Only 114 men volunteered DNA to the Bowman muder hunt detectives, so detectives have had to promise not to check that DNA against other unsolved crimes, and not to keep the DNA. I don't believe that for a second. However, I am puzzled by the following quote :


"Police say there is no need to make an appointment, but they must not have consumed any coffee, food or sweets and should not have smoked for 20 minutes prior to the sample being taken."

I noticed the times I was arrested at a military base they kept taking my DNA even though I told them my name and that they already had it. Is there a way to ruin the enforced DNA samples by eating or smoking ?

 http://www.thisislocallondon.co.uk/news/topstories/display.var.696358.0.114_men_give_dna_to_help_catch_models_killer.php

Could we fool DNA tests by french kissing lots of people just beforehand ?
Even if that wouldn't work it may be a good recruiting tactic.

Danny,

Patronising bit: (It's science so it is patronising).

DNA is a series of Four chemicals (Adenosine, Guanine, Cytosine and Thymine AGCT) These are placed in pairs. A-T, G-C. One of the pairs on one strand one on the other. Your genes are described as a long sequence of letters which occur in threes. (AAA, AAG, AAC, AAT - there are sixty four. If you have compulsive tidyness you could work it out). These are placed together in a gene map (genome, genotype - various words describe this part) which then describe a gene. These genes then make enzymes which make proteins which make Dannies which ask the obvious about DNA evidence. For a much more convincing explanation, try DNA for Beginners, Genetics for Beginners and Darwin For Beginners. Read these three and you already know more than most Chief Constables on the matter.

First of All DNA evidence is not the same as I have described for the rough working of molecular genetics. DNA evidence is an inference not a fact. When you give a sample the first thing that is done is the sample is amplified. Listening to your favourite Piano Concerto gains nothing by being played by excessively amplified guitarists who know most of the notes most of the time. Give them cider and it could go wrong. (Death Metal enthusiasts may be annoyed - but science is infuriating).

So the amplified DNA from your sample is subject to noise. This is the same as the Concerto above. You recognise bits BECAUSE it is your favourite. Your familiarity is what enables the identification. You could be completely right and spot it right away. This BECAUSE is essentially what DNA evidence relies on. Volume of examples. Because DNA identification is a learning process. The facts are that the Genetic Code has been described and can be sequence. The learning is that there are very few genes identified, the majority of DNA seems to do nothing and - very importantly for Danny - your body contains more non human DNA than Human DNA. This is noise. If you amplify the noise you get something very unrecognisable.

Non Human DNA (things like gut bacteria, bacteria off recent food intake, fungi from the air conditioner) inhabits lots of parts of your body. The SA of MRSA is simply a naturally occuring bodily Staphlococcus aureus which is resistant to a lot of different drugs. It gets into the wrong places and causes trouble. It's all a matter of balance really. Which is what DNA as evidence fails to take account of. Getting the balance right - DNA Evidence for legal purposes has to be gathered in as standard a way as possible.

Perfect human DNA samples contain only WHOLE human cells. If you smoke, the nicotine can cause your cells to burst and also reacts with the Base Pairs (AGCT). Eating food might leave DNA from any one of a number of organisms in your mouth. Then this is amplified. Which results in distortion. So, having unwashed teeth after a meal and a pint of real ale (that you suspect might be ripe) and a cigar and then going for a DNA swabbing would reduce the reliablity a lot. If you were to also to exchange some oral body fluids immediately prior (providing it was not with a relative - the DNA might be too similar and so boost reliability) you could probably produce some pretty crap DNA identifications. Vegetarians are at a slight disadvantage in the foreign DNA stakes - but only if the carnivores eat well cooked meats. With a fresh salad made from organic vegetables (to increase the variablity of plant DNA) you could have a mouth full of misleading information. This could become worse if you were a little under the weather with a bacterial infection or something viral.

The importance of DNA identification as evidence is overplayed. At best it is circumstantial. Your Genome (total body map) is not unique. You have 98% in common with a chimpanzee and 60% in common with a banana. The idea that it uniquely identifies you in a sense that should be allowed to deprive you of liberty is not held up by these two simple statistics. What if a malicious banana were to commit a crime and the DNA evidence was so poor you got the blame? You'd be most vexed.

Unless the collection, amplification and identification is done carefully by trained people (I mean proper scientists who are doing it without having investment in the outcome) then there is a lot to go wrong. This is usually in the form of a false positive or false negative.

The entire fallacy of "Race Science" is being played out again. Not necessarily by inventing superior/inferiror races but by seeking to say Identity is unique and immutable and in a tiny box that can be identified by machines. Which is a large problem for DNA as Legal Evidence. If the process is automated, the machines need to be correctly calibrated and so on. Unless the state is prepared to pay the premium for scientists this is not going to happen.
Which will result in utter nonsense being put forward as science (many respectable Soviet Scientists followed Lysenko because it made social not scientific sense; similarly in Nazi Germany). Simply seeking to fool DNA profilers is not the correct approach - because the science itself is sound. You are simply providing false postive or false negative readings - which works pragmatically but not long term.

The best solution is to ensure that the Technology and Science do not get misused. The way to do that is not by attacking the science but the structures that use the science.

The next time you get asked for a DNA sample ask to provide it in a double blind protocol.
This is standard research technique. This would mean the Profiler overtly acknowledging that they might have false positives and false negatives. Don't hold your breath though.

Arguing in favour:
 http://dnaspecialist.com/News/74005-DNA-Testing-Breaks-Down-Barriers-in-the-Court-Room.asp

About False Positives
 http://en.wikipedia.org/wiki/False_positive
 http://www.passyourdrugtest.com/false-positives.htm
 http://www.fathom.com/course/21701758/session2.html
 http://www.scientific.org/articles/JFS%20excerpt.htm