A New map of the Amination-1 Locus of Neurospora Crassa, and the Effect of the Recombination-3 Gene

Abstract

The sites of difference from the normal gene of 13 am-I alleles have been mapped, almost without ambiguity, in rec-3 background. Repulsion-phase crosses were made between pairs of the auxotrophic mutants and prototrophic recombinants selected. The recombinants were then classified into the four possible classes specified by different combinations of chromatids flanking am-I, by using markers at the closely linked loci sp and his-I. The sites of difference of the alleles were ranked in an order obtained using two criteria-the first based on significant differences between the two classes of prototrophic recombinants with non-parental combinations of flanking regions, and the second based on prototrophs with parental combinations. The unambiguous order, proximal to distal, of 11 sites is 6-14-4-2-5-17-1-7-11-3-9. The site of 19 is very close to 2, immediately adjacent either proximally or distally. The site of 8 could not be related unambiguously to the sites of 2 and 19, but it is placed unambiguously between 4 and 5. The data suggest that recombination in am-I frequently results from conversion without associated crossing-over, and that a gradient in the frequency of such conversion occurs, with more always occurring proximally.