Low-Copy-Number (LCN) PCR
Definition
PCR protocol using increased cycle numbers (typically 34 cycles) developed at the UK FSS to generate profiles from template inputs below ~100 pg; requires enhanced contamination controls and probabilistic genotyping for interpretation.
- Developed by
- UK Forensic Science Service
- Cycle number
- Typically 34
- Sensitivity
- Profiles from inputs below roughly 100 pg
- Interpretation
- Requires probabilistic genotyping
Common questions
Is LCN PCR the same as low copy number DNA analysis?+
They describe the same underlying idea from different angles. Low copy number DNA names the sample category being targeted, while LCN PCR names the specific increased-cycle protocol the FSS developed to amplify it.
Why does LCN PCR require probabilistic genotyping rather than standard allele calling?+
At such low template levels, stochastic effects like allele dropout and drop-in make simple binary allele calls unreliable, so results are evaluated with software that models the probability of the observed peaks under competing hypotheses.
Related terms
- Allelic Drop-Out
- Failure of one allele of a heterozygous locus to amplify detectably, a stochastic effect of low-template amplification where sampling of limited template...
- ESSplex SE QS
- Qiagen kit covering the European Standard Set of 17 loci plus DYS391 and Amelogenin; optimised for EU Prüm database upload.
- GlobalFiler
- Applied Biosystems 25-plex STR kit covering 24 STR loci plus Amelogenin, compatible with both CODIS 20 and ESS17 requirements.
- Haematin
- Degradation product of haemoglobin that inhibits Taq polymerase by chelating Mg2+ ions and binding to the polymerase active site; most common inhibitor...
- Humic Acid
- Organic polymer from soil degradation that inhibits PCR by intercalating into double-stranded DNA and disrupting primer annealing.
- Identifiler Plus
- Applied Biosystems 16-plex STR kit covering the original 13 CODIS loci plus D2S1338, D19S433, and Amelogenin. Widely used through the 2010s; insufficient...
- Investigator 24Plex QS
- Qiagen 26-plex STR kit with Quality Sensor (IPC) and covering 24 STR loci plus DYS391 and Amelogenin. GO! variant uses increased cycles...
- IPC (Internal PCR Control)
- A non-forensic DNA sequence spiked into the PCR reaction at fixed concentration; a shift in IPC Ct value relative to the expected...
- PowerPlex Fusion 6C
- Promega 23-plex STR kit covering all 20 CODIS core loci, all 17 ESS loci, DYS391, and Amelogenin across 6 dye channels.
- Probabilistic Genotyping
- Software-based interpretation of complex DNA electropherograms using continuous statistical models (e.g. STRmix, TrueAllele, ArmedXpert). Generates a likelihood ratio for complex mixtures previously...