British scientists have invented a method of "fingerprinting" the genes of a person so that they can be compared with the genes in samples of blood, semen or a hair root.

If the method can be refined, it could prove of major importance to police detectives investigating a crime and to other forensic scientists trying to establish paternity or maternity in legal disputes.

Existing methods of comparing blood types can often disprove a relationship between one person and another or between one person and a blood or semen sample but frequently leave relationships in doubt. The new method can give an answer, proving or disproving a link, with a chance of error of about 3 in 100 billion.

The method takes advantage of the fact that each person's genes are distributed in slightly different patterns along the strands of deoxyribonucleic acid (DNA) that make up each chromosome. The researchers have developed a standard set of 15 short pieces of radioactive synthetic DNA, called probes, that will bind to specific places on the DNA of persons or specimens being studied.

By comparing the distances between the sites where the probes attach, they can tell whether two DNA samples came from the same person.

The method, detailed in several articles in the British journal Nature over the past year, was developed by Alec Jeffreys and his colleagues at the University of Leicester and Peter Gill and David Werrett of the Home Office Forensic Science Service in Aldermaston, England.