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STR Data Analysis and Interpretation for Forensic Analysts


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Image of Spikes
National Institute of Justice (NIJ) (see reuse policy).

Spikes are narrow peaks usually attributed to fluctuation in voltage or the presence of minute air bubbles in the capillary. Spikes can also be caused by crystals in the polymer and/or fluorescent material in the polymer or formamide. Spikes, unlike other artifacts, are generally seen in the same position in all colors. However, it is possible to detect spikes in a single color.

Analysts should view both the raw and analyzed data for each sample. The raw data produce a non-filtered view of the sample run, while analyzed data can obscure detection of a spike. Frequently, spikes are more readily detected in raw data versus analyzed data. The analyzed data provide an exact data point and base pair size for each peak. Spikes that are not obscured in the analyzed data can be assigned an exact data point for each color displayed.

The occurrence of spikes can be minimized by following the instrument manufacturer's procedures for reagent and sample handling. If spikes persist, analysts may need to contact the manufacturer. Frequent electronic spiking can occur due to poorly functioning instruments.

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