Studies on the Mechanism of Reversion in Biochemical Mutants of Neurospora Crassa

Nutritional mutants of either spontaneous or induced origin in various microorganisms provide excellent material for investigations of mutational changes of a particular kind. These mutational changes are included under the general term “reversion,” by which is meant any change resulting in growth by a nutritional mutant in the absence of an originally required specific substance. This broad definition of reversion is used since such types are initially recognized phenotypically and only subsequent testing makes possible a decision as to the type of change responsible for the observed growth. Thus, on this definition, reversions include nonheritable adaptations as well as clearly inherited changes. As used by some investigators, the term reversion is restricted to inherited changes. And, in fact, all the reversions dealt with in this discussion are clearly of the inherited type.