What is the role of a negative and a positive control in PCR-based DNA testing?

• A. Positive controls verify the assay works; negative controls monitor for contamination.
• B. Negative controls monitor for contamination.
• C. Positive controls monitor for contamination.
• D. Controls measure DNA quantity.

Answer: (A)

In PCR-based DNA testing, controls ensure the results you see are trustworthy. A positive control uses known target DNA and goes through the same PCR process as the samples; if it amplifies, that shows the reagents, primers, and cycling conditions are working correctly. A negative control contains all reagents except the DNA template and should show no amplification, indicating there isn't contamination or carryover that could falsely appear as a true signal. Together, these controls confirm that a real sample result reflects genuine DNA amplification rather than an artifact. The other options fall short because a negative control alone only checks for contamination and doesn’t prove the assay is functioning properly, while a positive control alone doesn’t reveal contamination issues. Controls are not used to measure DNA quantity.