The effect of synergistic epistasis on the inbreeding load.

The magnitude of inbreeding depression in Drosophila melanogaster appears too large to be accounted for by mutational load with multiplicative fitness interactions among loci, if current estimates of mutation and selection parameters are valid. One possible explanation for this discrepancy is synergistic epistasis among the fitness effects of deleterious mutations. A simple model of the effect of synergistic epistasis on the inbreeding load is developed. This model is used to show that deleterious mutations could account for the Drosophila data on the effects of inbreeding on components of fitness such as viability.