In this investigation, patterns of variation in the nucleolus organizer regions (NORs) in the chromosomes of Spalax leucodon and Spalax ehrenbergi were studied. The chromosomal location of the Ag-NORs was determined in two mole rat species. S. leucodon has 3 pairs of nucleolar chromosomes, but S. ehrenbergi has only 2 pairs of nucleolar chromosomes in their whole chromosome sets. In both mole rat species, the chromosomal locations of Ag-NORs were determined to be on the terminal of the short arms of the subtelocentrics. The possibilty of Robertsonian translocation and the loss of paracentric NORs in S. ehrenbergi were discussed from an evolutionary point of view.

In this investigation, patterns of variation in the nucleolus organizer regions (NORs) in the chromosomes of Spalax leucodon and Spalax ehrenbergi were studied. The chromosomal location of the Ag-NORs was determined in two mole rat species. S. leucodon has 3 pairs of nucleolar chromosomes, but S. ehrenbergi has only 2 pairs of nucleolar chromosomes in their whole chromosome sets. In both mole rat species, the chromosomal locations of Ag-NORs were determined to be on the terminal of the short arms of the subtelocentrics. The possibilty of Robertsonian translocation and the loss of paracentric NORs in S. ehrenbergi were discussed from an evolutionary point of view.