DNA sequencing The Sanger DNA sequencing method uses dideoxy nucleotidcs to terminate DNA synthesis, yielding a series of DNA fragments whose sizes can be measured by electrophoresis.The last base in each of these fragments is known,because we know which dideoxy nucleotide was used to terminate each reaction.Therefore,ordering these fragments by size-each fragment one (known) base longer than the next-tells us the base sequence of the DNA.DNA sequencing The Sanger DNA sequencing method uses dideoxy nucleotidcs to terminate DNA synthesis, yielding a series of DNA fragments whose sizes can be measured by electrophoresis. The last base in each of these fragments is known, because we know which dideoxy nucleotide was used to terminate each reaction. Therefore, ordering these fragments by size-each fragment one (known) base longer than the next-tells us the base sequence of the DNA