Nature Medicine Essay

COMMENTARY LASKER CLINICAL MEDICAL RESEARCH AWARD Genetic fingerprinting Alec J Jeffreys Southern, n.2 Used attrib. (chiefly in by good fortune, teamed up with Richard Southern blot, blotting: see *BLOT n.1 1 f, Flavell on a project to purify a single-copy *BLOTTING vbl. n. 4) with reference to a mammalian gene—the gene encoding rab- technique for the identification of specific bit β-globin—by mRNA hybridization. The nucleotide sequences in DNA, in which problem was how to monitor purification. The fragments separated on a gel are trans- answer was provided by Ed Southern and his ferred directly to a second medium on blots (incidentally, and with typical modesty, http://www.nature.com/naturemedicine which assay by hybridization, etc., may be Ed never calls them Southerns but generally carried out. DNA transfers), which we showed, much to Genetic fingerprinting, the obtaining or our surprise, were capable of detecting single- comparing of genetic fingerprints for iden- copy genes in complex genomes. This led to the tification; spec. the comparison of DNA in a first physical map of a mammalian gene1 and person’s blood with that identified in matter one of the first descriptions of introns2. found at the scene of a crime, etc. – Oxford English Dictionary Human DNA variation Figure 1 Alec Jeffreys at age eight. A budding In 1977 I moved to the Department of Genetics scientist not yet familiar with the focal plane. There can be few higher accolades in sci- at the University of Leicester and, at the tender ence than making it into the Oxford English age of 27, was faced with the thorny issue of Dictionary—except perhaps receiving the where to go next with this arcane new science tively uninformative biallelic markers. Spurred Lasker Award! So how did my involvement in of genomics. The choices were endless but the on by a report in 1980 from Arlene Wyman and 2005 Nature Publishing Group Group 2005 Nature Publishing DNA and forensics come about? The follow- answer, to me, was fairly obvious—why not try Ray White of the accidental discovery of a hyper- © ing is a brief personal account of an explora- to marry together genomics with the classic variable multiallelic locus of unknown physical tion into human genetic variability at the most discipline of human genetics and try to detect basis4, we turned our attention to a search for fundamental level of all, namely variation in heritable variation directly in human DNA? other such informative loci. Intuitively, we felt DNA, and of a wholly unanticipated excur- Within months we had found our first variant that tandem-repeat DNA loci should be a rich sion into the extraordinary world of forensic in the form of a restriction fragment–length source of such markers. This hunch proved cor- medicine and the law. polymorphism (RFLP) and had soon surveyed rect, with reports soon appearing on variable I think I was born a scientist, perhaps thanks the β-globin gene cluster (at the time one of the tandem repeats discovered by chance in the α- to genes inherited from my father and grand- few accessible regions of the human genome) globin gene cluster5 and near the gene encoding father, both prolific inventors with the latter for RFLP abundance3. In a wild extrapolation insulin6. The problem now was how to develop developing the Jeffreys Three-dimensional from the cluster to the entire genome, I pre- generic methods for isolating these loci—which Photosculpture Process that was all the rage in dicted the existence of 15 million single nucleo- we subsequently dubbed minisatellites—from London in the 1930s. I was active in science tide polymorphisms (SNPs; actually I predicted complex genomes. by the age of eight, thanks to my father’s gift 30 million but I made a twofold error—no The answer came unexpectedly from our of a microscope (Fig. 1) and a remarkably one’s perfect!). This prediction, based on the work on the evolution of the globin gene fam- dangerous chemistry set (I still bear the scars). tiniest of surveys, is remarkably close to the ily, including the distant relative myoglobin. These triggered an abiding interest in biology current inventory of 10 million human SNPs Inside the gene encoding human myoglobin and chemistry and led directly to me pursu- logged into dbSNP. Beginner’s luck? was a minisatellite. Curiously, there were ing a degree in biochemistry at the University sequence similarities between its repeat unit of Oxford, starting in 1968. But genetics soon Hypervariable DNA and the repeats of the few other minisatellites emerged as my passion—even in those distant These RFLPs provided human geneticists with described at the time. To explore this further, days, it was clear that penetrating the human a vast new range of mendelian markers and led we screened a human genomic library with the genome was going to be one of the greatest directly to the emergence of the first human myoglobin minisatellite and successfully iso- challenges facing biology. So after my doctoral linkage maps and to the detection of inherited lated additional variable loci. DNA sequence studies on human genetics at Oxford, I moved disease loci by linkage. But RFLP assays for SNPs analysis revealed a short (10–15 basepairs) to the University of Amsterdam in 1975 and, were cumbersome and generally yielded rela- motif shared by these minisatellites7 (Fig. 2). xiv VOLUME 11 | NUMBER 10 | OCTOBER 2005 NATURE MEDICINE COMMENTARY Myoglobin gene tives such as aunt-nephew, and the boy thus faced the threat of deportation from the UK. Minisatellite At the lawyer’s request, we therefore used DNA fingerprinting to test blood samples from the family in the spring of 1985 (Fig. 4). These tests showed that the boy was a member of the immediate family and established the power of DNA typing for positive identification rather than just for exclusion9. The British Home Office dropped the case against the boy and he remained with his family in London as a UK citizen. To my knowledge, this was the first case ever resolved by DNA. Other applications followed swiftly. The first paternity case in the summer of 1985 led to DNA evidence being considered in a UK Magistrate’s Court, the first time that DNA had entered a court of law. Completion of a pilot study with the Home Office on immigration cases, primarily from the Indian subcontinent, Multilocus probe established the utility of DNA fingerprinting in resolving cases involving a UK sponsor http://www.nature.com/naturemedicine attempting to bring his wife and children into GGAGGTGGGCAGGARG Minisatellite core the UK in the absence of adequate documen- tary evidence (and incidentally showed some Figure 2 The minisatellite core sequence. Cross-hybridization of the myoglobin minisatellite to other interesting discrepancies between DNA evi- human minisatellites allowed definition of a sequence motif shared by these loci and the design of dence and the decisions of Entry Clearance multilocus minisatellite hybridization probes7. Officers who had conducted family investiga- tions, village interviews and the like). Zygosity testing appeared on UK television in a popular Even today, the significance of this core DNA fingerprinting in practice family show on which we established that twin sequence remains unknown, though presum- We were now faced with two major challenges. sisters who were unsure as to their status were ably it predisposes these loci to DNA duplica- First, could we improve the technology? indeed monozygotic twins. The audience of tions. But its existence immediately suggested Second, would anyone ever take notice of this over 10 million viewers probably represented a general method for isolating hypervariable obscure new approach to identification? at the time the largest public exposure ever to 2005 Nature Publishing Group Group 2005 Nature Publishing loci, namely by hybridization with probes con- We soon improved the method to the point the concept of DNA technology. Nonhuman © sisting of repeats of the core sequence itself. at which rich and highly informative DNA fin- applications soon emerged, ranging from stud- gerprints could be obtained from human DNA8. ies of mating behavior in house sparrows (like DNA fingerprints Family analyses showed that these patterns were humans, they indulge in spouse-swapping10) to We tested this idea of detecting multiple hyper- derived from many highly variable loci dis- the verification of Dolly the sheep as an authen- variable loci by hybridizing a core repeat probe persed throughout the human genome and that tic clone11 and the reconstruction of the entire to an arbitrarily chosen Southern blot carry- each minisatellite band could, at least as a first pedigree of a colony of Waldrapp ibises at the ing DNA from a family group plus a range of approximation, be treated as a statistically inde- Zurich Zoo12, identifying instances of incestu- DNAs from various nonhuman species (Fig. pendent characteristic. Comparison of different ous mating and helping zookeepers optimize 3). Although the autoradiograph was indistinct people revealed huge levels of variability, even outbreeding in this endangered species. and messy, the results were amazing—emerg- between first-degree relatives, but, as expected, ing from the gloom were what seemed to be identity between monozygotic twins. DNA profiling highly variable profiles of DNA that looked as The second problem was solved by the press. Although Peter Gill at the Home Office though they were simply inherited in the fam- Our first publication on DNA fingerprinting Forensic Science Service and I soon estab- ily. The penny dropped almost immediately— was reported in a British national newspaper lished that DNA could survive remarkably we had accidentally stumbled upon a DNA and came to the attention of Sheona York, a well in forensic specimens such as blood method with potential for individual identi- lawyer working at a community law center and semen stains13, it was clear that DNA fication.

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