What are "short tandem repeats" in the context of genetic testing?

Short tandem repeats (STRs) are specific sequences of DNA consisting of repeating units of 2 to 6 base pairs in length. They are located in various places throughout an individual's genome and are particularly valuable in the context of genetic testing because they serve as highly variable markers. The number of repeats for STRs can differ from person to person, making them useful for genetic identification.

In forensic science and paternity testing, STRs are commonly analyzed to create a genetic profile of individuals. This profiling involves comparing the number of repeats at specific loci across different individuals. Because the likelihood of two unrelated individuals having the same STR pattern is extremely low, STRs thus become powerful tools for establishing identity.

While it may be useful to know that unique sequences found only in certain genes, templates used for DNA replication, and variations that do not affect traits can play roles in genetics, they do not specifically serve the purpose of genetic identification in the same way that STRs do. Therefore, STRs are most accurately characterized as DNA markers used for this purpose.