Mutagenesis at the ad-3A and ad-3B loci in haploid UV-sensitive strains of Neurospora crassa. I. Development of isogenic strains and spontaneous mutability

7 different mutations that confer sensitivity to inactivation by ultraviolet light have been investigated for their effect on spontaneous mutation at the ad-3A and ad-3B loci in haploid strains of Neurospora crassa. The collection and development of strains isogenic to wild-type 74A is described as well as experiments to determine the effects of each mutation on the spontaneous ad-3 mutation frequency. 6 of the strains showed spontaneous ad-3 mutant frequencies not significantly different from the wild-type strain. Strain uvs-3 is highly mutable spontaneously with marked variation from experiment to experiment; the mean mutation frequency in this strain in about 40-fold higher than that found in the wild-type strain.