Low Copy Number (LCN) DNA
Definition
An approach to analysing low-template samples by increasing the number of PCR amplification cycles, typically to 34 cycles. Increases sensitivity but also amplifies contaminants and stochastic noise, requiring strict quality controls and replicate analysis.
- Approach
- Increased PCR cycle number, typically ~34
- Benefit
- Higher sensitivity to trace DNA
- Cost
- More stochastic noise and contamination risk
- Requirement
- Replicate analysis, strict contamination controls
Common questions
Why does raising the cycle count cause problems as well as benefits?+
More amplification cycles let very small amounts of DNA produce a readable profile, but the same extra cycles also amplify stray contaminant DNA and increase allele dropout and drop-in, making a single LCN result less reliable than a standard-input profile.
How do laboratories compensate for LCN's added noise?+
By running replicate amplifications from the same extract and reporting only alleles that appear consistently across those replicates, combined with tighter anti-contamination protocols during sample handling.
Related terms
- Corneocyte
- A terminally differentiated, anucleate cell forming the outermost skin layer (stratum corneum). Corneocytes shed continuously. Nucleated cells from deeper epidermal layers are...
- Double-Swab Technique
- A collection method for dried biological stains in which a moistened swab rehydrates and lifts the stain from the surface, followed immediately...
- Secondary Transfer
- The movement of a glass fragment from a primary surface (which contacted the broken glass) to a secondary surface (which contacted the...
- Stochastic Effect
- A random sampling artefact that occurs at very low template quantities. Examples include allelic dropout (an allele fails to amplify), allelic drop-in...
- Touch DNA
- Minute quantities of epithelial cells transferred by skin contact with a surface, without leaving a visible stain. Collected by swabbing contact points...