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DNA at SVP



Mike Turton asked a question about the Schweitzer et al. results of the
biochemical analysis of T. rex bones at the Museum of the Rockies, asking
if the rex showed a closer affinity to ostriches than to crocs.  I have the
abstract before me that the team submitted to SVP, and they don't meantion
anything about the ostrich/croc comparison in their text.  I am assuming 
from this ommission that the comparison results are not scientifically
significant to warrant putting in print.  I would guess that they mentioned
it in the talk to raise some interesting speculations.  From the text of the
abstract, I do not think they even _contemplated_ doing PCR analysis on the
bones as rigorously as biologists do on DNA extracted from living animals.
The abstract indicates that they definately confirmed collagen in the bone,
but they seem to have stopped short of actually confirming even partial
DNA sequences; instead they reported, and I quote, "Chromatographic separations 
show fractions with absorbance maxima corresponding to nucleic acids AND/OR
proteins."  This means the chromatographic test indicates that the proteins
may have come from other parts of the T.rex tissue other than the DNA.  As a
result, the way they report the findings, they may or may not have found
partial DNA strands.

A question comes up here.  If there is partial DNA in the T.rex, it would
be interesting to find out if the DNA chains were damaged the same way
within different parts those long bones.  If they were _not_ all damaged the
same way, it may be theoretically possible to get enough DNA to do a real
PCR analysis.  This would involve taking _numerous_ samples of bone from
many different parts of the long bone; then doing a chromatographic
separation on each batch in order to see if the molecular weights of the
biomolecules are consistent or are discordant.  If the results are consistent,
that is bad news (at least from a DNA reconstruction point of view).  
Consistent results would indicate that the DNA was "clipped" the same way
every time, and that the portions of the DNA sequence that are missing because
of destruction will always be missing.  On the other hand, if the 
chromatographiresults are different every time a new batch is run, that means 
that,
statistically, we are seeing a different part of the sequence each time we
run the test.  With enough samples (hundreds? thousands?) we could "see"
every part of the DNA chain. 

Unfortunately, there would be no way to know how these fragments were ordered
in a living T. rex.  But at least we could finally do PCR on the stuff,
and prove that birds and dinos are closely related.