CHROMOSOMAL CHARACTERIZATION OF CALOMYS MUSCULINUS (RODENTIA, CRICETIDAE)

The chromosomes of the South American rodent Calomys musculinus have b een analyzed by standard Giemsa C-banding, chromomycin A3, distamycin A and DAPI fluorochrome staining and ''in situ'' digestion with the re striction endonucleases Alul, HaeIII and HindIII. Constitutive heteroc hromatin is restricted to the centric regions, and fluoresces after ei ther chromomycin A3 or DAPI treatments, indicating the co-existence of AT and GC-rich sequences in these regions. The restriction enzymes as sayed induce diffuse, overlapping patterns of centric and interstitial bands in the chromosomes of this species. Our results agree with othe r authors' biochemical analyses that indicate the existence of moderat ely to highly repetitive DNA sequences in C. musculinus that do not ap pear as a satellite in neutral CsCI DNA gradients, as well as a great abundance of the cleavage sites of these restriction enzymes in the ge nome of this rodent.