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Re: Mosquitoes in Jurrasic Park



jamolnar@juno.com wrote:

> >1) There are other nucleated celltypes in  blood (which should be
> >thought of as a fluid tissue). Dinosaurs presumably had a similar
> >complement of immune system cellular components floating around in
> >addition to the RBC's.
> >
> Point well taken.  DNA could be derived from these blood elements, but is
> it as easily extracted as from nucleated RBCs?

Yes. As long as the DNA is *there*, you can extract it from virtually
anything. ABout the hardest thing to get it out of is clay colloids
(thats
part of why counting bacteria or monitoring GEM release in soils is so
hard)
but even that is possible with a multistep washing protocol.
Admittedly the
yield goes down if the substrate from which to extract is 'difficult',
and I
have no idea how hard it is to seperate DNA from Amber (although I
assume a
single phenol partitioning would do it), but the point is that
whatever you
get out is going to be PCR'd anyway, so even just a handful of
molecules would
be enough...

> >3) Even if a given mosquito contained blood from several species, the
> >PCR amplification of the extracted sample would selectively hit
> >sequences from the target type, since that is what the primers would
> >be tailored towards...>
>
> If we knew exactly how to tailor the primers.  Would you use avian or
> reptilian-based primers?

I'd use generic primers to amplify all the sequences there in order to
have
a large enough stock of DNA to work from. The I'd use a panel of all
the
vaguely appropriate primers I could think of, pair by pair, and see
what got
amplified. Sequence any strong bands and compare the sequence against
modern
databases to identify the modern analog gene if any. Check its a
'real'
dinosaur gene by checking how long ago it deviated from the modern
analogues.
Then construct primers that matched up to the 'ancient' DNA, and maybe
play
around with a looped-DNA single primer strategy to 'walk' along the
ancient
fragment until I'd sequenced all of it... Expensive but sure.

Sounds easy, huh? I spent 3 years pcr-ing an unknown gene sequence out
of a
rat. The devil's in the details, despite the overall strategy being
clear...

Of course, there the DNA (well RNA in my case) I'd extracted was
intact. Any
fossil DNA would be fragmented. But a shotgun strategy of sequencing
all the
fragments you could find and then finding all the overlaps to build a
single
long sequence would work (like building a dendrochronology from lots
of
young trees of overlapping age). At least to a certain extent.

Basically I'm pretty sure that you could recover maybe even up to a
few
kilobases of contiguous sequence from several genes... But from there
to
reconstructing an entire genome is a much bigger step... So the whole
'Jurrassic idea' is pretty silly - but it *does* have promise for,
say,
getting back to a mammoth-like form from a modern elephant...
Next question is whether that is ethical or desirable, I guess.

> My incredulity was for the entire sequence to happen, not for just the
> mosquito part.

I understand that. But I still disagree with your rating of the
likelihood.
I know of two shops within walking distance of where I sit that
stock amber that contains insects - I've drooled over them often
enough
(always wanted to own an entombed insect). Basically, amber
preservation of
insects isnt incredibly rare.

>  Granted there were tons of mosquitoes in the Mesozoic.
> How many fed on dinosaurs? Lots of the females.  How many of those
> females got caught in amber? A fair number.  How many amber pieces
> fossilized with the mosquito intact, preserved the DNA inside, and
> were
> actually found?  This part of the chain is just as dicey to me as the
> first part.

The 'Mars Life' papers were based largely around a single meteorite
find,
yet I'd guess you don't find the sequence of impact blasting fossils
into
space, landing on another planetary body, being buried in sterile ice,
being
uncoverred by weathering at just the same time a survey team were
there to
collect it etc etc etc. to be unbeleivable... I personally rate that
as a
far less likely sequence than the one you outline above.

> How much DNA has survived from the Mesozoic?  Nothing confirmed as
> yet, from what I have read.  Anybody with references?

I beleive there have been fragmetn sisolated, but I don't have a ref
so I'll
have to check.

> >However, there are many better-based reasons to think any kind of
> >revivification of a dinosaur genome is possible, mostly relating to
> >the limitations DNA preservation and to the technology available to
> >pull out authentic sequences...
> >
>
> Nothing is impossible.  But lots of things are improbable.

The first statement I disagree with (mainly because it's one of the
'arguments' people like Geller advance). The second I agree with
strongly,
but in applying it to this particular instance I think you are being
unneccessarily pessimistic. You might have to search the museums of
the
world for the finest specimens of preserved insects, and pay huge
summs to
obtain the right to take a sample, but it is eminently possible, to my
mind...

M.

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