Chromosome segmental dosage analysis of maize morphogenesis using B-A-A translocations.

The B-A-A translocations have enabled us to simultaneously assess the possible dosage-sensitive interactions of two nonhomologous chromosome segments in affecting maize plant development. Maize B-A-A translocations contain segments of two nonhomologous essential A chromosomes in tandem arrangement attached to a segment of the long arm of a supernumerary B chromosome. By utilizing the frequent nondisjunction of the B centromere at the second pollen mitosis we produced plants containing an extra copy of the two A chromosome segments. We compared these hyperploid plants with nonhyperploid plants by measuring leaf width, plant height, ear height, internode length, stalk circumference, leaf length, and tassel-branch number in 20 paired families that involved one of the chromosome arms 1S, 1L, 4L, 5S, and 10L. One or more of the seven measured traits displayed dosage sensitivity among 17 of the 20 B-A-A translocations, which included the involvement of chromosome arms 2L, 3L, 5L, 6L, and 7L. The most obvious effect of an increased dosage of the B-A-A translocation was a significant decrease in the traits in the hyperploid plants. These effects may be either the additive effects of hyperploidy for the two chromosome segments or a result of gene interaction between them.