| Summary: | <p>Abstract</p> <p>Background</p> <p>To contribute to the knowledge of coleopteran cytogenetics, especially with respect to the genomic content of B chromosomes, we analyzed the composition and organization of repetitive DNA sequences in the <it>Coprophanaeus cyanescens</it> karyotype. We used conventional staining and the application of fluorescence <it>in situ</it> hybridization (FISH) mapping using as probes <it>C</it><sub><it>0</it></sub><it>t</it>-1 DNA fraction, the 18S and 5S rRNA genes, and the <it>LOA-like</it> non-LTR transposable element (TE).</p> <p>Results</p> <p>The conventional analysis detected 3 individuals (among 50 analyzed) carrying one small metacentric and mitotically unstable B chromosome. The FISH analysis revealed a pericentromeric block of <it>C</it><sub><it>0</it></sub><it>t</it>-1 DNA in the B chromosome but no 18S or 5S rDNA clusters in this extra element. Using the <it>LOA-like</it> TE probe, the FISH analysis revealed large pericentromeric blocks in eight autosomal bivalents and in the B chromosome, and a pericentromeric block extending to the short arm in one autosomal pair. No positive hybridization signal was observed for the <it>LOA-like</it> element in the sex chromosomes.</p> <p>Conclusions</p> <p>The results indicate that the origin of the B chromosome is associated with the autosomal elements, as demonstrated by the hybridization with <it>C</it><sub><it>0</it></sub><it>t</it>-1 DNA and the <it>LOA-like</it> TE. The present study is the first report on the cytogenetic mapping of a TE in coleopteran chromosomes. These TEs could have been involved in the origin and evolution of the B chromosome in <it>C. cyanescens</it>.</p>
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