Fig. 2. Potential crosses and outcomes for a dominant, autosomal modifier of a Y-linked melanism gene in Gambusia holbrooki. Percentage refers to male fish from a given cross that would have a melanic phenotype. Mean at bottom refers to percentage melanism that would result if sires were heterozygous or homozygous dominant for the autosomal modifier and dams were used from all three diplid genotypes at equal frequency (it is assumed that males are not aa, otherwise they would not be melanic).