The ability to identify an individual based on their unique genetic makeup revolutionized forensic science and altered the landscape of criminal justice. This technology, often called DNA fingerprinting or DNA profiling, operates on the principle that while most human deoxyribonucleic acid is identical, tiny sections exhibit significant variation. By focusing on these highly variable regions, scientists can create a distinct and individualized pattern, much like a traditional fingerprint. This process provides an unprecedented level of certainty in personal identification, marking the beginning of a new era in both biological research and legal investigation.
The Breakthrough Discovery
The scientific foundation for this revolution was laid in the United Kingdom during the mid-1980s. Geneticist Sir Alec Jeffreys, working at the University of Leicester, was researching inherited markers through family lineages, focusing on DNA sequences that varied between people. This work unexpectedly led him to a profound realization about the distinctiveness of the human genome.
The discovery occurred on September 10, 1984, when Jeffreys analyzed the results of an experiment involving a specific type of repetitive DNA sequence. He termed these short, repeated segments minisatellites. Crucially, the number of these repeats varied significantly from person to person, making the overall pattern highly individualistic.
When he examined the film, Jeffreys saw a complex pattern of dark bands unique to each person sampled. He recognized that the pattern represented a composite of the minisatellite sequences inherited from both parents. This variable inheritance meant that, except for identical twins, every individual possessed a genetic structure that could serve as a biological barcode. Jeffreys immediately grasped the potential for this finding to be used as a definitive method of identification.
The Original Fingerprinting Technique
The original methodology developed by Jeffreys to produce these unique genetic patterns was known as Restriction Fragment Length Polymorphism (RFLP) analysis. This technique was complex, requiring a relatively large and well-preserved sample of DNA to be successful. The process began by isolating the DNA from a biological sample, such as blood or tissue, and subjecting it to a precise chemical treatment.
The purified DNA was exposed to specialized proteins called restriction enzymes, which act like molecular scissors. These enzymes recognize and cut the DNA strand wherever a specific short sequence of nucleotides occurs. Because the repetitive minisatellite regions varied in length between individuals, the cuts made by the enzyme produced DNA fragments of different sizes for each person.
The resulting mixture of DNA fragments was then separated using a method called gel electrophoresis. The fragments were placed into a jelly-like slab, and an electric current was run through it, causing the negatively charged DNA pieces to migrate toward the positive electrode. Shorter fragments moved quickly through the gel’s matrix, while longer fragments lagged behind, effectively sorting the DNA by size.
To visualize the specific, identifying fragments, a technique called Southern blotting was employed, which transferred the separated DNA bands to a nylon membrane. A radioactive probe, a single-stranded piece of DNA designed to bind only to the minisatellite sequences, was then applied. This probe attached itself to the variable fragments, and when the membrane was placed against X-ray film, the radioactive areas created a distinct, visible pattern of bands. This final pattern, unique to the individual, constituted the first true DNA fingerprint.
Establishing Legal Precedent
The application of this groundbreaking technology quickly moved out of the laboratory and into the public sphere, beginning with a unique case that established its utility in family law. In 1985, Jeffreys was asked to assist in a complicated British immigration dispute involving a Ghanaian boy whose identity papers were being questioned by authorities. The mother was already in the UK, but the boy was facing deportation because officials doubted he was her biological son.
Jeffreys used his new technique to compare the boy’s DNA pattern with that of his mother and siblings. The resulting genetic fingerprint clearly showed that the boy had inherited half of his genetic markers from the mother, irrefutably proving their biological relationship. This successful resolution marked the first time DNA fingerprinting was used to settle a legal matter, demonstrating its power to clarify familial ties.
The technology’s most significant leap into the legal system came with its first forensic application in a criminal investigation. In 1986, police in Leicestershire sought Jeffreys’s help in the case of two separate murders and rapes, those of Lynda Mann in 1983 and Dawn Ashworth in 1986. A local man, Richard Buckland, had confessed to the second murder but not the first.
Jeffreys analyzed the semen samples recovered from both crime scenes and compared them to Buckland’s DNA. The DNA evidence proved that the same person had committed both crimes, but it showed that this person was not Richard Buckland, leading to his exoneration. The police then undertook a voluntary mass screening, or “DNA dragnet,” collecting thousands of samples from local men. This investigation eventually led to the identification of the true perpetrator, Colin Pitchfork, who was subsequently convicted in 1987. This case established DNA fingerprinting as an invaluable tool for both identifying the guilty and protecting the innocent, permanently embedding the technology into the framework of modern jurisprudence.