Safety of genetic evidence is put to test: Steve Connor reports on doubts over the use of DNA profiles in court

Six years after genetic fingerprinting was first used in a British court, there is grave concern that it is not the powerful identification tool it was initially said to be.

Defence lawyers in two recent court cases in the UK successfully challenged DNA evidence on the grounds that it could not be relied on to produce a safe conviction. One of the judges involved ruled that if scientists themselves could not agree on the value of genetic fingerprinting, it was unfair to expect a jury to do so.

Next week, forensic experts and leading geneticists will attempt to resolve the issue at a conference in London organised by the Metropolitan Police.

Some of the world's most eminent geneticists are astonished at the British court ruling. They believe anxieties - first expressed more than two years ago - should have been dispelled by now.

'It's the lawyers who keep the pot boiling,' Victor McKusick, professor of medical genetics at Johns Hopkins University in Baltimore, Maryland, said. 'It's their business to defend clients and anything they can say to cast doubt on genetic fingerprinting, they will. I think it's unjustified.'

Professor McKusick chaired a committee of American scientists who last year produced a report that should have answered the criticism. He said the report 'lays their concerns to rest'.

Although the committee, which was called together by the prestigious US National Academy of Sciences, confirmed the general reliability of the technique, the scientific consensus failed to prevent DNA evidence being thrown out by the courts.

Professor McKusick was mystified: 'I can't see why they find it unacceptable.'

Alec Jeffreys, professor of genetics at Leicester University and inventor of the technique, said the case against DNA fingerprinting was groundless. The dispute had led to a situation where 'scientific logic and legal logic get lost'.

The problems are perhaps the inevitable result of the technique's complexity. Defence lawyers have bombarded judges and juries with a welter of contradictory claims about scientific intricacies. Genetic fingerprinting works by comparing the DNA present in a tissue sample left at the scene of a crime - blood, semen, hair, skin or even saliva - with that of the defendant. Forensic scientists use a process of separating DNA fragments - dark bands in a gel - in an electric field. When the positions of two bands coincide, then they are said to match.

One of the arguments used by defence lawyers is that it is not always possible to agree on whether a 'match' is genuine. Even using the same scientific procedure on the same person can produce bands that end up in slightly different positions to each other.

However, Professor Jeffreys said the question of matching bands was not an issue because the interpretation of a match was biased in favour of a guilty defendant. But this has not stopped defence lawyers successfully challenging the forensic scientist's definition of a match.

More importantly, defence lawyers have raised the possibility that a 'match' between defendant and sample is the result of an innocent defendant and the guilty person sharing the same characteristics used in the analysis.

This is why DNA evidence is always accompanied by a statistical estimate of the probability of a chance match. There is more than one way of estimating this probability and different estimates can result in what appear to be huge discrepancies to a judge or jury. In one celebrated murder case in New York, the probabilities of a chance match were given as 1 in 500 using one statistical method, and 1 in 739 billion using another. This extreme example illustrates the difficulties of using a statistical procedure called the multiplication rule, whereby extremely small probabilities arise as a result of multiplying individual probabilities together.

The multiplication rule does not take sub-grouping of genetic traits - such as different races - into account because it assumes the genes in question are independent of each other. Defence lawyers have exploited this limitation.

Critics say there are subgroups of people - such as Scandinavians or Africans - who are likely to share the same genetic profile.

The argument's two chief proponents were Richard Lewontin, a geneticist at Harvard University, and Daniel Hartl, professor of biology at Harvard. They said genetic differences between races within a society mean that some genetic traits used in DNA profiling may not occur independently of each other.

Lewontin and Hartl were right in principle, but in practice it makes no difference, said Professor Jeffreys and others. For the genetic traits used in DNA profiling, there are no major differences between racial groups that could make the technique unsafe. In fact, genetic differences within races rather than between races are greater.

Professor McKusick's scientific committee concluded that even assuming there were differences between groups within the population, this could be taken into account by being ultra-conservative with the statistics, biasing the evidence in favour of the defendant.

Providing scientists follow this procedure and take due care in analysing tissue samples 'DNA typing should be able to provide virtually absolute individual identification', the committee said.

Professor Hartl accepted these conclusions and now endorses genetic fingerprinting. 'It's a terrific technique. It's so powerful at identifying people you don't have to fudge the data.' Even though probabilities will now have to be amended, so that some smaller estimates such as 1 in 100 million are changed to 1 in 10 million, they are 'still within the range that you can convict', he said.

Professor Lewontin, however, is sticking to his position, providing comfort for defence lawyers. 'I don't think it does change anything. I have the same problems I've always had,'he said.

Meanwhile, Professor Jeffreys is adamant that genetic fingerprinting is safe. 'It's here to stay.'

PROMOTED VIDEO
Have you tried new the Independent Digital Edition apps?
News
ebooksAn unforgettable anthology of contemporary reportage
Life and Style
food + drink
News
Liam Payne has attacked the media for reporting his tweet of support to Willie Robertson and the subsequent backlash from fans
peopleBut One Direction star insists he is not homophobic
Arts and Entertainment
A bit rich: Maggie Smith in Downton Abbey
tvSeries 5 opening episode attracts lowest ratings since drama began
Arts and Entertainment
Ben Affleck stars as prime suspect Nick Dunne in the film adaptation of Gone Girl
filmBen Affleck and Rosamund Pike excel in David Fincher's film, says Geoffrey Macnab
Life and Style
fashion
News
news
News
people
Travel
Warner Bros released a mock-up of what the new Central Perk will look like
travel
Arts and Entertainment
Lena Dunham
booksLena Dunham's memoirs - written at the age of 28 - are honest to the point of making you squirm
News
i100
Arts and Entertainment
Jake Quickenden sings his heart out in his second audition
tvX Factor: How did the Jakes - and Charlie Martinez - fare?
Latest stories from i100
Have you tried new the Independent Digital Edition apps?
Independent Dating
and  

By clicking 'Search' you
are agreeing to our
Terms of Use.

iJobs Job Widget
iJobs General

KS2 Teacher with SEN responsibilities

£115 - £130 per day: Randstad Education Luton: KS2 teacher with SEN responsibi...

Administrative Assistant

£60 - £75 per day: Randstad Education Luton: Administrative Assitant Hertford...

Web Application Support Manager

£60000 Per Annum: Clearwater People Solutions Ltd: Our client based in Reigate...

** Secondary History Teacher Required In Liverpool **

£120 - £165 per day: Randstad Education Liverpool: Job opportunities for Secon...

Day In a Page

A roller-coaster tale from the 'voice of a generation'

Not That Kind of Girl:

A roller-coaster tale from 'voice of a generation' Lena Dunham
London is not bedlam or a cradle of vice. In fact it, as much as anywhere, deserves independence

London is not bedlam or a cradle of vice

In fact it, as much as anywhere, deserves independence
Vivienne Westwood 'didn’t want' relationship with Malcolm McLaren

Vivienne Westwood 'didn’t want' relationship with McLaren

Designer 'felt pressured' into going out with Sex Pistols manager
Jourdan Dunn: Model mother

Model mother

Jordan Dunn became one of the best-paid models in the world
Apple still coolest brand – despite U2 PR disaster

Apple still the coolest brand

Despite PR disaster of free U2 album
Scottish referendum: The Yes vote was the love that dared speak its name, but it was not to be

Despite the result, this is the end of the status quo

Boyd Tonkin on the fall-out from the Scottish referendum
Manolo Blahnik: The high priest of heels talks flats, Englishness, and why he loves Mary Beard

Manolo Blahnik: Flats, Englishness, and Mary Beard

The shoe designer who has been dubbed 'the patron saint of the stiletto'
The Beatles biographer reveals exclusive original manuscripts of some of the best pop songs ever written

Scrambled eggs and LSD

Behind The Beatles' lyrics - thanks to Hunter Davis's original manuscript copies
'Normcore' fashion: Blending in is the new standing out in latest catwalk non-trend

'Normcore': Blending in is the new standing out

Just when fashion was in grave danger of running out of trends, it only went and invented the non-trend. Rebecca Gonsalves investigates
Dance’s new leading ladies fight back: How female vocalists are now writing their own hits

New leading ladies of dance fight back

How female vocalists are now writing their own hits
Mystery of the Ground Zero wedding photo

A shot in the dark

Mystery of the wedding photo from Ground Zero
His life, the universe and everything

His life, the universe and everything

New biography sheds light on comic genius of Douglas Adams
Save us from small screen superheroes

Save us from small screen superheroes

Shows like Agents of S.H.I.E.L.D are little more than marketing tools
Reach for the skies

Reach for the skies

From pools to football pitches, rooftop living is looking up
These are the 12 best hotel spas in the UK

12 best hotel spas in the UK

Some hotels go all out on facilities; others stand out for the sheer quality of treatments