CHROMOSOMAL LOCATION AND REORGANIZATION OF THE 45S AND 5S RDNA IN THEBRACHYSCOME LINEARILOBA COMPLEX (ASTERACEAE)

The chromosomal locations of the 45S (18S-5.8S-26S) and 5S ribosomal D NA in the Brachyscome lineariloba complex and two related species have been determined by the use of multicolor fluorescence in situ hybridi zation (McFISH). The Brachyscome lineariloba complex includes five cyt odemes with 2n=4,8,10,12 and 16, Each of the 5S and 45S rDNA loci occu rs at two sites on chromosomes in cytodemes with 2n=4, While in cytode mes with 2n=8, 10, 12 and 16, the number of 5S rDNA sites increases fr om four to eight paralleled to the genomic addition of diploid (4 chro mosomes) or haploid (2 chromosomes) dosage, Of the 5S rDNA sites, only one pair is major, except for the cytodeme with 2n=10. The remaining 5S rDNA sites are minor and seem to have reduced the unit number of th e 5S rDNA during the successive genomic additions, The 45S rDNA site i s detected only at two nucleolar organizing regions in all cytodemes r egardless of successive genomic addition, The loss or diminution of 45 S rDNA sequences seem to have proceeded more rapidly than 5S rDNA sequ ences in the B. lineariloba complex.