The bases constitute a code for different proteins, much like the letters of an alphabet form words and sentences. Certain areas of the DNA molecule have no currently understood function, but they appear to vary widely among individuals. The most common form of DNA profiling, abbreviated RFLP, is a way of showing the unique patterns of bases in some of these areas. Even blood or semen that has soaked into a rug or dried in the sunlight can be a source for sample cells. Restriction enzyme s cut the DNA into pieces of various sizes.
Gel electrophoresis separates pieces by size.
Separated pieces are transferred to a nylon membrane, and some sequences are labeled with a radioactive substance called a probe. X-ray film is exposed by the radioactive emissions of only the labeled sequences. The developed film, called an autorad, shows the familiar track pattern of a DNA profile. To eliminate any possibility of a mistaken identity, analysts use several different probes to look at several different DNA fragment patterns in a sample. More than one person might have a particular RFLP pattern, but it becomes less likely that multiple people will have two or more sequences in common.