De-Extinction

Sometimes even the most useless pursuit can turn up some fascinating trivia.  I’ve never been able to remember the difference between mastodons and mammoths (turns out the easiest is mastodon tusks stick forward like oversized elephant tusks while mammoth tusks curve up and back…not that I’ll retain that).  Looking for some factoid that would help me keep them separate, I didn’t have much luck, but I was delighted to learn that the name mastodon comes from the Greek and means “breast teeth.”  Seems that the mastodon has conical-shaped molars unlike the great rippled slabs of the mammoth or the modern elephants.  (“Hey, big boy.  Wanna see my molars?”)

Despite all those huge-looking pictures, both the mammoth and the mastodon were about the size of modern African elephants.  The mastodon died out right around the end of the last Ice Age, but the wooly mammoth survived long enough to leave a fair number frozen in the Siberian permafrost.  Which, aside from providing the basis for numerous “legends” (e.g., they all died at the same time, were frozen so fast the meat is still edible, etc.), may soon give us a unique opportunity.

But more about that later.

Meanwhile, let’s take a look at what’s been happening with DNA.

While we’ve been focusing on the potential wonders of decoding of human genome, folks have been working on lots of other mammals: horses, cats, chimpanzees, etc.  But the head of the list (for size, anyway) is the African elephant.  The Broad Institute has already completed the first analyses and plans to do more to eliminate errors and remove gaps.

This brings some hope for endangered species.  Over the last few years, there have been attempts, with varying success, to implant fertilized eggs of one species into females of closely related species.  And as a hedge against an uncertain future, institutions such as the San Diego Zoo have for years been harvesting and cryogenically preserving sperm and eggs from endangered animals.  Ever since the cloning of Dolly, the sheep, the “Frozen Zoo” has been saving tissue samples and stem cells as well.

The trick here is that genetic technology means that if you can get a complete set of chromosomes in a Petri dish, you can insert it into a (compatible) ovum, convince it to start dividing, put it in a (compatible) female, and, voila! you can produce an animal, even if it belongs to a species that had become extinct.

We should soon be able to go further than that.  As of now, there are less than 20 Northern White Rhinoceros in the world, which is hardly enough to sustain any species.  But, even if the entire species died out and there were no tissues in the Frozen Zoo, if there was a genetic map, the species still might survive.

How?

What you would do is take the DNA from a cell of a close living relative, say the Southern White Rhino (a conservation success story, there are now more than 10,000 living), and engineer it to duplicate the genetic map of its extinct northern cousin.  Go through the cloning process and you have a shot at recreating an extinct species.

All of which (finally) brings me to our Wooly Mammoth.

When an animal dies, the RNA repairing service that keeps the DNA intact stops operating.  Ergo the hugely long DNA molecules start to break down. Unless you can cryogenically stop the process, the first stage of decomposition leaves all the cells filled with a jumble of random pieces of genetic code.

Despite the legends, the Siberian mammoths were not frozen quickly enough to keep that process from happening.  (People are still looking for mammoth cells with intact DNA, but the odds are lousy.)  Still, the mammoths were frozen fast enough to leave large chunks of DNA molecules intact.

Those DNA chunks, although completely non-viable, still offer scientists the opportunity to create a complete genomic map of the mammoth.  The DNA molecules break at different points, so with enough money and persistence, one can find the chunks with overlapping information to complete the picture.

Here is the kicker: the McMaster Ancient DNA Centre has announced two fascinating things: First, the mammoth information decoded to date is 98.5% identical to the African elephant, so an African elephant female could easily serve as a surrogate mother for a mammoth calf.  Second, they expect to have the entire Wooly Mammoth DNA mapped by the end of 2007!

When I was a kid, practically every science fiction movie was based on some monster created by science gone wrong.  I don’t know how it will all turn out, but soon, and I do mean soon, we will probably see and hear and smell a living Wooly Mammoth.

Where’s the popcorn?

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