Darwinian Genetic Drift

Genetic drift is stochastic fluctuations of alleles frequencies in a population due to sampling effects. We consider a model of drift in an equilibrium population, with high mutation rates: few functional mutations per generation. Such mutation rates are common in multicellular organisms including humans, however they are not explicitly considered in most population genetics models. Under these assumptions the drift shows properties distinct from the classical drift models, which ignore realistic mutation rates: i) All (non-lethal) variants of a site have a characteristic average frequencies, which are independent of population size, however the magnitude of fluctuations around these frequencies depends on population size. ii) There is no “mutational meltdown” due to “low efficiency of selection” for small population size. Population average fitness does not depend on population size. iii) Drift (and molecular clock) can be represented as wandering by compensatory mutations, postulate of neutral mutations is not necessary for explaining the high rate of mutation accumulation. Our results, which adjust the meaning of the neutral theory from the individual neutrality of the majority of mutations, to the collective neutrality of compensatory mutations, are applicable to investigations in phylogeny and coalescent and for GWAS design and analysis.