Abstract
In Neurospora crassa, 20 isoleucine and valine requiring mutants including a temperature mutant were found to be separable into 3 groups genetically, I, II and III. The mutants are located at sites distal to lysine-1 and poximal to spray in linkage group V in the order III, II and I. Certain unexpected ratios of recombinants with respect to outside markers were noted and discussed. In addition, selfing crosses were described some of which resulted in a high frequency of progeny with a wild phenotype.