How DNA Fingerprinting Works: It's First Ever Use

Sir Alec Jeffrey's published "Hypervariable Minisatellite Regions in Human DNA" in 1985. Like many groundbreaking scientific papers, the title, to the untrained eye, can sometimes belie the breathtaking research within. Sir Alec's paper was a little different. Not long after it's publication the mainstream press picked up on it and stories began to appear in the newspapers. This was the beginning of DNA fingerprinting.

DNA Fingerprinting history was about to be made when London-based lawyer, Sheona York, was thumbing through her copy of the Guardian newspaper and saw a report about the work of Alec Jeffreys. At the time she was representing a Ghanaian family who were UK citizens. They were locked in a dispute with the British government over one of their sons. He had travelled to Ghana and then returned to the UK. It was suspected by the authorities that he was not a family member but someone else trying to get into the country. At this time in the 1980's fingerprinting was used to resolve immigration issues.

York got in touch with Jeffreys at his office in the University of Leicester to see if DNA fingerprinting could help.

The challenge was to prove that the boy was an immediate, not a distant relation or unrelated member of the family. His mum had sisters in Ghana so conceivably he could've been a nephew. The father was missing, but Sir Alec had access to the mother and three of her other sons. He used the genetic profiles of the three boys to establish the father's DNA fingerprint. When this was compared with the mum's DNA fingerprint and the boy at the heart of the dispute, it was clear that he was their son. DNA fingerprinting made history and it was big news.

DNA fingerprinting works by exploiting the fact that in our DNA there are highly variable sequences that are repeated throughout our genome. The pattern of these repeats is unique to every individual. They are called Variable Number of Tandem Repeats (VNTRs).

The first method of obtaining a DNA fingerprint was RFLP. Cells are broken into by chemicals called restriction enzymes that recognise specific DNA sequences within the VNTR sections. The enzymes cut up the DNA into smaller chunks which are then called Restriction Fragment Length Polymorphisms (RFLPs). They are then arranged in order of length on an agarose-based gel.

DNA is a charged particle and when electricity is applied the smaller segments move quicker through the gel than the larger ones. They separate, and a banding pattern, unique to each individual is formed. Radioactive probes are applied. They bind to specific DNA sequences and a photographic plate is obtained showing the DNA bandings. This approach, however, needs quite a large amount of DNA to work with.

The technique most commonly used today is PCR (polymerase chain reaction). It can replicate tiny segments of DNA for further analysis. PCR analyses Short Tandem Repeats (STRs), small sections that are contained within the VNTRs, and are specific to an individual.

The Wellcome Trust

http://genome.wellcome.ac.uk/doc_wtd020878.html