Fixation of Beneficial Mutations in the Presence of Epistatic Interactions

We inves tigate the effect of deleterious mutations on the process of fixation of newadvantageous mutants in an asexual population. In particular we wish to studythe dependence of the process on the strength of the deleterious mutations. Wesuppose the existence of epistatic interaction between the genes. We study themodel by means of branching process theory and also by numerical simulations.Our results show the occurrence of two distinct regimes of behavior for the prob-ability of fixation of these variants. The occurrence of either regime depends onthe ratio between the selective advantage of the beneficial mutation s