Short Tandem RepeatEdit

Short tandem repeats (STRs) are short sequences of DNA—typically 2 to 6 base pairs in length—that are repeated end to end at specific locations in the genome. Because the number of repeats at these loci varies widely among individuals, STRs form a highly polymorphic set of genetic markers. When translated into a profile, the pattern of repeat counts across a chosen panel of loci can uniquely distinguish one person from another in most populations, much like a molecular fingerprint. The technology rests on well-established methods in molecular biology, notably polymerase chain reaction (PCR) and capillary electrophoresis, to amplify and size these repeat regions. Forensic laboratories, immigration agencies, and many clinical laboratories rely on STR profiling to establish identity, relationship, or evidence linkage. See DNA profiling and PCR for foundational methods, and explore the nationwide use of STRs in the CODIS system.

Biological basis and terminology - STR loci are scattered throughout the genome. At each locus, individuals carry two alleles (one inherited from each parent), each defined by a particular number of repeats. The combination of alleles across multiple loci constitutes an STR profile. - The core strength of STRs lies in their high polymorphism: even small changes in repeat number can produce distinct alleles that are rare in the population. This makes matches highly informative when used in aggregate across several loci. See Autosomal STR for the common kind used in most identity testing, and Y-STR for Y-chromosome–specific STRs used in lineage tracing. - Analytical methods rely on PCR to amplify the STR regions and on capillary electrophoresis or similar techniques to determine fragment lengths, which translate into allele designations. See Capillary electrophoresis and PCR for technical background.

Forensic applications and practice - In criminal justice and forensic science, STR profiling is a cornerstone technology. A crime scene DNA sample is compared against reference samples (e.g., from a suspect or a databank) by evaluating a standard panel of STR loci. The resulting profile is described statistically, usually in terms of a random match probability or a likelihood ratio, to judge whether a sample could have originated from a particular individual. - Many jurisdictions maintain DNA databases that store STR profiles separately from raw sequence data. The best-known international example is the CODIS program, which maintains core loci and standard reporting conventions to facilitate cross-jurisdiction comparisons. Over time the set of core loci has expanded in various regions, increasing the discriminatory power of the databases. - STRs are also used outside criminal investigations: in paternity testing to establish biological relationships, in disaster victim identification, and in some genealogical contexts where lawful and ethical frameworks permit it. See Paternity testing and Genetic genealogy for related applications.

Population genetics, limitations, and privacy considerations - STR allele frequencies differ across populations. When evaluating a match, laboratories rely on reference databases to estimate how common a given allele is in the relevant population group. If the reference data are incomplete or biased, the estimated probabilities can be affected. This is a recognized area of ongoing research in Population genetics and Genetic diversity. - Without careful interpretation, STR data can mislead about ancestry or relatedness beyond the intended purpose. Modern practice emphasizes limiting inferences to identity or relationship that the test was designed to assess, and it relies on well-characterized panels and transparent statistical reporting. See Genetic privacy for discussions about who should have access to STR data and under what safeguards. - The power of STR databases to solve crimes must be balanced against civil liberties and privacy concerns. Advocates for robust oversight argue for clear restrictions on who may submit samples, how data are stored, how long records are retained, and how results are used. Critics may push for broader protections or limitations on retention. In many legal systems, these debates center on due process, proportionality, and the appropriate scope of government data collection. See Fourth Amendment and General Data Protection Regulation for treatment of privacy and data-protection principles in various jurisdictions.

Controversies and debates from a policy perspective - From a public-safety standpoint, STR profiling offers a means to deter and solve crimes, exonerate the innocent, and bring perpetrators to justice with a relatively precise genetic tool. Proponents often emphasize that STR data are highly processed and do not inherently reveal health information, reducing some types of privacy concerns. - Critics focus on privacy, data ownership, consent, and the potential for misuse or overreach. They point to the possibility of database expansion beyond immediate investigative needs, risks of unequal representation in allele-frequency databases, and the danger of stigmatization if STR results are interpreted beyond their validated scope. The debate typically centers on how to implement safeguards, oversight, and limitations that protect individual rights without unduly hampering legitimate investigative work. - In this context, some critics argue that privacy protections are sometimes framed as absolute rights in tension with public safety, while others contend that proportionate safeguards can preserve both security and liberties. A practical balance often cited includes targeted access, minimization of retained data, accountability mechanisms, and clear statutory limits. See privacy, genetic privacy, and Fourth Amendment for related discussions. - On the question of demographics in databases, the core issue is ensuring that allele-frequency estimates are based on representative samples. Inaccurate representations can skew match probabilities, which has prompted calls for improved sampling strategies and ongoing validation across diverse populations. See Population genetics and Genetic diversity for background on population structure in genetic data.

See also - DNA - DNA profiling - CODIS - PCR - Capillary electrophoresis - Autosomal STR - Y-STR - Paternity testing - Genetic genealogy - Population genetics - Genetic privacy - Fourth Amendment - General Data Protection Regulation - HIPAA