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. 2 Karyotype: 2n = 64 and FN = 92. Autosomal complement: 15 biarmed pairs large to small decreasing in size, and 16 acrocentric pairs medium to small decreasing in size. Sex chromosomes: X, a large subtelocentric; Y, a medium acrocentric ( Fig. 15A ). C-banding metaphases exhibited blocks of constitutive heterochromatin on the pericentromeric region of the majority of autosomal pairs. The X chromosome presented the short arm entirely heterochromatic. The Y chromosome was almost entirely heterochromatic ( Fig. 15B ). G-banding was performed to allow the correct identification of all homologous pairs ( Fig. 15C ). FISH with telomeric sequences revealed signals at the ends of all chromosome arms, and additional telomeric sequences was found on the pericentromeric region of one medium submetacentric pair ( Fig. 15D ). We compare the karyotype of Oecomys sp. 2 (2n = 64, FN = 92) with O. auyantepui (2n = 64, FN = 110) from Rio Jatapú, Amazonas state of Brazil . These two complements were distinct mainly by the presence of nine acrocentric pairs in Oecomys sp. 2, instead of nine biarm pairs in O. auyantepui , and by the morphology of sex chromosome. Also, the karyotype of Oecomys sp. 2 presents more conspicuous heterochromatic C-band than O. auyantepui . The G-band patterns between the two karyotypes were equally distinct. In addition, Oecomys sp. 2 presented an interstitial telomeric sequence on the pericentromeric region of one medium submetacentric pair, while O. auyantepui presented an interstitial telomeric sequence on the centromeric region of the X chromosome. Based on these comparative analyses, we suggested that the species mentioned here as Oecomys sp. 2 was distinctly from O. auyantepui .