In observing the frequency of somatic reversion in bz2-mu-1 materials we have noted several classes of interesting events: (1) individual kernels with crown-only or base-only patterns of revertant sectors; (2) half kernels or smaller sectors in which one part has a low (5%) frequency of coverage by somatic reversions and the other part has a high frequency (50%); (3) an ear of medium Mu copy number of genotype bz2-mu-1/bz2, testcrossed by a bz2 hybrid tester, had a sector comprised of approximately 30 kernels which exhibited the expected 50:50 segregation for spots. Of the remaining ca. 300 kernels on the ear, however, only 5 had spots.

These observations on the distribution of spotted kernels on the ear and changes in the distribution of spots on individual kernels suggest that a change in the capacity to undergo somatic reversion can occur in cells during ear and kernel development. Changes in reversion frequency may reflect changes in the copy number of Mu in cell lineages, a phenomenon parallel to the observation that Mu copy number influences the apparent transmission of the spotted kernel phenotype, as discussed in the accompanying article.

Virginia Walbot
 
 

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