Sunday, October 24

Million-Year-Old Mammoth Genomes Set Ancient DNA Record | Genetics


Mammoth teeth buried in the Siberian permafrost for more than a million years have led to the sequencing of the world’s oldest known DNA, according to A study that illuminates the deep past with a genetic spotlight.

The researchers said the three tooth specimens – one approximately 800,000 years old and two more than a million years old – provided important information about the giant mammals of the ice age, including the ancient inheritance of, specifically, the Woolly mammoth.

The genomes surpass the oldest previously sequenced DNA, that of a horse dating from 560,000 to 780,000 years ago.

Love Dalén, a professor of evolutionary genetics at the Stockholm Center for Paleogenetics, was the lead author of the study, published in Nature. He 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. “

Mammoths were originally discovered in the 1970s in Siberia and had been kept at the Russian Academy of Sciences in Moscow.

Love Dalén and Patricia Pecnerova
Palentologists love Dalén and Patricia Pecnerova with a mammoth tusk on Wrangel Island, Arctic Ocean. Photograph: Gleb Danilov University of Stockholm / PA

The researchers first dated the specimens geologically, using comparisons to other species, such as small rodents, that are known to be unique at particular time periods and found in the same sedimentary layers.

This suggested that two of the mammals were ancient steppe mammoths over a million years old. The youngest of the trio is one of the first woolly mammoths ever found.

The team also extracted genetic data from small dust samples from each mammoth tooth, “essentially like a pinch of salt that you would put on your plate,” Dalén said at a news conference.

Although the material had broken down into very small fragments, the scientists were able to sequence tens of millions of chemical base pairs, which make up the DNA strands, and make age estimates from the genetic information.

This suggested that the oldest mammoth, named Krestovka, was even older than previously thought, at about 1.65 million years old, while the second, Adycha, was about 1.34 million years old, and the youngest , Chukochya, was 870,000 years old.

Dalén said that, regarding the older mammoth, the DNA dating process could indicate that the creature was probably around 1.2 million years old, as the geological evidence suggests. But it was possible that the specimen was older than that and had thawed from the permafrost at one point and then got stuck in a more recent layer of sediment.

Tom van der Valk of the Science for Life Laboratory, Uppsala University in Sweden, said that the DNA fragments were like a puzzle with millions of tiny pieces “much, much, much smaller than what you would get with the High-quality modern DNA. ” .

Using a genome from an African elephant, a modern relative of the mammoth, as a model for their algorithm, the researchers were able to reconstruct parts of the mammoth’s genomes.

The study found that the mammoth named Krestovka represented a previously unrecognized genetic lineage, which the researchers estimated diverged from other mammoths about two million years ago and was ancestral to those that colonized North America.

The study also traced the lineage from the million-year-old Adycha steppe mammoth to Chukochya and other more recent woolly mammoths.

The researchers also found genetic variants associated with life in the Arctic, such as hairiness, thermoregulation, fat deposits and cold tolerance in the older specimen, suggesting that mammoths were already hairy long before the woolly mammoth emerged.

Siberia has alternated between dry and cold ice age conditions and hot and humid periods. Now climate change is causing the permafrost to melt and reveal more specimens, Dalén said. However, there was a risk that, amid more rains, the debris could be washed away.

Dalén said that new technologies could allow the sequencing of even older DNA from remains found in permafrost, dating back 2.6 million years.

Researchers are interested in observing creatures such as the ancestors of the elk, musk ox, wolves and lemmings, to shed light on the evolution of modern species.

“Genomics has been pushed to the depths by the giants of the ice age; the small mammals that surrounded them could soon have their day, too,” said Alfred Roca, a professor in the department of animal sciences at the University of Illinois, USA. In a comment published in Nature.


www.theguardian.com

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