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Sunday, Nov 22, 2009
So, what's the holdup? Why haven't we seen a mammoth clone yet?
Researchers haven't found an exquisitely preserved mammoth specimen yet. The Jarkov mammoth was a disappointment. There wasn't much of it left. They found another sample this past spring, and there was more flesh there, but it's not clear how much of it had stayed frozen through millennia. They still need to find that very well-preserved specimen.
How do scientists hope to resurrect the mammoth?
Either through cloning or breeding. Right now, the technology won't allow cloning, because a lot of the mammoth DNA that we have is broken. It's well-preserved as far as ancient DNA goes, but it has breaks in it. The technology needs to develop where you can make repairs to DNA and essentially stitch together an entire mammoth genome to clone.
In Siberia, there are remains that had been in the permafrost for 10,000 years. The DNA of the Australian extinct species, like the huia bird, that's much more degraded DNA. The hope in looking for mammoth or woolly rhino DNA is that it's going to have relatively few breaks, so you can surgically repair the DNA sequence.
If the cloning technology isn't there yet, how would breeding work?
The Japanese reproductive biologist Kazufumi Goto wants to breed mammoths by taking mammoth sperm and implanting it in an elephant egg. Sperm tends to survive for decades frozen, with preserved DNA. Human sperm, for instance, kept frozen under the right conditions, scientists think, can last actually forever, for thousands of years.
So, if you could find frozen mammoth sperm, with its DNA intact, you would take the sperm and inject it into an elephant egg.
You would essentially just defrost it?
Essentially, which is what they do routinely now for couples who have trouble conceiving. They take sperm samples and keep them on ice and try to fertilize embryos.
First, you would select for sperm to ensure a female offspring. If you can get fertilization of a mammoth sperm and an elephant egg, it would divide a couple of stages in a test tube; you would implant it in the womb of an elephant and see if it took. Then, you'd have a half mammoth, half elephant. Then, you would breed it with another mammoth sperm, and after three generations, you'd have a 90 percent mammoth.
Assuming they found well-preserved mammoth DNA, then how would cloning work?
Then, you would essentially do what they did to create Dolly, the sheep. You take the mammoth nucleus, which had the DNA in it, and stick into an elephant egg which had its DNA removed, and then you have this mammoth DNA inside this elephant egg as if fertilization had already taken place. You would essentially try to get this cell to start dividing by zapping it with electricity.
If this Dolly procedure worked, from there it becomes the same as the breeding procedure, but if it's born then you have 100 percent mammoth. With Dolly, the sheep, it took many, many, many of these attempts to get a live birth, and presumably that's going to happen with a cloned mammoth as well.
