Amplicon
Definition
The double-stranded DNA fragment produced between two PCR primers. In forensic STR typing, amplicon size determines whether a locus can be recovered from degraded DNA: smaller amplicons survive better than larger ones.
- Nature
- Double-stranded DNA fragment
- Produced by
- PCR between two primers
- Forensic relevance
- STR locus recovery from degraded DNA
- Size relationship
- Smaller amplicons survive degradation better
Common questions
Why does amplicon size matter for degraded casework samples?+
Environmental and time-related degradation fragments genomic DNA into progressively shorter pieces. A locus with a large amplicon needs a longer intact template to amplify, so it drops out first; loci engineered with short amplicons keep working on more degraded evidence.
How do labs exploit this size dependence?+
Mini-STR kits deliberately redesign primers closer to the repeat region to shrink amplicon size, letting the same loci be typed from bone, hair shafts, or old stains that would fail with standard-length CODIS primer sets.
Related terms
- 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...
- Mini-STR
- A PCR assay in which both primers sit within a few base pairs of the STR repeat, producing amplicons as short as...
- 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...