The population cytogenetics of crepis capillaris. III. B-chromosome effects on meiosis

Abstract

The B-chromosomes of Crepis capillaris, 2n =6, modify the pattern of chiasma formation in PMCs. With increasing B number, mean chiasma frequency increases in a linear fashion. The between-PMC variance for chiasma number also increases independently of the mean. All three bivalents increase in chiasma frequency in the presence of Bs but the smaller bivalents D and C increase disproportionately with respect to length. The “additional” chiasmata are predominantly distal in the long arms, with a decline in short arm and proximal long-arm regions. The chiasma effects of Bs are observed in comparisons between plants growing in natural populations, between plants in segregating families, and between PMCs within plants. B-chromosomes in this species markedly change the pattern of recombination in the genome. © 1990 The Genetical Society of Great Britain.