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Crime Scene and DNA Basics for Forensic Analysts

Short Tandem Repeats (STR)

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Later in the 1990s, short tandem repeat (STR) testing appeared in forensic DNA analysis. In keeping with the name, STRs are VNTR-like regions that have very short sequences, ranging approximately 2 to 6 base pairs (bp). Although individual STR loci are not as discriminatory as RFLP markers, the short size and number of available STRs allowed scientists to amplify and analyze three or more loci simultaneously (multiplexing).

Read more about STRs in course: DNA Amplification.

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STR analysis is the current method of choice for DNA testing in crime laboratories and yields results that are nearly equivalent to individualization. The keys to the success of STR typing are multiplexing and the ability to label nucleotides with fluorescent tags. It should be noted that early work on STRs did not involve multiplexing, but rather visualized the separated fragments by the use of silver staining or a special type of green dye.

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