Interlocus Drop-Out
Definition
Failure of larger-amplicon loci to amplify in a degraded-DNA sample while shorter loci succeed. Results in a partial profile that includes only the lower molecular-weight markers in a multiplex.
- Field
- Forensic DNA typing
- Cause
- DNA degradation reducing large-amplicon amplification
- Result
- Partial profile favouring shorter loci
- Contrasts with
- Allele drop-out at a single locus
Common questions
Why do larger loci fail before smaller loci as DNA degrades?+
PCR amplification requires an intact template spanning the full primer-to-primer distance, and degradation fragments DNA randomly, so longer target sequences are statistically more likely to have a break somewhere within their span than shorter ones, making them fail first.
How do laboratories address interlocus drop-out when interpreting a degraded sample?+
Analysts may use mini-STR kits designed with shorter amplicon targets, interpret the resulting partial profile with appropriate statistical caveats, or attempt additional extraction and concentration steps to recover enough intact template for the larger loci.
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...
- 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...