Once a piece of DNA has been amplified, it can be sequenced. In this process, four reaction mixtures are set- up. Each one including:
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DNA to be sequenced
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a supply of nucleotides: A, C, G, and T
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a small amount of labeled chain terminating variant of one of the four nucleotides
The enzyme DNA polymerase incorporates the chain terminating variant at random, eventually ending the chain at every possible nucleotide position every few hundred bases.
The products of the reaction mixture are run on an electrophoresis gel. The sequence can be deduced by reading form the smallest to the largest piece.
If different fluorescent labels are used for the variant bases, sequencing can all be one in one single reaction. The bands can be detected and sequence read out automatically.
The entire process of DNA sample preparation and sequencing is now highly automated. The development that has been essential for the timely and cost-effective completion of the human genome project.
