English Audio Request

Once a DNA sample has been collected from an exhibit – and, hopefully, separated from any impurities or chemical inhibitors, such as the dark blue dye in a pair of jeans – the next thing to do is see how much human DNA you've got, and whether there's still anything else in there with it. Then, assuming you've got a decent amount of clean DNA, it's ready to be analysed.
To get someone's DNA profile you don't need to sequence their entire genome. (Only around 20 people have had their full personal genomes sequenced, including Archbishop Desmond Tutu and the actor Glenn Close.) The profiling system in use in Britain looks at 11 very small regions of DNA – about one millionth of the total. One of them tells you the person's sex; the other 10 are short tandem repeats or STRs. In lots of places in our so-called "junk" DNA (the vast majority of it which isn't involved in making proteins) there are repeating patterns of short sequences of base pairs (the molecules DNA is made up of). The number of times each short sequence is repeated varies from person to person, though within a limited range of, say, 10 to 25. However, the chances of two unrelated individuals having exactly the same number of repeats in all 10 regions used for DNA profiling are one in a billion.
I didn't go into the laboratories, but peered in through the glass in the doors, to see figures in green and red colour-coded outfits working on colour-coded equipment to reduce the risk of cross-contamination between different procedures. I had a mouth swab taken before I was even allowed in the corridor: LGC keeps a record of the DNA profiles of all staff and visitors as a further precaution against contamination.