In criminal cases, why does it take longer to obtain a genetic fingerprint if the DNA sample is very small?

• A. The lab must sequence the entire genome first
• B. The sample is too large to analyze without amplification
• C. PCR amplification is required to increase the DNA quantity
• D. Small samples are ignored and not tested

Answer: (C)

Genetic fingerprinting in forensics relies on analyzing specific short tandem repeat regions, and you need enough DNA to get clear signals at those loci. When the starting material is very small, the lab uses PCR to amplify the targeted DNA sequences, producing many copies so the fragments can be detected and typed accurately. That amplification step takes time—preparing the reaction, running multiple PCR cycles, and often confirming results with replicates in low-template situations—because there’s more careful handling to avoid contamination and to address potential stochastic effects like allelic drop-out. So, the process isn’t about sequencing the whole genome or dealing with overly large samples; it’s about increasing the quantity of the relevant DNA to obtain a reliable fingerprint, which adds to the turnaround time.