Oligoryzomys microtis

Karyotype: 2n = 64 and FN = 66. Autosomal complement: one large submetacentric pair, one small metacentric pair, and 29 acrocentric pairs medium to small decreasing in size. Sex chromosomes: X, a medium subtelocentric; Y chromosome presented two different morphologies, a small metacentric, and a small acrocentric (Gardner & Patton 1976, pp. 8, Fig. 3B; Aniskin & Volobouev 1999; Patton et al. 2000). Another fundamental number of 64 was reported for a sample from Mato Grosso, state of Brazil, due to the presence of one large acrocentric pair instead of a submetacentric one (Di-Nizo et al. 2015). C-banding metaphases exhibited blocks of constitutive heterochromatin on the pericentromeric region of the autosomal pairs, with the exception of one the large submetacentric pair and five acrocentric pairs of medium-sized. The X chromosome presented the short arm entirely heterochromatic. The metacentric Y chromosome was entirely heterochromatic (Aniskin & Volobouev 1999). G-banding was also performed (Aniskin & Volobouev 1999; Di-Nizo et al. 2015).