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 Nectomys rattus Karyotype: 2n = 52 and FN = 52. Autosomal complement: one small metacentric pair and 24 acrocentric pairs large to small decreasing in size ( Gardner & Patton 1976 , pp. 13, Fig. 6B ; Maia et al . 1984 ; Yonenaga-Yassuda et al . 1988 ; Barros et al . 1992 ; Bonvicino et al . 1996 ; Silva & Yonenaga-Yassuda 1998a ; Andrades-Miranda et al . 2001b ; Oliveira & Langguth 2004 ; Bonvicino et al . 2005 ). Sex chromosomes: X chromosome presented three different morphologies, a large submetacentric, a large subtelocentric, and a large to medium acrocentric; Y chromosome presented two different morphologies, a medium submetacentric, and a medium to small subtelocentric ( Gardner & Patton 1976 ; Maia et al . 1984 ; Yonenaga-Yassuda et al . 1988 ; Barros et al . 1992 ; Silva & Yonenaga-Yassuda 1998a ; Andrades-Miranda et al . 2001b ; Bonvicino et al . 2005 ). A different diploid number of 53 to 55 were reported due to the presence of 1 to 3 supernumerary chromosomes. Three different types of supernumerary chromosomes were reported: a large subtelocentric, a medium submetacentric, and a small acrocentric ( Maia et al . 1984 ; Yonenaga-Yassuda et al . 1988 ; Barros et al . 1992 ; Silva & Yonenaga-Yassuda 1998a ; Andrades-Miranda et al . 2001b ). C-banding metaphases exhibited blocks of constitutive heterochromatin on the pericentromeric region of all autosomes. The X chromosome presented a large variability on the amount and distribution of heterochromatin that encompass the pericentromeric region, the entirely short arm, and sometimes a lightly band on its long arm. The Y chromosome presented a large variability on the amount and distribution of heterochromatin that encompass the pericentromeric region, the distal portion of the long arm, the whole long arm and a large part of the short arm. C-banding of B chromosomes presented different patterns on the distribution of heterochromatin: entirely heterochromatic, the long arm entirely heterochromatic, or a heterochromatic block on the end of the long arm. G- and R-banding were also performed ( Maia et al . 1984 ; Yonenaga-Yassuda et al . 1988 ; Silva & Yonenaga-Yassuda 1998a ). Multiple NORs, varying from two to fourteen were localized at the telomeric regions of the short arms of acrocentric pairs ( Yonenaga-Yassuda et al . 1988 ). FISH with telomeric sequences revealed signals exclusively at the ends of all chromosome arms and no interstitial signals were observed ( Silva & Yonenaga-Yassuda 1998a ).