Meiosis and B-chromosomes in listera ovata (Orchidaceae)

Abstract

In Listera ovata the chiasma frequency is higher in embryo sac mother cells than in pollen mother cells. In both types of cell the chiasma frequency is raised by the presence of euchro- matic B-chromosomes. The rise is not linear but zig-zag with odd numbers of the B-chromosome having a greater effect than even numbers. It is suggested that B-chromosomes prolong the time available for chiasma formation allowing the utilization of more sites for chiasma formation so accounting for the rise in chiasma frequency. © 1972, Taylor and Francis Group, LLC.