DNA profiling is a technique in which a sample of DNA is run through a laboratory assay to generate information about it, looking specifically for DNA which could identify the source of the sample, or be used as a base of comparison between two samples. It can utilize the DNA of someone who is unknown, or the DNA of someone who is known, and it can be used in a variety of ways, from law enforcement to genealogy.
This technique relies on the presence of what are known as short tandem repeats (STRs) in the genetic code of every organism on Earth. These repetitive strings of DNA are non-coding, meaning that they do not contribute to the expression of an organism's genome, but they can provide valuable information about an individual, because they tend to be very unique. DNA profiling is sometimes referred to as DNA fingerprinting for this reason, referencing the idea that finding an exact match between STRs in two different people would be very rare under most circumstances.
Several techniques can be used to extract the DNA and look at the areas of interest. Usually, DNA profiling relies on a reference sample, such as known DNA from a missing person, or DNA from a crime scene, with a comparison sample being taken from a person of interest to look for a match. It is also sometimes used to look for indications that two people are related, as people who are related can share some STRs in their DNA, although a lack of a conclusive match does not necessarily mean that two people are not related.
The profiling process is accomplished by a technician who has been trained to work with a wide variety of samples, and to look for specific areas for comparison. DNA profiling can also examine similar alleles, areas of the genome which code for particular proteins, although this process can be less reliable, as many people share alleles.
DNA typing, as it is sometimes known, debuted in the 1980s, and by the late 1990s, it was in widespread use. A number of misconceptions also arose about the process: fans of crime shows, for example, may be under the impression that DNA profiling can be done in minutes, and that samples of DNA are always easy to work with. In fact, some samples can be very difficult to work with, and the process of DNA profiling can take weeks or months, especially at a busy lab. The process is also not totally infallible, as samples can be damaged or contaminated, resulting in false negatives or positives.