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Twist on DNA Privacy
ConfusedVorlon writes "The BBC is reporting the conviction of a man for the murder of a prostitute 15 years ago. The interesting twist is that his DNA was not on record - 'But it partly match[ed] that of a youth's who was known to the police - but who had not been born at the time of the murder. The teenager, it turned out, was a close relative of [the murderor].' There has been concern in the past at the idea of keeping DNA of those interviewed but not charged with crimes. I haven't previously heard of the privacy implications of being related to a criminal/suspect. If you've done nothing wrong, you've nothing to fear?"
You, out of the pool!
There are two ways of comparing DNA that are used. The first, more common method, is to look at something called Restriction Fragment Length Polymorphism (RFLP). The spaces between known regions that can be cut vary. Look at enough of these and you can statistically say with some confidence that its your person.
The second method, which isn't used as often last I saw, involves looking at the DNA sequences in regions which do vary. Perhaps well studied regions like those associated with organ rejection in transplantation.
Both methods are more reliable than the people carrying out the work. With RFLP, there is a certain amount of subjectivity involved in calling two sizes the same. With sequencing, contamination is easy.
I'm sure the procedures have improved since I last observed them. The weakest link in both procedures is the human factor.
A recent case here in Canada had me a bit uncomfortable.
A young girl was murdered and police asked Men in the neighbourhood to volunteer DNA samples. About 20 men refused. 19 were innocent and refused for personal reasons. One of these men was eventually implicated in the crime when Police followed these 20 men and picked up "pop cans, et al" used by these men to obtain DNA samples.
This implies - You have no right to refuse to give a DNA sample because one will be taken secretly against your will anyhow.
What happens to these samples? Could I be implicated in a completely separate crime because my second cousin lived NEAR a murder victim who's and had his DNA "stolen" by police?
This can only get scarier without laws to protect us.
The system that the FBI uses to keep track of DNA is called CODIS - Convicted Offender DNA Identification System. It relies on DNA profiling, sometimes called DNA fingerprints.
There are areas in the genome that science currently believes do not contain any genetic information that is actually used. In this "junk" DNA, there are areas called STRs - Short Tandem Repeats. These are places where there is a short sequence of DNA (e.g., ACC) that is repeated n1...n2 times (where n1 and n2 usally range from single to low double-digits.) Since there is (normally) one copy of each gene from each parent, each person will get a section of some length from one parent, and a section of some length from the other parent (the lengths may be the same.)
Glossing over some of the details, and all of the lab work, this means that for each of the 13 loci recognized by the US forensic community (the Brits use a slightly different set) an individual will have 13 pairs of numbers. For each loci, each number has a different frequency, so it is possible to build up a likelihood (i.e., chance that the DNA came from a person other than the person in question.) These numbers get much, much larger than the number of people on the planet for full profiles.
Identical twins will have the same numbers. Children have one number from each of their parents. Siblings are likely to share numbers. Two unrelated people may have some numbers in common.
This is how paternity test are done. (The child will have one number at each loci in common with the father.)
This is how rapists are linked to victims. (Their profile matches exactly with DNA from semen, skin under fingernails, blood from the scene, etc.)
This is how people behind bars are cleared of crimes. (See above.)
This is how many of the victims of the World Trade Center attacks are being identified. (By matching DNA from victims' toothbrushes, razors, hairbrushes, dirty clothes, etc. to the DNA of the body parts found at the site; and also by kinship analysis.)