The chromosomes of the New World flying squirrels (Glaucomys volans and Glaucomys sabrinus) with special reference to autosomal heterochromatin.

There are two species of New World flying squirrels included in the genus Glaucomys: G. sabrinus, the northern flying squirrel, and G. volans, the southern flying squirrel. During a study of local rodents around Hanover, New Hampshire, several flying squirrels were caught and their chromosomes were analyzed. The occurrence, in this region, of both species allowed a comparative study of their respective karyo types. Since the fossil record of flying squirrels is scant and the early history of this group highly speculative, new insight was hoped to be gained into their taxo nomic relationship. Their identical karyotypes, in the presence of only minor morphologic differences, raises the question of whether their separation into two species is justified. During this study, analysis of the karyotypes revealed a striking fuzziness of some of the chromosomes (Fig. 1). Autoradiography showed these segments to be late replicating. While all animals of the two species studied possessed hetero chromatic blocs, the distribution of these segments on the autosomes varied; two different labelling patterns were found among adult animals of the same species. Other expressions of heterochromatin included the presence of large chromocenters in interphase nuclei and, cytologically, absence of pairing and crossing-over at meiosis.