DNA Fingerprinting

DNA fingerprinting was first used in criminology in 1986 and it exonerated a man with learning difficulties who had confessed to the murder and rape of a schoolgirl. He was also suspected of committing a similar crime three years previously. UK Police turned to the new technique of DNA fingerprinting, and although it revealed that the same person had committed both crimes it was not the man that police had in custody. But it did eventually lead to the perpetrator.

The police embarked on the first ever DNA mass screening program and thousands of local men had their blood and saliva samples analyzed. Although this didn’t directly lead to the murderer, a woman overheard a man called Ian Kelly boasting that he had been paid to take the place of a friend of his, Colin Pitchfork. She went to the police and both men were arrested, and subsequent DNA analysis revealed that Pitchfork was the killer

The scientist who invented DNA fingerprinting is Professor Sir Alec Jeffreys from the University of Leicester in the UK. The big breakthrough came on Monday September 10th 1984 when he examined a piece of X-ray film and observed some fuzzy but variable patterns of DNA. He had been studying genetic variation and how it could be used to track hereditary diseases through families, but when he saw the DNA patterns he realized almost immediately that he had chanced upon a new form of individual identification.

DNA fingerprinting was first used in 1985 shortly after it was described in Jeffrey’s landmark paper in Nature. But its first use was not in criminology. A London-based lawyer read about the technology in a newspaper and got in touch with the scientist to see if it could help resolve an immigration dispute. Jeffreys compiled genetic profiles of the individuals involved and they revealed that a Ghanaian boy who was facing deportation from the UK was entitled to stay as he was the son of a UK citizen of Ghanaian descent.

So how can DNA fingerprinting solve crimes? Chemically everybody’s DNA is the same; it’s made up of the same four bases. However, the sequence of these chemicals is different. Jeffreys found regions of DNA called microsatellites that are highly variable, and repeat many times over. It’s the pattern of repeats that is different between people, and forensic scientists compare a number of microsatellites in a given region of DNA. Although variable, the patterns are passed down the generations from parents to children.

Since its introduction DNA fingerprinting has helped to send thousands of criminals to prison; and it has also spared the innocent. One of the most famous cases is that of former Death Row inmate Kirk Bloodsworth. He had his murder conviction overturned after he badgered his legal team to have the material evidence used against him tested. The results showed that he could not have committed the murder he was convicted of. He was released and pardoned.

DNA fingerprinting can also solve crime with relatives' DNA. This is based on the premise that DNA profiles of individuals who are related to each other will contain more similarities than the profiles of those who aren't. For example, detectives in Denver, Colorado tracked down a suspect through his brother’s DNA.

In 2008 two cars were broken into and police found blood samples at both scenes. They ran the DNA through their database, but couldn’t find a match. Then they extended their search to see if the genetic material was a close enough match to any samples already in the database. It came up with 6 potential matches; five didn’t pan out, but one led officers to a convicted car thief and his brother Luis Jaimes-Tinajero who pleaded guilty to one case of criminal trespass.

And it’s not just nuclear DNA that can track down suspects; mitochondrial DNA is used in forensics too. It has many attractive features:-

• There are hundreds of mitochondria in each cell and therefore many copies of genes.

• It appears to be hardier than nuclear DNA and survives where the nuclear material is usually degraded. Mitochondria DNA have been recovered from aged and decrepit hair, teeth, and bone samples.

DNA fingerprinting is without doubt a powerful crime-fighting tool, but concern has been raised that there is a technology that can fake DNA fingerprinting evidence. A team of Israeli scientists wrote a paper detailing how they took the blood and saliva of one individual and replaced the original DNA with that of a donor.

However, it is unlikely that your average criminal is going to have access to the sort of front-line scientific equipment that made this possible. However, the paper did highlight the fact that DNA fingerprinting should be used as one tool amongst several. DNA fingerprinting may well place someone at a crime scene, but many crime scenes are littered with DNA belonging to a countless number of innocent people.

Multiple and mixed copies of DNA at crime scenes cause problems for forensic scientists. It is almost impossible to tease out the DNA from different individuals. That is until a new technology called DNAboost made an appearance. It was developed by the Forensic Science Service in the UK, and can create profiles from mixed samples.

DNA fingerprinting has also found many other innovative uses in addition to those already discussed. It was used to verify that the man discovered hiding in a hole by the Tigris River in Iraq in 2003 was indeed Saddam Hussein. Other innovative uses include piecing together the Dead Sea Scrolls, and the identification of endangered animals.