Short Tandem Repeat (STR) Polymorphism
What are STR polymorphisms?
Short tandem repeats, or STRs, are short (typically between 2 and 10 base pairs long), variable regions of DNA that repeat many times. Over generations,
these regions of DNA have developed polymorphisms, variations in the number of repeats in the DNA sequence. This has made them useful as unique
genetic identification markers. The number of repeats varies from individual to individual, and the repeats are inherited in a predictable pattern from parent to child.
Why use STRs?
Since STRs are inherited from both biological parents, they can serve as useful DNA fragments for identification.
Labs examine STRs at specific loci
 and identify the number of repetitions
found in a particular individual's DNA. Because children receive half of their DNA from their mother and half from their father, it is possible to
verify the biological relationship between parents and children by comparing their STRs. STRs are used in many other DNA tests as well.
Labs typically use STRs more often than other loci because they are small, making them easily amplified through PCR.
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