Why was PCR used on the DNA sample from the toothbrush?

• A. It provides a large amount of DNA for analysis
• B. A toothbrush sample yields a very small amount of DNA, so amplification is needed
• C. It sequences DNA directly
• D. It repairs damaged DNA

Answer: (B)

PCR is used when only tiny amounts of DNA are available because it makes many copies of targeted DNA segments. A toothbrush tends to carry only trace DNA from saliva and skin cells, so there isn’t enough material to analyze directly. PCR uses primers that flank specific regions and a DNA polymerase to copy those regions repeatedly, resulting in millions of copies. Those amplified copies provide enough material for downstream tests like profiling or sequencing.

PCR doesn’t sequence DNA by itself, nor does it repair damaged DNA. It simply makes more copies of the existing DNA so the next analysis can be performed reliably.