A review on the cytogenetics of the tribe Oryzomyini (Rodentia: Cricetidae: Sigmodontinae), with the description of new karyotypes Author Moreira, Camila Do Nascimento Author Ventura, Karen Author Percequillo, Alexandre Reis 0000-0001-9490-5457 cmoreirabio@gmail.com Author Yonenaga-Yassuda, Yatiyo text Zootaxa 2020 2020-11-06 4876 1 1 111 journal article 7983 10.11646/zootaxa.4876.1.1 4ee8b608-7c73-4980-9e86-3e3719e91c7f 1175-5326 4423612 190EC586-E14B-4AEF-A5EF-3DA401656159 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 ).