Why We Can’t Always Trust DNA Evidence

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DNA fingerprinting has improved throughout the years. But, contrary to popular TV shows, it isn't as accurate as one might believe.

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Sir Alec John Jeffreys - Genetic Fingerprints
"Jeffreys' broad goal was to track genetic markers in the DNA of members of the same family, looking for inheritance patterns for illness and disease. He and his colleagues concentrated on 'mini-satellite' sections of human DNA, which contained more apparent, dramatic variations than other strands, known as 'core' sequences. These would make for better markers for tracking the positions of genes."

How Does DNA Testing Work?
"Because all cells in the body contain exactly the same DNA, samples can be taken from almost anywhere in the body, including skin, hair follicles, blood and other bodily fluids. A forensic scientist might be asked to compare DNA from skin cells found underneath the fingernails of an attack victim, with the DNA from a blood sample taken from a potential suspect."

Limits of Traces - The Phantom of Heilbronn
"The 'Phantom of Heilbronn' was one of Germany's most-wanted criminals. As the traces were connected to a female offender, 'she' was suspected having committed a series of different crimes (murders, break-ins, theft) across Germany over more than 15 years. Tests showed her DNA at 40 different crime scenes. The only connection between the crimes was this DNA trace."

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Written By: William Poor

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When you're working your factory job and all of a sudden you're a criminal mastermind.

TheXzurae

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.

kittymaximum

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.

Kneedragon

I'd actually say his DNA seems a little twisted.

dhawthorne

#BTS: The yell in the intro was also me because we couldn't get rights to The Who.

TraceDominguez

Yet another reason to abolish the death penalty.

Linkous

More like:

Why we can't always trust (current) science.

bluebotlivingston

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.

JeremyWS

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.

afterthedrjay

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!!!)

ReptarsaurusRex