DNA profiling

DNA profiling emerged from an accident at 9:05 AM on September 10, 1984. Alec Jeffreys at the University of Leicester was studying the myoglobin gene when a radioactive probe bound not just to the target sequence but to repetitive "minisatellite" regions scattered throughout the genome. The resulting X-ray film showed a pattern of dark bands unique to each individual—a genetic fingerprint. Within half an hour, Jeffreys realized he had invented a method to identify any human from a trace of biological material.

The adjacent possible had aligned through decades of molecular biology. Restriction enzymes, discovered in the 1970s, could cut DNA at specific sequences. Gel electrophoresis separated fragments by size. Southern blotting transferred DNA patterns to membranes for analysis. Radioactive probes could bind to complementary sequences and expose film. Each technique existed; Jeffreys combined them into something transformative by recognizing that minisatellite variation was not noise but signal.

Jeffreys published his discovery in Nature in March 1985. The first application was not criminal—it was immigration. A Ghanaian family needed to prove their son was genuinely related; Jeffreys' DNA test confirmed the relationship when bureaucratic documents could not. But crime would define the technology. In 1986, police investigating two teenage murders in Narborough, Leicestershire asked Jeffreys to test their suspect, Richard Buckland, who had confessed. The DNA didn't match. Buckland became the first person exonerated by DNA evidence—freed despite his own confession.

The police then conducted history's first genetic dragnet, collecting samples from over 4,000 local men. No match emerged until someone overheard a man boasting that he'd given a sample on behalf of a colleague. That colleague was Colin Pitchfork. His DNA matched both crime scenes. In January 1988, Pitchfork became the first person convicted of murder through DNA evidence. The same technique that freed an innocent man caught a guilty one.

PCR transformed DNA profiling from laboratory curiosity to forensic standard. The original technique required substantial samples and took weeks. After Kary Mullis' polymerase chain reaction became practical in the late 1980s, investigators could amplify DNA from a few cells—a cigarette butt, a licked envelope, skin cells under a victim's fingernails. By the 1990s, short tandem repeat (STR) markers replaced restriction fragment analysis, enabling faster and more reliable identification.

The cascade from DNA profiling restructured criminal justice. The FBI's Combined DNA Index System (CODIS) now contains over 20 million profiles. Cold cases decades old have been solved when DNA databases matched new arrests to old crime scene evidence. The Innocence Project has used DNA to exonerate over 375 wrongly convicted people in the United States alone. Familial DNA searching has identified suspects through their relatives.

By 2026, DNA profiling extends far beyond crime. Ancestry testing has created databases of tens of millions, raising privacy concerns Jeffreys never anticipated. Forensic genetic genealogy—using consumer DNA data to identify suspects—has solved cases from the Golden State Killer onward. The technique born from an unexpected pattern on X-ray film now shapes justice, identity, and the boundaries of genetic privacy.