Why We Can’t Always Trust DNA Evidence
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Why We Can’t Always Trust DNA Evidence


DNA is a double-helix, so I guess you could
say guess his DNA was bent into shape. [YYEEAAAHHH] Hey all you Gary Sinise groupies, Trace here
for DNews. DNA evidence is often seen as the silver bullet
of crime scene investigations…start with a tiny dab of blood, add a 10 second lab montage,
and the perp is behind bars. Right? Well, no. As powerful as DNA analysis is, it’s not
the perfect evidence that the general public, and the court system, make it out to be. First, a little background. DNA fingerprinting was developed back in 1984,
and it exploits some basic truths about genetics. All DNA is comprised of four chemical bases:
Adenine, Cytosine, Guanine, and Thymine. These link together to form base pairs, and
long chains of base pairs link up to form strands of DNA. Different combinations of those base pairs
define different genes, and thus different traits. In total, the human genome contains about
3 billion base pairs… but only about point one percent of those vary from person to person,
and that tiny slice of the pie accounts for everyone’s unique traits. And it’s that 0.1% that DNA fingerprinting
utilizes. When samples of blood, saliva, or other “leavings”
are found at a crime scene, experts analyze the DNA fragments within those samples and
compare them to a suspect’s DNA…or to a database of people with criminal records. The more distinct sets of base pairs you can
find, the more confidently you can match, or rule out, samples. Since 1984 this procedure has gotten quicker,
cheaper, and more accurate, and has exploded in use. But here’s the problem: as useful as DNA
testing is, it’s not necessarily the forensic turn-key solution that shows like CSI make
it out to be. And that’s largely because the process of
collecting and analyzing DNA can be surprisingly ambiguous. First off, DNA is everywhere. Tiny traces of skin, saliva, blood or other
DNA-containing material are often found all over a crime scene, and collecting samples
is low-tech, time-consuming, and fairly error-prone. Once samples are in, investigators must figure
out which are relevant to the crime…no small task. Worse, DNA from the perp is often mixed with
that of the victim, requiring lab techs to tease out which is which. All in all, DNA evidence is frequently messy,
requiring experts to try and extrapolate whether an incomplete or mixed DNA profile truly matches
a reference sample. It’s sort of like trying to figure out whether
a few scattered puzzle pieces even belong to the picture on the box, let alone fit together. This ambiguity can lead to labs fudging results
to help out investigators, or genuine errors in analysis, or outright fraud. And all that opens the door for false positives
in DNA matches. Sadly, there are many examples of misused
DNA evidence ruining lives. In 1998 Josiah Sutton was arrested and charged
with raping a woman in Houston, Texas. A crime lab employee testified at the trial
that Sutton was an “exact match” with the DNA recovered from the scene. He was convicted, and spent almost five years
in prison before a second round of testing found he was in no way an “exact match.” That second test didn’t make use of any
new evidence…it simply interpreted the DNA more accurately. And then there’s DNA mixups wasting valuable
time and money. For more than 15 years, investigators in Europe
searched for the Phantom of Heilbronn, a criminal mastermind who left identical DNA traces at
more than 40 crime scenes across the continent. After an exhaustive manhunt, the DNA in question
was finally matched…to a factory worker who helped make DNA test kits. So, look. We’re NOT arguing that, “DNA evidence
doesn’t work because some people don’t use it right.” DNA fingerprinting has revolutionized forensics,
and to date has exonerated 347 wrongfully-convicted people in the US alone. But there is a perception that DNA testing
is both simple and infallible. Jurors tend to overcommit to physical evidence
when it’s presented as fact by experts. Researchers have even proposed a “CSI Effect,”
which is the tendency of juries expect fast and conclusive DNA evidence in every trial. These are dangerous trends because, as sound
as the science is, it’s no good to anyone unless it’s used within its limits. Like any science. If you’d like to learn more about DNA, check
out this video we have on CRISPR which could actually edit your DNA. What other questions do you have about forensic
science? Let us know down in the comments, make sure
you subscribe for DNews and thanks for watching.

65 thoughts on “Why We Can’t Always Trust DNA Evidence

  1. They have to be careful when clearing someone through DNA evidence. If the DNA they have is sperm then the person's tested DNA should be sperm not mouth samples etc. Because of the possiblity of an absorbed twin DNA which can be quite different. This condition isn't rare even.

  2. It's a running joke in the family that we cannot "prove" the father of my brother and myself. My dad is an identical twin. So the joke comes into play with little things. My dad hates beets. My uncle loves beets. I love beets. "Well, clearly she's YOUR daughter!" And so on. Even when I was little it was "daddy" and "uncle daddy."

    So other than "circumstantial" evidence that proves my father is my father, you can't prove it one way or another who's my dad using DNA.

    I swear, this had been a plot more than once in a crime show.

  3. So people watch CSI and all of a sudden they are expert criminal investigators? lol

    What a joke. CSI the show sucks too it doesn't really represent reality it is entertainment. Do people forget the entertainment part?

  4. Does licking something count when you tried to not leave any DNA traces but you found a cute rubber duckie in the bathroom when you needed to clean up the blood?
    And what if you forgot to wash the cute rubber duckie?

    (Asking for a friend!!!)

  5. Is this DemocratNew’s way of trying to discredit bill Clintons abandoned black son danney Williams that spoke out against him?

  6. People hate me cause I'm a stran of cholera but I don't infect people if someone gets me I wriggle out of the person as fast as I can then I make a mound full of crisps to cheer them up and the crisps have no bacteria or fungi or viruses living on it

  7. I wanna edit my DNA to include the DNA of tigers and cheetahs, so that I can tap into the speed force. You know like the flash in DC Comics. jk lol 😉

    Great video. Keep up the good work.

  8. So everyone is going crazy and trying to kill people over Trump winning and Drews makes a video basically saying that If everyone went on a killing rampage, it will be overwhelming for police to investigate and prosecute.

  9. … Zero point one…. why SAY the zero…. a chunk of people would hear .01 instead of .1… better to say point 1 or 1 part in 1000… less ambiguity.

  10. I love how he is like we can't trust it but we should use it. I feel sometimes they need to lie to grab attention. If you can't trust something prove why it shouldn't be used. By saying that it has put a lot of bad ppl away you are simply proving why it should be trusted

  11. long time fan, you all make a great show. in my opinion one of the best on youtube. also because i have the same raybans.

  12. Another problem is deliberate mishandling of evidence by police. If police are gathering evidence to figure out who dunnit, that's one thing. But very often, they've already got a firm opinion who dunnit, and what they want is evidence that has one chance in 32 million of being wrong… So you take a pair of panties (let's say) from a crime scene, and you take a T-shirt from the chief suspect, because of search warrant, and you put both in a plastic bag and shake it. Then you look at both and you find clear traces of the suspect's DNA on the victim's panties. Open and shut case, right? You would be amazed how many open and shut cases have been proved that way. It's not the science that's wrong, and it's not the genetic labs, it's what the cops do with the evidence, and the complete lack of any understanding by the jury that this can and does go on.

  13. And now.. government is wanting to get into DNA companies test database.. to solve cold cases, even if it's not the dna of the person of interest.. They want anyone's to compare from old dna possibly contaminated from years of handling and storage..

  14. DNA is not admissible as evidence in a court of law and soon precedence will be set that it can no longer be presented 100% as evidence, except maybe in certain cases. The incidence of human chimerism is unknown. Recent findings of 2 women initially having different DNA than their own naturally birthed children have brought this light. Innocent people can be prosecuted still and be put on death row and the reverse is also possible, ie having 2 sets of DNA, but the one found in the DNA sample may not be the same as the one found at the crime scene. That is because hair might contain one set while cheek, blood, semen, etc might have a different set. Truly upsets the apple cart

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