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Extracting Mummy DNA

Examining Mummy Genes Egypt's mummies are among the best preserved of all ancient remains, but even in them the recovery of DNA -- the genetic fingerprint of every individual -- is insidiously difficult. Molecular biologist Scott Woodward of Brigham Young University may know this better than anyone; he and his lab recovered the DNA from hundreds of Egyptian mummies, from commoners to pharaohs.

Dr. Woodward's genetic work on the pharaohs of the 18th Dynasty (which includes the legendary King Tutankhamun), while not yet complete, has helped to verify the ancient written genealogies that define how the pharaohs were related to one another. "The DNA analysis looks consistent with them being connected in the ways that we thought they were, with, for example, brother-sister marriages among members of the royal line," Dr. Woodward says.

Some of the very best preserved of Egypt's ancient royalty were the kings of the 18th Dynasty. But that does not necessarily make studying their DNA easy. As in any analysis of ancient DNA, the specter of contamination with modern DNA looms large. If so much as a single cell from a lab worker gets into a sample being analyzed, the results will be worthless. "We try to address the problem head on, first by being very careful about where we get tissue samples from the mummies," Dr. Woodward says. "In the case of the common people, we are very picky about that. We go to a piece of tissue or bone that we know is very unlikely to have been contaminated by modern sources -- from a tooth, for example, or the inside of a bone." That's not so easy when it comes to the zealously guarded remains of the pharaohs. "We can't go into where we want on the body, but have to rely on parts that have already fallen off the body. Since they are far from the ideal samples that we'd like, we take two or three and compare the sequence that we get from each to be sure that it is the same."

Once tissue samples are recovered, they are taken back to Dr. Woodward's lab, where the DNA is extracted under carefully controlled conditions. Any previously isolated DNA samples are removed from the lab, for instance, and the final sequences are compared to all other DNA patterns that have been deciphered in the lab. "They have to be unique, and to make sense within the expected genealogical structure," Dr. Woodward says.

An Egyptian Mummies Teeth The DNA of any organism will quickly begin to degrade after death. Exposure to environmental conditions like moisture, sunlight, and air, will speed the process. The Egyptian mummies were uniquely preserved, and protected from much of that assault, which increases the likelihood of recovering DNA from their tissue. But at best, the fragments are small, and don't hold enough information to describe a single gene. To make the most of what can be found, Dr. Woodward and other experts probe the extracts with particular probes that home in on information-rich bits of ancient DNA. "We pick areas of DNA that have the maximum amount of variability among individuals. The sequences of those areas will be similar among related individuals, but not shared among the general population," says Dr. Woodward. Finally, a technique called polymerase chain reaction, or PCR, is used to produce millions of copies of the DNA fragments so their sequence can easily be read.

In a living human, the entire procedure could be accomplished in just one day. But in mummies, Dr. Woodward says, "you could reasonably expect months, because you have to be able to replicate the results in separate samples, tested independently. It is really very difficult and time-consuming." For that reason, Dr. Woodward and many other researchers are suspicious of the results of most ancient DNA studies. "If someone gets an ancient sample, goes through and gets amazing results in six days or two weeks even through it's the only ancient tissue they've ever done, I would be very wary of the results," he says.

For more information: Experts to use DNA tests in Tutankhamun analysis.

Secrets of the Pharaohs