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 Oecomys sp. 1 Karyotype: 2n = 54 and FN = 84. Autosomal complement: 16 biarmed pairs large to small decreasing in size, and 10 acrocentric pairs medium to small decreasing in size. Sex chromosomes: X, a large acrocentric; Y, a medium submetacentric ( Fig. 14A ). C-banding metaphases exhibited blocks of constitutive heterochromatin on the pericentromeric region of the majority of autosomal pairs. One medium submetacentric pair presented a pericentromeric heterochromatin block that extend to the short arm and one small acrocentric pair presented an interstitial C-band on its long arm. The X chromosome presented a conspicuous pericentromeric heterochromatic block and an interstitial lightly stained C-band on its long arm. The Y chromosome was almost entirely heterochromatic ( Fig. 14B ). Gbanding was performed to allow the correct identification of all homologous pairs ( Fig. 14C ). FISH with telomeric sequences revealed signals exclusively at the ends of all chromosome arms and no interstitial signals were observed ( Fig. 14D ). We compare the karyotype of Oecomys sp. 1 (2n = 54, FN = 84) with O. rutilus (2n = 54, FN = 90) from Rio Negro, Amazonas state of Brazil . These two complements differ mainly by the presence of three medium to small acrocentric pairs in Oecomys sp. 1, instead of three biarm pairs in O. rutilus , and by the morphology of X chromosome. Also, the karyotype of Oecomys sp. 1 presents more conspicuous heterochromatic C-band than O. rutilus . The G-band patterns between the two karyotype were equally distinct. Based on these comparative analyses, we suggested that the species mentioned here as Oecomys sp. 1 was distinctly from O. rutilus . In addition, the same diploid and fundamental number of Oecomys sp. 1 was mentioned by Gomes-Júnior et al . (2016) (unpublished data from T. Lira). However, as these authors provided no additional information, a more thorough comparison was not possible. Nevertheless, as the karyotype mentioned by Gomes-Júnior et al . (2016) were from populations from Rio Cuieiras, Amazonas state of Brazil , it was likely that they may belong to the same species.