Degree Type


Date of Award


Degree Name

Doctor of Philosophy




The unstable bz-rcy allele arose by the insertion of a receptor element, rcy, into the Bz locus of a single gamete from the TEL population. Mutability of bz-rcy is controlled by the independently segregating regulatory element Cy (Cycler). In the absence of Cy, bz-rcy conditions a stable bronze aleurone. In the presence of Cy, bz-rcy conditions many small fully colored spots on a bronze background. These two elements, rcy and Cy, were previously undescribed;Genetic tests have established a relationship between Cy and the Mutator system. Cy is not functionally homologous to any of the non-Mutator transposable element systems;The number of genetically active Cy elements in a plant can increase or decrease via Cy transposition;Nonresponsive derivatives of bz-rcy have been isolated. A model has been established to explain the loss of the distal markers C and Sh coincident with the origin of some of these derivatives;The original isolate of bz-rcy often generates derivative alleles (states) that condition altered spotting patterns, e.g., reduced numbers of spots and/or larger and smaller spots, that reflect alterations in the frequency and timing of rcy excisions from bz-rcy. In contrast to receptors of the Ac and En(Spm) systems, which undergo changes of state only in the presence of the appropriate regulatory element, bz-rcy can undergo changes of state in the absence of an active Cy;Cy changes of state occur less frequently than those of bz-rcy. States of Cy have been isolated that induce reduced rates (but not altered timing) of rcy excision from bz-rcy. Many of the Cy states show progressive loss of function over succeeding generations;Many bz-rcy states and some Cy states have the ability to revert to fine-high spotting (cycling). Cycling is developmentally regulated and occurs only in the presence of Cy. A model has been proposed which evokes a form of reversible DNA modification to explain the cycling phenomenon and the origin of bz-rcy states in the absence of Cy;Of 47 diverse maize lines assayed, only two sources were found to contain strong Cy elements, i.e., Mutator-related stocks and the TEL population. Of the remaining lines, six, contained weak Cy elements and the rest lacked genetically detectable Cy elements.



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Patrick S. Schnable



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916 pages

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Genetics Commons