A Piece of the Puzzle When used, DNA analysis is often just another piece of the puzzle used to prosecute lawbreakers. It is important to note that DNA analysis does not prove beyond doubt that a person was at a crime scene, nor does it prove guilt. But it can be a piece of evidence used to help identify a defendant in conjunction with eyewitness testimony and other evidence. But in some cases, DNA analysis helps resolve a case before it goes to court. "Once someone is confronted with this physical evidence, they admit" to the crime, said Tom Rogers, an Alameda County, Calif., assistant district attorney. "Usually, it resolves the case."
How Testing Works The nucleus of the body's cells contain 23 pairs of chromosomes, which are inherited from a person's parents. Genes - located inside chromosomes - are made up of deoxyribonucleic acid, or DNA, which determines the growth and development of organisms. A person's DNA is the same in each cell and doesn't change during a lifespan. DNA is a long string of repeating units called nucleotides. There are four types of nucleotides: adenine, cytosine, guanine and thymine. Each adenine binds only with thymine, and each cytosine binds with only guanine. The reverse is also true of the pairs, which form a chain called a double helix. DNA molecules are found in cells that contain a nucleus, such as white blood cells, spermatozoa or saliva. There are two kinds of DNA tests currently used. One is called restriction fragment length polymorphism (RFLP), which requires a sample about the size of a dime, and the other is called polymerase chain reaction (PCR), which can accommodate a smaller or degraded sample for typing. With RFLP, the first step is to extract the DNA out of the sample, which is done by dissolving the cell walls with chemicals. The sample is then cut into small fragments with a restriction enzyme called HAE III. The HAE III acts like a molecular scissor and cuts the DNA at certain sites. The fragments of DNA are inserted into a gel which has the consistency of Jell-O. A small electric current is then applied, and the lengths of DNA migrate through the gel. The distance that the DNA fragments move through the gel is determined by the length of the fragment. Longer fragments of DNA will move slower through the gelthan shorter fragments. The position of these fragments in the gel and the length of the fragments is used to determine whether two samples match.
PCR Testing PCR analysis utilizes a smaller or degraded sample and makes more copies of the sample by heating and cooling it. The heating and cooling is repeated and the DNA sample is built geometrically to create millions of copies of the original DNA. The final product can be visualized by looking at a particular segment or length of fragments. PCR testing is ready in a matter of days, while RFLP takes three to four months.
DNA In Court In order for a new scientific procedure, such as DNA analysis, to be accepted in a court as evidence, it must meet guidelines and tests contained in an area of the law known as the rules of evidence. The most common legal procedure for getting a new scientific development accepted as evidence in a trial is called a Frye hearing. There are other mechanisms and tests for allowing evidence, but they contain basically the same tests and procedures as Frye. Frye comes from a 1923 case having to do with admitting lie detector tests as evidence. Hearings usually involve dueling scientists and academics testifying on the merits or demerits of a procedure in question. The court test, in short, is that a scientific procedure must be considered trustworthy in both accuracy and consistency by the scientific community before a court will allow a jury to hear the evidence. Courts have been allowing DNA analysis to be accepted as evidence with increasing frequency, said Erik Wasmann, an Oregon assistant attorney general. "The acceptance of the basic science is OK, but the interpretation" is questioned by the courts and defense lawyers.
Inconsistent Use Although DNA analysis has been increasingly accepted by courts over the past few years, it is still far from universal. In California, for example, Los Angeles and Alameda counties allow it on a case-by-case basis, while Sacramento County has yet to allow a jury to hear DNA evidence. Some states have passed statutes allowing DNA evidence and statistics to be admitted in court, though the defense can still challenge the statistics, laboratory procedures, and later, analysis techniques developed after the legislation. Appeals courts are also increasingly supporting DNA analysis. The Florida Supreme Court established the admissibility of DNA testing with a unanimous decision in June. The court acknowledged that DNA test results are generally accepted in the scientific community when labs follow established procedure, but DNA testing "has not yet reached the level of stability of other forms of identification such as fingerprint comparison," the court wrote in Hayes vs. State of Florida. There is no magic bullet - such as a court ruling - that will allow DNA to be entered as evidence. But with time, as the knowledge and acceptance of the technology by scientists is acknowledged by the courts, judges will likely allow it to be included as evidence without Frye-like evidence hearings.
Defense Not Resting Despite the growing trend of acceptance, defense attorneys continue to argue against allowing DNA analysis to be used as evidence. A key argument against its use in criminal prosecution is that calculations are made using the statistical likelihood of another person matching the defendant's DNA pattern, rather than precisely pointing to the defendant. "That kind of imprecision is troubling," said James R. Ramos, an attorney in the California public defender's office. "If you have to create a number to demonstrate a match, those numbers should be fair game" to dispute, he said. Although the courts are taking time to reach acceptance of the new technology, the trend indicates that DNA analysis may become as common as fingerprint evidence at some point. But it would be difficult to become frustrated with the legal community's resistance to the technology when, after all, the scientific community has only recently reached a relatively solid consensus after often contentious peer review and debate. And as scientists continue working on DNA-related research, including gene manipulation, it is unlikely that we've heard the last of the debate over DNA technology. As a matter of fact, we may just be starting. Explanation of DNA and testing provided by Jill Spriggs, a criminalist at the Sacramento County, Calif., Crime Lab.
