Mixture Ratio
Definition
The proportional representation of each contributor's DNA in the mixture, estimated from the relative peak heights of non-overlapping alleles across multiple loci.
- Estimated from
- Relative peak heights at non-overlapping alleles
- Expressed as
- Proportion or ratio between contributors, e.g. 3:1
- Affected by
- Degradation, stochastic effects, allele sharing
- Used for
- Assigning major and minor contributor status
Common questions
Why can a mixture ratio differ across loci in the same sample?+
Differential degradation, PCR stochastic variation, and locus-specific amplification efficiency can shift relative peak heights, so analysts average across multiple informative loci rather than relying on a single one.
Does a minor contributor status mean weaker evidentiary value?+
Not necessarily. A minor contributor can still be included or excluded with a strong likelihood ratio if enough informative loci show consistent, unambiguous minor-component alleles.
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
- A DNA sample containing contributions from two or more individuals. Identified by the presence of more than two alleles at one or...
- 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.