Genetic polymorphism and evolution in parthenogenetic animals

A stochastic model has been constructed to study the heterozygosity in a diploid parthenogenetic lineage. Mutation produces new alleles and two kinds of mutant alleles are distinguished: those coding for a functioning enzyme, and those coding for defective enzymes. Individuals with two different functioning alleles are called functioning heterozygotes. It is assumed that population size does not fluctuate and that selective processes need not be considered if an individual has at least one functioning allele at a given locus. It is shown that the amount of heterozygosity depends on time. Mutation pressure first increases functioning heterozygosity to a maximum value. This is a function of time, mutation rate and initial heterozygosity. Subsequently functioning heterozygosity decreases owing to the increase in the frequency of nonfunctioning alleles. The model is discussed in connection with experimental data.