STR is preferred with there is only a small amount of DNA that has questionable quality. The repeats that are analyzed by STR are typically 2 to 9 bp long. The small size of STR's allows for very efficient PCR amplification and also permit the the use of partially degraded DNA. An example of the STR locus is the TH01 locus, that was observed in this lab. It contains a variable number of repeats of the four-base sequence [TCAT].
Simple sequence or short tandem repeats (STRs) are segments of taridemly repeated DNA with repeat lengths up to about 6 bp and with total lengths usually < 60 bp (Weber, J. and Carmen, W., 2016). Hundreds of thousands of STRs are interspersed throughout mammalian genomes. STRs are of special interest because the numbers of repeats within specific STRs tend to be highly variable, and because these short tandem repeat polymorphisms (STRPs) can be rapidly analyzed using PCR (Weber, J. and Carmen, W., 2016). The number of STRs at a specific locus are variable between individuals and the flanking regions that PCR primers binds to are constant.
If two different STR lengths are detected at a locus then the individual is deemed heterozygous. The two STR lengths that are the same are detected at one locus then the individual is deemed homozygous.
If two different STR lengths are detected at a locus then the individual is deemed heterozygous. The two STR lengths that are the same are detected at one locus then the individual is deemed homozygous.