Scientists have reconstructed the woolly mammoth’s genetic code in unprecedented detail after discovering fossilized chromosomes in the skin of a 52,000-year-old carcass preserved in Siberian permafrost.
The mammoth’s enormous mane led scientists to name it after Chris Waddle, the former England footballer with the mullet. After death, it was lyophilized, a process that preserved the 3D structure of the chromosomes in the animal’s skin.
Armed with the ancient genetic material, scientists were able to assemble the mammoth genome, determine that it had 28 pairs of chromosomes, and see which genes were turned on or off, details that are key to understanding what it meant to be a mammoth.
Professor Erez Lieberman Aiden, director of the Center for Genome Architecture at Baylor College of Medicine in Houston, said the samples were “a new kind of fossil” that “preserved biomolecules for a long time” and contained much more information than those studied. before.
Dr. Olga Dudchenko, also from Baylor, said the discovery of the fossil chromosomes was a “game changer” because knowing the shape of an organism’s chromosomes allowed the complete DNA sequence of an extinct creature to be assembled and provided insights into their biology that were previously unknown. range.
An international team of researchers tested dozens of samples over five years before striking gold with a piece of skin taken from behind the ear of a mammoth excavated in northern Siberia in 2018. They believe the animal’s skin spontaneously freeze-dried shortly after death, preserving the tissue through a process similar to the for beef production.
The mammoth was named Chris Waddle when scientists who found the carcass noticed its impressive mane. “It is not clear that this is the exact hairstyle that the mammoth had when it was alive,” Dudchenko said. “And later it turned out that the mammoth was a female.
Analysis of the skin revealed that the 3D structure of the mammoth chromosomes was preserved in the dehydrated cells after they were transformed into a robust glass-like material. Once formed, the fossil specimens, labeled chromoglass, could last for millions of years, the researchers wrote in the journal Cell. In a series of unusual tests, scientists have shown that DNA can survive in tissues that have been run over by a car, hit by a baseball or fired from a shotgun.
Until now, ancient DNA obtained from extinct species has been highly fragmented. The snippets allow scientists to detect subtle genetic differences between extinct animals and their living relatives, but little else. In contrast, the new samples contain hundreds of millions of letters of code that reveal the large-scale structure of the genome.
In addition to being able to assemble the mammoth genome and count its chromosomes, the researchers found that the arrangement of chromosomes inside the cells showed which genes were activated, including genes associated with wool and cold tolerance.
The work supports plans to bring back the woolly mammoth, which scientists hope to achieve by rewriting the Asian elephant’s genome to match that of the mammoth. “Is it enough to become extinct? Probably not,” said Professor Marc Marti-Renom of the National Center for Genomic Analysis in Barcelona. “If one wants to transform a modern elephant into a mammoth, there is still quite a bit of work to be done. It’s a step forward in that direction.”
Scientists hope to find more fossil chromosomes in other extinct animals and in Egyptian mummies, many of which may already exist in museum collections.
Professor Adrian Lister, a mammoth expert at the Natural History Museum who was not involved in the study, described the research as “amazing”.
“Until now, ancient DNA research has relied on a ‘soup’ of small DNA fragments extracted from ancient tissues,” he said. “In the case of this mammoth carcass preserved in Arctic permafrost, scientists were able to obtain intact chromosomes with their DNA and intact chromatin protein essential for their function.”
He added: “This new work opens up great new possibilities for investigating the biology of extinct species. This exceptional preservation can be found in fossils much older than the 51,000-year-old mammoth, back to 2 million years ago, opening up the possibility of investigating the biology of much older extinct species and their relationship and differences from living relatives.