CHROMOSOMES OF OCTOMYS-MIMAX AND OCTODONTOMYS-GLIROIDES AND RELATIONSHIPS OF OCTODONTID RODENTS

Octomys mimax possesses a chromosomal complement of 2n = 56, FN = 108, with heterochromatin restricted to the pericentric regions in all chr omosomes except one autosomal pair and the X chromosome. One chromosom e also has heterochromatin in a secondary constriction. C-bands of Oct odontomys gliroides reveal the clear presence of pericentric heterochr omatin on the X chromosome and six autosomal pairs. Lightly stained, p ericentric C-bands also were present in five other autosomes. A satell ite-bearing chromosome did not band. In both species, two active nucle olar organizing regions (AgNOR) were located at secondary constriction s. Based on chromosomal differences found among 0. mimax and other oct odontids, we hypothesize that the identical or similar 2n and FN obser ved for 0. mimax, Aconaemys fuscus, and some other octodontid species is a result of parallel evolution.