Sex-chromosome variability in Zygodontomys lasiurus (Rodentia, Cricetidae).

Specimens of Zygodontomys lasiurus have been collected in different regions of Brazil such as the State of Sao Paulo (Yonenaga 1972, 1975), Amazon region (Bar roso and Barros 1978), and the State of Pernambuco, in the Northeast region (Maia and Langguth, in press). The basic karyotype (2n=34) includes 32 autosomes consisting of 15 acrocentric pairs and one small metacentric pair. The X chromo -some is a medium sized acrocentric morphologically undistinguishable from the autosomes of equal size, and the Y is a small submetacentric. Some female spe cimens from Sao Paulo had slightly different karyotype having heteromorphic sex chromosome pair (Yonenaga 1972, 1975). One of the X chromosomes presented a subterminal centromere while the other had 1/3 of the length of the first probably due to a gross deletion in the long arm. A polymorphism (2n=34, 33) due to a centric fusion between autosomes was also found in specimens from Pernambuco (Maia and Langguth 1981). This paper presents further data on the sex chromosomes in Z. lasiurus from the State of Sao Paulo. The G and C-banding patterns were studied and the silver stained nucleolus organizer regions (NORs) were detected in the karyotype.