Fig 4. The influence of the replicon copy number (nrc) and the strength of selection (s) on the establishment probability of a beneficial allele.
Allele establishment is achieved if the subpopulation of cells with the novel phenotype is sufficiently large, such that stochastic loss of the allele becomes unlikely. The dashed line shows the strength of selection s(50%) that is needed for a given replicon copy number, n(rc), to yield an establishment probability of 50%. Allele establishment in the simulation is defined by the time point when the frequency of novel homozygotes at the end of a growth phase (before a bottleneck) is sufficiently high such that the probability of allele extinction is below 10−4. The initial population consists of 107 cells, where one cell has a single mutant replicon copy and the rest is of the wild-type. The cell population grows until a carrying capacity Nc = 109 before a population bottleneck occurs, where a fraction b = 10−2 or b = 10−3 of cells is transferred to form the new population in the next growth phase. Simulations stop either when the novel allele goes extinct or when the allele is established in the population.