Question

After ______ cycles of PCR, a DNA sequence may be amplified a million-fold.

a) 10-15
b) 20-25
c) 25-30
d) 30-35

Answer 1

After 20-25 cycles of PCR, a DNA sequence can be amplified a million-fold because each cycle doubles the number of DNA sequences, leading to exponential growth.

Step-by-step explanation:

The question pertains to the number of PCR cycles required to amplify a DNA sequence a million-fold. The Polymerase Chain Reaction, or PCR, is a method used to amplify DNA sequences exponentially. During each cycle of the PCR, the number of DNA sequences doubles, which can be expressed as 2¹. Therefore, to achieve a million-fold increase (2¹⁶), one would need to complete around 20 cycles, as each cycle doubles the number of DNA sequences. Specifically, after 20-25 cycles, the DNA can be amplified to reach this level, therefore the correct answer is option b) 20-25.