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During PCR, each cycle amplifies existing DNA by 75 % (i.e., each existing copy produces 0.75 additional copies). Starting from a single copy of template DNA, how many copies will be present after 30 cycles? Round to the nearest whole number.

hard 3 marks Class 12 · Biology · Molecular Basis of Inheritance
Answer
Approximately 1.96×10^7 copies

The correct answer is Approximately 1.96×10^7 copies — Round to the nearest whole number: 1.96×10^7.

Step-by-step solution

  1. Recognise that after each cycle the number of copies multiplies by 1+0.75 = 1.75.
  2. Write the formula: N = 1.75^30, where 1 is the initial copy.
  3. Compute ln(1.75) ≈ 0.5596.
  4. Multiply: 0.5596 × 30 = 16.788.
  5. Exponentiate: e^16.788 ≈ 1.96×10^7.
  6. Thus about 19.6 million copies are obtained.
  7. Round to the nearest whole number: 1.96×10^7.
Common mistake: Using addition instead of multiplication or forgetting the exponent

Concept tested: PCR exponential amplification

Published · How this solution was prepared and checked

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