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The DNA sequencing process makes it possible for researchers to discover the amino acid sequence in a substance. Shown here is Step 2 in the process: After the target material has been transferred into eight-strip tubes and combined with fluorescent chemistry, it is placed in the thermal cycler where the four base chemicals that make up DNA--A (adenine), G (guanine), C (cytosine) and T (thymine)--receive fluorescent tags.