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

The A and B chromosomes of different karyotype variants (cytodemes A1, A3, A3 and A3) of Branchycome dichromosomatica were analysed by computer-aided chromosome image analysis and fluorescence in situ hybridisation (FISH). Ri bosomal DNA and the B chromosome-specific sequence Bd49 were detected on al l B chromosomes. In addition to minor size variation of the Bs, polymorphis m of the rDNA and Bd49 position and copy number revealed two major types of B chromosomes. The B chromosomes of all the cytodemes were indistinguishab le from each other in length, but that of A3 showed evidence of rearrangeme nts consistent with its long-term geographic isolation. The results present ed suggest a monophyletic origin of the B chromosomes of B. dichromosomatic a.