Oligoryzomys moojeni

Oligoryzomys moojeni

Karyotype: 2n = 70 and FN = 74. Autosomal complement: three small metacentric and submetacentric pairs, and 31 acrocentric pairs (one large and the remaining medium to small decreasing in size). Sex chromosomes: X chromosome presented two different morphologies, a large submetacentric, and a large subtelocentric; Y chromosome presented two different morphologies, a medium subtelocentric, and a small acrocentric (Andrades-Miranda et al. 2001a, pp. 1088, Fig. 4; Lima et al. 2003; Bonvicino et al. 2005; Weksler & Bonvicino 2005; Agrellos et al. 2012; Di-Nizo et al. 2015). Variation in fundamental number, with 72 and 76, was reported due to a pericentric inversion affecting one medium and one small autosomal pair (Lima et al. 2003; Di-Nizo et al. 2015). These variation in fundamental number occurs sympatrically on specimens collected in Goiás (FN = 72 and FN = 74) and Tocantins (FN = 74 and FN = 76), states of Brazil (Table 9, Fig. 17). C-banding metaphases exhibited blocks of constitutive heterochromatin on the pericentromeric region of almost all autosomal pairs. The X chromosome C-band encompasses from the pericentromeric region to the short arm almost entirely heterochromatic. The medium subtelocentric Y chromosome was entirely heterochromatic (Andrades-Miranda et al. 2001a; Lima et al. 2003). G-banding was also performed (Andrades-Miranda et al. 2001a; Lima et al. 2003; Di-Nizo et al. 2015). Multiple NORs, varying from three to ten were localized at the telomeric regions of the short arms on acrocentric pairs from large to small size (Andrades-Miranda et al. 2001a; Lima et al. 2003). FISH with telomeric sequences revealed signals exclusively at the ends of all chromosome arms and no interstitial signals were observed (Andrades-Miranda et al. 2001a). Whole chromosome probes of O. moojeni was made by flow cytometry, from sorted chromosomes of fibroblast cell culture. These probes were used to established maps of chromosomal homology between five Oligoryzomys species (O. fornesi, O. microtis, O. moojeni, O. nigripes and O. rupestris). The results showed extensive chromosomal rearrangement, such as pericentric inversions or repositioning of centromeres, Robertsonian rearrangements and tandem fusions/fissions, as well as gain/activation or loss/inactivation of centromeres and telomeric sequences have driven the huge genome reshuffling in these closely related species (Di-Nizo et al. 2015). In order to infer the chromosomal rearrangements directions that occurred during the karyotype evolution of Oligoryzomys, the authors compare these results of chromosome painting with a molecular phylogeny of the genus and concluded that chromosomal evolution of these species were associated with both, decrease and increase of diploid number.