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Cenozoic Park: Cloning the Tasmanian Tiger
Mirk writes "The
Australian Museum
reports a breakthrough in their plans to clone the Tasmanian Tiger. The ``tiger'', actually a carnivorous marsupial, became extinct in 1936, when the last known
specimen died in captivity. Er, did I say ``extinct''?
Now it looks like what everyone thought was an extinction may be
``a 70-year hiccup'', to quote the press release. The museum's Evolutionary Biology Unit have successfully replicated individual Tasmanian Tiger genes using a process known as
PCR (Polymerase Chain Reaction)."
You can find out more about "Tasmanian Tigers" at The Thylacine Museum. In reality it's a marsupial, not a mammal, and so it's closer to an opossum than a feline like a tiger. The only reason it's called a "tiger" is because of its stripes, as seen in the photo at the top of this webpage about mysterious animals. And it may not even be extinct...
PCR doesnt get you a clone
you need a host egg and the actual DNA I would like to see them synthsize it but somehow I dont think so
regards
john jones
I'm capped, and yet I still whore.
DNA, as I'm sure we all know, is double stranded. One strand is a complement of the other. A complements T and C complements G. So, if one strand is:
5' ATTTC 3'
then the other strand is:
3' TAAAG 5'
The DNA is "read" from 5' to 3'. 5' and 3' refer to particular atoms on the sugar backbone that are attached to one another via a phosphate.
When DNA is replicated, you split it into two strands:
5' ATTTC 3' and 5' GAAAT 3'
(notice that the two complements read in opposite directions)
and each strand has it's complement added.
5' ATTTC 3' and 5' GAAAT 3'
3' TAAAG 3' and 3' CTTTA 5'
The problem with this is, in order for this happen to DNA, you need an RNA "primer." This primer is a complement to the beggining of what you want to replicate. So, for example, if you have (RNA bases I'm putting in bold. U is the same as T:)
UAA
floating around in solution, which compliments ATT, then any sequence beggining with ATT will be replicated, but other sequences will NOT be replicated, because no RNA primer is available to get them started.
So, if you have a whole mess of DNA, including a piece that you're interested in, which reads:
5' ATTTG (long space........) TCGTC 3'
3' TAAAC (long space........) AGGAG 5'
and you add:
TAAAC and TCGTC
You get a chain reaction; the sequence flanked by the complements of the two things you add (the sequence printed above) is replicated, and then the replication product is replicated, and so on and so on. Other sequences, which are flanked by only one compliment (only ATTTG, say) will be replicated occasionally, but there replication products cannot in turn replicate, so you get no chain reaction.
More history here.
A thermophile (heat loving organism), thermus aquaticus, provided a polymerase (an enzyme which polymerises, that is to say replicates sequences of, nucleic acids like DNA and RNA) that works extremely fast at high temperatures. In general, the higher the temperature you run a reaction at, the faster it goes. However, most biological enzymes (from, say, a person) cease to function when temperatures rise (this is one of the ways heat kills you.) Thermophiles, bacteria that live in geysers and in volcanic ocean vents, have evolved enzymes that continue to function at higher temperatures.
The good and new comes from no quarter where it is looked for, and is always something different from what is expected.
The Sydney Morning Herald have just done an article on this. While it doesn't cover much more than the one linked in the article, it has links to some other SMH articles. One Of them is an interview with one of the main scientists behind it, and is quite insightful. The other is a gallery of relevent photos.
This post will enter the public domain 70 years after my death, unless Disney buys another extension.
That's human mitocondrial DNA. The mitocondrial Eve is not our common ancestor, or even our common genetic ancestor. She is the most recent common ancester of all humans alive on earth today w.r.t. matrilineal descent. See the BBC explanation for further enlightenment. The existence of the Mitochondrial Eve is a mathematical fact (unless something like a multiple-origins theory of human evolution i.e. the human species arose independently in different geographically separated populations, and that the present-day ease of interbreeding is the result of a remarkable convergent evolution, is true. Few people subscribe to the multiple-origins theory, and the Mitochondrial Eve observation is a refutation of multiple-origins). Since she has been identified as well (as much as possible,) this is not a theory.
That said, the chances of mutation from breeding two related individuals may be higher than those of unrelated individuals, but they are not absolute certainties. Some degree of variation can be recovered, and while that may not be a huge amount of variation, it's more than they've currently got.
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see 1998 report at http://www.trussel.com/prehist/news50.htm
The Tassie devil has been suggested as a host. The big advantage for the thylacine, and the reason why it will probably be the first successful recovery, is that it is a marsupial, which means it is born when it is basically still a foetus. This means that the host animal can be kept on immunosuppressants for the short duration of pregnancy without rejecting the embyo or getting too screwed up itself. Something like a mammoth, on the other hand, would need to be carried for 18 months inside what would end up being a very sick elephant.
Where did you get this RNA primer stuff from?
...
I believe that's how it was done, back when PCR was invented (back in 1985 or so) but nowadays, no one uses RNA as primers without a very good reason to do so. Why? RNA is unstable, and you have RNAses (enzymes that break up RNA) on your hands, in your spit, everywhere
What's used today is short oligonucleotides as primers. These are short, single-stranded DNA stretches that are synthesized by a chemical process and subsequently purified. They are available from commercial suppliers at something like 50 cent a base.
I am a biologist, and I've never understood why people, even people that don't believe in a "higher power" of some sort, still believe that extinction happens for some mystical, Gaia-esque "reason" (beyond the obvious direct causal mechanism). It doesn't. Extinction just happens. Evolution doesn't CARE about fitness - less "fit" animals just happen to be less sucessfull over time and in a changing environment - there is no moral judgement going on by nature!
Please tell me how an animal that was hunted to (supposed) extinction is poorly adapted? It's a predator, not a fast-reproducing herbivorous animal with a low gestation time and large number of offspring - EXACTLY the kind of species that is most vulnerable to extinction via humans.
Now, there are valid concerns here in this case, most of them being technical, IMHO. Chromosomal damage from the ethanol, the task of repairing said chromosomes, host-animal interactions, and the genetic defects and abnormal growth patterns seen in other mammalian cloning efforts are all hurdles. In addition, there is the question of the genetic diversity of a founder population being enough to maintain a viable population in the future. As to the "ecological balance" option - this is not a true foreign species, and poses little threat to indigenous fauna. Predatory animals like this are MUCH less dangerous to "bring back" (as would be mammoths and yes, dinosaurs) - as their impact is much more easily calculable, and their population more easily controllable. The vast majority of ecological damage by people has been due to introduction of truly foreign organisms that have high-reproductive capacities and large tolerances to attempts made to control their growth - organisms such as rodents, rabbits, cane toads, insects, kudzu and other weeds, as well as domestic pets.
I feel that restoring extinct animals whose ecological effects are minimal or easily controlled (as would be in the Tasmanian Tiger) and whose extinction was caused by humans is a laudable goal. In addition, the zoological and evolutionary benefits of cloning extinct animals is a worthy goal in and of itself, even if the only specimens are kept in zoos/labs for study. Finally, I would once again like to point out that JURASSIC PARK IS NOT REAL SCIENCE, and that Hollywood moralizing in ANY movie should always be taken with a grain of salt.
Sincerely,
Kevin Christie
Neuroscience Program
Universtiy of Illinois at Urbana-Champaign
crispiewm@hotmail.com
Eh, nobody will read this because I'm not going to bother to register. But since I've been to Tasmania and talked to people about this...
1. The habitat is still intact, and set aside as a preserve.
2. The prey is still intact.
3. There are a lot of specimins in jars - in theory there's enough for a viable population.
4. They were hunted out by ranchers (like wolves).
5. Some people believe that they aren't actually extinct.
His statement makes perfect sense, you just have trouble accepting it.
-- this is not a
Our minds evolved to create tools, the tasmanian tigers evolved to carry around its embryos in a pouch. We developed ethics, mathematics, nuclear science, and the theory of evolution that you bring up, the tasmanian tiger developed a screaching other worldly howl. We won.
An Education is the Font of All Liberty
Fitness has everything to do with it. A meteor falls and drastically changes the environment. Only those animals who are fit for this new environment survive. If all the animals with a body mass over 100kg die, they were unfit for the new environment.
Your building on fire analogy doesn't work. It only applies to individuals or a small group, evolutionary fitness applies to a species as a whole.
To address your comments, the reason why cloning animals is difficult has a lot to do with what is called epigenetics, or information stored in the chromosomes that is beyond the mere sequence of the genome. For example, reversible modifications to the chromosomes that activate or inactivate certain regions during the process of cell differentiation. "Cloning" a multicellular organism is the name given to de-differentiating existing adult cells all the way back to the differentiation state of a fertilized egg, then growing them back up into adult organisms. However, even if you have the genome 100% correct, problems with the structure of the chromosomes will lead to horrible birth defects (some textbook examples of this in humans are Angelman's and Praeder-Willi syndromes, which cause mental retardation and characteristic deformities).
The thing is, what they are proposing to do with this extinct marsupial is actually not cloning, but actually synthesizing DNA molecules and building one of these animals FROM SCRATCH. This makes the problem of chromosomal structure MUCH more significant than it is when you "clone" an animal using standard techniques. To address your second point, however, it is extremely unlikely they would try to turn a related animal into the extinct animal like they did in Jurassic Park. First of all, this would not work, and second, even if it did, you would just get a different third animal. The real obstacle here is creating artificial chromosomes out of individual genes, and this is where the work would have to start. Most likely, this would not be done in cells from some exotic mammal, but something very standard like a mammalian tumor cell line or maybe even yeast.
As for your third point, a female mammal can be cloned from a male in theory, and you could breed them. Obviously this is not a perfect arrangement, but it is the case with certain strains of genetically identical lab mice, and they're generally healthy. In any case, the small problems here pale in comparison to the giant problem of assembling artificial chromosomes. This hasn't even been done with bacteria, much less a multicellular eukaryotic organism.