Data and code from: Multiple sex chromosome drivers in a mammal with three sex chromosomes

Eukaryotes with separate males and females display a great diversity in the way they determine sex, but it is still unclear what evolutionary forces cause transitions between sex-determining systems. Rather that the lack of hypotheses, the problem is the scarcity of adequate biological systems to test them. Here, we take advantage of the recent evolution of a feminizing X chromosome (called X*) in the African pygmy mouse Mus minutoides, to investigate one of the evolutionary forces hypothesized to cause such transitions, namely sex chromosome drive (i.e., biased transmission of sex chromosomes to the next generation). Through extensive molecular sexing of pups at weaning, we reveal the existence of a remarkable male sex chromosome drive system in this species, whereby direction and strength of drive is conditional upon the genotype of males’ partners: males transmit their Y at a rate close to 80% when mating with XX or XX* females, and only 36% when mating with X*Y females. Using mathem...