Molecular organisation and chromosomal localisation of 5S rDNA tandem arrays in evolutionary polyploid cyprinids from the genera Carassius and Barbus

Some evolutionary polyploid Carassius and Barbus species are poorly differentiated morphologically and hybridise to form viable intrageneric hybrids. 5S rDNA arrays and their chromosomal localisation were studied in C. carassius, C. gibelio, B. barbus, B. carpathicus and B. waleckii distributed throughout Poland, in order to contribute to the knowledge of their genetic and cytogenetic differences. Two 5S rDNA array classes in C. carassius (203 bp, 380 bp) and in three Barbus species (196 bp, 215 bp) were characterised by a highly-conserved coding region. The adjacent non-transcribed spacer (NTS) of C. Carassius exhibited a relatively high level of variation due to base substitutions and insertions/deletions, whereas the NTS of the Barbus species were highly conserved. Fluorescence in situ hybridisation with 5S rDNA array classes as probes indicated their syntenic chromosomal location and the utility of these sites as suitable marker of the analysed Carassius taxa ploidy. 5S rDNAs in two chromosomes of the Barbus species was discovered. The observed low variability of 5S rDNA arrays makes them an inappropriate tool for an investigation of the Barbus species, whereas the suitable for investigation within karyologically varied in the Carassius taxa.