Stochastic Effect
Definition
A random sampling artefact that occurs at very low template quantities. Examples include allelic dropout (an allele fails to amplify), allelic drop-in (a spurious allele appears), and peak height imbalance between alleles at a heterozygous locus.
- Cause
- Very low template DNA quantity
- Manifestations
- Allelic dropout, allelic drop-in, peak height imbalance
- Context
- Touch DNA and trace biological material analysis
Common questions
How does allelic dropout affect the interpretation of a low-template DNA profile?+
When one allele at a heterozygous locus fails to amplify, the profile can falsely appear homozygous, which can wrongly exclude a true contributor or distort a mixture deconvolution unless the analyst accounts for dropout probability in the statistical model.
Why can't a lab simply repeat a low-template amplification to eliminate stochastic effects?+
Because the effects arise from random sampling of a small number of template molecules, replicate amplifications from the same limited sample can each show different dropout or drop-in patterns, which is why labs use consensus profiling or probabilistic genotyping across replicates rather than trusting a single run.
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