Oligoryzomys stramineus

Karyotype: 2n = 52 and FN = 68. Autosomal complement: nine metacentric pairs (two large, five medium, and two small), and 16 acrocentric pairs (one large and the remaining medium to small decreasing in size). Sex chromosomes: X, a large submetacentric; Y, a medium metacentric (Maia et al. 1983; Bonvicino & Weksler 1998, pp. 94, Fig. 2; Andrades-Miranda et al. 2001a; Weksler & Bonvicino 2005; Geise et al. 2010; Fernandes et al. 2012). Another fundamental number of 69 was reported due to a pericentric inversion in one chromosome of a small acrocentric pair (Bonvicino & Weksler 1998), and these authors mentioned a fundamental number of 70 apparently due to an inversion in a small acrocentric pair (unpublished data from A.L. Gardner mentioned by Bonvicino & Weksler 1998). These variation in fundamental number occurs on specimens collected in Minas Gerais and Pernambuco, states of Brazil (Table 9, Fig. 17). C-banding metaphases exhibited blocks of constitutive heterochromatin on the pericentromeric region of the majority of the autosomes, but were absent in one large metacentric and on the X chromosome. The Y chromosome was entirely heterochromatic (Andrades-Miranda et al. 2001a).