"This suggested that the 10 platypus sex chromosomes used to be in a ring shape. "What surprised us is that, from the new sex chromosome sequences, we found the last Y chromosome, Y5 does not share many sequences with its pairing X5 chromosome, but with the first X chromosome of the chain, X1," says Qi Zhou. ![]() "The new genomes are a hugely valuable public resource for research in mammalian biology and evolution, with applications in wildlife conservation and even human health," says Frank Grützner at University of Adelaide in Australia. ![]() "With further laborious cytogenetic experiments, we improved the genome quality and mapped over 98% of the sequences into 21 autosomes, and 5X and 5Y chromosomes of platypus" says Guojie Zhang from BGI-Shenzhen and University of Copenhagen. The genetic makeup and the evolution process of such a complex and unique sex chromosome system remained unclear, because the previously published platypus genome is was from a female, and only a quarter of the sequences is was mapped onto chromosomes.Īn international team of researchers adopted a new sequencing technique (called PacBio, or third-generation sequencing) that can "read" the genome information for over 300-fold longer in length than the last-generation technique, and the new chromatin conformation capture technique that can connect and map the genomic sequences into the chromosome level. These ten sex chromosomes pair with each other in a head-to-tail manner and form a chain during meiosis when sperm cells develop. It turns out that male platypus has five pairs of XY chromosomes (named as X1Y1, X2Y2, etc.), and none of them are homologous to the XY of human or mouse. Previous work showed that platypus, although undoubtedly a mammalian species, have sex chromosomes that do not share the same origin with those of human. With its venom, duck-bill, egg, and milk, platypus features an extraordinary combination of reptiles, birds and mammals.
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