The reduction in fitness from genetic drift at heterotic loci in small populations

Abstract

SUMMARY: In finite populations, loci maintained segregating by hétérozygote superiority will be disturbed from their equilibrium positions by genetic sampling and the mean fitness of individuals will consequently be reduced. A general expression for this reduction is obtained for the segregation of two alleles. If the probability of continued segregation at the locus is high, the reduction tends to 1/4N, irrespective of the strength of selection, whereNis the effective population size. This will always be much less than the segregation load. Ifnalleles are segregating, so that all heterozygotes have the same fitness, the reduction tends to (n−1)/4N.