Oryzomys couesi

Karyotype: 2n = 56 and FN = 56. Autosomal complement: one small metacentric pair, and 26 acrocentric pairs large to small decreasing in size. Sex chromosomes: X, a large submetacentric; Y, a medium subtelocentric (Benson & Gehlbach 1979, pp. 227, Fig. 1A; Haiduk et al. 1979). C-banding metaphases exhibited blocks of constitutive heterochromatin on the pericentromeric region of all autosomes. The X chromosome presented a pericentromeric heterochromatic blocks (Haiduk et al. 1979). G-banding karyotype was performed by Baker et al. (1983).