Neacomys paracou Karyotype: 2n = 56 and FN = 66. Autosomal complement: six metacentric and submetacentric pairs, and 21 acrocentric pairs. Sex chromosomes: X, a medium subtelocentric; Y, a small acrocentric. Another fundamental number of 62 was reported due to presence of two pericentric inversions (Silva et al. 2015, pp. 4, Fig. A1 and A 2). This variation in fundamental number occurs in different localities of Pará, state of Brazil (Silva et al. 2015). C-banding metaphases exhibited blocks of constitutive heterochromatin on the pericentromeric region of all autosomes. The X chromosome presented a pericentromeric heterochromatic block. The Y chromosome was almost entirely heterochromatic. G-banding was also performed. FISH with 18s rDNA sequences revealed signals of NORs on the short arm of five acrocentric pairs, and on the distal region of the long arm of a small acrocentric pair. FISH with telomeric sequences revealed signals exclusively at the ends of all chromosome arms and no interstitial signals were observed (Silva et al. 2015). The same diploid number was presented by Voss et al. (2001). Another fundamental number of 64 was reported by Silva et al. (2019) due to the presence of one acrocentric pair instead of a biarmed pair. The authors also reported a different morphology for the X chromosome, a medium-sized acrocentric.

Published as part of Moreira, Camila Do Nascimento, Ventura, Karen, Percequillo, Alexandre Reis & Yonenaga-Yassuda, Yatiyo, 2020, A review on the cytogenetics of the tribe Oryzomyini (Rodentia: Cricetidae: Sigmodontinae), with the description of new karyotypes, pp. 1-111 in Zootaxa 4876 (1) on page 34, DOI: 10.11646/zootaxa.4876.1.1, http://zenodo.org/record/4423612