MEIOTIC BEHAVIOR AND EFFECTS OF B-CHROMOSOMES IN TALL FESCUE

Chromosome pairing and chiasma frequency were studied in seven genotypes of allohexaploid tall fescue (Festuca arundinacea Schreb., 2n = 6× = 42) from the Swiss Alps. All genotypes showed diploidlike pairing, which previous work has shown to be genetically enforced. These genotypes had 0 to 10 B chromosomes, which, when present, paired only as univalents and bivalents. Multivalent formation among Bs also may be genetically suppressed. Although A-chromosome chiasma frequency and its variance did not respond linearly to B dosage, both were higher with six or more B chromosomes than with fewer Bs. Chiasmata were also more evenly distributed between A-chromosome arms with increased dosage of Bs, as might result from decreased chiasma interference. We suggest that the bivalent formation by the Bs is an indirect consequence of the pairing regulation of the As and that it probably does not reflect preferential pairing among them. © 1990 The American Genetic Association.