DNA Fingerprinting Using STRs

Genetic testing is an ever-expanding field for scientific and criminal investigations. DNA technology, such as the use of multiplex PCR to analyze short tandem repeats (STRs) – gene segments that are highly polymorphic and are abundant in the non-coding regions of the human genome – has become a new alternative to traditional methods such as southern blots using variable number tandem repeats (VNTRs). VNTRs are also comprised of repeating sequences, but are much longer per repeat (10-100 base pairs vs. 2-9 base pairs) and are generally not as conserved across generations compared to STRs, which makes familial testing more difficult.

The use of STRs for genotyping individuals is commonly known as “genetic fingerprinting” or "DNA profiling". Multiplex Polymerase Chain Reaction (PCR) kits are commercially available, allowing several STR locations (loci) to be amplified and characterized all in one reaction per sample versus several individual reactions of the same sample using regular PCR; this process is quicker and more efficient. The results include the allele patterns for each autosomal locus tested (numbers and locations vary between kits) as well as the Amelogenin locus, which gives the sex of the individual. The more loci you add, the more unique the profile becomes, which is why CODIS uses 13 loci plus the sex marker. Since the small nature of these markers allow them to be more resistant to mutations and degradation, this technique has become highly popular not only for crime scene analysis or paternity testing, but also in the identification of remains from highly traumatic events such as fires, explosions, and airplane crashes, amongst others.

To get a better break-down of this method, watch the video below: