Brief History of the Development of DNA Forensic Testing
DNA testing has become the “gold standard” of forensics. Since its invention it was claimed to be infallible by its inventor and the many companies that were advertising the technique. Although it has faced criticism in the past, it has continued to come out on top. It’s creation has facilitated many cases and freed many innocent people however its usage has raised many ethical questions as to how to go about obtaining that information, who should have access to it, how it should be stored and whose information should be stored. This issue is complicated as it affects not only science, law and criminal justice, but the general public’s safety, well being, and privacy as well.
The DNA fingerprinting method was first discovered in 1984 by Alec Jeffreys, a geneticist at the University of Leicester in Britain. Alec Jeffreys accidentally invented the DNA fingerprinting method when he used restriction enzymes to indentify and classify “microsatellites” called variable number tandem repeats (VNTR) he noticed while doing his research. VNTR are composed of a stretch of nucleotides which are repeated in parallel, the “core set” of repeated nucleotides can be 15-20 base pairs long. Using a technique called restricted fragment length polymorphism (RFLP), Jeffreys was able to demonstrate that VNTR are different from one individual to the next (except in the case of identical twins) and that this pattern was consistent in somatic cells, which meant that any type of cell (except for egg and sperm cells) could be used to carry out the technique and produce the same result. He developed a probe which could hybridize to “many highly polymorphism minisatellites simultaneously.” The probe’s ability to hybridize was centered around the VNTR’s “core set” of nucleotides repeated in parallel, he based the creation of a probe on a sequence found in many different VNTR. These probes are called multi locus probes (MLP). One MLP produces thirty bands on an autoradiograph. Later on single locus probes (SLP) were developed which hybridize specifically to one locus. One SLP produces one or two bands on an autoradiograph. Jeffreys was originally hoping to quantify variable number of tandem repeat markers (VNTRs) to make them useful for medical testing purposes, his method was used for quite some time for this purpose but it has been replaced by single nucleotide polymorphisms (SNPs), named due to the fact they differ by a single base pair. Even though the bi-allelic SNPs are less informative than the multi-allelic VNTRs, SNPs are useful because they are small and frequently occur in the genome about once every 300 bases making them easy to identify and locate.
Figure 1. This figure shows the process of restriction fragment length polymorphism (RFLP). A sample is collected from an individual (usually a suspect and/or the victim), the DNA is then extracted from the sample (using standard laboratory techniques), and that DNA is cut by a restriction enzyme. The DNA is then subject to agarose gel electrophoresis, and then this gel is then laid on a piece of nylon filter during a process call Southern blotting which is used to transfer the DNA from the gel onto the filter. During the Southern blotting process the gel is treated with denaturation solution which will allow the probe to hybridize with the now single stranded DNA. The nylon filter is placed in a container with a probe (MLP or SLP) which hybridizes to the DNA. Then the nylon filter is placed on x-ray film, and later the x-ray film (autoradiograph) is used to analyze the profile. If the suspect profile matches the evidence sample then the probability of that sample being present in the general population is calculated. A standard set of population genetics equations (such as the Hardy-Weinberg equilibrium) are used to determine the population frequency of that profile.
Not too long after Jefferys work was published in Nature in 1985, he was approached by a lawyer desperately trying to close an immigration case, where an application to enter the United Kingdom as British citizen was denied. The application was filed by London-born boy who had been living in Ghana. The government claimed that his old British passport had been “tampered with” and that he was not in fact who he said he was. Jeffreys was asked to perform genetic tests that would prove the boys identity. Even though the DNA profile was never observed by the court, its inclusion along with other convincing evidence (a positive serological maternity test and photographic evidence) resulted in the dismissal of the case. It was this event that pushed DNA fingerprinting into the spotlight for everyone to see.
A year later, when the police had a difficult serial rape and murder case to crack they approached Jeffreys in an attempt to use DNA fingerprinting to catch the perpetrator. This time Jeffreys was asked to type evidence and a suspect to see if the two coincided. Although the evidence sample did not match the suspect, the evidence samples from the two different rape and murder cases in question matched each other, proving the serial rapist theory. Volunteer samples from thousands of men in the village where the crimes occurred were collected but none of them were a match. The perpetrator was eventually revealed by his drunken friend who was recounting a story to some acquaintances at a bar. Apparently, the perpetrator told his friend that he had had a past criminal record and didn’t want to be framed by the police, so he asked his friend to step in to give in a sample in his place. A woman at the bar overheard this story and called the police. The police arrested the friend who led them to the perpetrator. The perpetrator was then arrested and his DNA yielded a match to the evidentiary samples. The case gained considerable public attention, and the account was featured in a book called The Blooding by Joseph Wambaugh.
Florida v. Tommie Lee Andrews (1987) was the first case to use DNA evidence in the United States. Andrews was caught snooping outside a woman's home and was apprehended as a suspect for the rapes that had been occurring in that neighborhood. The prosecutor wanted to build a stronger case against the suspect, so he approached a colleague who had had heard of the case in England where DNA was used to catch a criminal. He decided to contact the company and use DNA profiling for his case. The results showed that Andrews was a match for two of the six rapes that had occurred. But since DNA typing was a novel technique it had to go through an admissibility hearing.
Frye v. United States (1923) or the Frye standard states that a novel idea or technique can only be admissible in court if it is generally accepted in the scientific community, and that it is a judge’s responsibility to make that determination. However, in Florida there is a law, that is very similar to Federal Rule of Evidence 705 (1975), that states an expert witness could be brought in to testify about the “scientific, technical, or other specialized knowledge” to help “in understanding the evidence.” The prosecution sought out Dr. David Housman, a molecular geneticist and biology professor at MIT. Although he had not been present when the DNA had been typed, he had visited the lab where the tests had been performed and examined “the companies protocols, on site performance, and qualify control measures.” He also reviewed the laboratory notebooks, to see if standard procedure had been followed. He was capable of making this determination because these methods were commonly used in molecular biology and medical research. Dr. Housman told the judge that based on his review of these materials and methods, the DNA typing that was performed was perfectly valid. He said that he himself routinely used these methods about five to ten times a day in his own laboratory and that the techniques were performed similarly all over the world. Also, during the hearing, the defense could not summon an expert witness to challenge Dr. Housman’s testimony, every scientist he contacted said that Dr. Housman was more than qualified in these basic, standard laboratory techniques, so if he stated that the DNA typing procedure is valid, then it must be. The judge saw no reason to deny this evidence from being admitted and so he approved the DNA evidence. This approval began to pave the path to DNA's current reputation as “infallible” evidence.
DNA typing has faced many challenges and stirred up considerable controversy but has continued to be considered the best method for determining suspects and catching the perpetrator.
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 National Research Council, Strengthening Forensic Science in the United States: A Path Forward, Washington, National Academic Press, 2009.