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Background

Starting in the 1980s, scientific advances allowed the use of DNA as a material for the identification of an individual. The first patent covering the direct use of DNA variation for forensics (US5593832A) was filed by Jeffrey Glassberg in 1983, based upon work he had done while at Rockefeller University in the United States in 1981.

British geneticist Sir Alec Jeffreys independently developed a process for DNA profiling in 1985 while working in the Department of Genetics at the University of Leicester. Jeffreys discovered that a DNA examiner could establish patterns in unknown DNA. These patterns were a part of inherited traits that could be used to advance the field of relationship analysis. These discoveries lead to the first use of DNA profiling in a criminal case.

The process, developed by Jeffreys in conjunction with Peter Gill and Dave Werrett of the Forensic Science Service (FSS), was first used forensically in the solving of the murder of two teenagers who had been raped and murdered in Narborough, Leicestershire in 1983 and 1986. In the murder inquiry, led by Detective David Baker, the DNA contained within blood samples obtained voluntarily from around 5,000 local men who willingly assisted Leicestershire Constabulary with the investigation, resulted in the exoneration of Richard Buckland, an initial suspect who had confessed to one of the crimes, and the subsequent conviction of Colin Pitchfork on January 2, 1988. Pitchfork, a local bakery employee, had coerced his coworker Ian Kelly to stand in for him when providing a blood sample—Kelly then used a forged passport to impersonate Pitchfork. Another coworker reported the deception to the police. Pitchfork was arrested, and his blood was sent to Jeffreys' lab for processing and profile development. Pitchfork's profile matched that of DNA left by the murderer which confirmed Pitchfork's presence at both crime scenes; he pleaded guilty to both murders. After some years, a chemical company named Imperial Chemical Industries (ICI) introduced the first ever commercially available kit to the world. Despite being a relatively recent field, it had a significant global influence on both criminal justice system and society.

Although 99.9% of human DNA sequences are the same in every person, enough of the DNA is different that it is possible to distinguish one individual from another, unless they are monozygotic (identical) twins. DNA profiling uses repetitive sequences that are highly variable, called variable number tandem repeats (VNTRs), in particular short tandem repeats (STRs), also known as microsatellites, and minisatellites. VNTR loci are similar between closely related individuals, but are so variable that unrelated individuals are unlikely to have the same VNTRs.

Before VNTRs and STRs, people like Jeffreys used a process called restriction fragment length polymorphism (RFLP). This process regularly used large portions of DNA to analyze the differences between two DNA samples. RFLP was among the first technologies used in DNA profiling and analysis. However, as technology has evolved, new technologies, like STR, emerged and took the place of older technology like RFLP.

The admissibility of DNA evidence in courts was disputed in the United States in the 1980s and 1990s, but has since become more universally accepted due to improved techniques.