Corngrass was originally mapped to the short arm of chromosome 3 by W. Galinat. Several years ago I obtained a stock of Cg which I subsequently used to try to locate the position of this mutation more precisely. These mapping studies demonstrated that the "Cg" mutation in this stock was unlinked to genes on 3S (MNL 58:170), creating some doubt about the actual location of Cg. I have since discovered that the mutation in this stock is tightly linked to Tp1 on chromosome 7, and that the stock was originally derived from an outcross of Cg to Tp1; it seems likely, therefore, that the mutation I had been working with is Tp1 rather than Cg. This conclusion is supported by the observation that the Cg mutation in the Coop's stock is linked to h on 3S (32% recombination, n = 136). A detailed linkage analysis is currently in progress.
A second dominant Corngrass-like mutation, which was discovered by J. Beckett, also maps to 3S. This mutation has a much less severe phenotype than Cg, and often displays poor penetrance. Although its most common effect is to increase the number of tillers, in some backgrounds it also causes an increase in node number, and the production of leaves in the tassel and ear. A detailed linkage analysis of this mutation is also in progress.
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