In Plantagolagopus the B chromosome has been reported by our laboratory to be the result of massive amplification of ribosomal DNA sequences. However, the presence of transposable elements and other repetitive DNA sequences together with rDNA could not be ruled out. The present study clearly demonstrated the presence of transposable elements in the B chromosomes. These transposable elements were characterized and their nature assessed. Physical mapping using double fluorescent in situ hybridization was performed using DNA probes for 5S and copia elements. The results clearly proved that the B chromosome is a mix of 5S, 45S rDNA and transposable elements. Based on the FISH and Fiber-FISH patterns, it can be concluded that while 45S rDNA sequences are restricted to the subtelomeric regions, the 5S rDNA sequences are interspersed with transposons in the body of the B chromosome. These results have further enhanced our understanding of the organization and evolution of B chromosomes.
© 2013 S. Karger AG, Basel.