Dr Robin Cotton and Dr Andy Hopwood discuss the accuracy of DNA profiling

Student:
How accurate is DNA profiling?

Andy:
We use 10 sites in our DNA profiling test in the UK and you use exactly the same test in New Zealand.

We've done lots of databasing for frequency calculations. So we've taken samples of populations of somewhere between 1 and 200 people each time and we look at how often we see particular lengths of DNA. So we see how common they are.

We can work out from those figures how common a profile is and that's where we get the 1 in a billion figure from, the 1 in a thousand million, 1 in a billion figure.

How accurate it is? Well, if you analyse the same DNA sample again and again and again and again you'll always get the same answer.

Lucy:
Okay.

Andy:
If you analyse DNA from blood, saliva, semen, vaginal cells, hair follicles of the same individual, you'd get the same answer.

Robin:
The other thing is that, except for identical twins, because of all the differences in the DNA, not only is everybody different but, for example, your closest relative which would be your parents or your siblings, you will be different from them.

Now if you have anyone in your school who's an identical twin, they are identical twins because they have identical DNA.