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 rutilus Karyotype: 2n = 54 and FN = 90. Autosomal complement: 12 metacentric pairs large to small decreasing in size, three submetacentric pairs (two medium and one small), four subtelocentric pairs large to medium-sized, and seven acrocentric pairs medium to small decreasing in size. Sex chromosomes: X, a large submetacentric; Y, a medium subtelocentric. C-banding metaphases exhibited blocks of constitutive heterochromatin, ranging from subtle to conspicuous, on the pericentromeric region of some chromosomal pairs. G-banding was also performed. NORs were localized at the telomeric regions of the short arms of one large and one small autosomal pair. FISH with 18S rDNA revealed signals at the telomeric regions of the short arms of one large and one small autosomal pair, while FISH with 5S rDNA revealed signals at the pericentromeric region of one large autosomal pair. FISH with telomeric sequences revealed signals exclusively at the ends of all chromosome arms and no interstitial signals were observed ( Gomes-Júnior et al . 2016 , pp. 412, Fig. 5 ).