Classical, C and Cd-banding karyotypes in mitotic and meiotic chromosomes of Calomys musculinus (Rodentia, Cricetidae)

SUMMARY

The karyotype of Calomys musculinus (Rodentia, Cricetidae) 2n = 38, was studied. There are 11 m and sm pairs, 7 st pairs, X and Y, m. C-banding allows to observe the existence of notable heterochromatin centromeric blocks in all autosomes, except for pair N° 10 which is C (−) and pair N° 1, which has a small centromeric band. The X chromosome has a notable centromeric band, and the Y chromosome is C (−). Pair N° 10 (m and C (−), could be originated from an st pair which presented a C (+) band (FORCONE et al. 1980) through a pericentric inversion with loss of heterochromatin portion. Such an inversion could appear as polimorphic in the cordobensis populations studied. The results obtained through Cd-banding was compared with those observed in the SC at EM. It was determined that the consecutive “centromeric” bands observed at OM through Cd-banding, were more separated than the kinetochores, such as can be observed at EM in metacentric chromosomes originated by fusion. Hence, it can be concluded that the Cd-banding does not resolve the kinetochores at OM, but probably does in some heterochromatic centromeric regions. This was confirmed because the only chromosomes which did not present Cd-banding were the Y and the N° 10 pair, neither of which presented heterochromatic blocks in such a region.