In criminal case testing, why does contamination slow obtaining a genetic fingerprint?

• A. Contamination prevents any DNA from being detected
• B. Other DNA is present; required DNA must be identified from the rest
• C. The DNA becomes damaged by contamination
• D. The lab uses more advanced equipment

Answer: (B)

Contamination introduces DNA from another source into the sample, creating a mixture rather than a single, clean source. In STR analysis, a clear genetic fingerprint comes from a single individual's DNA. When there’s mixed DNA, investigators must figure out which alleles belong to the person of interest and separate or interpret the overlapping signals. This adds extra steps, time, and sometimes more testing to resolve the mixture, so obtaining a usable fingerprint takes longer. So contamination slows the process because other DNA is present and must be identified from the rest.