Hi. It's Mr. Andersen and in this podcast I'm going to talk about DNA fingerprinting.
We sometimes refer to this as DNA profiling or your genetic fingerprint. And basically
it started with this guy Alec Jeffries. Basically in his lab he was working with x-ray and looking
at DNA and what he figured out is he could tell a lot about a person by looking at their
DNA quote, unquote, fingerprint. In other words he could see who they were related to
and who they weren't. He could tell paternity for example. And so he was working at the
University of Leicester and basically figured out this whole idea of DNA fingerprinting.
This was around 1984. And basically for the next three years all DNA fingerprinting on
the planet went through this university. And so eventually it was privatized and this was
everywhere. And it will probably eventually be replaced by just DNA sequencing, sequencing
all the letters in DNA. But to make it understandable essentially what we have in a human is we
have long linear segments of DNA. But within that we have these genes. And so 99.9% of
our DNA in everyone is going to be exactly the same. The genes are going to be the same
but again you're going to have different copies or alleles of those genes. That's what makes
you, you. But if we look into this area in the middle, we used to call this junk DNA
but now we know it's really important in controlling gene expression we find that there's quite
a bit of variability in here, which shouldn't surprise us because this, the gene, makes
the protein and the protein makes the phenotype and that's really what natural selection is
selecting for or against. But this in the middle can go crazy. And so it does. And so
an example of one that we use in DNA fingerprinting is something called short tandem repeats.
Originally we started with something called VNTR, variable number tandem repeats and you'll
find in DNA sequencing that you have all kinds. So we had STRs we have VNTRs. Before that
we had restriction fragment length polymorphisms and so there's a bunch of different things
that we could look at. But we've kind of moved to this idea of these short tandem repeats.
They work great. There's quite a bit of variability in individuals. And so what is it? You basically
have letters of DNA that repeat over and over and over and over and over and over and over
and over. So sometimes, fifty times it repeats. And so what does that look like? Well if we
have these three individuals, we'll call this Mr. Blonde, Mrs. Red and then Mr. Mustache,
and so if we look at these three people their genes are going to be the same, but these
STRs are going to be different. These single or short tandem repeats are going to be different.
You can see that Mr. Blonde has more than Mr. Mustache and less than Mrs. Red. And so
if I make that a little bit easier to grasp onto, if I count them out and then remove
everything else, what we get is variability between all individuals. Everything else was
the same but we see variability in here. And we can cut these sections out using restriction
enzymes and them we can amplify them using polymerase chain reaction. And then we can
separate them using gel electrophoresis. So how does that work? Basically I'll take the
DNA and I'll put them in a little well. And so we're looking down on this. This is an
agarous gel. I could put Mrs. Red's and then Mr. Mustache, I could put those all in DNA.
Basically I would then turn on the voltage. So there's going to be a positive charge here
and a negative charge up here. DNA is a negative charge and so it's going to be pulled towards
the positive and so what's going to happen is those little fragments of DNA are going
to migrate. And so what does that allow me to do? It allows me to tell the difference
between each of these individuals. And so this is their fingerprint. But you can tell
this is a really bad fingerprint because we've got some, these two are exactly the same here
and so when they really do DNA profiling what they do is they generally us thirteen different
sections like this. And then those thirteen section are each going to be highly variable.
And so it's a good way to tell who's who. When would we ever want to do this? Forensics
is one reason and then also in paternity, figuring out who's dad. And so let's talk
about the murder. There was a murder that was committed Somebody was brutally murdered
by one of these three suspects, Mr. Blonde, Mrs. Red or Mr. Mustache. But they left blood
at the scene. And so what I can do is I can grab samples of DNA from each of our suspects
and then I could grab the blood itself and then I could do DNA fingerprinting on them.
So before we separate them you may think to yourself which of these looks guilty? Who
looks like they're capable of murder? And if we separate them then using that gel, what
we can see is that Mr. Blonde is guilty. In other words his blood matches up with the
crime scene. And so what do I mean by matching up? Well, those single or those short tandem
repeats, if we look horizontally are going to be exactly lined up. And if we were to
look at Mr. Blonde's son we'd find more similarities than we would between the others. And so basically
that's DNA profiling, DNA fingerprinting. It's much more sophisticated than that but
then again it's kind of on its way out. We'll eventually replace this with DNA sequencing.
In the US we, the FBI has started creating this database of DNA, which is a little scary.
And basically what they use are 13 different areas within the chromosome or the genome
and they they're looking at those short tandem repeats in there. Now why do I say that's
a little bit scary? I think you really want to protect your DNA because as we learn more
and more about genetics what's going to be found in your DNA, well predisposition to
Alzheimer's or breast cancer. Any of these things your insurance company would love to
get a hold of. And so it also doesn't answer the idea of Mr. Blonde, did he really do it?
Did the police frame him and contaminate the blood? So we don't know that. All it does
tell us is if we have two samples of DNA, the odds of two people having the same DNA
fingerprint are astronomical. Unless they're identical twins. And I hope that's helpful.