Figure 1.

Graphical representation of the 9 two-locus two-allele models considered. Models 1–5 capture the dynamics of a mitochondrial Mother’s Curse mutation and a nuclear restorer located on an autosome or sex chromosome, respectively. In each model, Locus 1 is the primary sex-asymmetric locus, and Locus 2 harbors alleles that act to restore the fitness of the disadvantaged sex, except Model 5, where it further contributes to the advantaged sex. In Models 6–9, we model how selection acting on a mutation on the uniparentally inherited sex chromosome (Y, Models 6–7; W, Models 8–9) can lead to the spread of a mutation that is beneficial in the heterogametic sex but deleterious in the homogametic sex, Father’s Curse and Nuclear Mother’s Curse respectively.