CENTROMERIC REPETITIVE DNA-SEQUENCES IN THE GENUS BRASSICA

Representatives of two major repetitive DNA sequence families from the diploid Brassica species B. campestris and B. oleracea were isolated, sequenced and localized to chromosomes by in situ hybridization. Both sequences were located near the centromeres of many chromosome pairs in both diploid species, but major sites of the two probes were all on different chromosome pairs. Such chromosome specificity is unusual fo r plant paracentromeric repetitive DNA, Reduction of stringency of hyb ridization gave centromeric hybridization sites on more chromosomes, i ndicating that there are divergent sequences present on other chromoso mes. In tetraploid species derived from the diploids, the number of hy bridization sites was different from the sum of the diploid ancestors, and some chromosomes had both sequences, indicating relatively rapid homogenization and copy number evolution since the origin of the tetra ploid species.