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.