BANDED KARYOTYPES AND THE LOCALIZATION OF RIBOSOMAL-RNA GENES OF EURASIAN FLYING SQUIRREL, PTEROMYS VOLANS ORII (MAMMALIA, RODENTIA)

Karyotypes of five males and four females of Eurasian (Siberian) flyin g squirrel, Pteromys; volans orii, were analyzed with G-, C-, Ag-NOR s taining methods. Fluorescence in situ hybridization (FISH) was applied to the location of 18S and 28S ribosomal RNA genes. The diploid chrom osome number of this species was 2n = 38 with the arm number (NF) of 6 8. C-bands were located at the centromeric region of all chromosome pa irs. Nucleolus organizer regions (NORs) appeared in the short arm of c hromosome 17, and the location of Ag-NORs was indistinguishable from t he site of the rRNA genes. The size variation of NORs was observed in each individual, indicating heteromorphism of NORs in this species.