Define PCR; describe the three main steps and the importance of primer design and melting temperature considerations.

• A. Polymerase chain reaction amplifies a DNA segment by cycling through denaturation, annealing, and extension; primers define the target; optimal annealing temperature depends on primer Tm (roughly Tm-5) and primer sequences to avoid dimers.
• B. PCR amplifies RNA segments by reverse transcription.
• C. PCR cycles through replication, elongation, and termination.
• D. Primers are optional in PCR.

Answer: (A)