Non-Mendelian breeding behaviour of sh1-B (shrunken1-Bombay) allele
--S. Nadiger and N. K. Notani

We have reported that upon self-pollination, plants carrying sh1-B allele yield kernels with varying 'shrunkenness'. Upon testcrossing to sh1-A (American tester stock), all the kernels are completely shrunken (Allagikar et al., J. Genet. 70:33-41, 1991). Self-pollination of sh1-A/sh1-B hybrids yields progeny kernels that are, with few exceptions (~1%), completely shrunken (MNL 67:21, 1993). This suggests that the 'silenced' sh1-B allele continues to remain repressed in the following generation. Non-shrunken kernels, when testcrossed to sh1-A, are no longer inhibited. We interpret these observations as follows:

1. There are alleles in maize, the expression of which is variable (metastable?). The molecular basis for this is not clear.

2. Hybrids of sh1-A/sh1-B have completely shrunken kernels indicating that the sh1-B allele has been 'silenced'.

3. The 'silenced' allele sh1-B continues to remain so in the next generation following selfing of sh1-A/sh1-B plants.

4. A few non-shrunken kernels in the progeny of sh1-A/sh1-B, when testcrossed to sh1-A, remain non-shrunken, presumably having become refractory. 

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