Reverse-Mutation and Adaptation in Leucineless Neurospora

Publisher Website
Google Scholar
Abstract
The leucineless mutant of Neurospora is a true gene mutation. The adaptation to leucine-independence, which this mutant sometimes undergoes, is due to back-mutation to the wild-type condition at the leucineless locus. This is demonstrated by the genetic behavior of the adapted strain in crosses with leucineless and by the genetic behavior of the leucine-independent F1 progeny in crosses with wild type. Moreover, the adapted and wild-type strains are physiologically identical. The incidence of adaptations is significantly higher in the presence of low concs. of leucine than in the presence of high concs. This apparent chemical induction of mutations has its explanation in the fact that a back-mutation in the leucineless strain always results in the formation of a heterocaryon. In a heterocaryon between the leucineless and the adapted or wild-type strains, the leucineless nuclei have an advantage in the presence of leucine. Whether a back-mutation will result in an adaptation depends upon whether conditions favor selection against the leucine-independent nuclei.