Fixation probability of a mutant influenced by random fluctuation of selection intensity

Abstract

SUMMARYThe probability of fixation of a mutant gene in a finite population was investigated by taking into account the effect of random fluctuation of selection intensity. It was shown that not only the product of the effective population number and average selection coefficient (Nes) is important, but also the ratio of the mean and the variance of selection coefficient (s/Vs) has an important influence on fixation probability. In particular, when this ratio is small, a mutant gene, even if selected against, becomes fixed in the population like a selectively neutral mutant. In general, when random fluctuation of selection intensity is not negligible it may be convenient to use ‘effective selection coefficient’. The bearing of the present findings on the neutral mutation-random drift theory of evolution and variation at the molecular level was discussed.