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Short Tandem Repeat (STR) polymorphisms have been established and validated as a method for the identification of forensic samples. At The Bode Technology Group, as well as Canada and the United Kingdom, STRs have been in use for well over 3 years. In the last year, STRs have come into more widespread use in the United States as various state crime labs have validated a variety of STR systems in a variety of formats. There are two basic methods of using STR loci: Multiplex and Monoplex. There are also two basic methods of visualizing the results from an STR amplification: silver stain and fluorescent detection. By far, multiplexed fluorescent methods are the overwhelming choice for analyzing STR loci, especially since this format provides the maximum opportunity for automation of the procedure. Even within the multiplex-fluorescent methodology, there are still two fundamental approaches to using STR loci: scanning detection methods (i.e. Hitachi FMBIO II^®) and vertical DNA sequencer methods (i.e. ABD 377). Clearly for the PCR based STR loci, the type at a given locus for a given individual should not change as a function of the test method, as was the case in the enzyme dependent RFLP tests.

In this study, STR loci were compared using the Hitachi FMBIO II^®, the Applied BioSystems (ABD) 377 and silver staining. A set of samples representing a forensic case were prepared and submitted for analysis to different laboratories using different analysis methods. The results were then submitted to a third party for review and further analysis. In addition, the Polymarker/DQA systems were analyzed for comparison purposes. The laboratories that analyzed the samples not only used different methods of visualizing the STR data, but also used different PCR conditions, different PCR primers, and different DNA isolation methods.

The fundamental question to be answered is whether or not laboratory/analysis method had any effect on the allele call. If in fact an individual is a CSF1PO 10, did all systems correctly identify the allele? Second, what, if any, difference existed between the ability of the analysis methods to discriminate between the samples, and what effect did the analysis method have on the overall quality of the results? The efficiency of the various analysis methods was also compared. Specifically, issues related to throughput were evaluated, as well as what effects, if any, different combinations of STRs had on the quality of the data. Finally, data was developed on new sets of STR marker systems and compared to the STR benchmark data.

Preliminary data based on validation studies done in The Bode Technology Group laboratories indicate that all of the variables mentioned do not effect the ability to accurately define the STR type at any of the validated STR loci.