Simply Forensic Reference Library

Allelic Dropout

Forensic DNA & Genetics

Definition. Failure to detect an allele that is present in the DNA of a contributor, often because of stochastic sampling or amplification in a low-template, damaged or inhibited sample.

How the term is used

An apparent single allele can represent a true homozygote or a heterozygote whose second allele is undetected. Analysts assess dropout with validated interpretation procedures.

Forensic example

A reference genotype 11,14 yields only allele 11 in a trace sample. Allele 14 may have dropped out.

Interpretation limitation

Absence of an allele peak is not proof that the contributor lacks that allele.

References and further reading

SWGDAM guidelines for forensic DNA analysis. The explanation and example are original educational summaries; consult the cited material and current laboratory guidance for authoritative application.

Related guide: Allelic Dropout in forensic practice.

Related glossary terms

Allelic Drop-InA detected allele-like signal that is not explained by the assumed contributors or known artefacts and may arise…Explore term Analytical ThresholdA validated signal threshold, commonly expressed in RFU, above which electropherogram peaks are sufficiently distinguishable from analytical noise…Explore term Combined Probability of InclusionAn estimate of the proportion of a specified population that would not be excluded as a possible contributor…Explore term DNA Degradation IndexA quantitative PCR indicator comparing assay targets of different sizes to assess fragmentation or related differential amplification of…Explore term

Related articles

Essential Guide to Low-Template DNA: Allelic Dropout and Peak Height BalanceExplore allelic dropout, stochastic PCR variation and peak-height imbalance in low-template forensic STR profiles, with five worked examples,…Read article Analytical and Stochastic Thresholds in Forensic DNA Interpretation: Validation, Dropout and Worked ExamplesA technical guide to analytical and stochastic RFU thresholds in forensic STR interpretation: baseline noise, dropout risk, laboratory…Read article