MOLECULAR CYTOGENETICS IN PLANARIANS - I - FLUORESCENCE IN-SITU HYBRIDIZATION (FISH) OF RIBOSOMAL DNA TO MITOTIC CHROMOSOMES OF DUGESIA-SICULA LEPORI (TURBELLARIA, TRICLADIDA)

The nucleolus organizing regions (NORs) were detected on mitotic chrom osomes of the freshwater planarian Dugesia sicula Lepori, by the in si tu fluorescence technique (FISH). The results show that ribosomal DNA (rDNA) sequences are located on medium-sized chromosomes, at telomeric positions. The application of the in situ hybridization method, which enables the molecular arrangement of specific DNAs to be visualized o n the chromosomes, improves the karyotypic characterization in planari ans and is of interest in a cytogenetic and cytotaxonomic perspective.