Figure 7.A.2. Dideoxy sequencing. Step 2: Add a "soup" of free nucleotides to the DNA. Tha majority of nucleotides are ordinary nucleotides, denoted by the black letters in the figure below. A small percentage of special dideoxy nucleotides are added (colored letters). The special dideoxy nucleotides have two imporant properties: (1) they have color-coded, fluorescent labels (e.g., green for Adenine, red for cytosine, etc.); and (2) they are chain terminating--i.e., whenever a special nucleotide in incorporated into the DNA strand further synthesis of the strand stops.

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