Detection of 5S and 25S rRNA genes in Sinapis alba, Raphanus sativus and Brassica napus by double fluorescence in situ hybridization

Different ribosomal RNA (5S and 25S) genes were investigated simultaneously by fluorescence in situ hybridization (FISH) in Sinapis alba, Raphanus sat ivus and Brassica napus. The chromosomes of S. alba carried four 5S and six 25S gene sites, and those of R. sativus four sites of each gene, respectiv ely, These two species have one chromosome pair with both rDNA genes; the t wo are closely located on a short arm of S. alba, while in R, sativus one i s distal on the short arm (5S) and the other more proximal on the long arm (25S). In B. napus we have confirmed 12 sites of 25S rDNA. The detection of 5S rDNA genes revealed 14 signals on 12 chromosomes. Of these, six chromos omes had signals for both rDNA genes. The FISH with 5S rDNA probes detected two sites closely adjacent in four chromosomes of B napus. These results a re discussed in relation to a probable homoeologous chromosome pair in B. o leracea.