strs

Short tandem repeats (STRs) are short sequences of 2–6 base pairs repeated in tandem in the genome. As a type of microsatellite, they are abundant across chromosomes and highly variable among individuals due to differences in the number of repeat units.

STR loci mutate mainly by DNA strand slippage during replication, producing gains or losses of repeat units. Mutation rates vary by locus, typically around 10^-3 per generation, higher than SNP mutation rates. Because individuals inherit two alleles per locus, STRs exhibit codominant inheritance, allowing heterozygotes to be distinguished from homozygotes.

STRs are widely used as genetic markers because many loci can be genotyped in parallel with PCR and fragment analysis. The typical workflow amplifies the STR region with locus-specific primers, then separates products by size with capillary electrophoresis to infer the number of repeats.

Applications include forensic identification and paternity testing, where STR profiles are compared to determine matches or exclusions. They also support population genetics, kinship analysis, and evolutionary studies, and are used in animal and plant breeding and conservation genetics. In practice, panels of multiple STR loci are used to maximize discriminatory power; panels vary by country and agency.

Limitations include stutter artifacts and null alleles when primer binding sites are mutated, which can complicate interpretation. Ethical and privacy concerns accompany the use of STR data, particularly in forensic and genealogical contexts.