Genome of the platypus
Pask, Andrew J. Department of Zoology, University of Melbourne, Melbourne, Victoria, Australia.
- Sequencing the platypus genome
- Venom genes
- Tooth genes
- Immune genes
- Genomic imprinting
- Sex determination
- Links to Primary Literature
- Additional Readings
The platypus (Ornithorhynchus anatinus) [Fig. 1] is a true mammal, possessing fur and producing milk in females to nurture their young. Although the platypus lactates, it does not have nipples like other mammals. Instead, the young drink milk secretions from patches of abdominal skin. Moreover, platypuses possess many unique characteristics that have fascinated and perplexed biologists since their discovery. Most notable is the manner in which they reproduce. Unlike other mammals, members of the monotreme lineage (to which the platypus belongs) lay eggs. Platypus eggs hatch about 11 days after being laid, and the young are fed milk for the next 4 months of their development. Platypuses also have a unique system for determining the sex of their offspring. Whereas almost all mammals have an X–Y sex chromosome system, the platypus has five X and five Y chromosomes that share almost no similarity to the human X and Y. Furthermore, the platypus is the only known mammal with electroreception, which enables the platypus to sense electric fields generated by other animals. The platypus uses this ability to locate food sources, such as crayfish, while foraging underwater. In addition, the platypus is a venomous mammal. Although venom is not uncommon in other vertebrate lineages, it is rare in mammals. The male platypus has specialized spurs on its hind limbs that are used to deliver the venom. A dose of the venom, which is not lethal to humans, is so excruciatinly painful that the victim may be incapacitated. The exceptional features of its biology therefore make the platypus genome a particularly interesting and unique resource in its own right. However, the platypus is an even more important resource because of its unique evolutionary origin. The monotremes have been evolving independently from the rest of the mammals, including humans, for over 166 million years (Fig. 2), making them our most distant mammalian relatives. By analyzing the genome of the platypus, it is possible to gain important insights into the evolution and development of the human genome.
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