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Last Updated: Thursday, 9 September 2004, 01:44 GMT 02:44 UK
Two decades of DNA fingerprints
Sir Alec Jeffreys (PA)
Sir Alec's breakthrough has transformed crime investigations
Scientists in Leicester are marking the 20th anniversary of the invention of genetic fingerprinting.

The breakthrough was made accidentally by Professor Sir Alec Jeffreys at the city's university on 10 September 1984.

Since then, the technique has been used to trap criminals, identify victims of war, settle paternity disputes, and prove the claims of clones like Dolly.

It has also led to a national database in the UK of 2.5 million genetic profiles, mainly from convicted criminals but also from unsolved casework.

It is a development Sir Alec has some qualms about, and he opposes the practice, approved by a court in 2002, of retaining DNA samples from suspects who are acquitted.

"My view is, that is discriminatory," he said. "It works on a premise that the suspect population, even if innocent, is more likely to offend in the future."

He would prefer to see a database that included all individuals, with strict guidelines on what information could be stored. The professor would not allow sensitive personal details such as a person's medical history or ethnic origin to be mined from the data.

'Fantasy' vision

Sir Alec refers to the time when his lab stumbled across the technique as a "eureka moment".

He and colleagues had been studying genetic variation and how it might be used to track hereditary disease through families.

Schematic diagram of DNA (BBC)
The double-stranded DNA molecule lies at the heart of nearly all our cells
Chemical components called bases - adenine (A), thymine (T), cytosine(C) and guanine (G) - spell out a profile unique to the individual
DNA fingerprinting looks for patterns in what appear to be random repeats in this code
Enzymes chop up a sample of DNA, with the fragments sorted according to size
Further processing with X-ray film produces a characteristic barcode
If two barcodes from two different samples match, they probably come from the same source
"That magic moment was on a Monday morning 20 years ago, when I pulled that grubby bit of X-ray film out of the developing tank and saw these fuzzy but extraordinarily variable patterns of DNA," he explained to the BBC.

"The penny dropped pretty well immediately; we could see the potential for individual identification."

Within a year, it had been used in a Leicestershire double-rape-and-murder case, to prove one man could not have committed the crimes and to confirm another had.

Indeed, it is in the area of criminal investigation that DNA fingerprinting has had its most profound impact.

Sir Alec recalls: "Not so long ago I was very kindly invited down to the Old Bailey, to have lunch with some of the judges there and sat opposite a judge who was very excited because he was trying a case at the Old Bailey that didn't have any DNA evidence."

Since the DNA profiling discovery in 1984, Sir Alec has won world acclaim for his work.

In April this year, he won the Louis-Jeantet Prize for Medicine, which is awarded to scientists who are distinguished for the highest quality of biomedical research in Europe.

"If you had told me that 20 years later this technology would directly touch the lives of 10 million people worldwide, I would have thought 'fantasy, no way'; I am amazed."

Prof Sir Alec Jeffreys
"The penny dropped pretty well immediately"

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