Oligoryzomys fulvescens

Karyotype: 2n = 60 and FN = 74. Autosomal complement: six metacentric and submetacentric pairs (two large, two medium, and two small), three large subtelocentric pairs, and 21 acrocentric pairs medium to small decreasing in size. Sex chromosomes: X chromosome presented two different morphologies, a large subtelocentric, and a large acrocentric; Y, a small acrocentric (Haiduk et al. 1979, pp. 611, Fig. 2A).