The expected number of alleles in a gene conversion model with mutation

Gene conversions and mutations affect the number of different alleles in a population as it evolves, Here these effects are studied for a sample of r individuals represented by one chromosome, each with n loci. The long-term evolution of the sample is modelled with the coalescent, Gene conversions c an only occur within a chromosome between a pair of loci. Recombination is not included in the model. Mutations occur according to the infinitely many alleles model. A new expression for the expected number of alleles is deri ved using the Backward time approach, It is then possible to simulate the e xpectation for various sample paths. The new estimator is computationally i nexpensive and has a lower variance than the conventional, forward time, ap proximation by simulation. (C) 1999 Academic Press.