DNA fingerprinting

What Sir Alec did next

David Willis talks to one of Britain's greatest scientists about his revolutionary discovery nearly a quarter of a century ago – and what has preoccupied him since.

Listening to Professor Sir Alec Jeffreys talk about his career in human genetic research, it is immediately apparent that he still applies as much enthusiasm and tenacity to his work as a new PhD student eager to impress their supervisor. It is this, amongst many more characteristics, that has undoubtedly led to numerous scientific firsts spanning an illustrious career.

Sir Alec freely accepts that after his 1984 discovery to identify people via variations in their DNA, he will always be labelled as 'Mr DNA fingerprinting' or 'The Father of Genetic Fingerprinting'. But with this, he takes great pleasure from the immense impact the discovery has had and how, he acknowledges, "it, more than anything, has put DNA right up into the public eye. It brought it into everybody’s living room."

DNA fingerprinting is however just one facet of Sir Alec's work. What he describes as his "driving interest" is research into human genetic variation and the processes that create it. This has stirred an immense passion to try and solve some of the most fundamental questions surrounding genetic differences amongst humans:

  • To what extent do people vary from one another?
  • How does human DNA change between generations?
  • What are the mechanisms involved?

His work has taken many great strides in achieving some of the answers and has spawned many other discoveries. Here are just a few of his landmarks since that day nearly 24 years ago.

Early history of genetic fingerprinting

"First, you must go back to work that people by and large have pretty much forgotten," he says. In the late 1970s, on the eve of the DNA fingerprinting discovery, Sir Alec, a fresh faced genetic scientist with the freedom to explore and experiment with novel ideas, was not only the joint first in the world to describe how to detect human genetic variation at the DNA level but also first to produce a pretty good estimate of how many sites in the human genome showed this variation. This is something he says is still very proud of, that despite the relatively primitive technology he used, "we got it pretty much bang on."

Over the next two decades the science of human genetic variation developed at a phenomenal rate. First it was that 'Eureka' moment of DNA fingerprinting, which catapulted the area of research into both the scientific and public eye. This technology relies almost exclusively on detecting highly variable repeated parts of DNA called 'minisatellites'. Sir Alec observed that these "pretty bizarre bits of DNA" found in the genome, seemed to be changing and "picking up mutations at an extraordinary rate" when compared to genes. In 1988, he was able to, for the first time, describe the mutation rate between parents and their child's DNA at these minisatellites. But how and why they did this, was still largely unknown.

In his hunt to find the answer, Sir Alec first had to overcome one of the greatest obstacles in human genetics. When investigating how DNA changes between generations, it is often limited by how small families are and how rarely these DNA changes occurred.

Said Professor Jeffreys: "By the late 1980s we'd shown how you can analyse these regions of DNA down to the single DNA molecule level. Using DNA amplification this opened up an entirely new approach. That is, if you stop and think about what you are doing in families, you're looking at a child to deduce whether the sperm or the egg giving rise to that child is carrying a new mutation. So why bother with the child, if you can analyze DNA at the single molecule level?"

The 'eureka' moment

The first DNA fingerprint was created at 9.05am on Monday 10 September 1984. Highly variable repeated part of DNA called 'minisatellites' could be clearly seen, and in 1988 Sir Alec was able to describe the mutation rate between parents and their child's DNA at these satellites. The 25th anniversary of the discovery will be marked in 2009.

Described as one of his highest points since 1984, Sir Alec defied all of his colleagues around the world by developing a technology that they said would be impossible, telling him: "you’d never get this to work." He devised a technique which would greatly enhance a scientist's ability to see how DNA changed between generations. This enabled the DNA of millions of sperm to be examined to directly measure the mutation rate and for first time observe these minisatellites or other regions of DNA before and after the mutational changes occurred during the process of sperm production. By using direct evidence from sperm analysis, Sir Alec armed himself with the knowledge that these minisatellites were highly unstable. He then moved quickly to try and unravel the secrets of when, how and why these DNA mutational changes occurred.

There are "two great engines that generate DNA diversity" - in the sperm and egg or germline cells of humans. For this reason, the research in the department separated off in two directions.

The first was rare 'direct mutation events'. Sir Alec and Professor Yuri Dubrova, another distinguished human genetic scientist in the Department of Genetics at the University of Leicester, were primarily concerned with how the environment has an effect upon DNA which is inherited between generations. Professor Dubrova completed some major studies in humans from regions affected by the 1986 Chernobyl disaster and parts of Kazakhstan where Russia tested above ground nuclear weapons. This work led to some of the first evidence that radiation can directly cause heritable mutations in human DNA.

The second, Sir Alec's main topic of interest, is 'recombination'. Apart from red blood cells, every cell in the human body contains 46 long strings of DNA called chromosomes: 23 are inherited from the mother and 23 from the father. When the body produces germline cells, all of the 46 chromosomes pair up and then separate, to halve the chromosome number. During this process, the chromosomes get tangled up and exchange genetic material, this is recombination. Sir Alec likens this process to the reshuffling of a deck of cards. The deck is the entire genome and the cards are all bits of DNA that make up the genome. What results is a completely new order of cards in the deck, reshuffling patterns of pre-existing mutations or genetic changes in the genome and greatly increasing the overall level of variation between different people. Most surprisingly, Sir Alec found that minisatellites were unstable because they were very good at getting hooked into this recombination process, with many errors occurring during recombination driving mutation at minisatellites.

Recombinant DNA

The process of recombination has been a focus of Professor Jeffreys' research since his landmark discovery of DNA fingerprinting.

So for Sir Alec, recombination was the driving force behind these highly unstable minisatellites. But what was fuelling it? Welcome the arrival of the recombination 'hotspot' - and yet another world first for Sir Alec. Hotspots are small regions of the human genome which exhibit extremely high levels of genetic change between generations by inducing recombination. For the first time his lab was able to explain exactly what a hotspot was and what it looked like. To his delight, one of his minisatellites was located right next to a hotspot, so perhaps the instability of the minisatellite was driven by this hotspot. But was this discovery just a stroke of luck or was this particular minisatellite the only region of DNA which had a hotspot adjacent to it?

"That led me into a very major programme of research, which was to basically to try and understand how these recombination events between chromosomes happened. How they distributed along the chromosomes? Do they fall into hotspots or are they more randomly distributed and what effect would that distribution have on patterns of human DNA diversity?"

With further developments of some extremely powerful technologies using sperm, Sir Alec was able to show that hotspots were not the exception but were the rule right across the human genome, though few were associated with minisatellites. Not only that, but he also showed that these hotspots have a huge effect on patterns of DNA variation between people.

So again imagine a deck of cards which represents the human genome, but this time when shuffling them, some of the cards are stuck together and so only certain parts can be shuffled, these are like recombination hotspots. Often clustered together in small regions of the genome, hotspots help signal where recombination will primarily happen. This work contributed to the revelation that 90 to 95% of the human genome is in fact not recombining, and that if no hotspot is present then this completely shifts the pattern of human variation into that seen typically in an asexual organism.

The published work by Sir Alec in 2001 that followed, helped initiate something called the 'International HapMap Project', a collaboration of scientists across the globe that allowed the extensive mapping of genetic diversity across the entire the human genome. This is where Sir Alec sees his work, other than DNA fingerprinting being most applicable. It will inevitably further scientists' ability to monitor mutations between generations and help identify the causes behind them. It will also help to unearth the genetic causes of common human diseases such as diabetes, obesity, rheumatoid arthritis and in particular for Sir Alec's work the very common inherited anaemia thalassaemia, which is caused when recombination goes wrong.

The hotspot paradox

To date there have been approximately 33,000 hotspots found right across the human genome. Each one is not only driving the genetic variation process but also helping scientists piece together the puzzle of human genetic diversity and why it occurs. However it is this elusive question of 'why' which remains unanswered. Why do hotspots have such an affect and why is it that some people have them and others do not?

The idea that hotspots can somehow be born and also mysteriously die remains a challenge for Sir Alec, as this has implications for all aspects of human genetic diversity, genetic disease and evolution. He talks of his great enthusiasm for the 'hotspot paradox', in which the actions of hotspots totally break every genetic rule ever written. Hotspots cause recombination which in turn drives genetic diversity and evolution, but strangely the process strongly favours mutations that may suppress recombination. These mutations may stop a hotspot from working which will ultimately deter recombination, and so "hotspots contain within them the seeds of their own destruction." So why is it that this happens? As of yet he does not know. But despite the answer so far evading him, he talks with a determination in his eyes that suggests he would love to one day be first to explain what is happening here.

So when asked what he enjoys doing most, Sir Alec quite simply replies, "It's the lab, I’m a bench scientist." This may come as no surprise as it is possible to imagine that this is the sort of thing what all world renowned scientists would say. But with great scientific discoveries often come even greater distractions away from the basic science which led to such achievements in the first place. It is only then you can appreciate how he has "fought tooth and nail" to remain where he is happiest, and for that reason Sir Alec is pretty unique.

Despite there being many questions surrounding human genetic diversity and its implications still outstanding, it is evident that he is thriving on the challenge,

"I've got this very privileged position of being a Royal Society Wolfson Research Professor, and that gives me the time and space to be able to get out to the lab bench and do my own stuff… I still get a terrific buzz out of getting an experiment to work, I've never lost that and I've being doing experiments since I was seven or eight years old."

There is certainty that in his quest Sir Alec's appetite will leave no stone unturned in his attempt to help find some of these answers.

Back to top