Genetic loads and estimates of mutation rates in highly inbred plant populations

Abstract

ESTIMATES of the rate of mutation to mildly deleterious alleles are fundamental to the testing of theories of the maintenance of sexual reproduction¹ and recombination^2,3. There are, however, few estimates of this parameter^4,5. We suggest that data on inbreeding depression in highly self-fertilizing populations might provide such estimates. The effect of inbreeding in reducing genetic load and inbreeding depression is well known^6,7, but little attention has been paid to the magnitude of these quantities in highly inbred natural populations. Modelling of mutational load shows that highly self-fertilizing populations should still have some genetic load and inbreeding depression^8–10. In such populations, inbreeding depression is the converse of heterosis and its magnitude can be estimated from the increase in fitness-related characteristics in individuals produced by intercrossing different strains. Here we derive the inbreeding depression expected in completely inbred populations, and use it to estimate mutation rates per genome for some plant species.