Forensics Crime Scene Practice Test 2026 - Free Crime Scene Investigation Practice Questions and Study Guide

Negative controls are used to detect contamination and to confirm that a test result comes from the sample, not from stray DNA or reagents. In a DNA testing workflow, a negative control contains all reagents but no DNA template. It should yield no DNA amplification or signal. If any DNA appears in the negative control, it signals contamination at some step—sampling, extraction, or amplification—and the results from actual samples may be unreliable, requiring investigation and possibly repeating the test.

They aren’t used to quantify DNA yields—that’s done with standards and calibration. They aren’t for calibrating sequencing machines, which involves instrument performance checks. They aren’t for deciding whether a sample is human or non-human—that depends on the specific markers and assays used.