Chapter 3 - DNA Quantitation

Abstract

The primary purpose of DNA quantitation in forensic casework is to determine the appropriate amount of DNA template to include in polymerase chain reaction (PCR) amplification of short tandem repeat loci to avoid off-scale data and associated artifacts. Determination of the amount of DNA in a sample is essential for most PCR-based assays because a narrow concentration range works best with multiplex short tandem repeat (STR) typing. If the amount of DNA in a sample is outside of the target range for creating a “just right” DNA profile, then the DNA amount is adjusted prior to putting it into the PCR reaction. The process of achieving a DNA concentration that fits the optimal window for analysis is called normalization. This involves diluting the sample down to the desired range or concentrating it by removing excess fluid. Evaluation of human DNA quantity in a sample is used to screen for samples that are sent forward through the DNA testing process. When having to wade through a large number of samples, a sample screening process based on the amount of human DNA present is very helpful and cost-effective. DNA quantitation that is performed well saves time during the data review process, as data signal is on-scale.