Mapping the distribution of the telomeric sequence (T(2)AG(3))(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 ka ryotype for the marsupial family Macropodidae (kangaroos and wallabies). Th e swamp wallaby, Wallabia bicolor, has the most derived macropodid karyotyp e with the lowest chromosome number (2n = 10 female, 11 male), and a multip le sex chromosome system (XX female, XY1Y2 male). All but one of the W. bic olor chromosomes are fusion chromosomes. Two of these chromosomes, the X ch romosome and chromosome 1, are composed of three plesiomorphic Thylogale-li ke chromosomes. The distribution of the vertebrate telomeric sequence (T(2) AG(3))(n) was examined by fluorescence in situ hybridization (FISH) in both species and a 'map' of non-telomeric (T(2)AG(3))(n) sites on W. bicolor ch romosomes relative to Thylogale chromosomes was constructed. (T(2)AG(3))(n) signals were observed at six fusion sites in the four fusions chromosomes examined, indicating that the (T(2)AG(3))(n) sequence is consistently retai ned during fusions. The distribution of the interstitial signals on the lon g arm of chromosome 1 of W. bicolor and the X chromosome suggests how a com bination of inversions, fusions and centromeric transpositions have resulte d in interstitial telomeric sequence.