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Biotech Science

Half-Life of DNA is 521 Years, Jurassic Park Impossible After All 315

Posted by Soulskill
from the unless-you-have-a-time-machine dept.
another random user writes with this quote from Nature News: "Few researchers have given credence to claims that samples of dinosaur DNA have survived to the present day, but no one knew just how long it would take for genetic material to fall apart. Now, a study of fossils found in New Zealand is laying the matter to rest — and putting paid to hopes of cloning a Tyrannosaurus rex (abstract). After cell death, enzymes start to break down the bonds between the nucleotides that form the backbone of DNA, and micro-organisms speed the decay. In the long run, however, reactions with water are thought to be responsible for most bond degradation. Groundwater is almost ubiquitous, so DNA in buried bone samples should, in theory, degrade at a set rate. Determining that rate has been difficult because it is rare to find large sets of DNA-containing fossils with which to make meaningful comparisons. To make matters worse, variable environmental conditions such as temperature, degree of microbial attack and oxygenation alter the speed of the decay process. By comparing the specimens' ages and degrees of DNA degradation, the researchers calculated that DNA has a half-life of 521 years. That means that after 521 years, half of the bonds between nucleotides in the backbone of a sample would have broken; after another 521 years half of the remaining bonds would have gone; and so on."
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Half-Life of DNA is 521 Years, Jurassic Park Impossible After All

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  • Re:Ummmm (Score:5, Informative)

    by biodata (1981610) on Wednesday October 10, 2012 @02:05PM (#41610149)
    It is an English phrase meaning 'putting an end to' but using fewer words.
  • by sed quid in infernos (1167989) on Wednesday October 10, 2012 @02:06PM (#41610167)
    Why do they need to know? 10,000 years is roughly 20 half-life periods, so they should expect roughly 1-millionth of the DNA to remain.
  • Re:Cryogenics (Score:5, Informative)

    by biodata (1981610) on Wednesday October 10, 2012 @02:07PM (#41610189)
    Cryogenics would pretty much stop most of the reactions that break the bonds, so half-life would be hugely increased, especially if material is properly dried first. Seeds can last for many decades and still grow if dried to 5% moisture content and frozen at -80. Not sure about animal embryos, but sperm and eggs also.
  • by slew (2918) on Wednesday October 10, 2012 @02:11PM (#41610249)

    The 521 year half-life is if the DNA is exposed to water in typical situations, ITFA (in the article) they give an estimate for the best case situation...

    The team predicts that even in a bone at an ideal preservation temperature of 5 C, effectively every bond would be destroyed after a maximum of 6.8 million years. The DNA would cease to be readable much earlier — perhaps after roughly 1.5 million years, when the remaining strands would be too short to give meaningful information.

    “This confirms the widely held suspicion that claims of DNA from dinosaurs and ancient insects trapped in amber are incorrect,” says Simon Ho, a computational evolutionary biologist at the University of Sydney in Australia. However, although 6.8 million years is nowhere near the age of a dinosaur bone — which would be at least 65 million years old — “We might be able to break the record for the oldest authentic DNA sequence, which currently stands at about half a million years,” says Ho.

    As other posters point out, the famous mammoth recreated from DNA was from about 10,000 years ago, much less than the 1.5 million year practical limit estimated by this research team.

  • Re:Question... (Score:5, Informative)

    by MaXintosh (159753) on Wednesday October 10, 2012 @02:37PM (#41610607)
    Scientist here (you can tell by my hat, and the fact that something like 90% of my comments on /. start with "I'm a biologist"). First, the DNA we get is from better preserved remains, which kicks the half life back further (It's in TFA, but not mentioned in the summary). There's still a 'deadline' around 7 MYA, where (allegedly) all the bonds would have pretty much been broken at that point - Frozen remains supposedly have a halflife around 158 kya. It's that dang phosphate backbone that's too willing to run off and go have reactions with any trallop of a molecule that wanders on by.

    This means even in the relatively recent past, the amount of DNA we're looking at is pretty dang tiny. Part of the reason ancient DNA is so dang tricky is because the much of what you sequence is not actually what you're interested in - doubly so when you're sequencing something closely related to humans. For example, did some spot sequencing of ancient/historic polar bear remains, and had to toss out a chunk of the data we got back, as it was soil bacteria(/fungi/pollen) contamination. How do we know which is which? We had good scaffolds to align our bear sequences back up again, though not everyone is as fortunate as us.

    In addition to being rare, what is left is fairly short. You can imagine if you start putting breaks in at random, your average length is going to start declining rapidly, and then level out at some small value that takes quite a while to get smaller. It'll get there, and given geologic time scales, a lot of what we want is that far back, but it'll take a while.

    Finally, what isn't mentioned in this summary is that there was massive variance in the estimates of half-life. Supposedly only 40% of the variance in halflife was explained by age. Preservation, inter-lab differences, and good old fashioned luck probably contribute considerably to variance in half-life.

    There are other factors too, but they're boring, and I should probably get work done instead of dragging out this reply.

    (And to answer your latter question, Neanderthals have been sequenced whole genome, not just mtDNA).
  • Re:Uh, what? (Score:2, Informative)

    by Anonymous Coward on Wednesday October 10, 2012 @02:49PM (#41610827)

    "Wikipedia seems to have a page all about doing what this article says is impossible"

    No, it doesn't. Dinosaurs (non-avian ones) are 65 million years old or older. The oldest ancient DNA that isn't regarded as bogus or probably so is less than a million years old. People had hopes that DNA extracted from dinosaur bones was real, but upon more careful testing, it was discovered to all be contamination. Neanderthals are a lot younger than dinosaurs. That time range works.

    This is all explained on the wikipedia page.

  • by Lonewolf666 (259450) on Wednesday October 10, 2012 @02:50PM (#41610853)

    Something must be wrong with the 521 years. 65 million years / 521 years = 124.760 half lifes.

    That means only 1 / (2^124.760) = 1 / (3,1787695069134767997232294562089e+37556) of the original DNA should be available for analysis today. Those guys would be lucky to find a single base pair that has not decayed. Hardly a sufficient basis to make a quantitative analysis ;-)

  • by buchner.johannes (1139593) on Wednesday October 10, 2012 @04:55PM (#41612485) Homepage Journal

    With the numbers of busyqth (mammoths died out 4500 years ago by the way):
    If you have 1 DNA in pieces of 1000 base pairs length from one mammoth, it must not be older than 8500 years.
    If you have 1 DNA in pieces of 81 base pairs length from one mammoth, it must not be older than 10000 years.
    If you have a million DNA pieces of 81 base pairs length from a million mammoths, they must not be older than 30000 years.
    The returns are diminishing quickly. 10000 years can not be exceeded significantly.

  • by Anonymous Coward on Wednesday October 10, 2012 @06:27PM (#41613493)

    You mixed up the , and . there.

    Only in some countries. http://en.wikipedia.org/wiki/Decimal_mark#Countries_using_Arabic_numerals_with_decimal_comma [wikipedia.org]

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