Link to research article (open access)
Snippet: “"It was extremely exciting to be able to count the chromosomes of an extinct creature for the first time. It's usually not possible to have this much fun simply counting from one to 28."
By examining the fossil chromosomes, which derived from the mammoth's skin, it was possible to see which genes were active. This is because of a phenomenon called chromosome compartmentalization—the fact that active and inactive DNA tends to segregate into two spatial neighborhoods inside the cell nucleus. For most genes, the activity state matches what researchers saw in modern elephant skin. But not always.
"The obvious question for us was: why is it a 'woolly mammoth?' Why isn't it a 'shockingly bald mammoth?'" said Dr. Thomas Gilbert, director of the Center for Hologenomics and co-corresponding author of the paper.
"The fact that the compartmentalization was still preserved in these fossils was critical, because it made it possible to look, for the very first time, at which genes were active in a woolly mammoth. And it turns out that there are key genes that regulate hair follicle development whose activity pattern is totally different than in elephants."
Researchers learned much but they were left with a puzzle: how could the DNA fragments of ancient chromosomes possibly survive for 52,000 years with their three-dimensional structure intact? After all, in 1905—his 'annus mirabilis,' or 'miracle year'—Albert Einstein published a classic paper calculating how quickly small particles, like bits of DNA, tend to move through a substance.
"Einstein's work makes a very simple prediction about chromosome fossils: under ordinary circumstances, they shouldn't exist," Dudchenko said. "And yet: here they are. It was a physics mystery."
To explain this apparent contradiction, the researchers realized that the chromosome fossils were in a very special state, closely resembling the state of molecules in glass. "Chromoglass is a lot like the glass in your window: it's rigid, but it's not an ordered crystal," said Dr. Erez Lieberman Aiden, co-corresponding author of the study, director of the Center for Genome Architecture and professor at the Baylor College of Medicine.“