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Forensics

DNA profiling has become an extremely powerful tool in forensics and is increasingly used in criminal trials. If the bodies of Mallory and Irvine are found, scientists hope to use these new, cutting-edge techniques to convincingly identify the climbers using just a shred of evidence. Gill Rysiecki works for Cellmark Diagnostics near Oxford in the U.K., a lab that specializes in just such testing.

NOVA: What sort of cases do you work on at Cellmark?

A lab technician analyzes samples of DNA.

RYSIECKI: In the early days, DNA testing was very expensive and very tricky. You actually needed a great deal of DNA to get a result. So it was really saved for the most serious cases: rapes, murders, that sort of thing. It's now a lot quicker, easier, and less expensive to do. You can test tiny amounts of tissue and get a result. So this has really opened up the field, and police can use it for all sorts of things.

NOVA: If the team on Everest were to find the remains of what they thought to be Mallory or Irvine, how would you test for their identity?

RYSIECKI: In this case, it's more like a paternity test that we would be doing, because we'd be comparing samples with living relatives to see whether we could establish a link. The key principles about DNA that we use in this analysis are the following. Each person has his or her own unique DNA. If I looked at your DNA it would be unique and different than mine. The only people that have the same DNA are identical twins. So, within an individual's body, all of the cells contain exactly the same DNA. When it comes to inheritance, we each inherit half our DNA from each parent. So, in the Mallory case, what we're looking for is some sample from the body that contains DNA. The difficulty in this case is that the death occurred such a long time ago, and DNA does get broken up and degraded quickly by bacteria.

NOVA: What makes you think you'll still be able to do a good analysis, given how old the samples will be?

A child inherits half of its DNA from each parent. In this result the child has two bands, one inherited from its mother, the other from the father.

RYSIECKI: If you can store DNA in a freezer, it will keep indefinitely. And I guess being on the top of Everest is quite close to that sort of condition. What we're hoping is that because of the cold, and because of the desiccation, the DNA will be well preserved. If they can bring some muscle, or a tooth, or a bit of bone—I'm very conscious that they don't want to desecrate these bodies in any way—but if they can bring some tissue down it doesn't have to be very much at all. What we'll then do is compare the DNA pattern we find there with the DNA patterns of living relatives. We would get blood samples from the relatives and then compare the patterns. If you give us DNA from George Mallory, then John, his son, would have half of the DNA pattern that George would have. If there are no similarities, then we know that John is not the son of the man they've found on the mountain.

NOVA: How has DNA testing improved in recent years?

RYSIECKI: There are now three generations of DNA testing. The main aim has been to make them more sensitive in terms of being able to detect smaller and smaller amounts of DNA. The push for that has been from the forensic applications. We have all three types of testing going on here. The very first type of testing is the most powerful, but it needs a lot of DNA. The latest type of testing requires very little DNA, it's very sensitive, and it's very quick. But it's not nearly as powerful as the first one.

NOVA: What is the process of DNA profiling?

RYSIECKI: In all three generations of DNA testing, what you have to do is extract the DNA from the sample, and that involves breaking open the cell. We usually do that with a detergent, which releases all the contents of the cell. There are proteins in there, there are lipids, and there is DNA. We purify the DNA away from the other components. The system we're most likely to use then is called the Polymerase Chain Reaction (PCR). That takes the DNA that you have and makes copies of it. So if you only have a small amount of DNA, by going through this PCR 20 or 30 times, you can amplify the amount of DNA you have until there is enough there to really analyze.

NOVA: Is there a specific area of the DNA that you focus on?

Could cutting-edge DNA profiling, only several years old, answer the 75-year mystery of Mount Everest?

RYSIECKI: When we are doing this PCR test, what we are doing is looking at seven or eight different areas in the DNA. And these are areas that are very variable in the population. While I said earlier that your DNA is unique to you, and my DNA is unique to me, actually, most of it is the same from one person to the next. We have masses of DNA in each of our cells—if I took just one of your cells, and if I stretched out all the DNA, there would be about a meter in there, so there really is a lot of it, and most of it is the same. But there are areas in the DNA which are "hypervariable," and that means there are lots of different forms in the population. And these are the pieces that are useful for what we are doing.

So we would focus in on eight or nine of such areas of variability. And in each of these areas, the person we're looking at has two copies, one that they inherited from their mother and one from their father. So if we look at eight or nine of these areas, and we look at a man and his son, we'd find that half of the pieces in the man had been passed on to his son, so we should see 50 percent or more concurrence between the two. Of course, the other half would come from his mother.

NOVA: How long would it take to get a definite result?

RYSIECKI: That very much depends on the sample that comes from Everest. It may be that we try and we can't get anything from it—the DNA that was in there is completely gone, it's been degraded into tiny pieces that are of no use. If that's the case, then that's it, there's nothing more we can do. Or it may be that we can get DNA from it, but we have to try two or three times. So it's hard to project. Two or three weeks would be a reasonable time-scale in which to get an answer.

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Photos courtesy of Cellmark Diagnostics.

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