Multiple maize minichromosomes in meiosis.

In this study, four distinct minichromosomes derived from the maize B chromosome, were increased in copy number using the B chromosome's accumulation mechanism, namely nondisjunction at the second pollen mitosis and preferential fertilization of the egg. These minichromosomes provide the unique opportunity to examine the behavior of many copies of a single chromosome in an otherwise diploid background. While multiple copies were associated in multivalent configurations, they often dissociated into univalents or bivalents prior to metaphase I. The largest mini's behavior closely resembled the progenitor B chromosome, but all smaller chromosomes showed failure of sister chromatid cohesion. In addition to the meiotic behavior, we observed many anomalies of univalent behavior and possible heterochromatic fusions of B repeat associated heterochromatin.