May 21, 2022

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Reviving an extinct species? Technically impossible

Woolly mammoth, dodo, steppe bison, and cave lions are destined to live forever only in museums and science books: according to one of them A study published in Current Biology We’re a long way from being able to revive extinct animal species by interfering with the DNA of their modern descendants because, even if we succeed, we’ll get samples Just seemingly similar to the missing.

claw concept eradicate extinction or biological resurrectioni.e. the artificial creation of an organism belonging to an extinct species, came from one of the rodents that disappeared from the circulation in the early twentieth century, the Maclear rat (Ratus McCleary).

This mammal, which disappeared in 1908 from Christmas Island, a patch of land located 1,200 kilometers west of the Australian coast, is in theory the ideal candidate for revival thanks to human intervention. We know his DNA well, thanks to several preserved samples, and he is genetically very close to that of the brown rat (norwegian rat) – pantigana – whose entire genome has been sequenced.

Ending Extinction: How To Do It. To revive extinct species, it is necessary to sequence their DNA and replace missing sequences from the code with very similar sequences taken from surviving relatives – a process made possible by advances in Crispr/Cas9 technology. With the full code we proceed to the creation of embryos with a “hybrid” genome that we try to highlight through a surrogate mother, as similar to the extinct animal as possible (eg a female Asian elephant to the woolly mammoth).

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Rape of McClear, an extinct resident of Christmas Island.
© Wikimedia Commons

Reconstruct the patient. In the new study, Tom Gilbert, an evolutionary geneticist at the University of Copenhagen, attempted to understand whether the process was theoretically possible by starting with a small “easier” animal like the extinct rat. He extracted rodent DNA from two preserved samples and sequenced them multiple times in order to derive as complete a genome as possible.

The problem with ancient DNA is that it breaks down into very small pieces, which are impossible to put together completely. So Gilbert used the Norwegian rat genome as a “model guide” to reconstruct a code as similar as possible to the missing rat’s code.

phantom genes. Despite all efforts, it is comparing Cut and sew DNA They were obtained artificially and the original version showed that 5% of the genome of Maclear rats (about 2,500 genes out of 34,000) was still missing, and not reconstructive. Gilbert explained: “We’ve preserved every possible piece of DNA – Gilbert explained – and yet there’s 5% left that we can’t understand.”

I’m missing the appeal The most important pieces of the puzzlethose that make a species unique, including genes that have evolved more rapidly and that characterize, with special and non-repetitive characteristics, even species that are very close from a genetic point of view.

It looks like him, but… The team was able to recreate nearly complete copies of about half of the genes of extinct mice, including those responsible for ear and hair traits, but for many other genes — such as those that regulate the immune system and the sense of smell — only partial reconstruction was possible. . Therefore, one could hypothetically bring back a rat with long dark hair and round ears very similar to the one that disappeared, but the rodents will behave differently in foraging for food, in partner selection and in defensive strategies due to different olfactory properties. In short, it will only be a virtual exact copy of the original.

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And 5% genetic diversity is no small matter: Only 1% of the DNA divides humans and bonobos. Not only that, the more time passed between the separation of an extinct species and its living relative in the family tree, the greater the proportion of irreversibly missing genes. The Christmas Island Rat and the Norway Rat took two different paths 2.6 million years ago; But the mammoth and the Asian elephant 6 million years ago. Cool shower for woolly mammoth extinction projects such as those for the start-up Colossal Project.

The real mammoth? And who wants it! Not everyone shares this pessimistic view. According to Andrew Paske, a University of Melbourne biologist who dreams of ending extinction Tasmanian tigers (or Tasmanian Tiger), an Australian marsupial that disappeared in captivity in 1936, the percentage of different genes may be redundant, i.e. repetitive regions of the genome and not affect the appearance and behavior of the new copy.

Other scientists assert that the purpose of de-extinction is not to recreate the species depicted but to Functional equationsFor example, elephants that are as tolerant of frost as the woolly mammoth. So the new work says nothing new.