of embryonic Yob expression resulted in male-specific lethality, suggesting a role of Yob in dosage compensation. Yob could be useful as a tool to produce male-only generations for transgenic approaches to control vector-borne diseases.