Spontaneous Mutation Accumulation Studies in Evolutionary Genetics

Mutation accumulation (MA) experiments, in which mutations are allowed to drift to fixation in inbred lines, have been a principal way of studying the rates and properties of new spontaneous mutations. Phenotypic assays of MA lines inform us about the nature of new mutational variation for quantitative traits and provide estimates of the genomic rate and the distribution of effects of new mutations. Parameter estimates compared for a range of species suggest that the genomic mutation rate varies by several orders of magnitude and that the distribution of effects tends to be dominated by large-effect mutations. Some experiments suggest synergistic interactions between the effects of spontaneous deleterious mutations, whereas others do not. There is little reliable information on the distribution of dominance effects of new mutations. Most evidence does not suggest strong dependency of the effects of new mutations on the environment. Information from phenotypic assays has recently been augmented by direct molecular estimates of the mutation rate.