Today marks the 30th anniversary of the discovery of DNA fingerprinting, a technique that has transformed forensic science and resolved questions of identity and kinship.

In 1984, Professor Sir Alec Jeffreys stumbled on a method for distinguishing individuals based on their DNA - which is now used worldwide by forensic scientists to assist in the identification of individuals by their respective DNA profiles.

Jeffreys, who said the discovery was a "glorious accident" at the University of Leicester, was knighted in 1994 for his services to science and technology.

How does DNA testing work?

At the centre of DNA testing is the molecule DNA, which carries our unique genetic code and determines our traits. Each cell in our bodies contains a complete set of our DNA.

Grand Duchess Anastasia Nikolaevna of Russia
DNA fingerprinting helped solve the mystery of Grand Duchess Anastasia Nikolaevna of Russia (pictured) and the identity of Anna Anderson Wiki Commons

Although 99.9% of human DNA sequences are the same in every person, enough of the DNA is different enough to make it possible to distinguish one individual from another.

Parental, forensic and genetic testing look for similarities in the genetic markers between two biological samples.

Firstly, the DNA is isolated from the cells and millions of copies are made, using a method called polymerase chain reaction.

PCR uses a naturally occurring enzyme to copy a specific stretch of DNA repeatedly, as having lots of DNA makes the genetic code easier to analyse.

The DNA molecules are then split into particular locations and analysed to create a DNA fingerprint.

Fingerprints from two different samples are then compared to see if they match.

When was it discovered?

In 1984, Jeffreys had a "eureka moment" in his laboratory, after examining an X-ray film image of a DNA experiment, which showed both similarities and differences between the DNA of different members of a technician's family.

Within half an hour, he realised the scope of genetic fingerprinting, which has since become essential to forensic science.

Jeffreys's methods were commercialised in 1987 but before then, his laboratory was the only facility carrying out DNA fingerprinting in the world.

The technique was first used in an immigration case involving the identity of a British boy whose family was originally from Ghana.

Cases cracked by genetic fingerprinting

The method was first used as a police forensic test to identify the rapist and murderer of two Leicestershire teenagers Lynda Mann and Dawn Ashworth, who were killed in 1983 and 1986 respectively. Colin Pitchfork was identified and convicted of murder after samples from him matched semen samples found on the two girls.

In 1992, genetic fingerprinting was used to confirm the identity of Dr Josef Mengele, an SS officer and physician in Auschwitz concentration camp during World War II. He was notorious for performing unscientific experiments on prisoners with no regard to human life. After his death in 1979, he was identified using DNA obtained from a femur bone of his exhumed skeleton.

In the 1950s, Anna Anderson famously claimed to be the Grand Duchess Anastasia, the only survivor of the Russian royal family and the youngest daughter of Tsar Nicholas II. After Anderson's death in 1984, DNA tests proved she was no relation to the Imperial family.