Polymerase chain reaction (PCR) amplifies DNA samples for analysis. PCR sensitivity amplifies even trace amounts of DNA, but contamination is a major concern. Sensitivity is critical in forensic analysis and can affect ancient DNA samples. The lab process and chemicals used can affect sensitivity, so documentation is crucial.
Polymerase chain reaction (PCR) is a technique used to amplify a DNA sample. PCR sensitivity refers to how effectively a sample is amplified. Sensitivity is both a blessing and a curse for people who use this technique to prepare DNA for analysis. Several things can affect PCR sensitivity, and researchers have conducted a number of studies to learn about things that can play a role in sensitivity and how those things can affect a test result.
Simply put, in a PCR procedure, a DNA sample is basically unzipped to create two strands and then encouraged to replicate, making multiple copies of the DNA strand. This technique takes advantage of how DNA replicates in the real world to create a large sample that can be used for analysis. Using PCR, people can amplify a small sample to look at a specific area of interest and identify particular segments of DNA that may be a cause of interest or concern.
The extreme sensitivity of this process means that PCR is very vulnerable to contamination. If the person administering the test contaminates the sample with DNA from their own body, such as pet hair or skin flakes, the sample will be distorted. PCR sensitivity is a major concern in laboratories because people want to avoid contaminated samples if possible.
However, PCR sensitivity is also a blessing. The ability to amplify everything and anything in the sample means that a PCR can be used to find DNA that may only be present in trace amounts in a sample. For example, someone with a chronic condition like HIV might have a very low viral load, making it difficult to actually find copies of the virus in the patient’s blood. Due to the sensitivity of PCR, even very low viral loads are detectable, because a single copy of the virus will be amplified when done via PCR.
In forensic PCR analysis, the sensitivity of the PCR can be critical, as it can allow a technician to identify foreign DNA in a sample that could provide a clue to a crime. Analysis of ancient DNA samples can also be complicated or facilitated by sensitivity. The ability to amplify a small sample of DNA can be a blessing when only a limited sample is available, such as when a forensic anthropologist has only one tooth to work with when identifying someone, but it also means that a limited sample can be compromised beyond use for contamination.
Many things can affect the sensitivity of PCR. The precise process used in the lab is a factor, as are the compounds used to process the sample. This is why technicians must carefully document the process, so that someone studying the results can look for problematic techniques or chemicals used that could invalidate the results or call them into question.
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