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How DNA became evidence: the method, the record, and the limits of a profile.

The Record · Entry 3.01

Leicester, 1984

Alec Jeffreys noticed repeating sequences that varied enough between people to identify them, and called the result a genetic fingerprint.

On the morning of 10 September 1984 an X-ray film came out of a developing tray in a laboratory at the University of Leicester carrying a dense pattern of bands that differed from person to person and was partly shared between parents and children. Alec Jeffreys called it a genetic fingerprint.

Its first use in a criminal investigation, two years later, cleared a man who had already confessed. That order of events — exclusion before conviction — is the reason the courts took the technique seriously, and it is where this register starts.

Read the entry
FIG. 01 Alec Jeffreys at a desk in his office at the University of Leicester
Alec Jeffreys at Leicester. The pattern he read off the film was individual enough to identify and regular enough to inherit — the two properties the whole method rests on.Photo: Alec Jeffreys · Wikimedia Commons

The method, in five moves

Every entry is one technique, and what it can and cannot carry.

  1. 01The Southern blot

    Micrograms of intact DNA, and days of film.

  2. 02Multilocus probes

    Individual enough to exclude, unreadable in a mixture.

  3. 03PCR and the single locus

    Nanograms will do, but too few types to name anybody.

  4. 04STR multiplexes

    Integers a register can search.

  5. 05Low-template DNA

    Alleles that come and go between runs.

The Method — six entries

Where to start

Three entries that carry the argument of the site.

FIG. 02 A university laboratory corridor with doors and noticeboards, institutional light
The first criminal use of the technique produced an exclusion, not an identification. A mismatch was visible to anybody standing at the lightbox; a match was an argued judgement about band positions.

The Record · Entry 3.02

The first exoneration

The technique's first use in a criminal investigation cleared a man who had already confessed, which is the reason it was trusted afterwards.

The Limits · Entry 2.01TransferDNA moves — hand to bench, bench to garment, glove to item — so presence establishes contact with the material, not participation in an event.The Registers · Entry 4.04S. and MarperA European court judgment in 2008 held that indefinite retention of profiles from people not convicted was disproportionate, and the law changed. The whole registerThirty-one entries in six sections, listed in one table.

Supported by

Laboratories and standards bodies advancing forensic evidence.

What this register is for

A profile answers whose cells these are. It does not answer how they arrived, or when.

Where a profile stops

A gloved adult hand loading a sample into a gel tray with a fine pipette, bench lighting
Loading a sample. Every hand and every consumable in the chain is also a route by which cells arrive on an item — which is the subject of the section below.

The Limits

Six ways a profile can be right about the cells and wrong about the event.

All six entries

Also supported by

The remaining seven.

Six sections

Every entry is one technique, one register, one instrument or one body, and what it can and cannot carry.

Institutions named in the register

The bodies that made, ran, standardised or judged the method.