Question

7. Every cycle of a PCR reaction results in a __________________ increase in the amount of DNA, so after 20 cycles, the amount of DNA will have increased approximately __________________.

Answer 1

7. Every cycle of a PCR reaction results in a two fold increase in the amount of DNA, so after 20 cycles, the amount of DNA will have increased approximately to one million copies.

Explanation :

• In one cycle of PCR the product formed is double. This means one double stranded DNA gives rise to two double stranded DNAs at the end of each cycle.
• This happens because, just like the process of cellular replication, in PCR also each strand of the double stranded DNA serves as a template for the synthesis of the complementary strand.
• Therefore since the product of each PCR cycle is exactly double the input volume, the formula of 2^{^n} can be applied to calculate the number of copies that will be formed after n cycles.
• In this case since it is 20 cycles, the number of copies formed will be 2^{^20} which is approximately one million copies. This means that there will be 500000 folds increase from the original input volume.