How many DNA molecules will be produced from one molecule after 6 complete cycles of the PCR?

• A. 128
• B. 64
• C. 32
• D. 256

Answer: (B)

PCR amplifies DNA exponentially because each cycle doubles the amount of target DNA. Starting with a single DNA molecule, the number of copies after each complete cycle follows 2^n. After six cycles, you have 2^6 copies, which equals 64 DNA molecules. This matches the familiar pattern where 2^n grows as 2, 4, 8, 16, 32, 64, and so on; the other numbers correspond to 2^7 (128), 2^5 (32), and 2^8 (256), which aren’t reached after six cycles.