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In a PCR experiment, the reaction starts with 5 copies of a 300‑bp DNA fragment. Each cycle has an amplification efficiency of 85 % (i.e., each existing copy produces 0.85 new copies). How many copies are present after 15 cycles? Round to the nearest whole number.

medium 2 marks Class 12 · Biology · Molecular Basis of Inheritance
Answer
50840 copies

The correct answer is 50840 copies — Round to the nearest whole number: 50840 copies.

Step-by-step solution

  1. The number of copies after n cycles = initial × (1+E)^n, where E is the efficiency.
  2. Here, 1+E = 1+0.85 = 1.85.
  3. Calculate (1.85)^15 ≈ 10168 (using logarithms or successive squaring).
  4. Multiply by the initial 5 copies: 5 × 10168 ≈ 50840.
  5. Round to the nearest whole number: 50840 copies.
Common mistake: Using 0.85^n instead of (1+0.85)^n

Concept tested: PCR amplification calculation

Published · How this solution was prepared and checked

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