Professor Sir Alec Jeffreys' 1984 development of genetic fingerprinting revolved around a technique that points out the unique nature of an individual's DNA code. He showed that restriction fragment length polymorphism, a variation in chromosome pairs, can occur in over 10,000,000 different places, indicating that a person's genetic code is unique to the point that it can be used for positive identification.
Variation in genetic code occurs in two manners: mutation, and crossover, also called recombination. The mutation of a person's DNA creates a change that can be passed on from generation to generation, and is caused by a wide range of inherent and environmental factors. The latter variation, recombination, occurs during the combination of paternal and maternal DNA at conception. Errors in replication of DNA pairs can cause disorders.
Jeffreys' research into "minisatellites" of recombination variation indicated that differences between one person's DNA and another's formed around these groupings. Subsequently developed tests were applied to a number of forensic science fields such as criminal investigation, paternity and immigration. Additionally, these patterns of recombination variation also occur in non-human species, making testing useful for tracking the genetic populations of wildlife. Notably, Jeffreys' tests allowed DNA profiling to confirm identification in criminal investigations as early as the mid 1980s, when it positively confirmed the identity of Colin Pitchfork, a serial rapist and murderer in England.