WEBVTT - DNA Forensics 0:00:04.240 --> 0:00:11.880 Get in with technology with tech stuff from stuff Peter 0:00:11.960 --> 0:00:14.840 are welcome to tech Stuff. I'm Jonathan Strickland and joining 0:00:14.880 --> 0:00:17.800 me in the studio today is the illustrious and Mr 0:00:18.000 --> 0:00:20.279 Ben Bowland of stuff they don't want you to know 0:00:20.400 --> 0:00:24.720 and car stuff, among other things. Welcome back to the show. Ben, Hey, Jonathan, 0:00:24.880 --> 0:00:27.960 thank you for having me. Oh man, illustrious? Is it 0:00:28.040 --> 0:00:30.640 the pain meds from my recent doctor visit? Or am 0:00:30.640 --> 0:00:33.839 I'm moving up in the world. It's literally that you're illustrated. Actually, 0:00:33.880 --> 0:00:37.279 there's true. Ben has had people mark all over him 0:00:37.320 --> 0:00:40.120 and crayon today. I'm not gonna ask why I don't 0:00:40.120 --> 0:00:42.400 get into personal lives in the show. Well, you know, 0:00:42.560 --> 0:00:44.280 it's it's a big deal. Whenever I could be on 0:00:44.320 --> 0:00:47.159 the show and I wanted to do something special, my 0:00:47.240 --> 0:00:51.000 suits at the cleaners got a bunch of Sharpie's and 0:00:51.120 --> 0:00:52.839 ask people to go nuts. Yeah, it's kind of like 0:00:52.920 --> 0:00:56.480 body paint, but really they'll super like on the cheap 0:00:56.520 --> 0:00:59.160 because we just can't. We don't have that in our budget, honestly, 0:00:59.400 --> 0:01:03.240 right note, but hope springs eternal. What's weird about having 0:01:03.600 --> 0:01:07.039 um all these all these colors and markers all over me? 0:01:07.160 --> 0:01:10.839 Is that anything I touched literally is leaving a trace? Yeah, 0:01:10.880 --> 0:01:12.800 and that kind of you know, we were going to 0:01:12.880 --> 0:01:16.640 have a really in depth conversation on how catalytic converters work, 0:01:16.720 --> 0:01:19.560 but once I noticed you doing that, I thought, why 0:01:19.600 --> 0:01:22.560 don't we talk about DNA forensics, like the traces people 0:01:22.680 --> 0:01:26.600 leave behind. So, uh, that's why I decided to switch 0:01:26.600 --> 0:01:28.440 in the last minute. I hope you can roll with it. 0:01:28.640 --> 0:01:33.000 Oh yeah, yeah, and just in in you know, Ben 0:01:33.080 --> 0:01:35.600 and I have talked a little bit about our our 0:01:35.760 --> 0:01:40.240 mutual interest in the true crime uh discipline, the whole 0:01:40.240 --> 0:01:43.040 the whole true crime like field, and it turns out 0:01:43.080 --> 0:01:45.000 we're not the only ones in the office. There are 0:01:45.000 --> 0:01:47.000 certain people in the office who have a really deep 0:01:47.400 --> 0:01:50.080 interest in this sort of stuff, and so we thought, 0:01:50.120 --> 0:01:52.080 you know, would be kind of fun to explore the 0:01:52.760 --> 0:01:55.680 concept in different shows. So if you listen to all 0:01:55.720 --> 0:01:57.960 of How Stuff Work shows, you may have noticed things 0:01:58.000 --> 0:02:01.520 popping up here and there that's not entirely by accident. 0:02:02.520 --> 0:02:05.080 So uh really was one of those things where as 0:02:05.120 --> 0:02:06.840 we all started talking, we're like, hey, you know, I 0:02:06.840 --> 0:02:08.440 would like to do something in that and we can 0:02:08.480 --> 0:02:11.120 kind of It's almost like an easter egg for those 0:02:11.160 --> 0:02:14.160 of you who subscribe to lots of different shows, and 0:02:14.200 --> 0:02:15.520 you should let us know if you thought it was 0:02:15.560 --> 0:02:19.760 really cool. So from the technology standpoint, we thought DNA 0:02:19.880 --> 0:02:23.560 forensics would be really really interesting to cover and to 0:02:23.639 --> 0:02:27.359 talk about how it actually works. Uh, what are the processes, 0:02:27.600 --> 0:02:30.160 what are some of the challenges, What are some of 0:02:30.160 --> 0:02:33.079 the things that people are doing with DNA forensics now 0:02:33.200 --> 0:02:37.240 that might end up helping, uh, like investigations in the future. 0:02:37.639 --> 0:02:40.600 Where could it actually end up giving us a false positive, 0:02:40.639 --> 0:02:42.919 because there there is the possibility of that as well. 0:02:43.400 --> 0:02:45.440 But to start it all off, we really kind of 0:02:45.480 --> 0:02:47.840 have to lay the groundwork. Yeah, I was gonna I 0:02:47.880 --> 0:02:49.880 was just gonna ask you. I hate to be the 0:02:50.480 --> 0:02:54.120 bad kid in class right now, but what's what's DNA? 0:02:54.720 --> 0:03:01.600 D oxy ribonucleic acid, man, Yeah, that's what is so obviously, 0:03:01.680 --> 0:03:04.040 you know, anyone who's had science class, like a biology 0:03:04.040 --> 0:03:08.320 class anything recently, you know all about DNA. But you know, 0:03:08.360 --> 0:03:10.919 we gotta build from the ground up. So DNA is 0:03:10.960 --> 0:03:14.880 a molecule that carries the genetic instructions that govern the development, function, 0:03:14.919 --> 0:03:18.880 and reproduction of organisms. DNA is found in all of 0:03:18.919 --> 0:03:22.639 your cells. Essentially an entire blueprint of what makes you 0:03:22.639 --> 0:03:25.960 you is in every single one of your cells in 0:03:26.000 --> 0:03:29.840 the form of d N a uh, and the molecule 0:03:30.040 --> 0:03:32.440 is in that double helix form. So that says, if 0:03:32.440 --> 0:03:34.520 you were to make a ladder and then twisted into 0:03:34.600 --> 0:03:39.200 a twisty shape, that's the DNA double helix. The rungs 0:03:39.200 --> 0:03:41.040 in that letter are made up of pairs of what 0:03:41.080 --> 0:03:45.240 we call nucleotides. Alright, So each rung on the ladder 0:03:45.320 --> 0:03:49.320 is two different nucleotides that that bond together. Uh. There's 0:03:49.680 --> 0:03:54.360 adenine and thymine. Those always pair up together. So those 0:03:54.400 --> 0:03:57.800 are your two base pairs of nucleotides that will always join. 0:03:58.080 --> 0:04:01.680 And then there's guanine and cytosine and those always join. 0:04:02.400 --> 0:04:06.640 And it's the sequence of these pairs that end up 0:04:06.720 --> 0:04:11.240 determining what makes you you, right, yeah, yeah, so it 0:04:11.280 --> 0:04:15.720 could be. And these pairs can affect multiple the order 0:04:15.720 --> 0:04:19.920 of these pairs can affect multiple characteristics. Sure, yeah, absolutely. 0:04:20.000 --> 0:04:24.920 And also what's really interesting to me is that point 0:04:25.080 --> 0:04:29.479 nine of all the DNA that is in you is 0:04:29.520 --> 0:04:32.599 shared with every other human Like we we have ninety 0:04:33.160 --> 0:04:36.200 nine percent of our DNA is in common, which means 0:04:36.360 --> 0:04:38.919 the stuff that makes you who you are as indifferent 0:04:39.000 --> 0:04:42.000 from every other person, makes up just point one percent 0:04:42.920 --> 0:04:45.479 of your DNA. But that's all it takes, is that 0:04:45.560 --> 0:04:48.479 point one percent. That's about three million base pairs that 0:04:48.520 --> 0:04:52.840 are unique to you unless you have an identical sibling. 0:04:53.160 --> 0:04:57.360 Ah ah the old Now this goes into um, this 0:04:57.480 --> 0:05:02.040 verges into some good detective fiction. Now, yes, that old trope, 0:05:02.120 --> 0:05:04.240 the evil twin, Yeah, exactly, it wasn't me. It was 0:05:04.240 --> 0:05:07.360 my evil twin or or evil triplet or evil quadruplet 0:05:07.560 --> 0:05:10.560 really which we did an ill fated brain stuff but 0:05:10.600 --> 0:05:13.599 it was, oh my gosh, we did. We did. Yeah. 0:05:13.680 --> 0:05:16.200 If you if you watch brain Stuff, the video series, 0:05:16.240 --> 0:05:18.840 and you look up how twins work, Ben and I 0:05:18.920 --> 0:05:26.520 did a funny At the time, I thought. I still 0:05:26.520 --> 0:05:28.839 thought there were parts of it that were funny. Honestly, Ben, 0:05:28.920 --> 0:05:31.160 I still fully enjoy it, but my sense of humor 0:05:31.200 --> 0:05:33.840 is very corny. So but if you want to see, 0:05:34.240 --> 0:05:36.720 if you want to see me and Ben dressing up 0:05:36.720 --> 0:05:39.720 in two different types of outfits, like we're the good 0:05:39.760 --> 0:05:42.120 Ben and Jonathan and then there's the evil Ben and 0:05:42.200 --> 0:05:45.600 Jonathan and we each have an eye patch. Jonathan and 0:05:45.720 --> 0:05:47.760 I were talking and it was it was strange because 0:05:47.800 --> 0:05:50.160 when we were talking about doing this episode, we said, wow, 0:05:50.279 --> 0:05:55.239 how could we represent evil twins like I I patches? 0:05:55.320 --> 0:05:58.880 Clearly because you know, the goatee is not gonna work 0:05:58.920 --> 0:06:01.120 for right because and like neither of us were going 0:06:01.160 --> 0:06:03.320 to end up shaving just so that I can be 0:06:03.400 --> 0:06:05.599 the good twin. But both of us are the kind 0:06:05.600 --> 0:06:08.640 of person who would have an I patch. And actually 0:06:08.680 --> 0:06:11.000 I ended up taking a quick walk to a nearby 0:06:11.040 --> 0:06:13.920 toy store to pick some up. Um. So, at any rate, 0:06:13.960 --> 0:06:16.719 if you do have an identical sibling, your identical sibling 0:06:16.839 --> 0:06:20.200 shares your DNA. There they are identical, like the DNA. 0:06:20.360 --> 0:06:22.200 If you were to compare the two and look at 0:06:22.200 --> 0:06:25.120 those base pairs, they're going to be the same all 0:06:25.160 --> 0:06:28.200 the way down, right. So that's one of the that's 0:06:28.240 --> 0:06:32.520 one of the exceptions, really the exception. So our DNA 0:06:32.760 --> 0:06:36.520 can be found in twenty three pairs of chromosomes. That's 0:06:36.520 --> 0:06:39.160 what humans have. Not all animals have that many, so 0:06:39.360 --> 0:06:43.520 have fewer and etcetera, etcetera. So chromosomes are ribbons of 0:06:43.560 --> 0:06:46.240 protein essentially have a strand of DNA that are wrapped 0:06:46.320 --> 0:06:49.680 up in that and within each pair, one chromosome comes 0:06:49.720 --> 0:06:52.719 from your mother. One chromosome comes from your father, and 0:06:52.800 --> 0:06:56.599 that's what uh you know, those are the ingredients that 0:06:56.720 --> 0:06:59.520 come together to create the unique individual that is you 0:07:00.720 --> 0:07:04.159 and or your identical siblings. Uh So, if we took 0:07:04.400 --> 0:07:06.560 look at each person's DNA and pay attention to the 0:07:06.640 --> 0:07:08.640 order of those base pairs, we get something like a 0:07:08.760 --> 0:07:12.480 DNA fingerprint. It is unique to that person. But we 0:07:12.560 --> 0:07:15.800 can't just look at one section. We have to look 0:07:15.800 --> 0:07:18.520 at several different sections also known as loci in the 0:07:19.000 --> 0:07:24.360 in the parlance of forensics to get a robust fingerprint profile. So, 0:07:24.760 --> 0:07:27.480 just as we would look at a fingerprint and look 0:07:27.520 --> 0:07:30.760 for points of comparison to from from a from a 0:07:30.760 --> 0:07:33.640 fingerprint that we've gathered from a suspect, let's say, and 0:07:33.720 --> 0:07:35.960 a fingerprint that was left at the scene of a crime, 0:07:36.240 --> 0:07:38.200 you would have to look at several different points to 0:07:38.280 --> 0:07:41.160 make sure that all those points correspond to one another 0:07:41.280 --> 0:07:43.640 to say that there's a match. Same thing with DNA 0:07:43.840 --> 0:07:47.240 DNA forensics, you would look at several different locations along 0:07:47.280 --> 0:07:51.160 a strand of DNA and see if the same sequence 0:07:51.360 --> 0:07:57.520 of nucleotides were appearing on both sets, because that would 0:07:57.560 --> 0:08:01.720 tell you what are the statistical probabilities of the person 0:08:01.920 --> 0:08:04.600 that you suspect and the the evidence that was left 0:08:04.640 --> 0:08:08.080 behind are one and the same, right, Okay, So each 0:08:08.120 --> 0:08:11.720 time there's a new location, the more loci there are, 0:08:11.720 --> 0:08:14.840 the more certitude you have that you've got your catch. Yeah, 0:08:14.880 --> 0:08:17.560 if you were to say, look at just one location, 0:08:17.760 --> 0:08:21.040 then that would mean you would have a very you know, 0:08:21.080 --> 0:08:24.560 there's actually quite a good chance, depending upon the sequence, 0:08:25.040 --> 0:08:31.440 that coincidence could could completely explain away any any uh 0:08:31.840 --> 0:08:34.920 duplication there. Right, So it could just be coincidence. It 0:08:34.920 --> 0:08:38.599 could be that this person just coincidentally has that same sequence. 0:08:39.760 --> 0:08:43.920 As you add more loci, that becomes less and less likely. 0:08:44.440 --> 0:08:49.000 Uh FBI. The FBI has thirteen that they suggest the 0:08:49.440 --> 0:08:53.120 thirteen specific loca that's their standard, and that that results 0:08:53.120 --> 0:08:56.440 in about a one in a billion chance that if 0:08:56.440 --> 0:08:59.200 you were to take all thirteen loca and compare the 0:08:59.280 --> 0:09:02.280 two strength you know, the stuff that was left at 0:09:02.280 --> 0:09:04.880 the evidence and the suspect or whatever is in the database. 0:09:05.440 --> 0:09:08.320 If you were to compare the two and they were 0:09:08.360 --> 0:09:11.720 to come up equal at all thirteen, it's a one 0:09:11.760 --> 0:09:15.600 in a billion chance that somebody else besides the person 0:09:15.640 --> 0:09:19.440 you're looking at, possesses that. So seven of the six 0:09:19.440 --> 0:09:22.400 other people in the world. Yeah, it's like flash forward 0:09:22.440 --> 0:09:26.080 to that day in court where someone's doing that horrible 0:09:26.120 --> 0:09:30.360 reference joke and going, so you're saying that there's a chance. Yeah, 0:09:30.440 --> 0:09:34.319 And and honestly, people who are analyzing the stuff, they 0:09:34.440 --> 0:09:38.720 speak in statistical probabilities, because you cannot say for certain 0:09:39.440 --> 0:09:42.320 that this person left behind that DNA. You can say, like, 0:09:42.640 --> 0:09:46.160 what is the statistical probability that they did, And then 0:09:46.200 --> 0:09:48.800 you look at other elements of the case, right, like saying, 0:09:49.000 --> 0:09:51.800 all right, can we put the person in that area, 0:09:51.840 --> 0:09:56.000 because let's say that it's in a small town. Well, 0:09:56.080 --> 0:09:57.920 if it's a one in a billion chance and you 0:09:57.960 --> 0:10:01.199 know that the suspect was in that small town, that's 0:10:01.559 --> 0:10:06.080 pretty darn compelling. Yeah, because why are the chances that 0:10:06.160 --> 0:10:08.600 the other one of the other six people in the 0:10:08.840 --> 0:10:12.079 entire world was also in that small town? Not good? 0:10:12.480 --> 0:10:16.240 So where do we get the DNA evidence from? Well, 0:10:16.360 --> 0:10:19.320 stuff that people leave behind, Uh, pretty much anything that 0:10:19.400 --> 0:10:23.120 has cells like living tissue that was left behind our 0:10:23.160 --> 0:10:25.400 living or stuff where living cells could have been in 0:10:26.160 --> 0:10:29.440 before being deposited at the crime scene. So stuff like 0:10:29.720 --> 0:10:37.400 blood or saliva or semen or skin cells, mucus, earwax, sweat. Yeah, 0:10:37.600 --> 0:10:41.200 all of that, All of that can leave behind cells 0:10:41.280 --> 0:10:44.320 that we can pull DNA from that. What about hair, 0:10:45.120 --> 0:10:49.600 hair not so much, not not not for traditional DNA 0:10:49.760 --> 0:10:53.120 hair follicles, Yes, but hair it self is dead. Those 0:10:53.120 --> 0:10:58.040 are dead cells. So you can do some some DNA analysis, 0:10:58.080 --> 0:11:02.320 but not the standard kind that most people use in DNA. 0:11:02.400 --> 0:11:06.560 For instance, Uh, fingernails, same thing, but fingernails often come 0:11:06.760 --> 0:11:09.920 with other tissue attached to it, and that's where you 0:11:09.920 --> 0:11:13.240 find the DNA. So if we want to look at 0:11:13.280 --> 0:11:15.560 the history of people actually saying, hey, why don't we 0:11:15.640 --> 0:11:21.559 use this this DNA stuff to try and help with investigations, 0:11:21.679 --> 0:11:24.640 you've got to look back to the nineteen eighties when 0:11:24.800 --> 0:11:28.079 a brit named Alec Jeffries, who now you may refer 0:11:28.200 --> 0:11:34.600 to as Professor Sir Alec John Jeffreys f R s okay, good, 0:11:34.640 --> 0:11:39.960 Professor Sir Alec John Jeffries, FRSH that would be his 0:11:40.040 --> 0:11:43.280 full title. Now, he hit upon the idea of using 0:11:43.400 --> 0:11:47.160 DNA as a means of genetic fingerprinting, and he realized 0:11:47.160 --> 0:11:49.480 that the unique sequences of DNA could serve as a 0:11:49.520 --> 0:11:51.880 means to link an individual to a scene where DNA 0:11:51.960 --> 0:11:54.920 samples were found, and his process was first applied in 0:11:54.960 --> 0:11:57.960 the court system in nineteen eight five. In that case, 0:11:58.040 --> 0:12:00.200 it was an It was an immigration case. It wasn't 0:12:00.240 --> 0:12:02.160 like a murder or a rape or something like that. 0:12:02.640 --> 0:12:05.840 It was to ascertain if the identity of a British 0:12:05.920 --> 0:12:11.040 boy was actually related to a family who had originally 0:12:11.320 --> 0:12:15.640 immigrated to the United Kingdom from elsewhere. And he did. Uh. 0:12:15.920 --> 0:12:18.520 The first time it was used in a criminal case 0:12:18.559 --> 0:12:23.360 would be seven. That was yeah, not not long after, 0:12:23.480 --> 0:12:26.560 and that wasn't a case. Uh. The the suspect was 0:12:26.640 --> 0:12:30.040 named Colin Pitchfork, which is a heck of a name, 0:12:30.840 --> 0:12:33.960 talking about nominative determinism. Yeah, and he was arrested on 0:12:34.040 --> 0:12:36.920 suspicion of rape and murder. And he was the first 0:12:36.920 --> 0:12:40.679 criminal caught as a result of DNA screening. So this 0:12:40.720 --> 0:12:43.800 was DNA screen that led to his capture. He actually 0:12:43.800 --> 0:12:47.280 confessed to his crimes, so the DNA didn't lead to 0:12:47.400 --> 0:12:50.680 his conviction. He confessed, uh, and he received life in 0:12:50.720 --> 0:12:53.439 prison as a result. So I wanted to talk a 0:12:53.480 --> 0:12:55.400 little bit before we get into some of the pros 0:12:55.440 --> 0:12:59.720 and cons about what actually happens with DNA's because you 0:12:59.800 --> 0:13:03.520 hear or like DNA forensics and you're like what goes 0:13:03.559 --> 0:13:05.680 into that. Yeah, this is a great thing to contextualize 0:13:05.760 --> 0:13:09.640 right now, because there are a lot of fans and 0:13:09.760 --> 0:13:14.640 tech stuff who have probably seen and scoffed at the 0:13:15.160 --> 0:13:21.000 various entertaining but inaccurate crime shows on order spe CSI, 0:13:21.280 --> 0:13:23.720 CSI being the big one, like they're there are are 0:13:24.080 --> 0:13:26.880 forensic specialists who say that c s I is probably 0:13:26.920 --> 0:13:29.040 one of the most damaging things that have happened to 0:13:29.080 --> 0:13:34.080 their their career path ever, because people have unrealistic expectations. Specifically, 0:13:34.520 --> 0:13:39.360 juries have unrealistic expectations, which can hurt a trial case 0:13:39.760 --> 0:13:44.520 because juries will often one want DNA UH data when 0:13:44.720 --> 0:13:48.120 it's not even relevant to a case, Like they're like, 0:13:48.360 --> 0:13:50.839 it's not necessary for them to make a determination in 0:13:50.920 --> 0:13:53.160 a case, but they want it because it's one of 0:13:53.200 --> 0:13:56.679 those things that people associate with. Oh, d NA gets 0:13:56.840 --> 0:14:00.199 you the the locked in answer was that person air? 0:14:00.720 --> 0:14:04.040 Were they not there? Um, just run the DNA enhance 0:14:04.120 --> 0:14:06.840 the photograph. I don't see what the problem right exactly. Yeah, 0:14:07.120 --> 0:14:09.720 let's pull up one of those three dimensional holographic images 0:14:11.000 --> 0:14:14.240 and we're just we're just throw every single science fiction 0:14:14.400 --> 0:14:20.120 CSI trope in there. So early forensic analysis actually used 0:14:20.200 --> 0:14:25.880 a process called restriction fragment length polymorphism or r f LP, 0:14:26.520 --> 0:14:29.400 and that involves taking a sample of DNA that has 0:14:29.560 --> 0:14:33.040 repeating base pairs like they can repeat from anywhere between 0:14:33.120 --> 0:14:37.200 one and thirty times. They're called variable number tandem repeats 0:14:37.360 --> 0:14:40.440 or v N t r s. And what they would 0:14:40.480 --> 0:14:43.120 do is they would dissolve this DNA in an enzyme 0:14:43.240 --> 0:14:47.680 to break the strand at specific locations along that the DNA. 0:14:47.880 --> 0:14:52.440 So uh saying like um, when there are this many repetitions, 0:14:52.560 --> 0:14:55.520 this enzyme is going to break the strand at that point. 0:14:56.000 --> 0:14:58.200 So that way we can measure how long the strand 0:14:58.360 --> 0:15:02.680 DNA is in a out point. Yeah. So imagine that 0:15:02.760 --> 0:15:06.120 you've got like a ribbon, right, and let's say that 0:15:06.160 --> 0:15:09.400 the ribbon is maybe three ft long, and you're going 0:15:09.480 --> 0:15:12.880 to cut out a six inch segment of that ribbon. 0:15:13.360 --> 0:15:16.080 Use this enzyme and it cuts it at the very 0:15:16.240 --> 0:15:19.960 specific locations along that strand that you want. You do 0:15:20.120 --> 0:15:23.800 the same thing with the material that was left behind 0:15:24.360 --> 0:15:26.480 at the scene. So let's say you've got you've got 0:15:26.600 --> 0:15:30.720 your your DNA sample from your suspect, you've got the 0:15:30.760 --> 0:15:33.200 sample from the scene, and you compare the two and 0:15:33.240 --> 0:15:37.280 you're essentially measuring them against each other, like literally measuring 0:15:37.360 --> 0:15:40.320 the length of them, because it's those repeating pairs that 0:15:40.440 --> 0:15:44.800 determine how long that segment is. So if the two 0:15:45.120 --> 0:15:48.720 are about the same length, or actually they are the 0:15:48.840 --> 0:15:51.280 same length, then you know, or at least you you 0:15:51.400 --> 0:15:55.360 have a good uh inclination to say that this person 0:15:55.640 --> 0:15:58.920 was the one who left behind that DNA. That's not 0:15:59.040 --> 0:16:03.080 really used that frequently anymore, but more frequently now we 0:16:03.200 --> 0:16:07.200 use a method called short tandem repeat analysis, which is 0:16:07.280 --> 0:16:10.840 more reliable, more popular. And in this method, analysts take 0:16:10.840 --> 0:16:13.640 a sample of DNA and they count the repetition of 0:16:13.720 --> 0:16:17.400 those base pairs along certain locations the loci of that sample. 0:16:17.960 --> 0:16:20.680 So four or five base pair repeats like where you 0:16:20.800 --> 0:16:23.760 get you know, your your those nucleo tide pairings I 0:16:23.840 --> 0:16:26.720 talked about, Sometimes those pairings repeat in a sequence, right, 0:16:27.720 --> 0:16:32.760 They look for uh, preferably four or five base pair 0:16:33.120 --> 0:16:37.440 repeat segments, so that way, because it's less likely than 0:16:37.480 --> 0:16:40.400 if you would have two or three in a row. Yeah, 0:16:40.560 --> 0:16:42.840 the more you have in a row, the less likely 0:16:42.920 --> 0:16:46.080 you're going to find that exact same repetition in another 0:16:46.360 --> 0:16:49.640 in an unrelated person's DNA. And these are by the 0:16:49.640 --> 0:16:53.560 way called tetra nucleotide or penta nucleotide repetitions because of 0:16:53.600 --> 0:16:56.960 the number tetra being four, penta being five. Um. There 0:16:57.120 --> 0:17:00.200 those are best in order to indicate an accurate man match. 0:17:00.440 --> 0:17:03.360 So the FBI, like I said, says, thirteen specific locai 0:17:03.600 --> 0:17:06.440 to find this, you would do this in thirteen different 0:17:06.480 --> 0:17:09.959 locations along the strand of DNA. And if you were 0:17:10.000 --> 0:17:13.560 to find these, uh, these base pair repeats that are 0:17:13.680 --> 0:17:17.040 identical in both and both samples, that's a really good 0:17:17.080 --> 0:17:20.560 indication that they belong to the same person. And this 0:17:21.080 --> 0:17:26.280 this investigation technique, while it is, while it's pretty solid 0:17:26.560 --> 0:17:30.240 and there's solid science behind it, it doesn't work in 0:17:30.520 --> 0:17:33.600 every In every case, it's not a silver bullet. And 0:17:34.000 --> 0:17:37.120 this is kind of some dark territory. Yeah. Yeah. In fact, 0:17:37.160 --> 0:17:40.200 there there are a lot of reasons why, uh, this 0:17:40.840 --> 0:17:45.320 can be this can be problematic. Um. One other thing 0:17:45.359 --> 0:17:47.399 I want to talk about before we get into the 0:17:47.960 --> 0:17:53.000 challenges specifically things like contamination and chain of possession and 0:17:53.960 --> 0:17:56.520 chain of custody, thank you, Before we get into that, 0:17:57.280 --> 0:17:59.240 is to talk about all right, so you know, I 0:17:59.440 --> 0:18:02.919 gave these these overviews of how they're analyzing the DNA, 0:18:03.280 --> 0:18:05.520 but One of the big issues here is that often 0:18:05.600 --> 0:18:08.920 when you're in the field and you're looking for anything 0:18:09.040 --> 0:18:13.240 that has, you know, remnants of DNA on it, you 0:18:13.359 --> 0:18:16.320 may not have a very large sample to work with. Right, 0:18:16.960 --> 0:18:19.840 So you've got a tiny amount of DNA. How do 0:18:19.920 --> 0:18:22.520 you make sure you can do the tests you need 0:18:23.080 --> 0:18:26.280 with a tiny little amount? And the answer is you 0:18:26.560 --> 0:18:30.320 duplicate the crap out of it? What how? Yeah? Okay, 0:18:30.359 --> 0:18:32.560 so this is this is gonna get super weird because 0:18:32.600 --> 0:18:35.960 I'm gonna get into molecular biology and chemistry but starting 0:18:36.000 --> 0:18:38.879 and I want to let okay, So they use a 0:18:38.960 --> 0:18:43.200 process called polymerase chain reaction or PCR to duplicate a 0:18:43.240 --> 0:18:45.800 specific region of the DNA in a sample. So this 0:18:45.920 --> 0:18:49.439 process was developed in three by Carrie Mollis who actually 0:18:49.560 --> 0:18:52.240 he won a Nobel Prize in chemistry for his work 0:18:52.280 --> 0:18:56.000 in this field. And what they'll do is they'll take 0:18:56.040 --> 0:18:58.600 samples of DNA. They'll take a string of DNA, so 0:18:58.640 --> 0:19:01.840 you've got your double helix, right, and then you heat 0:19:01.920 --> 0:19:06.520 it to between ninety four and ninety six degrees celsius 0:19:06.680 --> 0:19:10.200 for a few minutes. Yeah, so it's almost boiling um 0:19:10.600 --> 0:19:13.719 for a few minutes. And this is to d nature 0:19:14.040 --> 0:19:17.080 the sample, which means that the DNA straightens out, so 0:19:17.240 --> 0:19:19.879 it's no longer twisted ladder. It's a ladder, and the 0:19:20.080 --> 0:19:24.320 rungs split apart, So those base pairs split and you 0:19:24.400 --> 0:19:29.240 get two strands two half strands of d N A alright, 0:19:29.359 --> 0:19:33.800 So then you end up changing the temperature. You lower 0:19:33.880 --> 0:19:36.840 it to between fifty and sixty five degrees celsius for 0:19:36.880 --> 0:19:38.520 a few minutes, so that first one only takes a 0:19:38.520 --> 0:19:40.639 few minutes to so you lower it down to fifty 0:19:40.720 --> 0:19:43.359 to six degrees celsius for a few more minutes. That 0:19:43.480 --> 0:19:48.440 allows the left and right primers. These are small sections 0:19:48.480 --> 0:19:53.840 of DNA that have matching nucleotides to the two separated 0:19:53.880 --> 0:19:56.080 pieces that you've created. Think of them as almost like 0:19:56.119 --> 0:19:59.359 half zippers. So you've got the right and left half 0:19:59.440 --> 0:20:02.640 of a zipper on either like that. They're spreading out 0:20:02.680 --> 0:20:05.800 there there there's apart from one another. You've got a 0:20:05.920 --> 0:20:09.720 small section that interlocks with each side. Because that you've 0:20:09.760 --> 0:20:15.120 got the the complementary base pairs. Uh, those will then 0:20:15.200 --> 0:20:18.520 connect to those sections. Now that's only a tiny little 0:20:19.800 --> 0:20:24.600 part overall part of the full DNA, but um they 0:20:24.720 --> 0:20:27.639 then raise the temperature to seventy two degrees celsius for 0:20:27.680 --> 0:20:31.679 a few minutes to allow the tach polyme race. Now, 0:20:31.760 --> 0:20:36.080 this is the material that can then build and synthesize 0:20:36.160 --> 0:20:39.520 new DNA to the two separate strands. So if you 0:20:39.600 --> 0:20:41.720 think about it like a video game. All right, so 0:20:41.800 --> 0:20:43.640 you get your little you get your little segment that's 0:20:43.720 --> 0:20:47.680 locked onto the half ladder of DNA, the stuff you 0:20:47.720 --> 0:20:50.080 started off with in the first place. At one end 0:20:50.119 --> 0:20:52.000 of that, imagine that you get a little bitty blob, 0:20:52.359 --> 0:20:55.959 all right, that little big blob just builds the corresponding 0:20:56.160 --> 0:21:00.680 rungs and goes down the line rebuilding the d N 0:21:00.760 --> 0:21:03.800 A and it doesn't you know, there's one on both sides. 0:21:03.800 --> 0:21:07.040 There's a primer on each half strand of DNA. So 0:21:07.320 --> 0:21:09.080 at the end of this process, you end up with 0:21:09.320 --> 0:21:14.280 two strands of DNA. Okay, I see, now you started 0:21:14.320 --> 0:21:17.320 with one, but because you've used this molecular biology slash 0:21:17.400 --> 0:21:20.919 chemistry approach, you've been able to duplicate it. And then 0:21:21.000 --> 0:21:23.600 you repeat that process. So you do it again. Those 0:21:23.680 --> 0:21:26.159 two become four, the four become a. You see how 0:21:26.200 --> 0:21:29.040 this expands very rapidly. You do it over and over, 0:21:29.119 --> 0:21:31.359 so that way even if you started with a very 0:21:31.440 --> 0:21:34.119 small sample of DNA, by the end, you've got plenty 0:21:34.280 --> 0:21:36.560 to work with, so you don't have to worry about 0:21:37.200 --> 0:21:40.399 you know, we had one little drop of sweat at 0:21:40.440 --> 0:21:43.080 the scene and and we blew it on on a 0:21:43.200 --> 0:21:45.400 test that didn't work out. You don't have to worry 0:21:45.400 --> 0:21:48.920 about that. I'm sorry to be like, uh, emotionally or 0:21:48.960 --> 0:21:51.720 mentally a nine year old here, Jonathan, but can we 0:21:52.000 --> 0:21:54.000 can we make it a booker? I just love picturing 0:21:54.119 --> 0:21:57.199 us as cops or like, no, no one knows who 0:21:57.320 --> 0:22:01.639 stole the vus. We have only this single. The Mysterious 0:22:01.720 --> 0:22:05.360 Picker has struck again. Yeah, yeah, okay, so you're in Yeah, 0:22:06.119 --> 0:22:08.080 well we weren't talking about urine. We were talking about 0:22:08.080 --> 0:22:11.320 the boogers. All right, you got me. But this is 0:22:11.440 --> 0:22:13.919 but this is a great that that's a great explanation 0:22:14.200 --> 0:22:20.240 of how this occurs. Because given that you're essentially destroying 0:22:21.040 --> 0:22:25.480 the evidence every time that you you conduct this kind 0:22:25.760 --> 0:22:29.240 of this this kind of investigation, than being able to 0:22:29.480 --> 0:22:33.400 reproduce it is fundamental. Yeah, it's absolutely key because again, 0:22:33.480 --> 0:22:37.160 if you do not have very much of that material, 0:22:37.560 --> 0:22:39.879 then you really have to be careful. And there are 0:22:39.880 --> 0:22:42.080 a lot of things that can complicate this, and that's 0:22:42.119 --> 0:22:44.080 kind of where we were leading to a little bit earlier. 0:22:44.200 --> 0:22:46.879 There are a lot of reasons why you cannot just 0:22:47.040 --> 0:22:50.080 say that DNA forensics is going to solve, you know, 0:22:52.160 --> 0:22:54.879 the crimes out there as long as someone's left something behind. 0:22:55.440 --> 0:22:58.280 Because even though it's versatile, even though we have this 0:22:58.400 --> 0:23:03.520 amazing capability, life is weird and things can go wrong, 0:23:03.880 --> 0:23:06.399 and they can go wrong either accidentally or on purpose. 0:23:06.640 --> 0:23:09.200 So one thing that can happen is multiple people could 0:23:09.200 --> 0:23:12.840 be involved in a an incident crime of some sort, 0:23:13.640 --> 0:23:16.600 and so the more people who are involved, the harder 0:23:16.680 --> 0:23:20.280 it is to be absolutely certain that the DNA samples 0:23:20.320 --> 0:23:24.000