Fig. 1.—

Two models to estimate the fitness cost of mono-SSRs. Schematic representation of two alternative models to estimate the selection coefficient associated with mono-SSRs. Both models assume that each locus evolves independently and has one of the two alleles S or P; the S allele is deleterious. In the first model, the population size is infinite, so that all loci are polymorphic in the population with the same frequency. In that case, the frequency of S for a given locus is estimated by the frequency of S among all loci of the same genome. In the second model, the population is sufficiently small so that polymorphic states are only transient and all loci are fixed for one of the two alleles. In this model, all genomes from the population are identical to the sampled genome.