15 June 1992 Making Life Harder for the Criminal

Following the lead of international scientists, a team of researchers from Lincoln University and the Institute of Environmental Health and Forensic Sciences (formerly DSIR Chemistry Division), Ilam, Christchurch, have established in New Zealand a cheaper, faster, and less cumbersome method of DNA profiling.

Collaborative work by Dr Marion Savill of the Institute and Dr Jon Hickford and Mr John Davidson of Lincoln University, is on the way to making life much harder for the criminal.

Through scientists' work worldwide, one small drop of blood, a plucked hair, even drops of saliva, may eventually be all it takes to identify an individual with a speed and accuracy never before known.

Now, as research develops internationally, not only will uniqueness of an individual identity be confirmed but the information could be expressed in a digital format capable of being stored in computers and transmitted through telecommunication networks.

The story starts with DNA, the chemical which acts as the information store for, and hence basis of, life. Dr Hickford, who is a Lecturer in molecular biology at Lincoln, explains:

"Most cells in the human body contain DNA and, with few exceptions, the DNA retrieved from these cells is a complete blueprint of each individual. In essence it is through DNA that humans inherit characteristics from their parents. It encodes why everyone is the way they are, and the variation seen among humans of different race, skin colour, height, build, etc. is a reflection of variation in DNA.

"Specifically the variation is in the sequential code carried by four chemical substances whose names are abbreviated as A, T, C and G. The order or sequence of these four chemicals designates the nature of the information carried by the DNA. Forensic DNA analysis relies upon comparison of these sequences to prove identicality.

"We are only just mastering the techniques that enable us to compare DNA sequences more easily, rapidly and cost effectively," says Dr Hickford.

"A turning point in forensic DNA analysis came in 1985. Two exciting discoveries changed the face of the science. Firstly, in the influential science journal 'Nature', Dr Alec Jefferies of the University of Leicester published a paper entitled Hypervariable 'mini-satellite' regions in human DNA.

"This paper outlined the discovery and analysis of certain pieces of human DNA that were highly repetitive and varied in both length and structure. Analysis of the length and structure of these regions, a process called DNA profiling, could be used to positively identify individuals. Furthermore, the regions were stably inherited from generation to generation and hence could be used to determine paternity and maternity.

"As time progressed many adaptations of the original method were investigated. Within months biotechnology companies and forensic laboratories had been created around the world to DNA profile humans. Law enforcement agencies worldwide sought the methodologies to identify criminals and the legal fraternity found a new tool in legal cases of paternity and maternity.

"Public fascination with the subject became so great that a book written about one of the first trial cases in Britain soared on to the best-seller list (Joseph Wambaugh's "The Blooding").

"However, a significant amount of DNA is needed for the test to be useful. Characteristically two micrograms of DNA is required. Two micrograms is two millionths of a gram, and as a rule of thumb a drawing pin weighs about one gram. This is a lot of DNA in terms of modern technology and may not be available from the drop of blood or plucked hair mentioned above.

"Furthermore, the DNA to be analysed must be of good quality.

"DNA occurs in human cells in long lengths known as chromosomes. We have 46 of these chromosomes, two are called X and Y (the sex chromosomes) and the other 44 consist of 22 similar pairs, each encoding information necessary for life.

"The good quality DNA required for analysis must be comprised of these long lengths.

"Unfortunately, the DNA recovered from crime scenes is frequently minuscule in quantity e.g. shed hairs, dried blood drops, skin under fingernails, and may have been exposed to a harsh environment (for example the ultraviolet rays in sunlight can damage the long DNA molecules). In some New Zealand cases DNA has been recovered from crime scenes but cannot be DNA profiled.

"The second discovery of 1985 solved these problems. Kary Mullis, a scientist in California, developed a method of artificial DNA amplification. The concept artificially creates the process of DNA replication. This process occurs every time a human cell divides and is, by necessity of the continuation of life, a highly accurate process. Repetitive cycling of the DNA replication process leads to the exponential amplification of DNA.

"The effective doubling of DNA at each cycle rapidly produces large amounts of DNA. This process has become known as the Polymerase Chain Reaction, PCR™. PCR™ is patented to Roche Molecular Systems of the United States of America.

"The technique theoretically implies that a single copy of a piece of DNA can be amplified millions of times. In practice this is achievable with the DNA of a single cell, potentially amplifiable to analytical levels (two micrograms).

"Most importantly the nature of the reaction is such that the DNA doesn't have to be in long lengths to be amplified. Characteristically, short and easily analysed pieces of DNA are amplified as a reference to the rest of the DNA.

"These techniques have now been merged by staff of the Environmental Health and Forensic Sciences Institute and Lincoln University. In a joint effort a technique has been developed and trialled that merges the best of the methods. It uses DNA amplification to amplify a hypervariable DNA sequence that is known to show large levels of variation between individuals.

"The technique is approximately 10 times cheaper than the existing DNA method and can realistically amplify DNA from a drop of blood or semen, or a single plucked hair. (The technique can amplify less than a thousand-millionth of a gram of DNA!) What is more, it is human specific. The technique is also considerably faster. The results illustrated were obtained in two days as opposed to approximately two weeks for the current methods.

"At present the disadvantage of this method is its much lower level of discrimination between samples than the initial technique. However, this problem is being addressed worldwide and is currently being solved both here and overseas with the introduction of new PCR based methods.

"As an indication of the ever changing face of science, Dr Jefferies has again published in 'Nature'. This time he has but gone one step further in making the results digitisable. In essence, rather than having to store photographs and images of results such as those obtained above, a simple binary code will describe accurately an amplified hypervariable sequence.

As a digitised code the information will be capable of being stored in databases and rapidly dispersed via telecommunication networks. This will certainly raise new ethical issues in terms of civil liberties and personal DNA data," says Dr Hickford.

In the meantime, research at the Institute and Lincoln University will, funding permitted, continue in the future to adapt the new Jefferies methodology to the Apolipoprotein B gene for eventual use in New Zealand's forensic DNA analysis.

Ian Collins, Journalist, Lincoln University, Canterbury, New Zealand