Restriction digest, also known as restriction fragment length polymorphism (RFLP), is the term assigned to the method of DNA fingerprinting in which a given restriction enzyme is applied to a genome, cutting the genome into fragments.
The resulting fragments are separated by the restriction sites in the genome corresponding to the given enzyme. Because of small-scale mutations on the genome, the lengths of the collection of fragments will differ between two individuals of the same species.
After amplifying the fragments, researchers could separate the fragments based on their length through a chemical process called gel electrophoresis. Longer fragments would migrate to one end of a membrane, and when the membrane was X-rayed or stained, the fragments would clump together into bands. Solely by examining this banding, biologists could compare one sample of DNA (i.e., taken from a crime scene) with another known sample (i.e., taken from a suspect).
RFLP was applied successfully time and again in countless criminal investigations and paternity tests; today, it has essentially been replaced by sleeker methods, many of which rely on partial genome sequencing.