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Comment by grondilu | Hacker News Reader

When talking about megafauna resurrection, it is often said that it's not possible because DNA degrades too much after a few thousand years. Yet apparently the DNA of this plant was still viable. What am I missing?

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A seed is a living organism essentially in suspended animation. Cells in the embryo have intact plasma membranes, DNA repair mechanisms are present (although working very slowly), each cell is surrounded by a cell wall, and the entire seed has an outer protective seed coat.

When people talk about DNA degrading, they are usually referring to DNA that is no longer inside living cells, and that doesn't have these multiple levels of protection.

Ah, but this was somatic (fruit placental) tissue rather than germ that was viable.

Plant's also generally contain much more DNA than animals. (fun fact of the day)

Why is that?

Plants are usually polyploid

Cool!

Basically just time scale. When people talk about DNA having degraded too much, it's generally in the context of bringing back dinosaurs. Dinosaurs went extinct about 65 million years ago, which is (obviously) much longer than 30,000.

Until recently it was thought that DNA degraded more quickly, indeed making it un-viable after only a few thousand years, but a relatively recent study put the half life of DNA at 521 years, meaning that it would take several million years to degrade fully, under ideal conditions.[1]

Therefore, bringing back animals like the woolly mammoth should be quite feasible, but probably not dinosaurs.

[1] http://www.livescience.com/23861-fossil-dna-half-life.html

I think DNA breakdown makes it much less likely to find viable DNA, but not that it's impossible to find. I'm no expert though.

I guess that even if the DNA breaks down into smaller strands, you can still computationally assemble the DNA back into its original form (just search for overlaps in the sequences, and stick these together).

(Remember that if you have multiple cells, you have lots of strands of the same DNA, all broken in different places.)

But I'm not an expert.

Not an expert, but I would think it depends how broken down they are. Assuming you have the tech to examine millions of fragments, you would still need long enough sequences for the overlaps to be unique. For instance, you probably couldn't put a book back together with nothing but ten character phrases, but you probably could with 100 characters. It would be interesting to run a simulation to see where the cutoff lies.

Also not an expert, but since a very large percentage of a given dino's genes should be common in other organisms, there's at least a large corpus to compare (most) fragments to.

Imagine taking a thousand copies of War and Peace, cutting them into strings of less than 10 characters, and mixing them all up. Even with the entire corpus of human literature to compare to, I doubt you'd be able to reassemble the scraps back to something even close to War and Peace. In fact, you could probably take those scraps and turn them into any number of completely different novels, because your building blocks are so small you've got essentially no constraints to work with. You don't have complex ideas, you just have the basic building blocks of language.

Now, I'm not saying this is the case for dinosaurs, just that, given enough time to decay, it makes sense that eventually DNA would reach a point where it isn't possible to reconstruct, because the information just isn't there any more. I'd be curious to know how long it would take to reach this point.

DNA that's hundreds of thousands of years old has been recovered [1]. Sorry for the non academic link but the number I've always been told was just under a million years, this seems reasonable at first blush.

[1] http://www.nbcnews.com/id/49366487/ns/technology_and_science...

Perhaps plant DNA is hardier against time, bacteria, freeze/thaw cycles, etc than animal DNA? I'm not a biologist, so I'd also love to know.

The tundra is primarily always frozen. As you point out freeze/thaw cycles are terrible for biochemical stability, but at the tundra below the surface (where earth acts as an heat insulator) I believe this effect is minimized

DNA has some remarkable stability properties when it comes to preservation. This is one of the reasons people are so interested in DNA storage technologies.

DNA chemistry allows for information to be preserved for millenia at sub-zero centigrade temperatures.

Robert N. Grass, Reinhard Heckel, Michela Puddu, Daniela Paunescu, Wendelin J. Stark. Robust Chemical Preservation of Digital Information on DNA in Silica with Error-Correcting Codes. Angewandte Chemie International Edition, 2015; DOI: 10.1002/anie.201411378

It depends of the species, but polyploidy is common in plants because plants often can work as colonial organisms that can clone itselves.

Is the same problem as to restore a file that is partially distroyed in four or five points. You can still recover the original file if you have five copies, each one with the damage in a different area. Polyploid organisms have several identical security copies of each chromosome. If something in a chromosome is damaged, they can quickly fix the damaged areas using the safety copy saved in his 'twin' chromosome.

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