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. E Karyotype: 2n = 62 and FN = 60. Autosomal complement: 30 acrocentric pairs (one large and the remaining medium to small decreasing in size). Sex chromosomes: X, a medium acrocentric; Y, a small acrocentric. C-banding metaphases exhibited blocks of constitutive heterochromatin on the pericentromeric region of all autosomes. The X chromosome presented a pericentromeric heterochromatic block. The Y chromosome was almost entirely heterochromatic. G-banding was also performed ( Silva et al . 2019 , pp. 7, Fig. 2D ). Maps of chromosomal homology were established between seven karyotypes of Neacomys species ( N. paracou (2n = 56, FN = 64); N. spinosus (2n = 64, FN = 68); Neacomys sp. (cytotype 1, 2n = 58, FN = 70; and cytotype 2, 2n = 58, FN = 64); Neacomys sp. A (2n = 58, FN = 68); Neacomys sp. B (2n = 54, FN = 66); and Neacomys sp. E (2n = 62, FN = 60)) by using whole chromosome probes of H. megacephalus . The results showed that chromosome diversity between these species were due to 17 fusion/fission events, one translocation, pericentric inversions on four syntenic blocks, and six syntenic autosomal blocks with amplification/deletion of constitutive heterochromatin ( Silva et al . 2019 ). We also presented two different karyotypes for the genus, mentioned here as Neacomys sp. 1 and Neacomys sp. 2. The cytogenetic analyzes was performed for specimens collected on the Rio Japurá and Rio Içá, Amazonas state of Brazil ( Table 1 ).