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Forensics reaches into the future

How far should we let the DNA database go?

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We began researching this piece long before the recent murders in Suffolk. That horror has served to remind us that forensic technologies are now often the first thought in any criminal investigation. The shiny power of DNA technology is in no doubt, but are we in danger of being dazzled by it?

The state of the art

The National DNA Database (NDNAD) was set up in 1995 by the then Conservative government. Eleven years on it is the largest repository of human genetic information on the planet.

It is run under a Home Office contract by the Forensic Science Service and governed by a tri-partite board comprising representatives from the Home Office, Association of Chief Police Officers, and Association of Police Authorities. Representatives from the government's genetic ethics advisory body the Human Genetics Commission are invited to sit in.

At the moment, the NDNAD stores DNA profiles. This data is not the raw sequences of DNA, instead it is reliant on a special species of DNA sequence present in every chromosome: tandem repeats. These are short stretches of up to 100 DNA "letters" which are repeated as if the sequence is stammering.

Because of the imperfect way DNA is copied and mixed up when we are making sperm or eggs, the number of copies of each tandem repeat is variable. This evolutionary quirk provides a neat shorthand for forensic scientists. While each variation of a tandem repeat may appear in a large proportion of the population, the additive effect of comparing their length at several locations (the FSS uses 20) is to uniquely identify each individual, even within families.

The technique was developed by Alec Jeffreys at the University of Leicester in the late 1970s, who was knighted for it in 1994.

DNA fingerprinting briefly breaks down like this: enzymes cut out the repeated stretches to be examined from the DNA and an electric current is applied to the mixture. Because of the negative charge on the DNA molecule, the fragments move with the electricity, and the lower the number of copies of a repeat, the faster it will move. Dyes are used to produce the famous banding pattern of a DNA profile.

Police have powers to take a buccal swab – from the inside of the cheek – from everyone they arrest, including children. And since January 2006, a change in the law means that every offence is now arrestable; there was a time when litterbugs did not risk a night in the slammer.

The CSI effect

The success of forensics-based dramas like CSI has ensured there's no shortage of applicants to study forensics. Hollywood and its public are enamoured by the supernatural potency of the discipline.

The ludicrous feats of deduction often scored by the stars of these shows have convinced many that modern forensics is fast-paced, glamourous work. But not so. The science backing up the evidence is becoming increasingly involved, expanding to include bioinformatics for genetic sequence data and chemistry and physics, as the limits of what molecules can tell us are tested.

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