Re: dna preservation over long periods - up to 3000 years

Christopher:

     That is a really interesting question, and there are many ways in 
which cloning is performed, and many interpretations on the manner in 
which it could be performed.  

You are correct.  For very high tolerance cloning of complicated 
organisms, 'fresh' DNA and eggs appear to be essential for the success of 
the project.  Typically these embryos are cultured in vitro and several 
dozens (or hundreds) are implanted into the womb for gestation.  

Ancient DNA unfortunately did not consult scientists on the manner in 
which it could best be preserved, but we know that typically moisture and 
light and heat are the two largest enemies.  This is why, for example, DNA 
is capapble of being recovered from insects and bacterial spores that are 
trapped in amber, a form of petrified tree sap, and the source of DNA for 
the 'Jurassic Park' novel by Michael Crichton. As for frozen Mammoths and 
such, the conditions there are actually fairly good for storing DNA.  They 
are cold, not exposed to light, and for the most part, despite all of the 
ice, are actually quite dry.  Freezing things and keeping them dry 
prevents the activities of proteins and chemistry from degrading the 
nucleic acids. 

I think that the long term use of cloning on ancient organisms and humans 
has a long way to go before we are capable of actually performing it, but 
already on simper prokarytoic organisms (bacteria) there is some evidence 
that spores of these creatures are viable after millions of years in an 
appropriately dessicated environment, but there is considerable scientific 
debate about this process.  For a great point counter-point on this topic, 
please see:
 http://whyfiles.org/008amber
/molec_bio3.html http://whyfiles.org/008amber/
molec_bio.html

If we had unlimited funds and access to developing technologies, we could 
probably make something very close to a true 'clone' by inserting in 
pieces of DNA fresh into areas that were damaged.  For example, if in an 
ancient mummy, we sequence a fragment of her DNA that contained the gene 
necessary to break down alcohol, but it was damaged, we could splice in a 
functional copy of that gene (Adh1, perhaps) and continue onto the next 
gene.  One of the great advantages of evolution is how well preserved the 
functions of many proteins are, and in particular humans how well 
conserved the DNA sequences are.  The differences in DNA between two 
average people are very, very low.

     You could certainly imagine utilizing advanced DNA repair mechanims 
from bacteria to help with the process.  Dinococcus Radiodurans, for 
example can repair its own genome even after it has been broken into 
several hundred if not thousand pieces, perhaps versions of this could be 
added to a mummified DNA cocktail to aid in the reassembly process?

     Currently, our best window into the genetic structure of ancient 
organisms is by comparing the differences genetically between organisms 
found today.  By examing how related organisms differ, we can infer back 
along the evolutionary timeline as to when they originated from the same 
common ancestor.  This is true for comparing humans to the apes, as well 
as comparing common soil bacteria to those that cause strep throat.  This 
process is wrapped up into a field collectively known as phylogeny, but 
has its hand in bioinformatics, evolution, dendeography, mathematics, and 
programming.

Thanks for the question.

-Matt-