It all looks the same, really.(Picture swabbed from here, where you can see just how expensive DNA analysis really is.)
Some commenters on this post were much more up to date with modern DNA technology than me. I’m a microbiologist who uses some DNA methods, not a molecular biologist who is expert in them all.
So it was especially interesting to hear from The Paragnostic in the comments there, who gave a description of the actual test used on those samples. It’s far simpler than I thought. All it involves is the use of a specific enzyme to break the strand at specific points. Where those points are will differ between individuals but will not differ much between close relatives, if at all. The number of bits left, and the sizes of the bits, gives the ‘profile’. It’s not really very specific at all, given the number of people our government want on that database.
The potential for your sample to match with Ronnie Kray is rather higher than it would be if they were testing actual gene sequences. Cross-matches will happen. Instead of a database of criminals, where a DNA sample might throw up two or three matches, we’ll have a database of millions of people which will throw up hundreds, maybe thousands of matches from a sample. Not much help if you’re trying to narrow your search. They’re building a haystack around a small pile of needles. Are they doing that because a) they are all astoundingly stupid and nobody has realised the problem, or b) because catching criminals is not, and never was, the purpose of that database?
This test will not distinguish between a human and a chimp. Since the lab will assume that the sample is human DNA and probably do no supplementary tests (such as checking to see if the sample contains human antigens), then the test might not spot the difference between a human and a banana.
So, coat your cheeks with banana and give your name as Mr. Fyffe. Then wait for that dawn raid on the greengrocer.
Seriously, this does lead to a rather more worrying scenario, which comes from a comment by Anonymous on the OH post.
My lady has just come back from a night in the small town of Cirencester which has recently seen some trouble.
Apparently there is a large police presence and they are going around swabbing people……….
Well, my first thought was ‘just another database-filling exercise’ but then I thought about it some more. Those police taking swabs are not scientists. They take the swab, demand ID, stick the ID to the swab and send it off. They are not trained to think about potential problems in sample collection.
Now, suppose they swab you. So what? You’ve done nothing wrong. You aren’t concerned about being mistaken for a kiwi fruit when the next crime happens. You aren’t worried about matching Gary Glitter’s profile. Nah, not worried at all. Your ID is tagged to your DNA and that’s that. Because you’re carrying your real ID.
A criminal might not be. A criminal might have fake ID. Very likely, they bought their fake ID from an identity-thief who has picked up thousands of real peoples’ ID details from bins and phishing attacks. In a random DNA-collection exercise, the criminal is the one with nothing to fear because their DNA sample ends up tagged to someone else’s ID. They don’t need to run or hide or protest at the sample collection at all – in fact they’ll be first in the queue. The DNA belongs to the criminal. The ID tagged to it does not.
It could be yours, and you won’t know until one early morning when the battering ram smashes your door in.
‘Oh’, you might say, ‘it won’t matter, as soon as they test my DNA they’ll see it doesn’t match’.
Will they test it? Why would they? It’s already on the database so why test it again? The evidence is already there and DNA is infallible so why re-test?
The criminal has nothing to fear from the DNA database. The innocent have plenty to fear from it.
Whether you have anything to hide or not.
One more thing. For those who think handling and extracting DNA is really hard – I first extracted human DNA from a cheek swab in 1979, in a biochemistry practical class, first year. Every student got it right first time. It’s very, very easy to do. That’s without modern automated machinery. So don’t believe the ‘it’s too hard for a criminal to do’ crap. Given a swab of your cheek cells, I can get the DNA out of that in my kitchen. Certainly enough to leave a good sample at a crime scene. Really, that sort of brute-force framing is a doddle.