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STR Data Analysis and Interpretation for Forensic Analysts


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DNA degradation is a process by which DNA breaks down into smaller fragments. Environmental factors such as sunlight, heat, and humidity can increase the rate of degradation. DNA samples that are subjected to environmental factors that promote degradation can pose challenges for data interpretation.

As DNA molecules randomly break down into smaller fragments, the STR regions of the DNA molecule can be fractured. If the STRs do not stay intact, amplification of these regions will not be successful. Degradation is more likely to occur at a large STR locus before occurring in a smaller STR locus.

Generally, degradation can be easily identified because the peak heights exhibit a downward slope across the electropherogram. The process of degradation can reduce the height of some alleles, making them too low to be distinguished from background noise in the data. In severely degraded DNA samples, no results will be obtained. Two or more biological samples that make up a mixture may show different levels of degradation, which can complicate the interpretation of these samples.

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