A Direct Method for Determination of Forward-Mutation Rates in Neurospora crassa

Abstract

THE main difficulty in estimating forward-mutation (from wild type to mutant) rates at specific loci in micro-organisms is the determination of the total number of specific mutations in a given population of cells after mutagenic treatment. In general, mutation rates are so low that the number of specific mutants cannot be readily determined by direct methods. An attempt has been made to determine forward-mutation rates at specific loci¹ by indirect methods, using the ‘filtration-concentration’ technique, which permits only partial recovery of the induced mutants. Later, an effort was made to determine what proportion of the total mutants induced at each of these loci is recovered with such techniques, by reconstruction experiments in which various mixtures of wild-type and mutant conidia were used. To circumvent the various assumptions that must be made to obtain estimates of the forward-mutation rates from the data obtained by such indirect methods, we developed an experimental technique that permits the estimation of the forward-mutation rates of specific loci by a direct method.