The polymerase chain reaction is used to

  • A. cut DNA into fragments of known length
  • B. make millions of copies of a specific DNA sequence in a few hours
  • C. read the amino acid sequence of a protein
  • D. insert a gene into a human cell

Explanation

Repeated cycles of heating to separate the strands, cooling so that primers bind, and extension by a heat stable polymerase double the amount of DNA each time, giving exponential amplification. Taq polymerase from a hot spring bacterium is used because it survives the near boiling denaturation step. The technique is what makes forensic work and viral testing possible from tiny samples.

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