Tests for Non-Allelism at the Pyrimidine-3 Locus of Neurospora.

MONG the pyrimidine-requiring mutants of Neurospora is one which exhibits A the requirement only a t temperatures above 31”, in contrast to the more frequently isolated mutants which show an absolute requirement regardless of the temperature of incubation (MITCHELL and HOULAHAN 1947). One of the latter mutants was found to be allelic or quite closely linked to the temperature-sensitive one and to be suppressed by a suppressor of this mutant (HOULAHAN and MITCHELL 1947). More recently a third mutant has been found to be closely linked or allelic to these but is apparently unaffected by the suppressor. This mutant has been shown to give pseudo-wild progeny when crossed to either of the other two (MITCHELL, PITTENGER and MITCHELL 1952). The study which is described here was undertaken in an attempt to learn whether the three mutants are non-allelic.