The Monotremata lineage comprises platypus Ornithorhynchus anatinus and two genera of echidnas, short-beaked echidna Tachyglossus aculeatus and the long-beaked echidnas Zaglossus spp. Methods A male platypus fibroblast cell line was established from skin biopsy following standard procedures and in accordance with the Australian National University Animal Experimentation Ethics Committee permit no.
But we think they do have a male determining gene on a Y chromosome. Comparison of gene structure between the platypus Monotreme sex chromosomes in Hobart and C6orf58 genes. BAC-end sequences were not available in the database for all BACs, so several were obtained using the vector monotreme sex chromosomes in Hobart.
This suggests that the monotreme's XY chromosome system is unrelated to the therian XY system. Audio Player failed to load.
Bottom: G-banded female karyotype of T. Ten chromosomes are completely conserved between echidna and platypus. Homology between platypus and echidna chromosomes Ten chromosomes are completely conserved between echidna and platypus. Name required.
This result shows that X 2 is the third and Monotreme sex chromosomes in Hobart 2 the fourth in the chain.
Support Center Support Center. Figure Author information Article notes Copyright and License information Disclaimer. Gene assignments to platypus contigs and platypus chromosomes, together with human and chicken locations.
Cytogenet Genome Res. We note that platypus X 4 homologous to the echidna autosome Tac 27 separates these two clusters, while in echidna the homologues of platypus X 5 and Y 4 that is, Tac X monotreme sex chromosomes in Hobart and Y 4 that carry the MHC genes are adjacent to X 3 and Y 3 monotreme sex chromosomes in Hobart, suggesting that the insertion of X 4 in platypus was a later event in the evolution of the monotreme meiotic chain.
A revision of the genus Zaglossus Monotremata, Tachyglossidaewith description of new species and subspecies. In the echidna, there are only four Y chromosomes, compared to five in the platypus, suggesting that the small Y 5 in platypus has been completely lost in the echidna lineage [ 21 ].
Marsupial sex chromosomes break the rule that recombination during first meiotic prophase is necessary to ensure reductional segregation during first meiotic division. In therian mammals placentals and marsupials , sex is determined by an XX female: XY male system, in which a gene SRY on the Y affects male determination.
Thus, mapping platypus homologues of chicken Z genes revealed homology not only with platypus X 5 but also with platypus X 1 , Y 1 , X 2 and X 3.