DNA (short for deoxyribonucleic acid) holds the genetic code of every organism on earth. While humans generally have no objections to the collection and mapping of fruit fly and mouse DNA, many feel it's a violation of privacy when the DNA in question is their own. From the tiniest sample of any tissue or fluid from your body, a molecular biologist can extract the DNA, make as many copies as he or she chooses (through a process called amplification), and then analyze the DNA for certain traits. How that information can be used is what excites some people -- and worries others.

The first step in profiling is extracting the DNA from the tissue or fluid sample. If the sample is small, the DNA can be amplified (copied) by a technique called polymerase chain reaction (PCR). Then the actual profiling begins. In one of the most common profiling methods, restriction fragment length polymorphism (RFLP), DNA is chopped into fragments using a set of enzymes that recognize and cut DNA at the same positions every time. Then the fragments are sorted by electrical charge and size on a gel, stained or radioactively labeled, and analyzed. The resulting banding pattern is the DNA profile.

Since the DNA in each person is a three-billion-base-pair sequence, only small sections of the DNA are profiled. Profilers choose short, highly variable sequences that effectively "fingerprint" individuals. These sequences occur in so-called "noncoding" regions of the DNA that do not code for proteins. In fact, a whopping 90 percent of your DNA is noncoding. Only the remaining 10 percent of your DNA contains the genes that make the proteins that make you you.

For now, DNA profiles are being used only to identify individuals, not their physical characteristics. But the same technology can be used for complete genetic profiling of coding DNA which would reveal highly personal information, such as a person having the gene for colon cancer, or heart disease. If such information became publicly available, individuals might face health insurance or job discrimination.

Many organizations that do DNA profiling are freezing and storing their original DNA-containing samples. Such practices have caused mounting public concern about "function creep": that samples collected for profiling individuals might later be used for other purposes, such as genetic profiling or cloning. But DNA profiling may also hold great promise for our future health. If the Human Genome Project achieves its goals, the entire set of roughly 30,000 genes will be mapped by 2003. Once a complete map is available, every sample in a DNA bank could be fully analyzed for every single heritable trait. Every child could be profiled at birth, giving him or her the chance to lead the healthiest life possible by avoiding triggers for diseases and conditions to which he or she is genetically predisposed. As with any new technology, the overriding challenge for the future of DNA profiling will be to use it wisely, respecting the privacy and the rights of individuals.