PLoS Biology has new papers from David Hartl's lab at Harvard University that looks into sex ratio distortion in Drosophila, finding an X-linked sex-ratio distorter called Dox and its dominant suppressor, Nmy. The researchers suggest that small interfering RNAs, made from the Nmy hairpin region, silence Dox. In a related Primer, Cornell's Patrick Ferree and Daniel Barbash write, "This first mechanistic glimpse of a sex-ratio distortion system provided by Tao and colleagues suggests that RNAi-mediated regulation, and its failure, may have important implications for understanding fundamental problems in evolutionary genetics and speciation."