nmDf1 removes all four tandem paralogs of the mss family (Cre-mss-1, Cre-mss-2, Cre-mss-3, and Cre-mss-4). Male sperm is less competitive than wild-type male sperm, and females have lower brood size due to inbreeding depression. Reference: Yin D, et al. Science. 2018 Jan 5;359(6371):55-61.