Answer
Frederick Sanger's dideoxy chain-termination method of DNA sequencing remains in widespread use today because it is a relatively straightforward and reliable method for determining the order of nucleotides in a DNA molecule. The method is based on the principle that when a DNA polymerase is synthesizing a DNA strand, it will incorporate a dideoxynucleotide (ddNTP) instead of a deoxynucleotide (dNTP) if a ddNTP is present in the reaction mixture.