Studies of Gene Mutation in Saccharomyces
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Excerpt
It can be argued that when two recessive mutant genes in combination produce the mutant phenotype, they are either variants of a locus (Pontecorvo, 1952), that is, they are alleles, or they are variants of neighboring loci and are exhibiting position pseudoallelism in combination (Lewis, 1955; Green, 1956). A principal criterion for pseudoallelism is the demonstration that the two loci are separable by crossing over. Thus the hybrid Ab/aB, in which a and b are pseudoalleles, yields both AB and ab from the same recombinational event. The genes a and b are regarded as functionally and spatially separate.
The study of gene mutation is therefore complicated by the problem of distinguishing between mutation at a single locus and mutation at a series of adjacent loci. Since the validity of the criterion of crossing over as a general indication of separate loci is open to question (Pritchard, 1955) and since the...
