Introdution Currently, there are 38 valid species of freshwater stingrays, and these belong to the subfamily Potamotrygoninae. However, cytogenetic information about this group is limited, with studies mainly using classical techniques, Giemsa and C-banding. Methods In this study, we used classical and molecular cytogenetic techniques (mapping of repetitive sequences 18S, 5S and SSRs) in order to investigate the karyotypic composition of P. schroederi and draw a parallel with the karyoevolutionary trends of this group. Results The species presented 2n=66 chromosomes with 18m+12sm+16st+20a, heterochromatic blocks distributed in the centromeric regions of all chromosomes, and terminal blocks in the q arm of pairs 2 and 3. Mapping of 18S rDNA regions revealed multiple markers on pairs 2 and 7 and a homolog of pair 24. The 5S region was found in the pericentromeric portion of the subtelocentric pair 16. Furthermore, dinucleotide SSRs sequences were found in the centromeric and terminal regions of different chromosomal pairs, with preferential accumulation in pair 17. In addition, we identified conspicuous blocks of (GATA)n and (GACA)n sequences colocalized with the 5S region (pair 16). Conclusion In general, this study corroborates the general trend of a reduction in 2n in the species of this subfamily. Also, we finding that the location of rDNA regions is very similar in Potamotrygon. Besides, the microsatellite acumulation in the second subtelocentric pair (17) seems to be a common trait amog Potamotrygon species.
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