Karyotypes and Chromosome Polymorphism in Brazilian Rodents

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Abstract
Karyotypes of ten species of Brazilian rodents, collected in the State of Sao Paulo are presented: Akodon (Thaptomys) nigrita nigrita (2 n = 52); Zygodontomys lasiurus (2 n = 34); Thomasomys (Delomys) dorsalis collinus (2 n = 82); Oxymycterus sp1. and Oxymycterus sp2. (2 n = 54); Calomys sp. (2 n = 66); Clyomys laticeps laticeps (2 n = 34); Euryzygomatomys guiara (2 n = 46); Proechimys iheringi iheringi (2 n = 62, 64) and Echimys sp. (2 n = 90). The analysis of 30 specimens of Zygodontomys lasiurus disclosed a diploid number of 34 chromosomes. In three female specimens the length of one X chromosome was half the length of the other, due to a deletion on the long arm. In this case, the probably normal X chromosome presents a subterminal centromere and is morphologically identified. A heteromorphic autosomal pair was found in Oxymycterus sp1. and Oxymycterus sp2. In Proechimys iheringi iheringi the male had a pair of dot chromosomes less than the female; such chromosomes might be centric fragments resulting from reciprocal translocations which behave as supernumeraries.