Aedes aegypti is the principal vector of several important arboviruses. Among the methods of vector control to limit transmission of disease are genetic strategies that involve the release of sterile or genetically modified non-biting males1,, which has generated interest in manipulating mosquito sex ratios2,3. Sex determination in Ae. aegypti is controlled by a non-recombining Y chromosome-like region called the M locus4, yet characterisation of this locus has been thwarted by the repetitive nature of the genome5. In 2015, an M locus gene named Nix was identified that displays the qualities of a sex determination switch5. With the use of a whole-genome BAC library, we amplified and sequenced a [~]200kb region containing this male-determining gene. In this study, w ...