Conditions for maintaining pseudo-overdominance

Deleterious recessive mutations should purge or fix within inbred populations, yet inbred populations often retain moderate to high segregating load. However, arrays of deleterious recessives linked in repulsion could generate appreciable pseudo-overdominance, mimicking overdominant selection that would sustain segregating load. We use analytical approches and simulations to explore whether and for how long pseudo-overdominant (POD) zones can persist once created (e.g., by hybridization between populations fixed for alternative mildly deleterious mutations). Balanced haplotype loads, tight linkage, and moderate to strong cumulative selective effects all serve to maintain POD zones. Tight linkage is key, suggesting that such regions are most likely to arise and persist in low recombination regions (like inversions). Selection and drift unbalance the load, eventually eliminating POD zones, but this process is quite slow, and could influence short term evolution of populations.