Chromosome evolution in kangaroos (Marsupialia : Macropodidae): Cross species chromosome painting between the tammar wallaby and rock wallaby spp. with the 2n=22 ancestral macropodid karyotype

Marsupial mammals show extraordinary karyotype stability, with 2n = 14 cons idered ancestral. However, macropodid marsupials (kangaroos and wallabies) exhibit a considerable variety of karyotypes, with a hypothesised ancestral karyotype of 2n = 22. Speciation and karyotypic diversity in rock wallabie s (Petrogale) is exceptional. We used cross species chromosome painting to examine the chromosome evolution between the tammar wallaby (2n = 16) and t hree 2n = 22 rock wallaby species groups with the putative ancestral karyot ype. Hybridization of chromosome paints prepared from flow sorted chromosom es of the tammar wallaby to Petrogale spp., showed that this ancestral kary otype is largely conserved among 2n = 22 rock wallaby species, and confirme d the identity of ancestral chromosomes which fused to produce the bi-armed chromosomes of the 2n = 16 tammar wallaby. These results illustrate the fi ssion-fusion process of karyotype evolution characteristic of the kangaroo group.