Mapping the Distribution of the Telomeric Sequence (T2AG3)n in the Macropodoidea (Marsupialia), by Fluorescence In Situ Hybridization. I. The Swamp Wallaby, Wallabia Bicolor

Thylogale spp. (pademelons) retain the plesiomorphic (ancestral) 2n = 22 karyotype for the marsupial family Macropodidae (kangaroos and wallabies). The swamp wallaby, Wallabia bicolor, has the most derived macropodid karyotype with the lowest chromosome number (2n = 10 female, 11 male), and a multiple sex chromosome system (XX female, XY1Y2 male). All but one of the W. bicolor chromosomes are fusion chromosomes. Two of these chromosomes, the X chromosome and chromosome 1, are composed of three plesiomorphic Thylogale-like chromosomes. The distribution of the vertebrate telomeric sequence (T2AG3)n was examined by fluorescence in situ hybridization (FISH) in both species and a 'map' of non-telomeric (T2AG3)n sites on W. bicolor chromosomes relative to Thylogale chromosomes was constructe d. (T2AG3)n signals were observed at six fusion sites in the four fusions chromosomes examined, indicating that the (T2AG3)n sequence is consistently retained during fusions. The distribution of the interstitial signals on the long arm of chromosome 1 of W. bicolor and the X chromosome suggests how a combination of inversions, fusions and centromeric transpositions have resulted in interstitial telomeric sequence.