Oligoryzomys messorius

Karyotype: 2n = 66 and FN = 74. Autosomal complement: five metacentric and submetacentric pairs medium to small decreasing in size, and 27 acrocentric pairs (one large and the remaining medium to small decreasing in size). Sex chromosomes: X, a medium acrocentric; Y, a small acrocentric. C-banding metaphases exhibited blocks of constitutive heterochromatin on the pericentromeric region of all autosomes, with the exception of the large acrocentric pair. The X chromosome presented pericentromeric heterochromatic blocks. The Y chromosome was entirely heterochromatic. Multiple NORs, were localized at the telomeric regions of the short arms of two autosomes pairs (Andrades-Miranda et al. 2001a, pp. 1084, Fig. 2C).