Mapping human X-linked genes in the phalangerid marsupial Trichosurus vulpecula

Karyotype relationships between distantly related marsupials from South America and Australia

Reciprocal chromosome painting and G-banding were used to compare the karyotypes of three Australian marsupials (Sminthopsis crassicaudata, Macropus eugenii, Trichosurus vulpecula) and one South American marsupial (Monodelphis domestica). The results revealed only a limited number of rearrangements between these species and that the four karyotypes can be described as different combinations of fifteen conserved segments. Five chromosomes are totally conserved between M. domestica (pairs 1, 2, 5, 8 and the X) and the presumed 2n = 14 Australian ancestral karyotype, while M. domestica pairs 3 and 6 and 4 and 7 would have been involved in fusion/fission rearrangements. Chromosome comparisons are presented in a chromosome homology map. Although the species studied diverged 70 million years ago, the karyotype of Monodelphis domestica is highly conserved in relation to those of Australian marsupials.

Characterization of the human Xq21.3/Yp11 homology block and conservation of organization in primates

The Xq21.3/Yp11 homology block on the human sex chromosomes represents a recent addition to the Y chromosome through a transposition event. It is believed that this transfer of material occurred after the divergence of the hominid lineage from other great apes. In this paper we investigate the structure and evolution of the block through fluorescence in situ hybridisation, contig assembly, the polymerase chain reaction, exon trapping, sequence comparison, and annotation of sequence data. The overall structure is well conserved between the human X chromosome and the Y chromosome as well as between the X chromosomes from different primates. Although the sequence data reveal a high level of nucleotide sequence identity for the human X and Y, there are regions of significant divergence, such as that around the marker DXS214. These are presumably the consequence of multiple rearrangements during evolution and are of particular importance with respect to the potential gene content in this segment of the interval.

Karyotype relationships between four distantly related marsupials revealed by reciprocal chromosome painting

Marsupial karyotypes have shown extensive conservation even between distantly related groups with a high diversity of life forms and reproductive biology. Banding analysis has been the main test for assessing their homologies and chromosome rearrangements. More recently, cross-species reciprocal chromosome painting has been developed and applied to several mammalian species and has shown homologies and rearrangements not revealed by banding analysis. Karyotype relationships between four marsupial species, Sminthopsis crassicaudata, Potorous tridactylus, Trichosurus vulpecula and Macropus eugenii, which are from different families in two orders, were investigated and presented in the form of comparative chromosome maps. These show that only a limited number of chromosomal rearrangements have occurred during their evolution. A karyotype phylogeny of the four marsupials was derived from these maps. A comparison between published gene location and the comparative chromosome maps for these species is presented and inconsistencies with previous gene mapping data indicated.

A linkage map of the ovine X chromosome

A genetic linkage map of the ovine X chromosome containing type I and type II markers has been constructed. The map contains 7 known gene markers and 14 microsatellite markers with a recombination length of 141.9 cM. Segregation of polymorphic markers was observed in a three-generation pedigree containing 480 animals. The maximum number of informative meioses was 912. Additional information was obtained for some markers by following segregation in the AgResearch International Mapping Flock, consisting of nine three-generation full-sib pedigrees. A pseudoautosomal region containing two markers has been identified at one end of the linkage map. Comparisons with mouse and human X chromosomes confirms the observation of Ohno (1973) that the gene content of the mammalian X chromosome is retained. In particular, the conserved grouping of the genes PHKA1, ATP7A, and XIST observed in both the human and the mouse X chromosome appears to be conserved in the sheep X chromosome, and XIST has been mapped to near the center of the chromosome. This study provides the first reported genetic linkage map combining both type I and type II markers for any ruminant X chromosome.