Best Evidence: NIST’s John M. Butler on Advances in Forensics
Scientist Interview: September 2011
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Do mini-STRs actually speed up what you can do? Or do they just allow you to work on smaller samples?
They allow you to use smaller pieces of DNA. You can do a result from a bone sample or a tooth or other things you couldn’t do before. Until mini-STRs, you had to use mitochondrial DNA, which is a more robust molecule and is present in higher copy number in cells. In order to do a sample back in the 1990s, if you had a bone, or a single hair or something, you’d have to do it with mitochondrial DNA. The challenge there is that all of a subject’s siblings, the maternal relatives, are going to have the same mitochondrial DNA as the subject, because it’s inherited from the mother. So you don’t have the capability to separate people as well. Having a technology like mini-STRs, which basically allows you to analyze smaller pieces or fragmented DNA—even from a bone or hair—can extend the capability of what you can do. That’s what fuels the interest.
What other significant developments in forensic DNA analysis have come about since your work with mini-STRs?
One would be Y-STRs. We did some of that work, and Mecki Prinz in the Office of Chief Medical Examiner in New York did a lot of it. Y-STR gives you the capability to look just at the male portion of a DNA sample. In a sexual-assault case, in particular, you have a mixture of the male perpetrator’s sperm and the female DNA. With Y-STR you can selectively extract the male DNA, because the female doesn’t contain a Y chromosome. So by making PCR primers specific to the male chromosome, you have that capability to fish out a Y chromosome—male information from a mixture.
Using only the Y chromosome also allows you to trace genealogy. The surname—such as Butler, in my case—is transferred from father to son, so you can actually trace genealogy with Y chromosome testing. We did a lot of the early work, in 2000 and 2001, on Y chromosome testing. I was personally interested in it because I wanted to develop a bigger multiplex—that is, the capability of simultaneously testing more DNA sites at once.
What do you consider the biggest advances in DNA testing that are in the works right now? In other words, if we look back in a decade on the highest-cited papers from 2011, what do you think they’ll be?
A big thing right now is working on rapid DNA. Can we speed up the process even further? Right now it takes about eight hours to do a DNA test. We’d like to move that down to less than an hour. One thing we’re working on is identifying enzymes that can be used to speed up PCR, which is the longest part of the process—amplifying 13 or 20 different sites in the human genome simultaneously.
"Right now it takes about eight hours to do a DNA test. We’d like to move that down to less than an hour,” says John M. Butler of the National Institute of Standards and Technology, Gaithersburg, Maryland..."
Another big area, although we’re not doing a lot in it right now, is ethnicity testing and the capability of figuring out what someone looks like from DNA—predicting their skin color, eye color, hair color, and their geographic origins, whether they’re from, say, Pakistan, or an African nation, for example. It could be very beneficial, depending on the matter being investigated. A lot of effort on that is being done by Manfred Kayser at Erasmus University in the Netherlands. If I was to predict who’s going to be the most-cited author ten years from now, my guess would be Manfred Kayser because of this work. He has a very large research group working on it.
Kayser just published an article claiming that with six different sites in the DNA you can actually establish with 80 or 90% reliability what eye color someone is going to have. He has another paper, published last December, describing the ability to age a sample within plus or minus nine years. So that means you can identify the age of the individual who deposited that biological sample to plus or minus nine years. Those types of things will extend the capability of forensic testing, far beyond this simple question of, “Is this the person who did it or not?”
If you can bring the speed of DNA testing down to an hour, how does that change the way DNA fingerprinting can be used in practice?
It totally changes the capability of what someone can do. The way things are done right now, a sample is taken back to the laboratory and a test is done. But if you have a situation like with Osama Bin Laden, where you’d like to identify somebody as quickly as possible, that would be very beneficial. Can you identify somebody on a battlefield? Or, say, someone’s getting on an airplane and you want to make sure, while they’re waiting there in the airport, that they are who they say they are, that they’re not on some watch list. Do you give somebody a visa when they show up at a U.S. embassy overseas and you want to know if they’re really related to somebody?
The Department of Homeland Security is really interested in using DNA for kinship analysis at high speeds, so you can determine within the embassy whether you give that person a visa or not—rather than sending the sample back to the U.S. or to some other laboratory to have a test done. Can you do that on-site and at high speeds? It will totally change the capability of what can be done. Even in biometrics: do you allow someone access to a facility or to a computer? It’s about identity testing—"Is this the right person?”— instead of determining what they look like or whether they’ll have heart disease ten years from now. But the types of markers used for forensic testing aim to separate two people from one another.
What are you spending most of your time working on now?
I’m now more interested in teaching and making sure people understand how to do things properly than in the research itself. My personal focus is more on writing books and putting together training materials. I think this is the biggest need right now—for people who use these commercial kits to have a far better understanding of what’s actually going on. I feel my most important legacy will be my books, in terms of training people how to do this. That will be far more valuable than the research.
Don’t you miss the puzzle-solving aspect of research?
There’s still puzzle solving. Teaching, for me, is a different type of puzzle. I just finished writing my fourth book. I spent a lot of time thinking about what’s really needed by the forensic science community. I visit labs all over the world and I have an opportunity to give talks in those labs. And every time I go to a lab, I ask to see the facility in detail. Sometimes I’ll spend a couple of hours going through the lab, seeing how do they do things, what challenges they’re facing, getting into the puzzle: How can they make it more efficient? I may offer some suggestions: "Have you thought about doing this?" Or, "This is what I saw in another lab where they did this type of handling of the evidence. This is how they separated these problems so they didn’t have contamination with their DNA." I feel I’m able to solve a different type of puzzle that way. The challenge is still there.
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