9-4 Short Tandem Repeats

Short Tandem Repeats Short Tandem Repeats, STRs, are locations on the chromosome that contain short sequences that repeat themselves within the DNA molecule.

Tandem Repeats They serve as useful markers for identification because they are found in great abundance throughout the human genome. Tandem repeats. MLVA is a method used to perform molecular typing of microorganisms. It utilizes the naturally occurring variation in the number of tandem repeated DNA sequences found in the microbial genome of most bacterial species. Such tandem repeats may be perfect, but often imperfect repeats containing mutations are encountered.

RFLP The entire strand of an STR is very short, less than 450 bases long.

Collection of Evidence This makes STRs much less susceptible to degradation, and they often recovered from bodies or stains that have been subjected to extreme decomposition.

Figure 1: Y-short tandem repeat profile of sample 029 using Multiplex I. S1, prevasectomy semen; B, blood; S2, postvasectomy semen; *fragment amplified from the X chromosome.

Population Percentage The more STRs one can characterize, the smaller the percentage of the population from which a particular combination of STR is can emanate.

Multiplexing This gives rise to the concept of multiplexing, in which the forensic scientist can simultaneously extract and amplify a combination of different STRs.

Small Amount Required With STR, as little as 125 pg of DNA is required for analysis - 1/100 of the amount normally required for RFLP analysis.