Genes at the scene

How is DNA evidence used to catch criminals?
14 February 2018

Interview with 

Eleanor Graham, Northumbria University


Hands covered in blood


If you’re a fan of TV cop shows like CSI, you’ll know all about forensic genetics - using DNA to help police with their investigations. But how do they actually do it? And how much DNA do they really need? In search of clues, Kat Arney donned her deerstalker and headed up to Newcastle to meet researcher Eleanor Graham, a lecturer in forensic science at Northumbria University.

Eleanor - Traditionally, forensic DNA profiling has basically been focused on areas of the genome known as STRs which are little bits of the genome, repetitive bits of the genome showing loads of variation between different people so they can be used to tell two people apart.

Kat - This is kind of genetic finger printing when you see someone holding it up and there's all the bars and you're like, “yeah, yes, that’s you and that’s not you.”

Eleanor - That’s basically what it is, yes and the finger printing term is the term applied to the original technique developed in the ‘80s by Alec Jeffries in Leicester Uni and then it was taken and developed on to be more applicable to casework examples.

One of the most challenging aspect of forensic genetics is the actual samples you have to work with rather than the actual DNA work because the techniques we use in the lab, if you’ve got loads of good quality, high quality DNA you can pretty much look at anything you want to in a genome. But with forensic case work, you're working with really badly decomposed samples or burnt samples or miniscule ones that you can't even see with your eye. So all the techniques basically have to work with these challenging sample types and that’s where the interesting bits come into it, I think.

Kat - So addressing that challenge, so you’ve got a tiny speck of blood or a couple of pieces of hair, what are the sorts of things that you could do to try and get some genetic information out of that?

Eleanor - Well as I said, traditionally, the genetic information that we’ve been focusing on really tells us the difference between two people or we can do things like kinship analysis: who is related to the owner of that DNA sample?

We’re now moving into the realm of more what we call ‘phenotypic’ characteristics. So, we are now in an area where it’s possible to determine things about what people look like in terms of hair colour, eye colour, skin tones, some aspects of stature, facial characteristics. So we are in a realm that we can do that.

There's also markers that we can use to trace geographic ancestry, so you may be able to tell something about where someone’s from in the world. But it’s all still on a very statistical basis, not a 100 per cent.

Kat - And in terms of dealing with these samples, how do you amplify the DNA? How do you get enough DNA to actually study from a tiny speck of blood and what are the challenges and the risks with doing that?

Eleanor - The lab techniques that we use are the same all over the world – genetics, molecular biology. It’s all around the basic polymerase chain reaction at the moment. So, PCR technique, you choose which bits of DNA you want to look at, you design a system which will amplify up those specific bits of DNA. The challenges that we have with our sample types are the extreme sensitivity of the methods that we use.

These methods are capable of developing a profile from as little as a single cell or even less than a single cell. I'm talking about fragments of DNA that may be present on surfaces that have been touched or literally fragments that are in the atmosphere. These fragments, if they can get into our test tubes in the laboratory, they can actually show up in our results. That’s how sensitive these tests are.

That obviously opens up a can of worms for contamination issues associated with forensic testing which have been a problem in the past. Gross contamination issues tend to be picked up very easily, but the more tricky ones to deal with are what we call ‘sporadic’ or ‘random contamination events’ where literally, fragments from the atmosphere may appear in our test results and we have to determine whether it’s from our sample or from somewhere else.

Kat - This is something I've always wanted to know like, everyone who works at the forensic lab, do you have to get your DNA analysed and put in the database so you know that if you have accidentally contaminated something, you know it wasn’t you that did the crime? “I'm innocent, guv!”

Eleanor - Yeah. This is one of the quite interesting aspect of our student projects as well because we always say at the beginning, “If you make a mistake, don’t hide it because we’ll know it was you.” So yeah basically, everybody that works in a DNA lab will have their DNA profiles on an elimination database. This goes for also, people who work at crime scenes – police officers, laboratory workers, but also extends to personnel who actually manufacture the reagents and the consumables used for forensic DNA testing.

This goes back to a case quite a few years ago now. In Germany, it is known as the Phantom of Heilbronn case where the same female DNA profile was turning up in crime scenes all over the country, all over Germany, ranging from homicides to thefts - a wide range of different types of crime with the same perpetrator turning up in the DNA profiles.

Kat - A master criminal!

Eleanor - It seems so but it was a bit too strange to be true. So eventually, someone looked into the details of this and it turned out that the profiles were all turning up on the swabs from the same manufacturer. When they went to the manufacturers and asked could they sample of stuff, lo and behold, one of the females who produce the swabs was found to match the crime scene stains. So since then, it is so important that we have these elimination databases in place.

Kat - From watching crime dramas and things like that, most of us will have an idea that using forensic genetic analysis is something you do for human crimes, murders, sexual assaults, that kind of stuff. But obviously, animals have DNA and animals can be involved in crimes and trafficking. What are some of the ways we can use forensic DNA information to solve other non-human crimes?

Eleanor - That’s absolutely the case and we do teach that in our classes here at Northumbria that it’s not all about the human DNA. Animals all have the same patterns of DNA, the same features in their DNA, some of them are incredibly similar to us like the chimpanzee showing 97 per cent DNA the same as us.

So, we do use the same methodology to work on crimes and we can think about these crimes in different ways. The animal could be a victim in the case of poaching and trafficking of illegal species, and they can actually be used as weapons as well. So we’ve had cases where the DNA profile of a dog has been taken from a victim when the dog has been used as an attack animal.

We have them in all different scenarios and this also extends to non-animal sources. We can use plant DNA in exactly the same way, tracing things like the origin of cannabis leaves. So, have they all come from the same plant? Have they come from the same plantation? Where in the world are they coming from? So we can use DNA to establish that as well.

Kat - What about ancient crimes or even ancient people? What are the challenges with trying to use your forensic method there?

Eleanor - This is something that’s always interesting quite a lot. It’s the really challenging aspect of how you can actually get enough information from the really, really degraded, really difficult sample types. But the techniques to actually recover the DNA from the materials that are left have really come along now. Both the sensitivity of the methods themselves and the recovery of the actual – what’s left – have advanced to a stage where we can actually paint quite an interesting picture of people of the past.

We have done some work on skeletons that were found at Roman sites up in Northumbria near Hadrian’s Wall. We were able to answer some questions that the archaeologists had conflicting evidence about like the actual origins of the skeletons found in certain environments within a fort. It was thought by archaeologists that maybe the people were the Roman army that had come in. But our genetic test showed that they actually had more of a British origin so we were able to answer questions like that.

And even in some cases for ancient DNA, the sex of an individual might not be obvious from the remains that are found. If you don’t find the skull or the pelvis, it can be quite difficult to assign sex to an individual. We’ve been out to do that as well to be able to determine biologically based on the presence of X and Y chromosomes or just a Y chromosome whether or not a skeleton remains are male or female which can also be really fascinating depending on the circumstances.

Kat - Eleanor Graham, from Northumbria University.


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