Discovering DNA fingerprinting 04/02/04 BY GILES NEWTON

Forensics, paternity and immigration: all have been revolutionised by DNA fingerprinting. Sir Alec Jeffreys describes its development.

DNA fingerprinting has become an indelible part of society, helping to prove innocence or guilt in criminal cases, resolving immigration arguments and clarifying paternity. Its inventor, Professor Sir Alec Jeffreys, University of , looks back at how it began. With highly automated and sophisticated equipment, the modern-day DNA fingerprinter can process hundreds of samples a day. Back in the late 1970s, however, molecular biology was in its infancy and was just beginning to be applied to human . "I'd been working in Amsterdam with Dick Flavell," says Professor Jeffreys. "We'd got to the point where we could detect single copies of human genes – which led to one of the first observations of introns [non-coding sections of DNA that split up genes]. But when I came to Leicester in 1977, I wanted to move away from the study of split genes, and to marry the new techniques of molecular biology with human genetics." Professor Jeffreys's plan was to use the primitive gene detection methods of the time to look at the structures of genes and understand inherited variation – the variation between people. An early outcome of this research was one of the first descriptions of a restriction fragment length polymorphism (RFLP). (DNA-cutting enzymes target short DNA sequences, and chop the genome into pieces. Some people have a small DNA change – a single nucleotide polymorphism [SNP] – in a target site, preventing the enzymes cutting the DNA at that site.) "We got our first SNP in 1978," says Professor Jeffreys. "Before that we knew about heritable variation in gene products, such as blood groups, but here we had examples of inherited variation in DNA, the most fundamental level of all. While RFLPs were proof of inherited variation at the DNA level, they were difficult to find and to assay, and did not tell you much about variation between people – you either had the change or you didn't." So Professor Jeffreys started looking for pieces of DNA that would be more variable than SNPs. A prime candidate was tandem repeat DNA – where a short sequence of DNA was repeated many times in a row. "Intuitively it seemed that regions of tandemly repeated DNA would be open to mutation processes such as duplication and recombination," says Professor Jeffreys. "They could be highly variable, informative genetic markers." The first fingerprint Tandem repeat DNA in the remained elusive at first, and the research went down several blind routes. The answer came from a totally different project in Professor Jeffreys's lab which was searching for the human copy of the myoglobin gene, which produces the oxygen carrying protein in muscle. The group decided to look for the myoglobin gene first in grey seals (as seals produce lots of myoglobin, and have high levels of myoglobin mRNA, which makes it easy to clone a cDNA), then use the seal gene to isolate its human counterpart. "The true story of DNA fingerprinting starts at the headquarters of the British Antarctic Survey in Cambridge," says Professor Jeffreys. "I collected a big lump of seal meat from their lock-up freezer and, to cut a long story short, we got the seal myoglobin gene, had a look at human myoglobin gene and there, inside an intron in that gene was tandem repeat DNA – a ." This minisatellite was to prove the key to the rest of the genome, for while it was not variable itself, its sequence was similar to the very few that had been described previously. Using the myoglobin minisatellite as a 'hook', the team could then identify more minisatellites and to their surprise discovered a core sequence - a piece of DNA that is similar in many different minisatellites. "Using the core sequence, we made a probe that should latch onto lots of these minisatellites at the same time," says Professor Jeffreys, "and, to test out the system, we hybridised the probe to a blot with DNA from several different people." On a Monday morning in September 1984, the X-ray of the blot was developed in the Leicester University darkroom. "I took one look, thought 'what a complicated mess', then suddenly realised we had patterns," says Professor Jeffreys. "There was a level of individual specificity that was light years beyond anything that had been seen before. "It was a 'eureka!' moment. Standing in front of this picture in the darkroom, my life took a complete turn. We could immediately see the potential for forensic investigations and paternity, and my wife pointed out that very evening that it could be used to resolve immigration disputes by clarifying family relationships." The potential of DNA fingerprinting was clear, but could the technology be improved? Two to three months later, the grubby mess of the first fingerprint had been refined into clean patterns where DNA fingerprints, unique to an individual, could be deciphered clearly. DNA fingerprinting was ready for prime time. Immigration issues When the first paper on DNA fingerprinting was published in spring 1985, it was covered in the press – and one report in the Guardian was read by Sheona York at the Hammersmith and Fulham Community Law Centre. Her clients, a Ghanaian family who were UK citizens living in London, were stuck in an immigration dispute. The youngest son had travelled back to Ghana, but on his return to the UK was detained due to an allegedly forged passport – the question being whether the boy coming back was in fact the son or was a substitute. Standard DNA fingerprints in an immigration dispute "We took the case on – and it was a tricky case," says Professor Jeffreys. "The woman had sisters back in Ghana, so the boy could have been a nephew, and we didn't have the father for analysis. All we had were three fully accepted children – so we used these children to reconstruct the DNA fingerprint of the missing father. When you compared mum, dad, and the boy, the results were clear-cut – the boy was definitely the son." The case against the son was dropped, and huge press coverage ensued. "It was a good news story of 'science fighting bureaucracy and helping families'", says Professor Jeffreys. The switchboards were soon jammed with calls about immigration. "I didn't realise the scale of the problem, thousands of families were trapped in exactly this sort of dispute," he adds. Indeed, DNA fingerprinting led to a change in the Immigration Act. Innocent or guilty? Although the principle of DNA fingerprinting seemed ideal for forensics, in practice the patterns would have been too complicated to explain in court. A slightly tweaked approach – termed DNA profiling – was the answer. As Professor Jeffreys's team uncovered more and more minisatellites in the human genome, they were finding some that were stupendously variable. DNA profiling therefore focused on just a few of these highly variable minisatellites, making the system more sensitive, more reproducible and amenable to computer databasing. In 1986, the Enderby murder case, a case local to Leicester, saw the first use of DNA profiling in criminology. Two young girls had been raped and murdered, one in 1983 and one in 1986. After the second murder, a young man was arrested and gave a full confession. The police thought he must have committed the first murder as well, so they asked Professor Jeffreys to analyse forensic samples – semen from the first and second victims, samples from the victims, and blood from the prime suspect. "The police were right – both girls had been raped by the same man," says ProfessorJeffreys. "But it wasn't the man who had confessed. At first I thought there was something wrong with the technology, but we and the Home Office's Service did additional testing and it was clear that it was not his semen. He had given a false confession and was released – so the first time DNA profiling was used in criminology, it was to prove innocence." Armed with the DNA profile of the assailant, the police launched the world's first DNA-based manhunt. Blood samples from more than 5000 men in the local community were collected. The murderer nearly got away with it – sending a proxy in to give a blood sample – but eventually he was apprehended and got two life sentences. "This man would have killed again, no doubt about it," says Professor Jeffreys. " DNA testing helped to save lives." Within a year, DNA profiling was being used around the world. But the development of the technique was not finished. The arrival of the polymerase chain reaction enabled another huge leap in forensics: the development of national DNA databases. In part three of the DNA fingerprinting story, Sir Alec Jeffreys discusses the introduction of PCR to DNA fingerprinting and the launch of the National DNA database, and argues for a DNA database for all citizens.

Further reading Jeffreys A J, Wilson V and Thein S L (1985) Hypervariable 'minisatellite' regions in human DNA. Nature 314: 67-73.