ABSTRACT
An intra and inter-laboratory study using the probabilistic genotyping (PG) software STRmix™ is reported. Two complex mixtures from the PROVEDIt set, analysed on an Applied Biosystems™ 3500 Series Genetic Analyzer, were selected. 174 participants responded. For Sample 1 (low template, in the order of 200 rfu for major contributors) five participants described the comparison as inconclusive with respect to the POI or excluded him. Where LRs were assigned, the point estimates ranging from 2 × 104 to 8 × 106. For Sample 2 (in the order of 2000 rfu for major contributors), LRs ranged from 2 × 1028 to 2 × 1029. Where LRs were calculated, the differences between participants can be attributed to (from largest to smallest impact): This study demonstrates a high level of repeatability and reproducibility among the participants. For those results that differed from the mode, the differences in LR were almost always minor or conservative.
Subject(s)
DNA Fingerprinting , DNA/analysis , Microsatellite Repeats , Software , Cooperative Behavior , Gene Frequency , Genotype , Humans , Laboratories , Likelihood Functions , Reproducibility of ResultsABSTRACT
We report a large compilation of the internal validations of the probabilistic genotyping software STRmix™. Thirty one laboratories contributed data resulting in 2825 mixtures comprising three to six donors and a wide range of multiplex, equipment, mixture proportions and templates. Previously reported trends in the LR were confirmed including less discriminatory LRs occurring both for donors and non-donors at low template (for the donor in question) and at high contributor number. We were unable to isolate an effect of allelic sharing. Any apparent effect appears to be largely confounded with increased contributor number.
Subject(s)
DNA/genetics , Genotype , Microsatellite Repeats , Probability , Software , Alleles , DNA Fingerprinting , Humans , Laboratories , Likelihood FunctionsABSTRACT
The choice of reagents for presumptive tests for blood, and subsequent extraction methodologies, can significantly affect both the quantity and quality of purified DNA. Blood samples directly tested with Hemastix(®) yielded <1% of the DNA recovered from untested samples when purified using the Qiagen BioRobot(®) EZ1 and EZ1(®) DNA Investigator kit. Full short tandem repeat profiles were obtained from both tested and untested samples, suggesting that the Hemastix(®) reagent(s) affect DNA binding, rather than produce DNA damage. The Hemastix(®) inhibition of DNA yield could be overcome by the addition of MTL buffer to the sample prior to extraction. Laboratories may wish to modify current procedures for extracting blood samples, utilize other extraction/purification methodologies, or inform their submitting agencies to avoid direct exposure of questioned bloodstains to Hemastix(®) reagents.
