... end of the gel. (3) The electrical current is connected, with the negative current closest to the wells. The DNA samples are repelled by the negative charge. (4) The short strands move faster through the gel so they will be farther from the start. Strands of the same lengths end up together in groups that are visible to the naked eye. (5) The lengths are measured in bp (base pairs), which is not an exact measurement but accurate enough for the comparisons. PCR is used to magnify a quantity of DNA in only several hours. (1) Thermocycler separates a strand of DNA from a double helix (works like helicase). Heat breaks the hydrogen bonds between base pairs. (2) The sample is cooled with a solution of free nucleotides, DNA primers, and Taq polymerase, for the primers to bind (anneal) to the end of DNA strands. (3) This makes a complete ...

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