dideoxy sequencing The process of DNA Sequencing:

Double-stranded DNA is dissociated and a radioactive or fluorescent base is annealed to the DNA [A].

Four separate reactions are performed to synthesize new DNA, each reaction contains all four deoxynucleotides (dNTP) and a small portion of one of the dideoxynucleotide bases (ddNTP) [B].

DNA is synthesized and is terminated each time a ddNTP is incorporated [C].

DNA from all four reactions is separated on a gel in side-by-side lanes to produce a sequence ladder [D].

the sequence is read from the bottom up, either radioactively or via fluorescent markers. It is the compliment (opposite) of the strand copied.