Jurassic Park? Still not close to being real.

But cloned woolly mammoths just became more possible, thanks to Japanese researchers who announced Monday that they'd cloned dead mice that had been frozen for 16 years.

When animal tissue freezes, cell walls burst and the DNA inside the cell nuclei can be seriously damaged. Because of that, most scientists had assumed it'd be impossible to get any good DNA from the thousands of frozen mammoths thought to still lie in Siberian permafrost.

The Japanese team figured, however, that the high concentration of sugar in brain tissue might preserve DNA. So they ground up frozen mice brains, found some useful DNA and put it into unfertilized live mouse eggs.

The resulting embryos were used to create stem cells, which in turn made more embryos. At the end, 13 mice were born.

Cloning mammoths would probably be tougher, since the temperatures of the frozen carcasses have fluctuated a lot over tens of thousands of years. If good DNA could be found, donor eggs could be used from Asian elephants, close relatives of mammoths. (African elephants are more distantly related.)

"It would be very difficult, but our work suggests that it is no longer science fiction," team leader Teruhiko Wakayama of the RIKEN Center for Developmental Biology in Kobe, Japan, told New Scientist magazine.

• Click here to read more about this story in New Scientist.

• Click here to read the abstract of the scientific paper in Proceedings of the National Academy of Sciences.

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