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Researchers have sequenced the oldest known DNA in the world. Using material from the Early and Middle Pleistocene sub-eras, analysis of ancient DNA shatters the world’s oldest sequenced DNA record. It comes from mammoth remains found in Siberian permafrost and proves that under the right conditions ancient DNA can survive over a million years.
But the analysis of this very old DNA also depends on researchers who have the right technology. Fortunately, an international team led by researchers at the Center for Palaeogenetics in Stockholm, Sweden, had cutting-edge sequencing and bioinformatics technology. A Nature A report for the new document says researchers have pushed current technology to its limits to allow the extraction of ancient DNA strands from mammoth teeth that had been preserved in Siberian permafrost. Lead author of the nature study Love Dalén, professor of evolutionary genetics at the Center for Paleogenetics, notes that the science team were lucky, saying:
“It’s not like everything in permafrost is still working. The vast majority of samples contain crappy DNA.
How ancient mammoth DNA broke records
The discovery is truly amazing because after an organism dies, its chromosomes gradually become smaller and smaller and in most cases the extremely old DNA strands have become so small that they have lost all of their contents. informational. But a new article published in the journal Nature shows that the team succeeded in obtaining 49 million base pairs of nuclear DNA from a 1.65 million year old tooth found near a village called Krestovka (the tooth was also nicknamed Krestovka ). They also extracted 884 million base pairs of ancient DNA from a 1.3 million year old tooth they call Adycha and 3.7 billion base pairs of DNA from a mammoth tooth. 600,000-year-old woolly tree that they called Chukochya. The three mammoth remains were discovered in the 1970s and are part of the collection of the Russian Academy of Sciences in Moscow.
Love Dalén and co-lead author Patrícia Pečnerová with a mammoth tusk on Wrangel Island. (Credit: Gleb Danilov)
The Nature A report explains that the ancient mammoth DNA study did not reveal the oldest biomolecular information in the fossil record – it’s a protein sequenced in 2016 from 3-year-old ostrich eggshells. , 8 million years ago from Tanzania. Second is a protein sequence from a 1.77 million year old rhino tooth from Georgia, which was analyzed in 2019. However, while the proteins are more resistant and can survive in extremely ancient fossils coming from places without permafrost, it is not as useful as DNA for researchers who wish to study the ancestry of an organism.
This is just one of the reasons the new mammoth DNA study is so important – it contains genetic information that was not available in older protein samples.
A second reason the study made headlines is that it broke up ancient DNA from a genome of a 560,000 to 780,000 year old horse leg bone found in the Yukon Territory in Canada for the oldest DNA sequence. Putting the age of the mammoth samples into context, Dalén said:
“This DNA is incredibly old. The samples are a thousand times older than Viking remains, and even predate the existence of humans and Neanderthals. “
The first example of hybrid speciation in ancient DNA
The new study also boosted researchers’ ability to track the evolutionary process of speciation – the formation of new and distinct species. A Nature The press release says this process generally occurs “over periods of time believed to be beyond the limits of DNA research.”
A woolly mammoth tusk found in the bed of a cove on Wrangel Island in 2017 (Photo credit: Love Dalén)
Nonetheless, scientists’ study of mammoth DNA suggests that there were not one, but two different lineages of mammoths living in the Early Pleistocene in the region of what is now Eastern Siberia. Adycha and Tchoukochya are believed to be members of a species that spawned the Woolly Mammoth, but Krestovka appears to be from an unknown and possibly entirely new line of mammoths. Tom van der Valk, lead author of the study and bioinformatician at the University of Uppsala in Sweden, explains the researchers’ shock at the discovery:
“It completely surprised us. All previous studies have indicated that there was only one species of mammoth in Siberia at that time, called the Steppe mammoth. But our DNA analyzes now show that there were two different genetic lines, which we call here the Adycha mammoth and the Krestovka mammoth. We can’t say for sure yet, but we believe these may represent two different species.
In their study, the researchers suggest that Krestovka’s genome may have diverged from other mammoths 2.66 to 1.78 million years ago. They also believe that this line of mammoths “was ancestral to the first mammoths to colonize North America.” It seems that the Colombian mammoths of North America ( Mammuthus columbi ) can trace half of their ancestry to woolly mammoths and the other half to the previously unrecognized Krestovka line of mammoths.
The Nature The press report says this means the new study also provided the first evidence of “hybrid speciation” – a new species forming by admixture – found in ancient DNA. Study co-lead author Patrícia Pečnerová, an evolutionary biologist at the Swedish Museum of Natural History, says the team believes that “the Colombian mammoth, one of the most iconic species of the American Ice Age of the North, evolved through hybridization that took place about 420 thousand years ago. ”
How far can researchers go?
Finally, the ancient study of mammoth DNA inspired Dalén to analyze more samples of permafrost animals dating back over a million years. Next on his list? Musk oxen, moose and lemmings. But the professor of evolutionary genetics knows there is an age limit that he cannot cross when analyzing ancient DNA – 2.6 million years old – “That’s the limit of permafrost. Before that it was too hot, ”he says.
Woolly mammoth tusk emerging from permafrost on central Wrangel Island, located in northeast Siberia. (Credit: Love Dalén)
Top image: The illustration is a reconstruction of the steppe mammoths that predated the woolly mammoth, based on the genetic knowledge we now have of the Adycha mammoth. Source: Beth Zaiken / Center for Paleogenetics
By Alicia McDermott
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