Euryoryzomys sp.

Karyotype: 2n = 58 and FN = 92. Autosomal complement: 18 biarmed pairs large to small decreasing in size, and 10 acrocentric pairs medium to small decreasing in size. Sex chromosomes: X, a large submetacentric; Y, a small submetacentric (Fig. 4A). C-banding metaphases exhibited blocks of constitutive heterochromatin on the pericentromeric region of the majority of autosomal pairs. One large submetacentric pair presented a pericentromeric heterochromatin block that extend to the short arm. The X chromosome presented the short arm entirely heterochromatic and an interstitial lightly stained C-band on its long arm. The Y chromosome presented the long arm entirely heterochromatic (Fig. 4B). G-banding was performed to allow the correct identification of all homologous pairs (Fig. 4C). FISH with telomeric sequences revealed signals at the ends of all chromosome arms, and additional telomeric sequences were found on the centromeric regions of one large and one small biarmed pairs (Fig. 4D). This karyotype could be a variation of E. macconnelli (2n=58 and NF=90) mentioned by Patton et al. (2000, pp. 143), and the difference in fundamental number resulted from a pericentric inversion involving one biarmed autosomal pair. However, was not possible to compare these two karyotypes since the metaphase plate of the karyotype mentioned by Patton et al. (2000) was not available.