Spontaneous Mutation at the R Locus in Maize. III. Genetic Modification of Mutation Rate

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Abstract
The frequency of seed color mutation of Rr: Cornell, which occurs at the rate of 18.2 x 10-4 in the Cornell stock, was reduced to zero in the F1 of a cross with a multiple linkage tester stock. The backross, F1 x Cornell stock, yielded 30 mutations (rate 9.2 x 10-4). The incidence of these mutations in relation to the segregation of the various marker genes indicates the presence of dominant genes favoring seed-color mutation of Rr: Cornell in the Y-marked segment and the J-marked segment of the tester stock. Similarly, the RS-marked segment shows an effect unfavorable to the occurrence of this mutation. The effect of the modifiers upon mutation frequency appears to be cumulative, so far as may be judged from the limited data. The use of such genes in the study of the nature of gene mutation is discussed, with reference to (1) the extraction of strains in which specific gene mutations are made frequent enough for direct experimental study of the mutation process, and (2) the use of the various mutation-modifiers as "differential reagents" in the analysis of gene differences.

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