Genetic drift and the loss of alleles versus heterozygosity

Most studies of the loss of genetic variation caused by bottlenecks in population size have used heterozygosity as a measure of genetic variation. In this paper, I compare the effects of bottlenecks on the loss of alleles, as well as the reduction in heterozygosity. Population bottlenecks of short duration will have little effect on heterozygosity but are expected to reduce severely the number of alleles present. Heterozygosity provides a good measure of the capability of a population to respond to selection immediately following a bottleneck. However, the number of alleles remaining is important for the long-term response to selection and survival of populations and species.