A PCR tube begins with exactly one double stranded template molecule. If every cycle doubles the product perfectly, how many double stranded molecules are present after four complete cycles?

Core Concept

Perfect doubling means the molecule count follows two raised to the cycle number. One starting duplex gives 2 after the first cycle, 4 after the second, 8 after the third, and 16 after the fourth. Exponential accumulation lets tiny template amounts become detectable within hours.