Here's a good myth, the idea that DNA fingerprinting is a foolproof way of identifying a criminal from a tissue sample. For one, I believe that the current statistical chance of sharing DNA with someone else is 1 in 14 million, correct me if you have a more accurate figure. This means that in Britain alone there are approximately 4 other people with your DNA. What people also aren't aware of is that when they compile the DNA databases, they remove duplicates, so, if you are the poor sap whose DNA goes on the system first, you'd better hope there isn't a criminal out there with your DNA. The best way to avoid this situation is to change your name to something like Zzzypp Zzzlotty as they generally order these things alphabetically and therefor, if it comes to duplicates, yours would be the one removed.

Hi nemisis,
currently the odds of two people having the exact same DNA sequence is 1 in 10 to the power 13 (1 in 10,000,000,000,000) so where there is a full DNA match you would have definitely proved beyond reasonable doubt! It all depends on having a full sample to analyse, best idea is to stay of the register (in other words dont break the 11th commandment "thou shalt not get caught!")

Deoxyribonucleic acid is not really a speciality of mine, but Lugh is quite correct, the F.B.I. CODIS DNA matching system quotes a 1 in 10,000,000,000,000 possibility of two people having DNA structures which are identical at all 26 points of measurement on the DNA strand. Since the world's population is currently a little over 6,600,000,000, you would need to compare DNA results with this and around another 1500 worlds, before you found an absolute match! Interestingly, however, the same F.B.I. report indicates that the chances of matching DNA structures at just one of those 26 points is only 1 in 1000 - if you go back far enough in time, there are only that many genetic mutations, (races) from which we are all descended. This is not admissible as evidence in court, however, only full 26 point matches are accepted for that - but the F.B.I. uses the one point, one-in-a-thousand method for initial comparison, simply to speed the process up - if you have 2,000,000 DNA samples in a computerised database, you can immediatly narrow it down to just 2,000 possibles, on which to do a full comparison.
"Duplicates" therefore, theoretically, do not exist, and are not, in fact, removed from the database, at least not in the UK or USA. What the systems do create, however, is "linked" files, on the assumption that if an identical sample is received under two different names, one of them is probably an alias.
As for the figure of 1 in 14,000,000 the only thing I know of with that same probability is winning the National Lottery!

As someone with first hand experience of working in the field of crime database creation and management, I can assure you that the process I have described is used in both the US and here in the UK. The statistical figures quoted by the FBI are figures they came up with after 'cleaning' their database of duplicates and therefore are totally erroneous and, contrary to what we might wish to believe, exact matches on all 26 indicators are not necessary for admission in court proceedings.

OK...well...The stuff I quoted was from a Home Office handout for the police, but I'm perfectly willing to bow to your first-hand knowledge, Nemesis. Let's face it, it wouldn't be the first time the FBI lied about something would it?

Or the Home Office for that matter, but I really oughtn't to say that should I

Nemesis - speaking as a former pistol shooter with thousands of hours and tens of thousands of pounds invested in my sport, all of which was arbitrarily removed by the government in 1997, I can state quite categorically and withouth equivocation or prevarication, the Home Office tells porkys all the time. The Office of Central Statistics produces a report indicating that the use of handguns in armed crime has doubled since the 1997 ban, (up from around 2,300 cases in 1993 to over 5,000 cases in 2003.) The Home Office simultaneously produces a document extolling the "unqualified success" of the 1997 Firearms (Amendment) Act, and calling for interested parties to put forward suggestions for futher gun controls to "further increase public safety."

Anybody who doesn't think the government lies, deserves every stupid law they get!

Ouch, guess I touched a raw nerve there J D. You're absolutely right though, governments lie all the time and as you quite correctly say, the banning of guns has indeed had absolutely no positive affect on gun crime whatsoever. But then, who am I to suggest that the first stage of ensuring the control of your populace is to disarm them and even better if you can persuade them it's for their own good. As Benjamin Franklin said, ' A society that gives up a little freedom for a little security will lose both and deserve neither.'

Back to the myth,

Lugh metioned earlier about not getting caught beacause your DNAends up on the database, but isn't it sometimes the case that you don't even have to be arrested for your details to end up on the database?

And, by the way, is there nothing that you don't know about Shootist following your years training how to kill people and teaching others the fine art? You always seem to have a detailed answer for everything. Perhaps a change of career, constructive teaching maybe?

Although I'm not sure that the RAF Regiment, the RAF Police and especially the three civilian Police Forces I've worked for, would be entirely comfortable with your description of my skills as "the fine art" of killing people, Flo, I kind of see your point. I've also been a teacher, of sorts. And I have a double-honours degree in buisness administration and law. But none of that explains why I seem to have an answer for everything. I'm afraid that's down to me being an unbearably cantankerous old smart-arse!

This message has been edited. Last edited by: J D Shootist,

Unfortunately Flo, you are right, you don't have to be arrested for your details to be held although it is generally done, at least here in Britain, in somewhat dubious cir****tances. For example, at the moment men in Croydon are being urged to come forward to donate their DNA to 'exclude' them from police enquiries. The truth is that typically, the police will assure those that come forward as dutiful civic minded subjects that their DNA will only be held for the duration of the enquiry and then conveniently 'forget' to dispose of the information and add it to a growing database of DNA. There are other cir****tances, like volunteers who come forwards to offer to help with the creation of such databases and in general the developers will add theirs.

You're quite right there are quite a few ways to end up on the database without being arrested, however being arrested is the only way of ending up on there with no choice in the matter. In any other circs you would have a choice. The exception is 'donating' your DNA at the scene of a crime, in those circs your DNA is on the system, but with a question mark next to the name section. In answer to the answer to my answer (!?) about the odds of two people having the same DNA those stats I quoted are not Home office or FBI (as a serving police officer I KNOW better than to trust those). The stats are from scientific analysis and are purely statistical based onj the number of permissible combinations of the 26 points. Pure maths guys, no spin. (Unlike accountancy, ask an accountant what's 2+2 and he'll tell you "anything you like but it'll cost you")

Ah well Lugh, there you go, that's the problem with statistics The number of theoretical mathematical combinations is not the same as the actual number of possible combinations. So I guess what we've learned here kiddies, is that no-one is really sure what the correct possibility of two people showing up as having the same DNA profile using the existing method is. Now, call me an old cynic, but I wonder what possible reason there would be for keeping that one quiet? It's not like it's difficult to work out if you just ask a DNA specialist some probing questions

All this discussion of mathematical probabilities and government, scientific and other opinions, whilst fascinating, (I, for one, laboured under the belief that the science on this was pretty much a "done deal," until now,) doesn't alter the fact that, within the UK, certainly, the legal precedent has been established regarding the use of DNA evidence in a court of law. Unless a case is brought with significant new scientific evidence to overturn the existing precedent, the current legal position remains that DNA "matching" is admissible in court and is very, very convincing to juries. I am not aware of any successful prosecutions using DNA and absent any other evidence, but some otherwise dreadfully thin, cir****tancial cases have been won when supported by DNA. Thus, given the apparent controversy evident in this forum, Lugh is probably right - best to stay off the DNA database, if you possibly can!