Oct. 1995 Brian Miller Features Editor Since scientists discovered the double helix in the 1950s, most use of DNA knowledge has remained in research laboratories. But in the past few years, the development of DNA analysis has helped bring applications out of the lab and, increasingly, into courtrooms where it has been used to help convict criminals and prove paternity. Scientists continue laboratory research, and have been looking at DNA structures, among other things, to determine if persons with certain patterns are more susceptible to maladies such as cancer. One of the questions scientists are trying to answer is if adjusting a person's DNA can lower susceptibility to disease. This will raise ethical and moral questions when brought outside the laboratory. When society begins debating in earnest whether DNA manipulation is desirable, it will be worthwhile to look at how DNA testing has become increasingly accepted as evidence in the courtroom. DNA analysis is one of the first uses of DNA knowledge outside the laboratory, and science has had to convince society - through the courts - that the analysis is an accurate and desirable application of the knowledge. Courts are allowing juries in criminal trials to consider DNA analysis as evidence that the defendant is very likely tied to the crime victim or scene. Evidence from crime scenes - such as blood or semen - are analyzed and compared with a sample provided by the defendant or suspect. DNA analysis is also used to exonerate suspects, and has led to the release of some wrongly-convicted persons.

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