Genome Analysis of the Platypus


The sequencing of the platypus genome represents a significant milestone in the study of mammalian evolution. The platypus is an egg‐laying mammal, a member of the order Monotremata, the most divergent mammalian clade. It is the first monotreme to have its genome sequenced. Its unique evolutionary position, as an offshoot between the early divergence of birds and the later emergence of therian (eutherian and marsupials) mammals, provides an unrivalled opportunity to understand the evolution of all mammals. Much like the physical characteristics of the platypus, the platypus genome shows traces of an amalgamation of mammalian and reptilian traits. Key findings to emerge from the genome project include the complex evolution of mammalian sex chromosomes, the transition from egg‐laying to live birth in mammals, and the evolution of immune genes and venom molecules in this unique species.

Key concepts:

  • The platypus genome is the first monotreme genome to be sequenced. The platypus's unique evolutionary position, as an offshoot between the early divergence of birds and the later emergence of therian (eutherian and marsupials) mammals, provides an opportunity to increase our understanding of the evolution of all mammals.

  • The platypus genome shows features of mammalian and reptilian traits.

  • The platypus has 10 sex chromosomes, some of which have homology to chicken Z. The mechanism used by platypuses to determine sex is not known.

  • The density of interspersed repeat elements in the platypus genome is greater than that seen in any other vertebrate genome.

  • The platypus genome contains a high G+C content (45.4%).

  • The platypus possesses a unique class of over 40 000 noncoding RNA known as snoRTE.

  • The platypus contains the largest repertoire of V1R vomeronasal receptors seen in any vertebrate.

  • The platypus genome contains the major egg yolk protein, vitellogenin.

  • Key mammalian milk genes, caseins, are present in the platypus.

  • The platypus genome contains an expansion of antimicrobial peptide genes.

  • Platypus venom molecules evolved independently to snake venom molecules.

Keywords: platypus; genome; mammals; evolution; monotreme

Figure 1.

A phylogenetic tree of showing the divergence times of major clades during amniote evolution.



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Wong, Emily SW, Lillie, Mette, and Belov, Katherine(Apr 2010) Genome Analysis of the Platypus. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0021554]