Part I, the analysis of spontaneous reversion in a serine auxotroph of Neurospora crassa; Part II, linkage data on a new serine requiring mutant: Ser-5.

A newly isolated serine auxotroph of Neurosporacrassa, ser (JBM 4-13), exhibited a high rate of reversion in mapping experiments. This study sought to determine whether reversion occurred at a specific frequency , and whether it was time dependent. Individually isolated ascospore cultures of the mutant, as well as subcultures of individual progeny, showed spontaneous reversion frequencies ranging from 1.0 x 10 to 1.0. Other properties of the ser(JBM 4-13) mutant demonstrated by this study include: 1) the apparent meiotic stability of the ser (JBM 4-13) gene, 2) the mitotically unstable and highly revertible state of ser (JBM 4-13) which occurs sometime during vegetative development, 3) the time dependence of the reversion phenomenon, 4) the independence of the reversion phenomenon from conidial population size, and 5) the independence of reversion from cell division or growth. (See more in text.)

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