Many DNA samples are either contaminated, degraded, or small in quantity. These problems are overcome by which process?

• A. Gel electrophoresis
• B. Polymerase chain reaction
• C. DNA sequencing
• D. Cloning

Answer: (B)

The main idea is amplifying the DNA to usable levels. Polymerase chain reaction uses primers that flank the region you want to study and a heat‑stable DNA polymerase to copy that region through many cycles of heating and cooling. With each cycle, the amount of target DNA roughly doubles, so even a tiny or degraded sample can yield enough material for analysis. PCR is flexible enough to work with degraded DNA by designing primers for short regions, which are more likely to remain intact in damaged samples. This amplification enables downstream work like sequencing or genotyping. Other techniques like gel electrophoresis, DNA sequencing, or cloning don’t increase the amount of DNA in the sample in the same practical, rapid way, so they don’t address the problem as effectively.