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CAIE A-Level Biology A2 19.1.8 Pcr to Clone and Amplify Dna Questions

Use real exam evidence to explain why PCR amplifies small DNA samples, sequence its temperature cycle, justify primers and thermostable Taq, and calculate amplification.

Syllabus
2028–2030
Course
Biology 9700
Level
A2

Exam points

  • Explain why PCR is used to clone and amplify a selected DNA sequence from a small starting sample for analysis, testing or gene transfer.
  • Sequence PCR cycling through DNA denaturation, primer annealing and extension at suitable temperatures, then repeat the cycle to amplify DNA.
  • Explain how sequence-specific primers, free DNA nucleotides and thermostable Taq polymerase enable selective, repeated synthesis of complementary DNA strands.
  • Calculate DNA copy number or relative starting concentration from cycle doubling and explain how Taq errors can be copied and amplified.

CAIE A-Level Biology A2 19.1.8 Pcr to Clone and Amplify Dna Questions question 1

[Maximum number: 3]

Myosotis is a genus of small flowering plants. Many different Myosotis species grow on the islands of New Zealand, which are an important site of Myosotis evolution. Lowland Myosotis species grow at low altitude while alpine Myosotis species grow at high altitude at the tops of mountains.

Scientists wanted to obtain molecular data to determine the evolutionary relationships of New Zealand's Myosotis species. They extracted DNA from individuals of Myosotis species collected from three different islands in New Zealand.

To carry out a polymerase chain reaction before DNA sequencing, the DNA samples were mixed with primers, deoxynucleotides and Taq polymerase and put through 35 cycles of treatment. Each treatment cycle involved one minute at 95∘C95^{\circ} \mathrm{C}, followed by one minute at 50∘C50^{\circ} \mathrm{C} and then four minutes at 72∘C72^{\circ} \mathrm{C}.

Describe what happened to the DNA at each temperature.

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