Physical map of two tammar wallaby chromosomes: A strategy for mapping in non-model mammals
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Marsupials are especially valuable for comparative genomic studies of mammals. Two distantly related model marsupials have been sequenced: the South American opossum (Monodelphis domestica) and the tammar wallaby (Macropus eugenii), which last shared a common ancestor about 70 Mya. The six-fold opossum genome sequence has been assembled and assigned to chromosomes with the help of a cytogenetic map. A good cytogenetic map will be even more essential for assembly and anchoring of the two-fold wallaby genome. As a start to generating a physical map of gene locations on wallaby chromosomes, we focused on two chromosomes sharing homology with the human X, wallaby chromosomes X and 5. We devised an efficient strategy for mapping large conserved synteny blocks in non-model mammals, and applied this to generate dense maps of the X and ‘neo-X’ regions and to determine the arrangement of large conserved synteny blocks on chromosome 5. Comparisons between the wallaby and opossum chromosome maps revealed many rearrangements, highlighting the need for comparative gene mapping between South American and Australian marsupials. Frequent rearrangement of the X, along with the absence of a marsupial XIST gene, suggests that inactivation of the marsupial X chromosome does not depend on a whole-chromosome repression by a control locus.
Key wordscomparative mapping genomics marsupial X chromosome evolution
bacterial artificial chromosome
basic local alignment search tool nucleotide
fluorescence in-situ hybridization
kilo base pairs
mega base pairs
major histocompatibility complex
million years ago
polymerase chain reaction
radioactive in-situ hybridization
standard sodium citrate
X added region
X chromosome inactivation
X conserved region
X inactivation centre
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