FREQUENCY OF SOMATIC MUTATION TO SELF COLOR IN MAIZE PLANTS HOMOZYGOUS AND HETEROZYGOUS FOR VARIEGATED PERICARP

Abstract

The effect of Modulator on stability of the variegated pericarp allele (Pvv or PrrM p) in somatic tissue was studied in three otherwise near-isogenic genotypes designated "medium variegated" (PrrMp/Pvr), "light variegated" (PrrMp/Pwr + tr Mp/ -), and "homozygous variegated" (PrrMp/prrMp). As Emerson had earlier observed in unrelated stocks, the single variegated allele in plants heterozygous for a stable P gene was found to mutate to self color approximately 3 times as frequently as either of the alleles in variegated homo-zygotes. It was postulated that the lower rate in the homozygote was the result of the action of the Modulator component in each variegated allele on mutation to self color of the other variegated allele. The test of this hypothesis which was applied was a comparison of the frequency of mutation in homozygous variegateds, carrying two pvv alleles embodying two Modulator units, and light variegateds, carrying one variegated allele and one transposed Modulator. If the mutation rate of a pvv allele is equally influenced by an additional Mp in any position, including the locus of the homologous allele, then twice as many mutations to self color would be expected in the homozygotes as in the light variegateds. The numerical results obtained on scoring the 2 classes of ears in question for mutations to the self color agreed closely with expectation on this hypothesis.