Autosomal and sex chromosomal polymorphisms with multiple rearrangements and a new karyotype in the genus Rhipidomys (Sigmodontinae, Rodentia)

Two diploid numbers and five karyomorphs were found in ten specimens of Rhi pidomys (Sigmodontinae, Rodentia) from three states in Brazil: 2n = 50 from Amazonas, and 2n = 44 from Mate Grosso and Bahia. CBG, GTG, and RBG-bandin g and Ag-NOR analyses were performed, as well as fluorescence in situ: hybr idization with (T(2)AG(3))(7) probes. The new diploid number of 2n = 50 was associated with two different fundamental numbers (FN = 71 and 72) as a re sult of pericentric inversions and addition/deletion of constitutive hetero chromatin. The samples from two localities Aripuana and Vila Rica) in the s tate of Mate Grosso shared 2n = 44 and FN = 52, but their karyotypes differ ed because of pericentric inversions. Although the single specimen from Bah ia had the same diploid number as the samples from Mate Grosso, its karyoty pe and FN were completely distinctive. Karyological comparison of GTG-bandi ng patterns revealed total homology between the karyotypes of the specimens from Bahia and Mate Grosso, implying the occurrence of 14 autosomal perice ntric inversions. Homologies between ten of the autosomes in the karyotypes with 2n = 50 (FN = 72) and 2n = 44 (from Vila Rica, MT) were demonstrated. The differentiation between 2n = 44 and 2n = 50 involved five pericentric inversions, addition/deletion of constitutive heterochromatin in both autos omes and sex chromosomes, at least one Robertsonian rearrangement and other not detected rearrangements. Despite the remarkable number of rearrangemen ts, interstitial telomeric sites (ITS) were not detected. Sex chromosomes a lso exhibited polymorphism in size and morphology.