RIBOSOMAL-RNA GENES AND THE B-CHROMOSOME OF BRACHYCOME-DICHROMOSOMATICA

Fluorescence in situ hybridization (FISH) with biotinylated rDNA revea led the presence of an rRNA gene cluster on both the A and B chromosom es of Brachycome dichromosomatica, an Australian native ephemeral plan t of the arid regions of south-eastern Australia. This species contain s only two pairs of A chromosomes and up to three B chromosomes. The r egular attachment of the B chromosome to a nucleolus suggests that the se ribosomal RNA genes are transcribed. Southern hybridization of DNA from OB and +B plants digested with a variety of restriction enzymes i ndicates that the rRNA genes on the A and B chromosomes are the same i n sequence and methylation status.