KARYOTYPE AND CHROMOSOMAL-POLYMORPHISM OF AN UNDESCRIBED AKODON FROM CENTRAL BRAZIL, A SPECIES WITH THE LOWEST KNOWN DIPLOID CHROMOSOME-NUMBER IN RODENTS

The diploid chromosome number of 2n = 10 found in a new species of Ako don (Cricetidae, Rodentia) from two localities of the state of Mato Gr osso, Central Brazil, represents the lowest chromosome number known fo r rodents. One female with nine chromosomes due to sex chromosome mono somy (2n = 9,XO) was also found. The karyotype comprises two large met acentric pairs (1 and 2); one large polymorphic pair (3), which could be acrocentric, submetacentric, or heterozygous as a result of a peric entric inversion; and one minute metacentric pair (4). The sex determi nation is of the XX/XY type. CBG, GTG, and RBG banding patterns, Ag-NO Rs, and meiotic data are presented. Fluorescence in situ hybridization with a (TTAGCG)(7) repeat as a probe revealed interstitial telomeric bands (ITBs) in two of the large pairs.