Non-coding requences of approximately 10 to 100 nucleotide pairs are responsible for variation among individuals and can be employed as a tool to create a genetic footprint of an individual. Some of these non-coding sequences contain highly repetitive sequences of base pairs. They are tandemly repeated many times and are found at many places throughout the length of DNA molecule. The number of repeats is very specific in each individual, and it is inherited. It is unlikely that the repeats of one individual are found in the DNA of another person. For example, one individual may have unit ACA repeated 55 times at one genome locus, 115 times at a second locus, and so on, whereas another individual is likely to have different numbers of repeats at these loci. Such polymorphic genetic loci are usually called STRs. (Simple Tandem Repeats).
