INTRODUCTION:

A tri-nucleotide repeat marker was chosen that would generate products within a size range of 240 to 336 base pairs (bp). Participating laboratories were sent the products of three samples amplified with a 6-FAM labeled primer set. Participants were asked to resolve the three samples and fill out a web-based survey regarding their protocols and results. Each sample contained two alleles with a unique size repeat, for a total of six differently sized PCR products. The actual size of each product was determined by automated sequencing. Twenty-three laboratories from seven countries responded to the survey, submitting 96 sample files containing a total of 192 PCR products. Seven different models of sequencers are represented in this study, including both capillary systems and slab gel platforms. The survey results were first analyzed to generate general demographics of participating labs. In an attempt to isolate particular factors that may contribute to obtaining accurate allele-size calling information, results were further analyzed with respect to the accuracy of the submitted results. Accuracy is reported as deviation from the actual size in base pairs (bp). In most figures, the absolute value of the sum of the deviations in base pairs of both alleles in a sample compared to true allele size is used. E.g., If the first allele is called 2 bp above than the true value and the second allele is called 3 bp less than the true size, then the total deviation for that sample would be 5. In some cases, the actual deviation, whether negative or positive, was used to illustrate an observed trend.
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