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reconstructing dinosaurs



>  The NOVA episode also claimed that genetic manipulation had successful
>produced birds with teeth, etc. Apparently the genetic programming from the
>birds' ancestors is still there, but 'switched off'. Thus it seems likely that

Yeah!  That's the stuff!  Some species are carrying around a ton of apparently
inactive DNA.  What _is_ all that stuff?  It seems reasonable that they are old
versions of the code for that species.  Some of it is in "current use", active
genes that describe the creature, some it is recessive - a genetic mechanism
that, in computers anyway, seems to be useful to protect genes that are going
out of use "soon" from being expressed very frequently, but not leaving them
completely inaccessible, so that it will be available if conditions changed to
favor them again - it seems likely to be the case in living organisms, too.
But many species seem to have a large library of "dead code", genes that are
neither dominant nor recessive but just along for the ride.  Since there is no
genetic mechanism for garbage collection, it seems most likely these are genes
that have gone completely out of use and cannot be expressed any more without
the aid of some considerable mutation.  This also makes "random" mutation into
something I didn't quite think of in those terms, a mechanism for randomly
yanking dead genes back into circulation, as well as just a random mutation.
If the mutation "switches on" a master control gene, it could re-express a
whole host of "new" traits, not just one random change.

Of course, it is unlikely that these genes are all fully functional - they, too,
will have mutated over time, and, because they confer no survival advantage or
disadvantage upon the organism, they have nothing to correct them.  But it would
be interesting if we could mix-n-match sequences across a large number of
species to see what we could get.  If we "factor out" all mutation later than
140 million years from the conglomerated DNA of all birds, _would_ we find
enough sequences to be at all close to their dinosaur (or whatever) ancestor?
Maybe.  Maybe we'd find a whole managerie of extinct creatures, ancestors of
current living things.

Kind of sad to think that the extinction of any current species denies us not
only that species, but all its ancestors as well.

>would could produce a 'dromeosaur' with today's technology, that would in fact
>be a 'true' dinosaur, instead of just a look-alike. Genetically changing an
>elephant, on the other hand, might produce something that looked like a
>dinosaur but might be behaviorally and functionally be very different.

:)  Well, at least my chimerae got a good conversation started.  But just
to stir the pot a little, I might note that, even with the above, we might
not have all the genes we need to express a given animal.  Lacking those,
does it not seem logical to raid genes from animals the occupy similar
niches today?

>For example, it would probably be warm-blooded, which tells us nothing about
>whether 'real' dinosaurs were.

True, if we couldn't find the genes for homeostatic control.  But then, it
might give us a real good look at what the _skin_ of the real dinosaur looked
like, even if it insisted on eating peanuts instead of ferns, if those _were_
the genes we had.

>  I have heard that the Russians have been working with frozen mammoth remains
>in Siberia for several decades now. I'm not surely exactly what they're trying
>to do, but I haven't heard of any progress at all. Presumably they're trying to
>find DNA fragments to 'cut & paste' into modern elephants to reconstitute
>mammoths. Does anyone know any more about this?

I had heard from a usually unreliable source that they were going to try to
clone a mammoth by swapping a set of mammoth genes into a modern elephant
zygote.  This might be plausible, but I doubt the Russians have the genetic
technology to pull it off - I'm not even sure _we_ do, but it would be a
wonderful test case for learning how to "bootstrap" DNA to begining the process
of growth.  With that bit of technology in our back pockets, maybe we _could_
build a dinosaur egg.

Wouldn't _that_ be a gas?

Larry Smith
larrys@alpha.zk3.dec.com