Mammoths lived and died pretty much exclusively in very cold climates, so paleontologists have been able to find a few of them freezer packed for freshness. With access to such well-preserved specimens, geneticists have sequenced roughly 70 percent of the species' genome. At the same time, some labs are hard at work sequencing the elephant genome, which is the closest match to the mammoth currently alive on Earth. So Nature decided to find out exactly what it would take to bring a real, living woolly mammoth into the world again.

1). Build the DNA from scratch using the basic chemicals that make up all base pairs, with the reconstructed mammoth genome as the recipe. You might have to fill in some gaps in the mammoth genome with elephant, in case we can't find enough frozen mammoths to complete theirs.

2). Get two copies of each of the dozens of mammoth chromosomes into the nucleus of a viable cell. This step is like giving someone directions to a far-away place by simply giving them the latitude and longitude. We can sort of do this on a small scale, but we probably don't have the technology to make this happen with mammoths yet.

3). Make the cells into an embryo. You'd probably use an egg from a modern female elephant to accomplish this, essentially creating a clone of the "artificial" mammoth DNA you'd manufactured.

4). Bring the embryo to term. Using an elephant as a surrogate mother seems logical, but apparently there are logistical problems with a modern elephant's internal structure. Robot mammoth mom, maybe?

5). Find some more frozen mammoths so you can create genetically distinct clones. You'll never have a breeding population without some genetic diversity.

Creating a real-world Jurassic Park (or, in this case, a Pleistocene Park) would be just about the coolest thing ever. Oddly enough, nobody mentions chaos theory in the Nature article, but there is a way we could cheat JP-style. By comparing the mammoth and elephant genomes, we could genetically engineer a "mammophant" that looks pretty much the same as a woolly mammoth, but isn't. Image by: rpongsaj.

Resurrecting the mammoth? New research raises the prospect. [Ars Technica]
DNA sequencing: Mammoth genomics. [Nature]

Although the tortoises vanished from the Floreana, a handful were preserved by the very sailors who contributed to their extinction. When they didn't need the tortoises for food, the sailors would drop the tortoises off at their whaling grounds, notably the Galapagos island of Isabela. There the Floreana tortoises interbred with the native tortoises, allowing their DNA to live on:

"The [living tortoise] samples were collected in 1994, but we had no idea what was in there because we didn't have Floreana data," said Gisella Caccone, an evolutionary biologist at Yale University in New Haven, Conn. "OK, now we have genotypes for 15 to 25 animals from the museums, so we did the analysis and boom!"

Sadly, the biologists won't be staging any Jurassic Park-style cloning to revive the reptile, as is being planned for a baby mammoth fossil discovered in Siberia last year. Instead, they will determine if there are enough tortoises carrying the Floreana DNA to begin a selective breeding program.

Extinct Giant Tortoise Could Be Revived [LiveScience]

A few photos and some specimens preserved in alcohol are all that remain of the Tasmanian Tiger - it was hunted to extinction early in the 20th century. Those alcohol-preserved bodies had enough DNA for the scientists to recover. They injected a few genes for cartilage development into mouse embryos, and the genes functioned, basically taking the place of the mouse genes that usually serve that function. It gave the researchers a new look into the genetics of a vanished species.

Pulling usable DNA from a fossilized bone or egg is a far cry from a preserved specimen, so species that were wiped out thousands or millions of years ago are going to be a little harder to bring back. There has been a lot of controversy regarding the Tasmanian Tiger project - is it even possible to bring back a living Tasmanian Tiger? And if it is possible, is it really something we should do? Even if the extinction was brought about by humans, I think the law of unintended consequences is going to bite us in the ass if we go too far down this road. Still, I'd be first in line to ride the automated SUV past the T-Rex enclosure. Image by: Universal Pictures.

Tasmanian tiger DNA 'resurrected'. [BBC News]