How many rounds of PCR would be needed to amplify a DNA sequence by a factor of approximately 64*10 12 ? Show a calculation. Hint: Remember, every round of PCR has a maximum amplification of 2-fold, and every ten rounds an amplification of approximately 1000-fold. So, to get an amplification of 4.000 one would do 2 + 10 = 12 rounds . This, of course, assumes high yields for each step.