Mini-STR
Definition
A PCR assay in which both primers sit within a few base pairs of the STR repeat, producing amplicons as short as 70-80 base pairs. Used when conventional kits fail due to DNA fragmentation below 200 bp.
- Amplicon length
- As short as 70 to 80 bp
- Primer design
- Placed close to the repeat region
- Use case
- Template DNA fragmented below 200 bp
- Field
- Forensic DNA profiling
Common questions
Why do conventional STR kits fail on badly degraded samples?+
Standard kits place primers a fixed distance from the repeat to include flanking sequence, producing amplicons often well over 100 bp; if the template DNA has fragmented shorter than that distance, no intact target remains for the primers to amplify.
What trade-off does mini-STR design accept to solve this?+
Bringing primers closer to the repeat shortens the amplicon and rescues amplification from short fragments, but it sacrifices some flanking sequence and can occasionally affect compatibility with size ladders or profiles generated by standard kits, requiring careful validation.
Related terms
- Amplicon
- The double-stranded DNA fragment produced between two PCR primers. In forensic STR typing, amplicon size determines whether a locus can be recovered...
- Depurination
- Hydrolytic cleavage of the N-glycosidic bond between deoxyribose and a purine base (adenine or guanine), generating an abasic (apurinic) site. Abasic sites...
- Interlocus Drop-Out
- Failure of larger-amplicon loci to amplify in a degraded-DNA sample while shorter loci succeed. Results in a partial profile that includes only...
- Taq Polymerase
- Thermostable DNA polymerase from Thermus aquaticus, the enzyme that makes PCR practical. Stable at 95°C, it extends primers in the 5'-to-3' direction...