Simple Tandem Repeats (STRs)
These are also tandem repeat regions of DNA, but where the repeat sizes are smaller, generally 2 to 7 bp in length
Starting in 1999, law enforcement agencies in both Great Britain and the United States began switching to a new version of RFLP analysis using shorter sequences called STRs ("Short Tandem Repeats").
STRs are repeated sequences of a few (usually four) nucleotides, e.g., TCATTCATTCATTCAT. They often occur in the untranslated parts of known genes (whose sequence can be used for the PCR primers). The exact number of repeats (6, 7, 8, 9, etc.) varies in different people (and, often, in the gene on each chromosome; that is, people are often heterozygous for the marker).
Restriction Fragment Length Polymorphism. The restriction fragments mentioned in the name are sections of a DNA sequence which have been cut by a restriction enzyme. The lengths of these fragments are polymorphic because certain differences in DNA strands such as "base substitutions, additions, deletions and other sequence rearrangements" can change the size of the restriction fragments by affecting the number and distribution of restriction sites (University of Nebraska-Lincoln 1997). Therefore, researchers have developed a method of comparing DNA samples based on this differential cleavage of DNA by restriction enzymes.