Today’s blog is written by guest blogger Dr. Jo-Anne Bright, New Zealand Institute of Environmental Science and Research (ESR). Reposted from The ISHI Report with permission.
In late August last year STRmix™ celebrated 10 years since it was first introduced to the world as sophisticated forensic software, capable of resolving mixed DNA profiles which previously were regarded as too complex to interpret.
Since that time, STRmix™ has become the accepted standard for DNA mixture interpretation, used by over 100 forensic labs worldwide to analyze DNA evidence in more than 380,000 cases. That includes more than 210,000 cases in North America, 30,000 in Europe and the United Kingdom, and 135,000 in Australasia.
The widespread adoption of STRmix™ and other probabilistic genotyping (PG) software is due to their ability to better distinguish true from non-donors in a complex forensic DNA profile. PG software use far more of the available DNA profile to determine whether a person of interest is a possible contributor to evidence in a criminal investigation. Our previous manual approach to DNA interpretation was binary and wasted much of the evidentiary value in a profile. Low-level, degraded, or mixed DNA samples that would have previously been dismissed as uninterpretable or inconclusive may now yield DNA results which are not only interpretable but stand up well in judicial proceedings.
Relying on proven methodologies routinely used in computational biology, physics, engineering, and weather prediction, STRmix™ works by rapidly assessing how closely thousands of proposed DNA profiles resemble or can explain an observed DNA mixture. The software calculates the probability of observed DNA evidence by assuming the DNA in question originated from either a person of interest or an unknown donor. These two probabilities are then presented as a likelihood ratio (LR), inferring the value of the findings and level of support for one proposition over the other.
The success of STRmix™ has led the team behind its development to launch two related products which, when combined with STRmix™, complete the full workflow from analysis to interpretation and database matching. These products include FaSTR™ DNA, expert forensic software which rapidly analyzes raw DNA data generated by genetic analyzers and standard profiling kits, and assigns a number of contributors (NoC) estimate; and DBLR™, an application which allows forensic labs to undertake superfast database searches, visualize the value of DNA mixture evidence, determine whether there is a common donor between samples and calculate any kinship relationship conceivable.
Incremental but significant changes have been made to the software since the introduction of the first version of STRmix in 2012. Like other software, STRmix™ has been regularly upgraded in order to enhance its functionality, improve its user experience, and add new features. New features are often in response to suggestions made by the forensic laboratories using the software, allowing them to better address on-the-job needs. This is also true of FaSTR™ DNA and DBLR™.
The latest release of FaSTR™ DNA (version 1.1) features a range of improvements, further strengthening it as a fast, user-friendly analysis software. Changes include:
- Inclusion of a sample to sample and sample to database comparison module to facilitate quality checks across your analysis project;
- Changes to the ILS review to improve the workflow for when alignment fails;
- Improvements to the ANN peak classification;
- Inclusion of a Number of Contributors (NoC) decision tree for the PowerPlex® Fusion 6C kit;
- Display improvements including a record of maximum allele count across the profile; and a record of distances in base pairs, peak height ratios, and averages (where applicable) across multiple peak selections.
Released late last year, version 2.10 of STRmix™ contains a number of new features, including the introduction of a Visualize Weights module to help analysts investigate DNA interpretation results and additional improvements to dropout modelling. These changes will allow a labs to set a low, or even no, analytical threshold. STRmix™ v2.10’s further integration with FaSTR™ DNA enables forensic labs using both software packages to achieve even greater speed and efficiency in the analysis and interpretation of raw data generated by genetic analyzers and standard profiling kits.
While the next major version release of DBLR™ is nearing completion, significant enhancements to the current version have extended its capability by allowing improved modelling through the introduction of linkage, mutation, and consideration of relatedness (FST) to the Kinship module. These enhancements enable users to apply advanced models in a simple and streamlined solution. It is also able to assign LRs within the Kinship module for single source profiles containing both STR and SNP loci generated using Next Generation Sequencing (NGS) technology. Other improvements to the latest release of DBLR™ include the introduction of a Direct Matching module for database-to-database comparisons, and the inclusion of cluster graphs in the mixture-to-mixture match reporting, enabling better visualization of the results.
Looking to the future, the STRmix™ team is planning to formulate suitable models for interpreting data as the forensic community embraces new analytical techniques such as massively parallel sequencing (or NGS). We are also working on probabilistic genotyping software for the interpretation of Y-STR (male specific) profiles, which are routinely developed during sexual assault investigations. We have a lot of really exciting projects in the works, and we look forward to our continued collaboration with our users and the wider forensic community.
Dr. Jo-Anne Bright is Senior Science Leader at the New Zealand Institute of Environmental Science and Research (ESR) and one of the developers of STRmix™. For more information, visit https://www.strmix.com/.
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