Short tandem repeat

A short tandem repeat (STR) in is a class of  that occurs when a pattern of two or more s are repeated and the repeated sequences are directly adjacent to each other. The pattern can range in length from 2 to 10 s (bp) (for example (CATG)n in a ) and is typically in the non-coding region, making it. By examining enough STR loci and counting how many repeats of a specific STR sequence there are at a given, it is possible to create a unique genetic profile of an individual. There are currently over 10,000 published STR sequences in the human genome. STR analysis has become the prevalent analysis method for determining in forensic cases.

Forensic STR Analysis
STR analysis is a relatively new technology in the field of, having come into popularity in the mid-to-late 1990s. It is used for the of individuals. The STRs in use today for forensic analysis are all tetra- or penta-nucleotide repeats (4 or 5 repeat units), as these give a high degree of error-free data while being robust enough to survive degradation in non-ideal conditions. Shorter repeat sequences tend to suffer from artifacts such as stutter and preferential amplification, as well as the fact that several genetic diseases are associated with tri-nucleotide repeats such as. Longer repeat sequences will suffer more highly from environmental degradation and do not amplify by as well as shorter sequences.

The analysis is performed by extracting from the cells of a forensic sample of interest, then amplifying specific  regions of the extracted DNA by means of the. Once these sequences have been amplified, they are resolved either through or, which will allow the analyst to determine how many repeats of the STR sequence in question there are. If the DNA was resolved by gel electrophoresis, the DNA can be visualized either by ing (not very high resolution, safe, inexpensive), or an such as  (fairly sensitive, moderate health risks, inexpensive), or as most modern forensics labs use,  (highly sensitive, safe, expensive). Instruments built to resolve STR fragments by capillary electrophoresis also use fluorescent dyes to great effect. It also used to follow up patients.