“We were expecting very few of these odor receptor genes because the animals spend the majority of their life in the water,” Warren says. Surprisingly, the researchers found the genome contains an expansion of genes that code for a particular type of odor receptor. The platypus swims with its eyes, ears and nostrils closed, relying on electrosensory receptors in its bill to detect faint electric fields emitted by underwater prey. Amazingly, duplications in the same genes appear to have evolved independently in venomous reptiles. When they analyzed the genetic sequences responsible for venom production in the male platypus, they found it arose from duplications in a group of genes that evolved from ancestral reptile genomes. The researchers also attempted to determine which characteristics of the platypus were linked to reptiles at the DNA level. Interestingly, the platypus lack nipples, so its young nurse through the abdominal skin. The researchers also found genes that support egg laying – a feature of reptiles – as well as lactation – a characteristic of all mammals. The chicken genome was chosen because it represents a group of egg-laying animals, including extinct reptiles, which passed on much of their DNA to the platypus and other mammals over the course of evolution. They found that the platypus shares 82 percent of its genes with these animals. “While we’ve always been able to compare and consider all of these creatures on the basis of their physical characteristics, internal anatomy and behavior, it’s truly amazing to be able to compare their genetic blueprints and begin to get a close-up look at how evolution brings about change,” Wilson says.Īs part of their analysis, the researchers compared the platypus genome with genomes of the human, mouse, dog, opossum and chicken. “But as weird as this animal looks, its genome sequence is priceless for understanding how mammalian biological processes evolved.” “At first glance, the platypus appears as if it was the result of an evolutionary accident,” says Francis S. The project was largely funded by the National Human Genome Research Institute, part of the National Institutes of Health, and includes scientists from the United States, Australia, England, Germany, Israel, Japan, New Zealand and Spain. The Nature paper analyzes the genome sequence of a female platypus named Glennie from New South Wales, Australia. The comparison also will allow scientists to date the emergence of genes and traits specific to mammals. “What is unique about the platypus is that it has retained a large overlap between two very different classifications, while later mammals lost the features of reptiles,” says Wes Warren, Ph.D., an assistant professor of genetics, who led the project.Ĭomparison of the platypus genome with the DNA of humans and other mammals, which diverged later, and the genomes of birds, whose ancestors branched off an estimated 315 million years ago, can help scientists fill gaps in their understanding of mammalian evolution. The platypus represents the earliest offshoot of the mammalian lineage some 166 million years ago from primitive ancestors that had features of both mammals and reptiles. “By comparing the platypus genome to other mammalian genomes, we’ll be able to study genes that have been conserved throughout evolution.” Wilson, Ph.D., director of the The Genome Center at Washington University and the paper’s senior author. “The fascinating mix of features in the platypus genome provides many clues to the function and evolution of all mammalian genomes,” says Richard K. Males possess hind leg spurs that can deliver pain-inducing venom to its foes competing for a mate or territory during the breeding season. One of only two mammals that lays eggs, the platypus also sports a duck-like bill that holds a sophisticated electrosensory system used to forage for food underwater. The platypus, classified as a mammal because it produces milk and is covered in a coat of fur, also possesses features of reptiles, birds and their common ancestors, along with some curious attributes of its own. An analysis of the genome, published today in the journal Nature, can help scientists piece together a more complete picture of the evolution of all mammals, including humans. Louis, has decoded the genome of the platypus, showing that the animal’s peculiar mix of features is reflected in its DNA. The duck-billed platypus: part bird, part reptile, part mammal - and the genome to prove it.Īn international consortium of scientists, led by Washington University School of Medicine in St.
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