Chromosomal polymorphism resulting from two pericentric inversions in Akodon arviculoides (2n = 14) has been described (Yonenaga, 1972a). In this paper the banding patterns are presented and identification of the inverted segments of the autosomal pairs 2 and 3 is made. The karyotype of Akodon sp., which varies in diploid number (2n = 24 and 25), is described and shown to be due to the presence of a small submetacentric chromosome in the 2n=25 individuals. The karyotypes of two 2n = 19 males studied show that they are hybrids between Akodon arviculoides (2n = 14) and Akodon sp. (2n = 24).
SUMMARY -Specimens of Rhipidomys collected in the states of Goias and SaoPaulo were analyzed cytogenetically and three karyotypes were identified, all with 2n = 44. A heterozygous pericentric inversion in pair 10, responsible for the variation in the fundamental number (FN = 48 and 49), was detected. Three types of X chromosomes were found: a large acrocentric (Xa) and two large submetacentrics (Xb and Xb + ). Comparisons between the G-banding patterns of our sample and of animals collected in other states allowed the conclusion that fourteen pericentric inversions are responsible for the karyotypical differences found.
SUMMARY-The chromosome complement and the G-, R-and C-banded karyotypes of 144 specimens of Oryzomys nigripes, sampled for the Brazilian states of Sao Paulo and Rio de Janeiro, was investigated. The diploid number found was 2n = 62 chromosomes and the fundamental number was FN = 82, 81 or 80. Three pairs of autosomes (pairs 3, 4 and 8) presented pericentric inversions, both in heterozygous and homozygous conditions. The X chromosome was either a large metacentric or a large submetacentric. The Y chromosome was visualized as a medium sized metacentric, a medium sized submetacentric or a large sized submetacentric. The possible causes of the variations observed in the sexual chromosomes are discussed.
Abstract. Cytogenetical data, including G-, C-bands and NORs distribution of Oxymycterus sp (2n = 54; FN = 64) captured in Distrito Federal, state of Goifis, Central Brazil are presented. Our results are compared to the karyotype information already available on this genus.
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