Support for a hypothesis to explain the coincident activation of Ac and the origin of a P-RR allele --Patrick S. Schnable We have previously reported (MNL 60:5) on an Ac activation event in a single kernel which coincided with the origin of a P-RR allele. We hypothesized that a P-WR or P-WW allele present in our lines consists of a P-RR allele inactivated by the insertion of an Ac element which is itself inactive. Activation and subsequent transposition of the resident Ac element restored the P-RR allele to its functional mode. Linkage of the newly activated Ac to the P locus would support this hypothesis.

The plant derived from the kernel exhibiting Ac activation was crossed as shown. From this cross 135 colorless

C-I Bz Ds/C-I Bz Ds P-WR/P-WR X C bz-m4/C bz P-RR Ac/P-WR

(no Ac) and 156 variegated (with Ac) kernels were obtained. This is not significantly different than the 1:1 ratio expected if a single Ac element is segregating. To test the linkage of this Ac to the P locus plants from kernels with and without Ac were grown to maturity at which point the ears were scored for the presence of colored pericarp. 63 of 65 plants with Ac carried the P-RR allele. In contrast only 1 of 29 plants that did not receive Ac carried the P-RR allele. This yields a recombination value between P-RR and Ac of 3.2 cM with a standard error of 1.7. This tight linkage between the newly arisen P-RR allele and the newly activated Ac element supports our original hypothesis.


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