DNA, the silver bullet for solving crime…or is it?’ With Dr Georgina Meakin
Jim: Welcome to Science in Focus. A free public lecture series showcasing the latest research from prominent UTS scientists. I'm Jim McNamara, Deputy Dean of the UTS Faculty of Science. In accordance with UTS custom, I would like to acknowledge the Gadigal people of the Eora nation upon whose ancestral lands our city campus now stands. We pay our respects to their elders past and present, and acknowledge them as custodians of traditional knowledge about this place. Now I hope you enjoy science in focus.
Laura: Hello, I'm Laura McCaughey, and I'll be the moderator for today's event. We have a great turnout, both Australia wide and internationally for what I'm sure is going to be a fascinating talk by Dr. Georgina Meakin. Before I introduce Georgina though, I have a few housekeeping details to cover. If you have any questions during Georgina's talk, then please use the question marks, question and answer box down at the bottom of your screen. This'll allow you to type in questions and I can take note of these and ask them to Georgina at the end of her presentation. There's also an up voting function as part of this Q&A. If you really like a question someone else has asked, then please click the little thumbs up and this will let me know that more people are interested in hearing the answer to that question. This talk will also be recorded. We won't be filming any of your video or audio. And if you have any queries or you want further information of this recording, please e-mail science.future@UTS.edu.au.
Laura: So now to introduce tonight's speaker, Doctor Georgina Meakin is a senior lecturer at the Centre for Forensic Science here at UTS. The main focus of her research is in the transfer and persistence of DNA and how this affects the interpretation of DNA evidence in criminal casework. Georgina moved to UTS from University College London's Centre for the Forensic Sciences, where she set up the forensic DNA research facility with whom she continues collaborations. Georgina has also practised as a forensic scientist working at the Forensic Institute in Glasgow, which is my mother city, and for which she continues to provide advice and consultancy casework. I'd like to now hand over to Georgina, for her to tell us more about the fascinating world of forensics.
Georgina: Well, thank you very much, Laura. And thank you all for attending. So in order to set the scene for today's talk, looking into this, are the issues and challenges of forensic DNA evidence. I'd like to start first by giving a little bit of history of forensic DNA profiling. It essentially all started in the mid 1980s when Sir Alec Jeffreys at the University of Leicester discovered the scientific basis of what he termed to be 'DNA fingerprinting', what we tend to refer to as 'DNA profiling' nowadays.
Georgina: I hope you're all familiar with this image of the cell from your high school biology. Within the cell we have the nucleus that houses the majority of our DNA. As humans, we have twenty three pairs of chromosomes, and our DNA is coiled into these chromosomes housed within the nucleus. You may also be familiar with this double helical structure of DNA. Within the backbones of that double helix, we have these chemical structures called nucleotides, which we refer to by the first letter of their chemical name, A, T, C and G. And that's really all the chemistry I want to get into in today's talk. My point of telling you about these nucleotides is that, it is locations within our DNA where we have repeating sequence motifs of these nucleotides, the number of which differ between individuals. And this is the scientific basis that Sir Alec Jeffreys discovered. So, for example, here you see the motif TCTA, repeated eight times. And that number of repeats can differ between each of us.
Georgina: We are aware of different areas within our DNA that have different sequence motifs that repeat different numbers of times and each location on each chromosome is referred to as a locus or plural loci. So let's take two individuals, for example, say we take this first individual and we examine and analyse a specific area or locus of their DNA. And we might observe that there are nine repeats of a particular sequence motif at that area. And we refer to this is as marker nine or allele nine. But I mentioned earlier that we have pairs of chromosomes, and that's because we inherit one set from our father and one set from our mother. So we have one marker from one parent. And then when we analyse, we'll see another marker from the other parent. So, for example, this individual might have 10 repeats or marker 10, as their other copy. When we analyse DNA in the laboratory, we generate essentially a graph of a series of peaks. So this will look like two peaks on that graph and the software will label it as 9 and 10. So let's take the other individual. We may analyse their DNA at the same location and see 11 repeats, or marker 11.
Georgina: It is also possible to inherit the same copy of ... it's also possible to inherit copies of the same marker from both your mother and father. And in this situation, for example, they might also have eleven repeats in their other marker. And in this case, we would see one peak at that location on the graph representing two copies of that allele. So when we look at a full DNA profile, we analyse DNA at a number of different locations. And this is an example that's generated by a particular chemistry called MGM select that is used by some casework laboratories within England and Wales. But the number of locations that are analysed, and the specificity of the different locations that are used depends on the kits and depends on the jurisdiction and country that is doing the analysis. But in this example, we see 17 different areas being analysed. 16 have those short tandem repeats, those repeating motifs that we're interested in the number of. And then an additional location that we refer to as amelogenin which examines the gender of the person who donated the DNA. So, for example, this DNA comes from a male because we see that X Y present at this location. But if we were to only see an X, then this DNA would be coming from a female. So within this profile we see and these grey bars at the top, which indicate the location of the DNA that's being tested, we see the peaks that are labelled with the numbers of repeats. And as I mentioned earlier, you expect to see two peaks, one representing a mark inherited from the mother, one from the father, although it is possible just to see a single peak. But if you were to see more than two peaks at one particular location, this would indicate that you're actually recovering DNA from a mixture of more than one individual.
Georgina: So going back to our timeline, we see that in 1986 was the first time that this form of DNA analysis was used within forensic casework. And it was ultimately used and lead to the conviction of Colin Pitchfork for the rape and murder of two girls in Leicestershire. And then what proceeded after that is what I like to refer to as the 'heyday' of forensic DNA profiling. This is when DNA profiling was used a lot and very effectively to aid criminal investigations. And at that time, you needed visible body fluids. For example, a coin sized bloodstain or a semen stain. And therefore, you could be confident that the DNA was coming from that body fluid and therefore was deposited during the commission of that crime. And then in 1997, a landmark article was published in Nature from scientists at the Victoria Police. What they found was that when you touch an item, you can also leave DNA that can be recovered and analysed.
Georgina: So let's see that in a case. So this is a case in 2012, in which Ravesh Kumar and his companion were at home. Intruders broke into their home and they tied up Kumar and his companion, and they used duct tape across their mouth and nose. Intruders then spent a couple of hours ransacking the house and during which time the companion was able to get free and call for help. But unfortunately, by the time paramedics arrived, Ravesh Kumar had suffocated to death. Samples were taken from his fingernails as part of the criminal investigation, and DNA was recovered. And it was, these samples were targeted because it was believed that Kumar had, had fought back with this one of the intruders who had tied him up. So they were hoping to find DNA from the offender. And they did find DNA from another individual on those fingernails. And that DNA matched the DNA from Lucas Anderson.
Georgina: So what I'd like to do is ask you a question. Now I'd like to run a poll and I'd like to ask you, do you think that Lucas Anderson should be charged with this murder? Simple yes or no. I'm just going to launch that poll now. Hopefully we'll see it on your screen. So please indicate yes or no. And I'll give you a few moments to respond.
Georgina: Most of you have answered now. Numbers are still going up just a little bit. So I'll just give another moment or two. I'm going to end the poll now, and just show you the results. So as you'll see the majority of you said no. A few of you said yes. You probably could tell from my tone of voice or just simply your interest in actually being here for this talk, that perhaps it's not as clear cut as this. So how about I gave you a little bit more information? What if I were to tell you that at the time of the home invasion, Lucas Anderson was unconscious, drunk, in hospital with a blood alcohol level of five times the legal limit for driving. If I relaunch that poll, what would your answer be now? Should you continue to prosecute Lucas Anderson? Or would you perhaps seek elsewhere for an answer?
Georgina: The rest of you have answered. I'm just going to share the results now. OK, so now we shifted to an even greater majority saying no. Still a couple of you thinking that you would proceed to charge, charge him. Interestingly, the prosecutor shared that view . I'll just stop sharing results now. So interestingly, the prosecutors did continue to share that view, because you know, they questioned the validity of the alibi. However, assuming that all of the hospital records are correct, then his alibi was ironclad. He genuinely was in hospital at the time of the invasion. So, of course, this raises the question of how did his DNA get to be on the fingernails of Ravesh Kumar? So if we return back to that key Nature paper that essentially revolutionised the way that we do DNA. Thew way we look for DNA evidence at crime scenes. Not only did they observe that when you touch something, you leave DNA. But they also observed that when you touch something that someone else has handled, you can transfer their DNA onwards. And this is known as 'indirect DNA transfer'. So going forward then, the number of researchers started to do some more experimentation to try and figure out under what circumstances does this happen, and what do we expect to see? So, for example, a number of the early studies looked at clean items, so they clean them free of DNA. So for example, a glass beaker or plastic tube. They then asked volunteers to shake hands, for example, for a minute or even as long as two minutes. And then one of the individuals handled the glass beaker, for example. And then it was swabbed for DNA. And what they observed was a whole variety of different results. It could be a single source profile coming just from the person who handled the item.
Georgina: It could be a mixture of DNA, in which the major component, the majority of the DNA, was coming from the person who handled the item and a minor profile being indirectly transferred from the handshaker; or it could even be a mixed profile with a major profile as the DNA from the handshaker and the minor profile was coming from the handler or even a single source profile from the handshaker and no DNA from the person who actually touched the item.
Georgina: So this led to obviously questions about this concept of indirect DNA transfer. And what do we expect to see? And when we recover DNA evidence at a crime scene, do we know whether the DNA got there directly or indirectly? Now, clearly, these were very controlled laboratory experiments. And so we wanted to do some research to kind of step in the direction of being a little bit more realistic. So this study comes from a student of mine at University College London from a few years ago. And what we did was we asked volunteers to initially handle the item so that we could have some sure background level of DNA on the item. We asked the volunteers to handle knives and they handled them in a particular way to leave this background level of DNA. We then asked volunteers to shake hands. But this time we asked them to shake hands for just 10 seconds. So a somewhat shorter handshake than what had been previously looked at and perhaps something a little bit more realistic to kind of the levels of casual contact that you might have with people on a day to day basis.
Georgina: And then we asked a volunteer to take one of their own knives and stab it into a foam block for a minute. So we had four pairings of volunteers. In the first instance, we only saw DNA from the what we refer to as the regular user, so the person who'd regularly use the knife and then stabbed it in the foam block. For that pairing of volunteers, we actually only saw DNA coming from that one person. We didn't see any DNA from the handshake.
Georgina: But with the other three pairs of volunteers, we saw about 10 percent of the DNA coming from the handshaker.
Georgina: So not only did this demonstrate that even when you have a background level of DNA, you can still detect indirectly transferred DNA from the handshaker.
Georgina: But it also showed that even with a 10 second quite short contact with someone, you can also transfer that DNA onwards. But more than that, we saw a certain amount of unknown DNA that these participants were bringing in to the lab with them. In particular, one pairing of volunteers, we saw quite a lot of unknown DNA, about 10 percent of the DNA that they left on the knife. And it was a particular male profile. So we asked the volunteer, did they have any idea where that DNA was coming from? And they said, "Well, I walk into campus every morning holding hands with my boyfriend". So we asked for his DNA profile. And yes, indeed, we found that the DNA matched his DNA. So this was DNA that ended up on those knife handles from someone who had never handled those knives, never even been in the laboratory where those knives were set up. So, again, providing further evidence of this concept of indirect DNA transfer under normal everyday circumstances.
Georgina: But what researchers have shown subsequently in a number of different papers is that we're commonly carrying around other people's DNA on our hand. And it can be up to 10, 15 percent of the DNA on our hands coming from someone else or several other people. Just to give you another research example, again from researchers from Victoria Police. They set up a clean room essentially where they cleaned down so that it was free of DNA so that they could observe where DNA was being brought in and where it was moving to. And they asked three participants to sit around this table for 20 minutes, whilst sharing, pouring out drinks from a shared jug into their own glasses, drinking the juice, having a chat for 20 minutes. Now, what this image shows is that the arrows indicate DNA just from Participant One. So Participant One has brought in the DNA obviously from their hands, they've handled the jug handle. And from there, the DNA has been transferred to Participant Two's hands when they've handled that jug, poured out their own glass of juice and from there onto the table, on to the chair, onto their own glass, etc. This is giving an illustration of how DNA can move around within a social situation.
Georgina: And then more than that. The researchers also identified again that unknown DNA that we brought in on the hands of the participants. And these arrows here, for example, show the unknown DNA that Participant One has brought into the room that they've then left on the table, on the glass, on the jug, etc. So, again, illustrating how easily DNA can be transferred.
Georgina: So what does this mean for casework? Well, firstly, there was quite a long debate as to whether indirect DNA transfer would actually occur within casework. Was it only within these kind of strict laboratory setting it was probably not until about the mid noughties that it was gradually accepted that indirect transfer is an issue and it is something that we need to consider within casework.
Georgina: So what about Lucas Anderson then? How did his DNA end up on the fingernails of the deceased? Well, as I mentioned, he was in hospital due to alcohol consumption and he had actually collapsed within a store and paramedics had been called to attend to him.
Georgina: So yes, you've guessed it, the same paramedics then attended the deceased at the crime scene. And what they think is that this little device that's used to clip onto the end of the finger to test for oxygen saturation in the blood, that that's the culprit that transferred the DNA from Lucas Anderson to Ravesh Kumar. Clearly, once this was identified, Lucas Anderson was released, having spent a number of months in jail awaiting trial.
Georgina: So in general, what does this mean for casework? Well, firstly, we need to think about contamination. When investigators attend the crime scene, they can't go dressed in ordinary clothes. As you can see, there is an example for those of you who might be fans of CSI Miami. She looks like she's dressed for a night out. She's probably examining her own hair in fact. For those of you in the U.K., might be more familiar with Silent Witness. And at least they're dressed in the right kind of crime scene suit that we're more familiar with. But still, the hair is on display, the face is on display, there's potential for DNA transfer from the investigator to crime scene.
Georgina: So what we need is that people dress appropriately when they attend crime scenes wearing a full crime scene suit with the hood up the mask on and ensure that the gap between the glove and the sleeve is appropriately sealed. Back in the day when we just needed a visible body fluid to get a DNA profile. It's no longer the case now. Yes, we would obviously still target visible body fluids at a crime scene that give valuable information. But now we can target items that we think have been handled within a crime scene and therefore get DNA, potentially get more mixed DNA profiles. And we need to start asking those questions of how and when did the DNA get there. Obviously, the most obvious explanation is that someone has handled the item. But we need to also consider indirect DNA transfer and also the possibility of transfer just by speaking, coughing within the vicinity of the item.
Georgina: So what do we need in order to answer these questions? Well, we need empirical research. We need to have more studies conducted under more real situations investigating different variables that we know can impact transfer and persistence of the DNA. In 2013 I co-authored a review article. Looking at all the publications at that stage, that had been studied in view of giving empirical data on DNA transfer. And we observed that more data was needed to inform and help forensic scientists give evidence on these matters. Then co-authored another review article in just last year. And although there's been a lot more research done on this subject, we still noted that more research is needed. There's still a lot of unanswered questions. And I'd like to illustrate the kinds of questions that we're tackling at the moment.
Georgina: There's essentially four different areas that we need information on in order to better understand DNA evidence when it's recovered from the crime scene. The first is transfer. Now, this can be direct transfer, ie. When you touch something and you leave DNA.
Georgina: So one of the key factors that we know can impact the amount of DNA you leave when you touch something is, your 'shedder status'. This was first identified in 2002. They basically showed that some people could be really good shedders and leave a lot of DNA and some people can be poor shedders and leave little DNA. A number of studies have been published investigating this, but I particularly like this one from researchers in Adelaide who have used DNA binding dye that fluoresces green. So when we see someone who is a really good shedder, he might be referred to as a heavy shedder. When they touch an item, so this is for example, a fingerprint on a glass slide. We see that there's a lot of DNA material present, a lot of green fluorescence. And then someone might be classed as an intermediate shedder. And as you can see there's less DNA present. And then someone might be considered a light shedder and even less DNA is deposited when they touch something.
Georgina: However, subsequent research has shown it's not quite as clear cut as being able to categorise people so easily and that people can leave DNA, different amounts of DNA, at different times of the day. And depending on whether they use the right or their left hand or other activities that they might have been doing immediately before touching something.
Georgina: In addition, the condition of someone's skin can impact how much DNA they leave. It's been shown that if you have a particular skin condition such as psoriasis or dermatitis, then they can leave, you can leave more DNA when you touch something because of those conditions.
Georgina: The age of the donor can have an impact. As you age, you leave less DNA. And this has been particularly observed for males rather than females.
Georgina: And I mentioned earlier the idea of activities prior to touching. So when we touch other items, we might be picking up more DNA from other people that we can then move on and leave when we touch the item of interest. Alternatively, we might also just be essentially touching ourselves: our hair, our face and therefore loading our hands with DNA material then therefore we might leave more DNA in that situation. But these are things that we still need to research a lot more. There's also a number of other factors, such as the type of surface or the nature of contact. For example, if you put more pressure, you'll leave more DNA. And these are all things that we need to research more. And there are more factors that perhaps we've yet to discover. What about indirect DNA transfer? Well, clearly the amount of DNA that's initially present on the surface is going to impact how much DNA is available to be moved on to another surface. So therefore, the amount of DNA that is initially present is going to completely depends on this fact, as I just mentioned. It's also going to be dependent on the biological source of the DNA and whether that is wet or dry. I mean, you'll know yourselves if you've had a nosebleed, for example, that when you have wet blood, that's going to transfer easily onto other surfaces and between surfaces. Whereas when it's dry, it's not ready to transfer so readily, although perhaps the blood, it might start flaking when it's dry and that is an additional variable to consider.
Georgina: And then the number of transfer steps. So talking about handshaking, we're talking about just one intermediate surface, and that's referred to as 'secondary transfer'. But tertiary transfer and other onward transfer is also possible that each time a transfer step occurs, less DNA is transferred. So this, again, affects the amount of DNA we might expect to see. And again, there'll be a variety of variables that we have yet to identify. So in addition to the ways in which DNA can get onto an item, we also need to consider how long the DNA has been on an item. Could the DNA have been at the crime scene before the crime occurred? So was it deposited completely irrelevant to the crime that occurred? So I'm commonly asked, how long does DNA last on a surface? And my answer is, how long is a piece of string? The challenge with persistence is that there is an awful lot of variables involved, and we don't really know them as fully as we would like. Hence the need for more research. So, for example, one key factor is the biological source of the DNA. And you'll be aware from news article that crimes, particularly sexual assaults, can be solved decades after the event occurred. And this is because sperm cells are really hardy. And they're hardy, they require an additional step during the laboratory analysis process to release the DNA from sperm cells so they can last for a long time and protect the DNA. And that's why we can get DNA from sperm cells literally decades after it was originally deposited.
Georgina: And similarly, if it's say, a lot of body fluid present, there's more DNA to persist for longer. But then on sort of touched or worn items, it tends to be less DNA and it may not last as long, although we need to do more research on this. The type of surface will impact how long an item, how long the DNA will persist for, environmental factors will affect it. So, for example, in summer conditions, when the temperature is hot, when there's a lot of UV and longer hours of daylight, the DNA is not going to persist as well as during wintery conditions when it's cold and darker. And we've demonstrated this being the case using a climate chamber from a student's research a couple of years ago. However, we also found the type of surface had an impact even on the ability of environmental factors to affect the persistence of DNA. And then whether the DNA has been treated in a particular way, by which I mean you might encounter a crime scene where the offender has tried to cover up the crime. So, for example, they've cleaned down the surfaces or perhaps they've set fire to it. And so when it comes to cleaning, again a student project from a couple of years ago, we looked at the impact of cleaning mugs and knives. And we saw that even just simply rubbing with the surface without any kind of cleaning product was enough to kind of physically remove a significant amount of DNA.
Georgina: So in addition to transfer and persistence, we also need to consider prevalence. Let's take background DNA. I mentioned earlier we don't live in a clean environment, there's going to be DNA on the surfaces around us. So on everyday surfaces, but also on like regularly worn items of clothing that might get left at crime scenes and regularly used tools that might be used as weapons. And then finally, we also need to understand more about the recovery of DNA.
Georgina: So, again, from the kind of TV shows, you might be familiar with this idea of using a cotton swab to recover DNA from the surface. And that probably is one of the most commonly used recovery methods. However, there is also a range of different kinds of swabs both in terms of shape, material and size. And therefore, how we go about swabbing can have an impact on the amount of DNA that we recover. In addition to the type of swab, how long you swab for, how much pressure do you put on the swab, whether you use one or two swabs, whether you wet the swab first, all of these variables have an impact on DNA recovery and I currently have a student working on this at the moment.
Georgina: And investigators might choose to cut out a sample, be it say from a bedsheet or an item of clothing or a cigarette butt, and recover DNA directly from the item. And then investigators might also use an adhesive piece of tape and within the UK this is routinely used for the recovery of DNA from clothing. So there's a variety of different methods and this is going to impact how much DNA we get from item of interest. And therefore research needs to be done to help inform the decisions being made about the type of method to use and what's best to maximise that DNA evidence.
Georgina: The other thing about recovery is a consideration of whether using a different method or targeting a different location on an item might give different information about the how and the when the DNA got there. I'd like to show you a piece of research that we're just in the process of finishing up that's trying to shed some light on this. And this is within the context of worn items of clothing, which are common items that are recovered from crime scenes.
Georgina: Now, ostensibly, when you recover an item of clothing, you're seeking DNA from the item of the most recent wearer, i.e., the person who committed the crime.
Georgina: But when we have mixed DNA profiles from an item of clothing, how do we know which DNA profile came from that person?
Georgina: And what about if the defendant were to provide the defence that yes, that is their item of clothing, but they gave it to a charity store the week before, for example. Or perhaps they lent it to a friend or left it on public transport. What then? How do we judge who was the last wearer of that item. Though it has been reported within the scientific literature that there are occasions when the last use or touch are results in the major contributor to mixed DNA profiles and that this has been observed in clothing.
Georgina: However in casework, I've also observed forensic scientists saying something like a major profile matching the defendant is what I would expect if he was the regular or usual wearer of the jacket. Now, clearly, it's possible that the regular wearer and last wearer are the same person. But what if, as I've just mentioned, the defendant provides an explanation and we as scientists need to try and evaluate these explanations?
Georgina: So a few years ago, we started the experimental work for a study at University College London that we are continuing on with the data analysis here at UTS. And in this experiment, we asked volunteers to regularly wear a brand new hoodie for four weeks. In order to do that, actually turn it into a regular worn item of clothing. And we tried to keep it fairly controlled so we could make comparisons across the different volunteers. And we asked them to wear the hoodies two days a week on Mondays and Wednesdays for six hours each day. But the six hours could be intermittent. At the end of the day, it's a hoodie, you put it on when you're cold, you take it off when you're hot. And we wanted to be as realistic as we could make it. We then asked volunteers to wash the hoodies on weekends with their, with the rest of their clothing in their routine way of doing their laundry. We then targeted one half of the hoodie for DNA. We sampled the inside collar, and inside cuff. These are areas that are routinely examined within casework for items of clothing and then also targeted underneath the arm and within the pocket, perhaps to see if these different locations could give us different information.
Georgina: We then asked a second person to wear the hoodie for four consecutive hours. And so again, we're envisioning that they just put on the hoodie, committed a crime and dumped it. And then we sampled the other half of the hoodie in the same locations being the inside collar, cuff, underarm, pocket.
Georgina: We used two different recovery methods. Firstly, we cut out a section from those different areas with the hypothesis that perhaps cutting out a section would give more DNA from the regular wearer, which might become a bit more ingrained into the item of clothing. We then used a second method, a mini tape, as I mentioned earlier, an adhesive piece of tape with the hypothesis that perhaps this would recover the DNA on the surface of the item and therefore give more DNA from the second wearer. Now, unfortunately, what we observed is very similar results across the different areas and across the two different methods. So unfortunately, neither of those hypotheses were ... the data didn't support either of these hypotheses. So just for the interest of simplicity, I'm just going to present to you one set of data. And this is looking at the inside collar and inside cuff using the minitape. So the way in which DNA is routinely examined from clothing within UK casework. So just to show you the results from one pair of volunteers. So from one pair of the volunteers, we saw the majority of the DNA was coming from the second wearer on both items with a little bit of DNA coming from the regular wearer.
Georgina: However, when we flip these two volunteers we saw a majority of the DNA is coming from the regular wearer with an even smaller amount coming from the second wearer. And what we observed, the reason for this is because coming back down to that concept to of shedder status that different people can leave different amounts of DNA. And with this pairing of volunteers, what had happened was we just by chance have paired a very good shedder with a very poor shedder. So when the very good shedder was the second wearer they left the most DNA, but when they were the regular wearer, they also left the most DNA. So having seen these two extremes with the other pairings of volunteers that we had, we saw everything in between. But with just four volunteers in this experiment, so it was a very small scale experiment, essentially a proof of concept study, what we showed was that neither of those earlier statements was true, or rather or alternatively, both of them are true but depending on the circumstances involved. So sometimes we see the major profile coming from the second wearer and sometimes we see the major profile from the regular wearer. So clearly, there's a lot more variables involved here and a lot more variables at play that we need to investigate further and better understand.
Georgina: So essentially, if you remember nothing from my talk today, I hope you remember this one concept. The finding of DNA from an exhibit does not necessarily come from the person who committed the crime, ie. DNA does not always equal guilty. And for those of you members of the public who live within jurisdictions that have juries, you may well serve on the jury one day. You may well be faced with DNA evidence. I'd like you to remember to think about the how and when of DNA evidence. And thinking about whether someone is guilty of a crime.
Georgina: And then finally, for those of you interested more broadly in the forensic sciences rather than just DNA, please do go check out our website at the Centre for Forensic Science at UTS and see what other kinds of fascinating research my colleagues are up to. Thank you very much.
Laura: Thanks Georgina. That was a really interesting talk. There's been lots of questions on the Q&A. Before I get to these questions, just to the audience, if you have any questions, pop them in the Q&A and I'll still be going through these as we ask Georgina the list we've already got. So to start off Georgina, are there any complications with X and Y peaks if the individual is intersex?
Georgina: Ok, so there are chromosomal alterations that can impact whether someone has, for example, an additional X chromosome. But here the area that's targeted, you're still just going to see a single peak for an X. So you're not going to see two peaks if there's two X chromosomes, if that makes sense. So perhaps the height of the peak might be informative. However, that's going to very much depend on whether you're seeing a mixture anyway. And also, there's a certain amount of variation that happens during the analysis process that can impact the peak height. So you don't always see exactly the same peak heights from two components as coming from the same individual.
Laura: Nothing in science is ever clear cut is it.
Georgina: No, not at all.
Laura: We've got a few questions about COVID. So can COVID-19 be transferred via DNA? And following on from that, do you think that because of COVID-19 and social distancing will help reduce contamination and confusion of DNA?
Georgina: Ok, so firstly, I'm not an expert in viruses at all, so I couldn't comment on whether the virus is transferred with the DNA or not. I'm afraid I can't help you with that. However, it's a really interesting question about whether social distancing is going to impact the issues of DNA transfer. Clearly, if we're not contacting people so much, we're not going to be transferring that DNA on so much. Similarly with the world that we're now living in, obviously we're cleaning a lot more, we're disinfecting a lot more, we're washing our hands a lot more. So I would hypothesise that this is going to have an impact on the amounts of DNA that are present due to the prevalence of DNA on everyday items. I would also hypothesise that it is going to impact the DNA that we're leaving on an item, whether the amount of DNA or perhaps we might be leaving less of other people's DNA simply because we're washing our hands. I don't know this is something that we're definitely going to want to research more going forward. And it also is going to make it even more challenging for forensic scientists simply because we rely heavily on the research that's currently being published to help inform decisions on the how and the when of the DNA. But now going forward, as crimes are committed in our essentially new world of being a bit more cleaner? Will that research still be relevant or do we need to do a lot more research in the new way that we're living in this cleaner environment to better understand prevalence and transfer of DNA? And I think we do.
Laura: I guess following on to that answer then is how far can DNA transfer via sneezing or coughing? Because it would seem hard, a bit hard to eliminate this from a crime scene.
Georgina: This is something that's been barely investigated. So there was an initial study. Well, I can't exactly when it was published. I think it is in the early noughties, so quite a long time ago that looked at the concept of coughing and talking at a crime scene and whether it was likely to contaminate a crime scene and the importance of being able to wear a mask to help prevent that. Or help to minimise it, sorry. So it's something that, you know, I've actually wanted to do some research with sneezing. And I started trying to do some pilot studies on this at University College London some years ago. And it's actually notoriously difficult to make someone sneeze on command. So that was the problem I was having using myself as a guinea pig obviously, of trying to make myself sneeze in order to get, trying to understand what impact sneezing might have on DNA position. So at the moment, it's more of a hypothesis that we believe that DNA can be deposited in this way and then there's a little bit of research to demonstrate that it can under very specific situation. But we definitely need to investigate that more. But like you say, it's a little bit a little bit challenging to investigate. But some people have started looking at speaking, in terms of what DNA can be deposited through speaking.
Laura: Yeah, there's a lot of research now regards to COVID, how far it can transfer via speaking and stuff, so -
Georgina: I saw a paper on this and they had a particular device that was simulating sneezing. And I thought that would be really great if I could get my hands on that device and use it from a DNA perspective.
Laura: Well, if only one good thing comes out of COVID, that could be it. Um, a lot of people like the question of what if there are identical twins? Can you tell them apart at all? And has there ever been a case where a wrong twin was convicted?
Georgina: Ok, so first part of the question. So the routine DNA profiling that I explained to you today, because it only looks at a number of different areas. So the example I gave you, 17 different areas or in some jurisdictions, perhaps 22 areas or even more. For identical twins, that DNA profile is going to be the same. However, we do have more advanced technology where we can sequence every nucleotide of the DNA, so all those letters we can actually read that sequence of the DNA. And there are occasions where even identical twins might have the odd letter that's different due to mutation. And then in addition to that, DNA goes through chemical modifications through life. So it has, it can gain what we call 'methylation' and the pattern of the methylation on DNA varies depending on a variety of habits.
Georgina: So, for example, if you smoke, what your diet is, if you drink alcohol, even the environment within the womb when you were developing as a baby, all those things have an impact on your methylation pattern. Which means that an identical twins will have a different methylation pattern. And that's a way in which we can also distinguish between DNA from, uh between identical twins. Whether there's been a case in which the wrong twin has been convicted, I don't know. That said though, I did work a case once some years ago in which there were identical twins. So it can happen.
Laura: We've got a couple of questions I'll ask them one at a time just to make it easier for you, though, that are all related to sort of contamination. Do police get proper training in DNA contamination?
Georgina: I hope so. I mean, I get involved sometimes and I've certainly given presentations to police officers on contamination minimisation and how best to wear the protective personal equipment. Obviously, we train our students as best we can to try and do it properly and they obviously go on and work within, some of them will go on and work within the police, but I don't know how routine it is. And I guess it will depend on the jurisdiction as well.
Laura: Do forensic labs collect and sequence the DNA of their staff and of police or first responders so that contamination can be identified?
Georgina: Yes and no. So I think the majority, if not all DNA laboratories, will have the DNA profiles of their staff. I can only speak for the UK on this, but I know that there's been a push by the forensic science regulator for crime scene examiners and police to provide their DNA and have a reference database for that. In terms of first responders though, when you think about a paramedic, I'm not sure. But certainly crime logs are kept. So anyone who has attended the crime scene will be recorded. So even if there isn't a database they can, if there's concerns over contamination, they can go and ask the person to take a sample of their DNA and make comparisons that way.
Laura: Well, that's good to know. Are there any problems with contamination of supplies from manufacturing? So in the labs, do you run unused swabs or materials to rule out any contamination?
Georgina: Yes, yes and yes. So there was a case again back in the day, I can't remember exactly when it was in Germany, and they referred to it as a phantom because they had this DNA profile that was coming up in all sorts of different cases all across the board. And it turned out that, yes, it was contamination of a particular tool that was being used at the manufacturing stage. So it is possible for that to happen. Only, we've learned more over the years. So manufacturers and suppliers have quite rigorous quality control processes in place to ensure that their supplies are DNA free when they're being used for forensic science purposes. And similarly, within forensic science laboratories, they will do background testing of the laboratories to ensure that their cleaning processes are appropriate. They'll do testing. You know, every test you do, you have a variety of negative controls and certainly with extraction blanks. So there will always be a test of kind of a blank tube from the start of the DNA extraction process to ensure that contamination isn't introduced at any point. Similarly, the kits that we use have serial numbers and they're always recorded within casework to ensure that if any contamination was discovered, that could be linked back to a particular serial number, it could be tracked. There are a lot of procedures in place to, to monitor for the risk of contamination because clearly DNA does get everywhere and we do have to be monitoring that and hopefully minimising it as best as we can.
Laura: In terms of cold cases,DNA evidence stay around indefinitely if it's being collected appropriately?
Georgina: It won't stay around indefinitely. It will degrade. But that rate of degradation is going to completely depend on how much was there in the first place, the biological source, you know, I mentioned earlier about sperm cells being super hardy and can hang around quite a long time. It'll depend on how the item has been packaged, how it's being stored. So there's, there is a lot of variables involved. And this is something that we don't fully understand and don't have complete research to fully understand the lengths of times involved. So that generally means that when you have a cold case, that we would sample it for DNA now, you probably would get a DNA result, but the question comes back to the: well how did the DNA get there and when did it get there? Is it a more modern sample because some form of contamination's happened during the time the item's been stored, so these will have questions that need to be asked when thinking about cold cases.
Laura: On that theme. Can you watch Netflix documentaries that focus on like bad forensics, the ones like the Innocence Files, or do you just get too annoyed?
Georgina: I do struggle with watching them. And I think, I think these days, because for me, DNA evidence is really about thinking about the how and the when did the DNA get there, these questions aren't commonly asked within these kinds of documentaries. That said though, the second season of Making a Murderer, I actually really enjoyed and it's because they actually did go and start doing some kind of some experiments to try and evaluate the different explanations for the findings of the different evidence. So I did quite enjoy that one I have to say. Guilty pleasure right there.
Laura: That's good. There are always our guilty pleasures. DNA was always seen in courts as being 100, well, never a hundred percent, but always like the golden standard for evidence. But now you're saying that it's not this silver bullet. So how are lawyers treating this? And what weighting is now given to DNA evidence in light of your research?
Georgina: Ok. So firstly, just to caveat that for a moment from saying, you know, using DNA from a visible biological fluid where we know the DNA, we're confident that the DNA came from that biological fluid for example blood. And we're pretty confident that that blood was deposited during the commission of the crime. That still means that DNA has a lot of power in those kinds of situations, so that that hasn't gone. But now the issues are, this idea of DNA being recovered from items that we think have been handled, that we're getting mixtures that we don't actually know which DNA is coming from who from the person who touched it or when it was deposited on there. And so now lawyers from a prosecution perspective are going to have to start thinking about these questions, you know, and thinking back to that case that I presented this evening. The prosecutors need to think about, is there sufficient evidence to go ahead with the prosecution? And the key question is, is there corroborating evidence? There really does need to be other evidence than just DNA when it comes to prosecuting someone. And then obviously from a defence perspective, defence lawyers are going to also be asking these questions because they're going to be trying to evaluate the evidence that's pointing towards their client and their defendant to see whether any scientific challenge can be made to it. So certainly in more recent years, these questions of the how and when are being asked a lot within the courtroom now when it comes to DNA evidence.
Laura: We've got another question here. One of our audience watched a crime TV show set in the future where the perpetrator sets off a little DNA bomb like a flea bomb, and it disperses hundreds of people's DNA into the air to provide a kind of anonymity. Do you think this could become a reality or is it too far fetched?
Georgina: That's an interesting one! I don't know. I mean, if you could spray DNA in that way, then certainly it would hamper the interpretation of DNA findings. But whether you'd be able to set off some kind of bomb to enable that, I really don't know. I think that's, that requires some physics knowledge, right there and I'm afraid I don't have that.
Laura: What samples can extract DNA from. You've mentioned a few, but can you extracted from things like sweat or any of the less obvious bodily fluids?
Georgina: So, sweat contains DNA and in essentially two ways that we're aware of. So one is that as the sweat comes out of the ducts, it brings cell, cellular material essentially from the ducts into the sweat. And so within those cells there'd be DNA. But there's a couple of researchers have shown that cell-free DNA exists within sweat as well. So this can also be detected and therefore will be deposited via sweat. But essentially, most biological materials you're going to get DNA from, but just to varying degrees. So, for example, you can get DNA from hair, specifically from the root of the hair. Although you can get different kind of DNA from the shaft. You can get DNA from urine, from faeces, from vomit. But it all depends on how much cellular material has been deposited within that fluid as it's come out the body essentially.
Laura: Well, unfortunately, we're all out of time for more questions. I'd like to thank Georgina for such an interesting and thought-provoking talk. And I'd also like to thank all of our audience for attending and for asking such great questions. If you want to watch this talk again or if you want to get your friends or colleagues to watch it, a copy of this talk will be available on our website, pretty soon. Have a lovely day, everyone, and keep safe.
Georgina: Thank you very much.
TV shows would have us believe that forensic scientists look like models and DNA found at crime scenes always comes from the offender. These are both wrong. Whilst many scientists would be happy to be mistaken for a model, misinterpreting DNA found at a crime scene clearly has much graver consequences.
Historically, when a visible blood or detectable semen stain was needed to provide a DNA profile, it was clear that the DNA had been deposited during the commission of the crime. However, with increased sensitivity of DNA technology, we can now obtain good quality DNA profiles from just a handful of cells that are not visible to the naked eye and not detectable by routine crime scene methods. As such, those cells could have been deposited at the time of the crime, but could also have been present before the crime occurred or have been inadvertently transferred to the surface of interest, and therefore could come from someone who had nothing to do with the crime. So when DNA is found at a crime scene, can we establish whether it came from the perpetrator or from someone innocent?
In this Science in Focus talk, Dr Meakin will discuss the latest research investigating the answer to this question…but be warned, you will not look at forensic science shows in the same way again!
UTS Science in Focus is a free public lecture series showcasing the latest research from prominent UTS scientists and researchers.