Internal Validation Study of Promega's Powerplex Y System




Donovan, Erin W.


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The expectations of this validation study and results obtained are similar. For the sensitivity study, Promega documents the optimal amount of DNA to be added to the PCR reaction 500pg to lng, (11) which is consistent with the results of this validation study. For the mixture study of male and female DNA Promega claims up to a concentration [greater than] 100X female DNA compared to male DNA is acceptable with no effects. This was the case in the validation study, which had a proportion of 1:50 with no effect. The substrate study showed leather to inhibit the PowerPlex Y System which has been see to happen in other DNA testing (11). The environmental study test showed humidity effects the results of the PowerPlex Y system. Also this frequently has been in other DNA testing due to the humidity causing DNA degradation, which results in a partial profile or no results for that sample. The results obtained from this internal validation study can be compared to other validation studies for Y chromosome specific STR multiplex systems. For example the paper “Validation and casework application a Y Chromosome specific STR multiple” written by Mechthild Prinz is comparable to that of this validation study performed (3). The Y-STR multiplex tested only four loci versus the PowerPlex Y System which tests twelve. The studies addressed in each of the validation studies consist of mixture, sensitivity, environmental, and substrate. For the male-female mixture study, the female DNA had no effect on the results up to 1:4000 ratios. These results are similar to the Powerplex Y System because no effect on the ability to obtain a full profile with a mixed sample of female and male DNA was observed. The sensitivity for the multiplex system showed allelic drop out at 125ph of DNA and optimal amount of DNA at 1-2ng. The PowerPlex Y System showed allelic drop out at 250ph and optimal amount of DNA to be 500pg-1ng. The environmental studies were similar because both showed allelic drop out for the humidity conditions. The multiplex with four loci did not use leather as a substrate, the other substrates were similar in both validation studies and reported similar results. Validation studies are frequently needed in order to validate a technique to be used in a forensic laboratory. Forensic cases are frequently under scrutiny by the judicial system. The questions due not lie in the science behind DNA testing but rather the process by which a laboratory performs the DNA test. In order to reduce the amount of questions validation studies are performed and interpretation guidelines are developed from those validation studies. Interpretation guidelines are written to direct and assist an analyst in making a final interpretation of each individual sample. The guidelines consist of the control, which must be run alongside each sample with the excepted results of each of the controls. The guidelines include types of identification for a sample such as no result, inconclusive, exclusive, and not excluded. Also DNA quantification information is included along with internal lane standard and allelic ladder guidelines. Interpretations of mixtures are included, which explains peak height ratios and how to determine a mixed sample. A calculation section is included to address the appropriate calculations to be used with the system to analyze the results. Interpretation guidelines will be pronounced based on this validation study for the University of North Texas Health Science DNA Identity laboratory.