Effect of changes in population size on the correlation between mutation rate and heterozygosity.

The effect of changes in population size on the correlation between mutation rate and heterozygosity was studied by using two models: sudden change in population size and gradual change. It was shown that the results for the two models are close to each other, unless the rate of change for the latter is exceedingly slow. Thus, in many cases, the former model, which is much simpler than the latter, can be used to treat the present problem. Numerical computations showed that the correlation in a population that is expanding or has expanded in the recent past is stronger while the correlation in a population that is decreasing or has experienced a population reduction or bottleneck in the recent past is weaker than that for an equilibrium population with the same mean heterozygosity. However, regardless of whether the population is at equilibrium or not, the proportion of variation in heterozygosity that is attributable to variation in molecular weight over loci is rather small if the mean heterozygosity of the population is low, say of the order 0.05 or smaller.