Five additional cases of simultaneous loss of Sh and Bz function have been recovered. These are in addition to the two cases previously reported (Schnable and Peterson, MGN 59:6). Five independent exceptional non-spotted bronze shrunken kernels (lines 1, 4-7 in the Table) were isolated from cross 1 (population size= 32,318 kernels).
Cross 1: C Sh bz-rcy/C Sh Bz Cy x C sh bz/C sh bz
In each case the new bz allele was shown to be a non-responder to Cy. Each exceptional type arose by a Sh bz-rcy change to sh bz-n(rcy) or a Sh Bz change to sh bz. In each case the sh phenotype is stable in the presence of Cy, arguing against the possibility of an imprecise excision of the rcy insert at bz-rcy (resulting in a non-responder), followed by its transposition into the Sh locus (resulting in a new sh-m allele).
In two of the seven total cases it has been shown that C function was also lost (Table). Of these two cases, female transmission is reduced in one case and normal in the other. In three cases C function remains intact. The C status has not been determined in the remaining two cases.
With the relation of Cy to Mutator, and the likelihood that these exceptional types represent deletions, it will be of interest to determine for each case whether the rcy insert is still present and whether it defines a deletion endpoint in a manner similar to that shown by Taylor and Walbot (EMBO J.4:869-876) for Mu1 at Adh1-S3034a.
Patrick S. Schnable and Peter A. Peterson
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