STRs, also called microsatellites, are short tandem repeats of nucleotide sequences consisting of 2‑7 bp, distributed abundantly throughout the genome. 10-15% of the genome encodes genes within the exon regions. In contrast, the enormous remaining nucleotide sequences comprising the introns were thought to be devoid of function and were therefore often referred to as “junk DNA”. However, many specific STRs are located within these introns, and the number of repeats varies between individuals.
The STRs can differ in their nucleotide sequence as well as in their number of repeats. The analysis of multiple STR loci provides sufficient data to guarantee specific identification on an individual level. For human cell line identification, the use of at least eight loci is recommended in a consensus standard which was published by the ATCC® Standards Development Organization as a member and accredited standards developer of the American National Standards Institute (ANSI) . The additional analysis of the gene encoding amelogenin - a protein which is involved in tooth enamel formation - is often used for gender determination.
3. ANSI/ATCC ASN-0002-2011. Authentication of human cell lines: Standardization of STR profiling.