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Posted by priya am 2004/9/9 9:03:08
Genetic profiles stored by police normally record the details of 10 specific parts of the long chain of molecules that make up a person's DNA. The chances of two unrelated people having the same details for all these 10 markers - and hence the chance of a false identification - is said to be about one in a billion. This method has traditionally been regarded as highly efficient at identifying suspects from DNA traces left at crime scenes.
However, Prof Jeffreys said the increasing number of records being held on the police database - currently about 2.5m - meant that having only 10 markers per person was no longer foolproof.
He suggested 15 or 16 markers to reduce the chances of two people having the same profile to one in more than a trillion. American law-enforcement authorities are already considering changing the profiles in their DNA databases along these lines.
In Britain, DNA evidence has been used in countless criminal investigations and the police regard it as an invaluable tool. Peter Gill, of the Forensic Science Service, which administers the national DNA database for the police, said his agency was "confident that the 10 markers currently used are sufficient".
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A scientific revolution
1984 Alec Jeffreys, a geneticist at Leicester University, discovers DNA fingerprinting by accident during research while studying how genes differ between people and how they evolve.
1985 His technique first used to reunite a boy with his family after an immigration dispute. It showed with a certainty of 99.997% that the boy was the true son of UK citizens originally from Ghana.
Also in 1985, the notorious war criminal Josef Mengele's remains, thought to be buried in Brazil, were positively identified by Prof Jeffreys using DNA fingerprinting.
1987 UK patent granted. Prof Jeffreys licenses technology to Cellmark Diagnostics, a subsidiary of ICI.
1988 Colin Pitchfork is first person to be convicted on the basis of DNA evidence for the rape and murder of two girls in Leicestershire. DNA evidence rapidly gains acceptance in US and UK courts.
1989 First serious attempt made to have DNA evidence excluded from a criminal trial in murder case against New York handyman Jose Castro. Though scientists concluded the DNA evidence was flimsy, Castro later confessed.</td></tr></table>He said: "The chance of an adventitious match is fairly small, yet we never discount the possibility, and all our reporting officers are aware of this.
"If the DNA profile is partial because the sample is degraded, then adventitious matches often occur. However, it is important to remember that the national DNA database is an intelligence database. This means that before a decision to prosecute can be given, all of the evidence in the case must be carefully considered. DNA is never reported in isolation. The jury makes its decision based on all of the evidence presented."
Prof Jeffreys also gave a warning against keeping DNA records of people who had been wrongly suspected of crimes - something the police have been legally allowed to do since 2001.
In certain parts of the country, this could lead to an over-representation of certain ethnic groups and could lead to resentment, he said. The solution was either to delete records of those who had been cleared of any offence or simply to extend DNA profiling to everyone in Britain.
He also expressed reservations about the idea of extracting anything more than simple identification data from DNA. "Police store not only the DNA profile but also the physical DNA," he said. "If they have that, there is the long-term risk that people could access health information in the future. Police have absolutely no right to that information."
He sought to calm civil liberty fears that police might reach the stage of producing Photofits based solely on DNA information, saying science would be a limiting factor.
There are few robust tests for identifying physical characteristics from someone's DNA - such as hair and eye colour and broad ethnic origin - although research in the area is continuing.
Outlining the challenges for DNA profiling, he said the basic science had been achieved, but the problems now lay in improving the technology.
He asked: "Can we speed up and simplify the procedure?" Within a decade, he pointed out, police may have hand-held devices that could profile DNA samples they found at the scene of a crime in a process taking only a few seconds and costing a few pence.
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