THE q LOCUS OF NEUROSPORA CRASSA

Abstract

A genetic study of 4 biochemically similar niacin-requiring strains of N. crassa has been under-taken. The mutants involved (q mutants) have been characterized as to linkage relationships. Only 1 of the mutants gives rise to spontaneous reversions (at an infrequent rate) in vegetative culture. Crosses between different q mutants yielded (rare) niacin-independent progeny, whereas "selfings" did not. Niacin-independent progeny were recovered whether or not a crossover was detected in a marked region including the q locus, and regardless of the direction of any such crossovers. For these reasons, and from a consideration of the relative frequency of niacin-independence in the various marker classes obtained, it was concluded that niacin-independence does not seem to be the result of crossing over in the usual sense. Nevertheless, in-creased crossing over in the marked region appeared to be associated with the occurrence of niacin-independence. The possibility has been discussed that various characteristics of the q mutants are occasioned by the insertion of chromosomal material at or near the region of the q locus.