Neacomys sp. A

Karyotype: 2n = 58 and FN = 68. Autosomal complement: six metacentric and submetacentric pairs of medium size, and 22 acrocentric pairs (one large and the remaining medium to small decreasing in size). Sex chromosomes: X, a medium submetacentric; Y, a small submetacentric. C-banding metaphases exhibited blocks of constitutive heterochromatin on the pericentromeric region of all autosomes, three biarmed pairs presented a conspicuous heterochromatic block. The X chromosome presented the short arm entirely heterochromatic. The Y chromosome was almost entirely heterochromatic. G-banding was also performed. FISH with telomeric sequences revealed signals exclusively at the ends of all chromosome arms and no interstitial signals were observed (Silva et al. 2017, pp. 6, Fig. 2). According to the authors, this karyotype was similar to those described by Silva et al. (2015) for specimens identified as Neacomys sp. (2n = 58 / FN = 70, and 2n = 58 / FN = 64). The comparative analysis of C-banding revealed that the difference among the three karyotypes were due to blocks of heterochromatin affecting the number of chromosome arms (Silva et al. 2017).