A monophyletic origin of the B chromosomes of Brachycome dichromosomatica (Asteraceae)

Abstract

The A and B chromosomes of different karyotype variants(cytodemes A1, A2, A3 and A4) of Brachycome dichromosomatica were analysed by computer-aided chromosome image analysis and fluorescence in situ hybridisation (FISH). Ribosomal DNA and the B chromosome-specific sequence Bd49 were detected on all B chromosomes. In addition to minor size variation of the Bs, polymorphism of the rDNA and Bd49 position and copy number revealed two major types of B chromosomes. The B chromosomes of all the cytodemes were indistinguishable from each other in length, but that of A3 showed evidence of rearrangements consistent with its long-term geographic isolation. The results presented suggest a monophyletic origin of the B chromosomes of B. dichromosomatica.