Monosomy and trisomy induced by the r-x1 deletion in maize, and associated effects on endosperm development

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Abstract
The r-x1 deficiency on chromosome 10 of maize conditions nondisjunction during embryo sac development. Variations in kernel size associated with r-x1 are found to be correlated with aneuploidy, both monosomy and trisomy, in the embryo. Among a sample of 70 normal-sized kernels only 10% had aneuploid embryos (4 monosomies, 3 trisomies), while 41 selected small kernels had 44% aneuploids (10 monosomies, 1 double monosomic, 7 trisomics) and 32 medium kernels also had 44% aneuploids (1 monosomic, 12 trisomics, 1 triple trisomic). On the assumption that reduced kernel size is due to aneuploidy in the endosperm following nondisjunction at one of the embryo sac mitoses, the observed proportion of hypoploid:hyperploid:euploid embryos among small kernels is inconsistent with nondisjunction at the first or third mitoses but fits well the expectation for nondisjunction occurring at the second mitosis. Nondisjunction at this division leads to both corresponding and noncorresponding constitutions between the embryo, and endosperm.Key words: Zea, aneuploidy, embryo sac, nondisjunction.

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