AN EMBARRASSMENT OF RICHES - THE STOCHASTIC GENERATION OF BENEFICIAL MUTATIONS

We present a series of models that allow beneficial mutations to arise as a consequence of small changes in mutations' selection coefficient s. We do this by extending a strictly deleterious shift model into one that incorporates intragenic regions such as introns and exons. The r esults show that populations segregate and fur a substantial number of beneficial mutations. In these simulations, the percentage is approxi mately 50%, though the specific number is a function of the population size and the underlying genic model. In general, it was quite easy fo r populations to counter their deleterious load and rise in an unbound ed increase in mean fitness. We discuss a possible application of the model to molecular evolution.