NEW KARYOTYPES OF 2 RELATED SPECIES OF OLIGORYZOMYS GENUS (CRICETIDAE, RODENTIA) INVOLVING CENTRIC FUSION WITH LOSS OF NORS AND DISTRIBUTION OF TELOMERIC (TTAGGG)(N) SEQUENCES

Comparative cytogenetics studies based on conventional staining, CBG, GTG, RBG-banding, Ag-NOR staining, fluorescence in situ hybridization (FISH) using telomere probes, length measurements, and meiotic data we re performed on two related but previously undescribed cricetid specie s referred to as Oligoryzomys sp. 1 and Oligoryzomys sp. 2, respective ly, from Pico das Almas (Bahia: Brazil) and Serra do Cipo (Minas Gerai s: Brazil). Oligoryzomys sp. 1 had 2n = 46 and Oligoryzomys sp. 2 had 2n = 44, 44/45. Our banding data and measurements as well as FISH resu lts support the hypothesis that the difference between the diploid num bers occurred by centric fusion events. The karyotypes had conspicuous and distinguishable macro-and micro-chromosomes, and we suppose that the largest pairs (1, 2, and 3) have evolved from a higher diploid num ber because of successive tandem fusion mechanisms.