The Platypus Genome
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If you didn't know it, decoding the platypus genome has long been an important goal for biologists seeking to understand the origins of mammal evolution.
The platypus looks as it if were assembled from spare parts, an animal so unusual it was thought to be a hoax when sent to Europe in the 18th century.
Although classified as mammals, they retain a number of primitive characteristics including egg-laying that are thought to have been passed down from mammal-like reptiles that lived over 300 million years ago. The egg-laying critter is a genetic mishmash -- part bird, part reptile and part lactating mammal. A study of the platypus genome of 2.2 billion base pairs spread across 18,500 genes, sequencing the genome of Glennie the female platypus, cost US$80 million and took several years to complete. The research involved more than 100 researchers worldwide.
The study, appearing in the journal Nature, gives scientists a new window into the genetic architecture of the earliest mammals.
Co-author of the Nature paper Professor Jenny Graves, from the Australian National University's (ANU) Comparative Genomics Research Group, says understanding the genome of the duck-billed platypus helps fill in the gaps of how mammals evolved.
The platypus is unique because it has a duck's bill, webbed feet, lives in water and lays eggs. Yet because it has fur and produces milk for its young it is considered a mammal.
Aquatic animals native to eastern Australia, platypuses have long perplexed biologists. The analysis confirms that the platypus comes from the earliest offshoot of the mammalian family tree, the group of animals called monotremes which includes the platypus and the closely related echidna is thought to have split from other mammals at least 166 million years ago.
That early divergence means platypus genes carry information from a transitional point on the evolutionary time line leading from reptiles to mammals.
The platypus is critical to helping us understand what genes were present in the ancestral reptilian lineage and how mammals evolved their particular traits.
A central goal of the study was to determine which platypus features may have been inherited from ancient reptilian ancestors and which evolved independently in the monotreme lineage.
For example, the researchers identified genes for egg yolk proteins shared only with reptiles and fish.
On the other hand, the set of mammalian genes responsible for lactation or milk production was also found in the platypus genome.
While milk production and giving birth to live young would seem to go hand in hand, the platypus genome shows that the two common mammalian traits evolved at very different points in evolutionary time.
The presence of the full repertoire of milk genes confirms that lactation evolved at least 166 million years ago, way before live-bearing.
But beyond those findings the platypus DNA was also found to include a number of genes not found in other mammals.
"The platypus is no more ancient than we are," Graves says.
"But the common ancestor was the intermediary between reptiles and mammals and the platypus gives us clues as to what our ancient ancestor looked like."
She says by comparing the platypus genome with the DNA of humans, kangaroos, mice and chickens, researchers can work out when genes and traits specific to mammals emerged.
"It's like being able to dig down in time," says Graves.
The platypus looks as it if were assembled from spare parts, an animal so unusual it was thought to be a hoax when sent to Europe in the 18th century.
Although classified as mammals, they retain a number of primitive characteristics including egg-laying that are thought to have been passed down from mammal-like reptiles that lived over 300 million years ago. The egg-laying critter is a genetic mishmash -- part bird, part reptile and part lactating mammal. A study of the platypus genome of 2.2 billion base pairs spread across 18,500 genes, sequencing the genome of Glennie the female platypus, cost US$80 million and took several years to complete. The research involved more than 100 researchers worldwide.
The study, appearing in the journal Nature, gives scientists a new window into the genetic architecture of the earliest mammals.
Co-author of the Nature paper Professor Jenny Graves, from the Australian National University's (ANU) Comparative Genomics Research Group, says understanding the genome of the duck-billed platypus helps fill in the gaps of how mammals evolved.
The platypus is unique because it has a duck's bill, webbed feet, lives in water and lays eggs. Yet because it has fur and produces milk for its young it is considered a mammal.
Aquatic animals native to eastern Australia, platypuses have long perplexed biologists. The analysis confirms that the platypus comes from the earliest offshoot of the mammalian family tree, the group of animals called monotremes which includes the platypus and the closely related echidna is thought to have split from other mammals at least 166 million years ago.
That early divergence means platypus genes carry information from a transitional point on the evolutionary time line leading from reptiles to mammals.
The platypus is critical to helping us understand what genes were present in the ancestral reptilian lineage and how mammals evolved their particular traits.
A central goal of the study was to determine which platypus features may have been inherited from ancient reptilian ancestors and which evolved independently in the monotreme lineage.
For example, the researchers identified genes for egg yolk proteins shared only with reptiles and fish.
On the other hand, the set of mammalian genes responsible for lactation or milk production was also found in the platypus genome.
While milk production and giving birth to live young would seem to go hand in hand, the platypus genome shows that the two common mammalian traits evolved at very different points in evolutionary time.
The presence of the full repertoire of milk genes confirms that lactation evolved at least 166 million years ago, way before live-bearing.
But beyond those findings the platypus DNA was also found to include a number of genes not found in other mammals.
"The platypus is no more ancient than we are," Graves says.
"But the common ancestor was the intermediary between reptiles and mammals and the platypus gives us clues as to what our ancient ancestor looked like."
She says by comparing the platypus genome with the DNA of humans, kangaroos, mice and chickens, researchers can work out when genes and traits specific to mammals emerged.
"It's like being able to dig down in time," says Graves.
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