Abstract
Were analysed cytogenetically 53 specimens of Imparfinis aff. schubarti of the basin of the Tibagi river (Parana ´,Brazil). The diploid number of 58 chromosomes was observed and a karyotype of 28M+28SM+2ST with a fundamental number (FN) of 116. The nucleolus organizer regions (NORs) were studied by means of AgNO3 and CMA3 staining, as well as by FISH using an 18S rDNA probe. NORs were found to be located at the interstitial po- sition on the long arm of the first metacentric chromosome pair, corresponding to a secondary constriction observed in the conventional staining. AgNO3 and CMA3 evidenced a size heteromorphism between the NORs of the homolo- gous chromosomes. However, after FISH no difference was observed in the size of the homologous NORs. The first M pair. showed a pale C-banding in the pericentromeric region.
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