The Chromosomes of the New World Flying Squirrels (Glaucomys volans and Glaucomys sabrinus) with Special Reference to Autosomal Heterochromatin

Abstract

The chromosome complement of both species of New World flying squirrels, Glaucomys volans and Glaucomys sabrinus, comprise 48 chromosomes, with identical karyotypes. The northern flying squirrel (Gl. sabrinus) distinguishes itself from its southern counterpart (GlL volans) mainly by different geographical distribution and by minor skeletal and coat differences. The discrete morphological differences and the identical karyotypes suggest that the two animals are taxonomically closely related.
Autoradiographic studies of somatic chromosomes have revealed the presence of large blocs of autosomal heterochromatin in both species. This heterochromatin was expressed at mitosis by a particular fuzziness of the respective chromosome segments, at interphase as large chromocenters, and at meiosis by heteropycnosis during the first prophase and by diakinetic figures suggesting absence of pairing. The meiotic findings are interpreted as indirect evidence of genetic inactivity of heterochromatin.
Autosomal heterochromatin was present in all animals studied (5) and in both species. Two different locations of heterochromatin were found in different animals of the same species (Gl. volans). The two late-labelling patterns appeared mutually exclusive and did not express tissue specificity. This variability of the location of heterochromatin remains unexplained.