The population cytogenetics of Crepis capillaris. II. The stability and inheritance of B-chromosomes

Abstract

Metacentric B-chromosomes in Crepis capillaris undergo somatic non-disjunction in the developing inflorescences. Non-disjunction occurs at several stages in development and is seen as differences in B-number (i) between pollen mother cells (PMCs) within florets, (ii) between florets within capitula, and (iii) between capitula within inflorescences. About half the plants studied showed variation in B-number within the inflorescence. The number of Bs in inflorescences is very variable but in most plants is greatly in excess of the zygotic number, ranging from 1.00 to 3.56 per PMC in 1B plants. Two rounds of non-disjunction occasionally occur in the same cell lineage. The inheritance of Bs is greatly enhanced over Mendelian expectation with average transmission of 0.90 through the pollen and 0.83 through the egg. The role of accumulation in the maintenance of the C. capillaris B-chromosome polymorphism is considered. Very strong selection pressures must operate against B-containing plants or gametes in natural populations. © 1989, The Genetical Society of Great Britain.