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.