Chromosome painting in marsupials: genome conservation in the kangaroo family

In order to deduce the ancestral genome arrangement in the karyotypically d iverse marsupial family Macropodidae, and to assess chromosome change in th is family, chromosome-specific paints from the tammar wallaby (2n = 16) wer e hybridized to metaphase spreads from the two species proposed to represen t the 2n = 22 ancestral karyotype, as well as species with derived 2n = 20 and 2n = 14 karyotypes. Identical patterns were observed in the two 2n = 22 species, from which the rearrangements to form the three derived karyotype s may be easily deduced to be 1, 3 and 4 different fusions, respectively. T he identical Thylogale and Dorcopsis genomes may both be used to represent the pleisiomorphic macropodid chromosome complement. Variation in the X chr omosome was also investigated by hybridizing an X-Y shared tammar wallaby 1 2-kb repeat element to chromosomes from the other four macropodid species, finding that it hybridized only to the most closely related species, and th erefore is of recent origin.