Karyotype characterization and gene mapping of 5S and 18S rDNA in three species ofOligosarcus(Teleostei: Characidae)
Oligosarcus is a monophyletic Characidae genus with 15 species described, distributed through the freshwater bodies of South and Southeastern parts of South America. Recently, a new classification of this genus has been proposed based on morphological characters and mtDNA sequence, but still now there are many uncertainties in relation to the taxonomic classification of this group. In this study, three Oligosarcus species were chromosomically analyzed using conventional and molecular techniques
... olecular techniques in order to characterize their karyotipic constitution. All the three species presented 2n = 50 chromosomes, distributed as follows: O. jenynsii -2M/24SM/10ST/14A, O. pintoi -2M/20SM/12ST/16A, and O. hepsetus -2M/16SM/16ST/16A. A metacentric chromosome, larger than any other chromosome in the complement, was identified in all cases and probably corresponds to the marker chromosome of the Characidae family. The first submetacentric chromosome may also represent a marker chromosome, but at genus or subfamily level. The most frequent NOR location pattern was a large acrocentric pair bearing the NORs in the short arm and presenting size polymorphism. The presence of heterochromatin was more evident in O. hepsetus and O. pintoi than in O. jenynsii, with centromeric and telomeric bands on subtelocentricacrocentric chromosomes. FISH with 18S rDNA identified three loci for O. hepsetus and O. pintoi and two for O. jenynsii. The 5S rDNA probe identified three loci for O. hepsetus and O. pintoi and two for O. jenynsii. A possible syntenic organization of these two ribosomal DNA sequences was identified for O. hepsetus and O. pintoi in the NOR-bearing chromosomes.