Mixture
Definition
A DNA sample containing contributions from two or more individuals. Identified by the presence of more than two alleles at one or more loci.
- Indicator
- More than two alleles at one or more loci
- Contributors
- Two or more individuals
- Common sources
- Touch DNA, sexual assault swabs, shared items
- Analysis approach
- Mixture deconvolution or probabilistic genotyping
Common questions
Why are DNA mixtures harder to interpret than single-source profiles?+
Analysts must resolve which alleles belong to which contributor, estimate the number of contributors, and account for peak-height variation and allele sharing, all of which introduce interpretive uncertainty that a single-source profile does not have.
Does every mixture get resolved into separate contributor profiles?+
No. Complex mixtures with low-level or degraded contributors are often reported only as a likelihood ratio for a specific hypothesis, without ever producing a clean individual profile for each contributor.
Related terms
- Continuous Model
- A probabilistic genotyping approach that treats peak heights as a continuous variable and models their probability under different contributor genotype combinations, as...
- EuroForMix
- An open-source continuous probabilistic genotyping platform developed by the Norwegian Institute of Public Health. Distributed as an R package and used by...
- LRmix Studio
- A semi-continuous probabilistic genotyping platform developed at Leiden University Medical Center. One of the first PG tools adopted by European forensic laboratories;...
- MCMC (Markov Chain Monte Carlo)
- A computational sampling method used by STRmix and TrueAllele to integrate the likelihood function over all possible contributor genotype combinations. Requires many...
- Mixture Ratio
- The proportional representation of each contributor's DNA in the mixture, estimated from the relative peak heights of non-overlapping alleles across multiple loci.
- Number of Contributors (NoC)
- The estimated minimum number of individuals whose DNA is present in a mixture, derived from the maximum allele count at any single...
- Probabilistic Genotyping (PG)
- A computational approach to mixture interpretation that models the entire electropherogram as a probabilistic output of a specified number of contributors, computing...
- Stochastic Threshold (ST)
- A validated minimum peak height below which allele calls are considered uncertain due to stochastic amplification effects. Profiles with peaks between the...
- STRmix
- A continuous probabilistic genotyping platform developed by ESR (New Zealand) and the Australian Federal Police. The most widely used PG platform in...
- TrueAllele
- A continuous probabilistic genotyping platform developed by Cybergenetics (Pittsburgh, PA). Used primarily in US criminal courts; available as a cloud-based service.