What is a negative control in forensic DNA or chemistry analysis, and why is it used?

What is a negative control in forensic DNA or chemistry analysis, and why is it used?

• A. A blank sample with no analyte; used to detect contamination or procedural errors.
• B. A sample with known analyte to calibrate reagents
• C. A duplicate of the evidence sample
• D. A control sample with high concentration to test instrument sensitivity

Answer: (A)

A negative control is a sample that includes all components of the analysis except the target analyte, and its purpose is to reveal contamination or procedural errors that could produce a false signal. In forensic DNA work, this is typically a blank PCR reaction with water instead of DNA; if any amplification occurs, it flags contamination in reagents, lab environment, or carryover from previous samples. In chemistry analyses, the negative control is a blank containing the solvent and reagents but no analyte to establish the baseline signal; any signal above baseline indicates something in the process is introducing material or energy that could be mistaken for the analyte. This is essential so that anything observed in the actual samples can be attributed with confidence to the sample itself rather than to contamination. The other scenarios describe different quality controls: using a known analyte calibrates reagents to ensure the system responds correctly; duplicating the evidence sample checks precision; and testing with a high concentration checks instrument sensitivity or the linear range. So the blank with no analyte, used to detect contamination or procedural errors, is the appropriate negative control.

A negative control is a sample that includes all components of the analysis except the target analyte, and its purpose is to reveal contamination or procedural errors that could produce a false signal. In forensic DNA work, this is typically a blank PCR reaction with water instead of DNA; if any amplification occurs, it flags contamination in reagents, lab environment, or carryover from previous samples. In chemistry analyses, the negative control is a blank containing the solvent and reagents but no analyte to establish the baseline signal; any signal above baseline indicates something in the process is introducing material or energy that could be mistaken for the analyte. This is essential so that anything observed in the actual samples can be attributed with confidence to the sample itself rather than to contamination. The other scenarios describe different quality controls: using a known analyte calibrates reagents to ensure the system responds correctly; duplicating the evidence sample checks precision; and testing with a high concentration checks instrument sensitivity or the linear range. So the blank with no analyte, used to detect contamination or procedural errors, is the appropriate negative control.