Sex chromosome-autosome translocations in the leaf-nosed bats, family Phyllostomidae. I. Mitotic analyses of the subfamilies Stenodermatinae and Phyllostominae.

Mitotic analyses using RBA- and C-banding were performed on Stenodermatine bats with X-autosome (XY1Y2) and X- and Y- autosome (neo-XY) translocations. RBA-banded metaphases of females revealed differential replication of the inactive X chromosome. An early replicating band comprises the short arm of the X, and an intermediate replicating band is located interstitially on the long arm. The early replicating short arm has a homologous counterpart either in the form of a free autosome (the Y2) or as part of the Y. Both the "autosomal" short arm of the X and its homologue fused to the Y are C-band negative and behave autonomously from the remainder of the sex chromosomes. They are separated from X and Y chromatin by centromeric heterochromatin which presumably acts as a barrier. The intermediate replicating region of the long arm of the X is also present in the subfamily Phyllostominae. In both subfamilies this region lacks a homologous counterpart. However, it may also represent a translocated autosome which, unlike the short arm of the X, is not separated from the inactive X by centromeric heterochromatin. Its intermediate replication time may represent a retarded replication due to its juxtaposition to late replicating X chromatin. These data are discussed in light of the theory of the evolution of sex chromosome heteromorphism, specifically as it applies to mammals.