DNA sequencing is a method used to determine the identity and order of nucleotide bases that make up a given strand of DNA. One of the earliest methods to sequence DNA, Maxam-Gilbert sequencing, involves the chemical treatment of DNA to generate a large number of radioactive cleavage products. Given the specificity of the chemical treatment for different nucleotides, the sequence of nucleotides can be determined by separating the DNA fragments by size. While the Sanger sequencing method was published two years prior to the Maxam-Gilbert technique, Sanger sequencing did not dominate the DNA sequencing market immediately. Sanger sequencing relies on the use of deoxynucleotide triphosphates (dNTPs) and labeled dideoxynucleotide triphosphates (ddNTPs) in a reaction with a DNA polymerase and a primer to make a duplicate copy of the DNA to be sequenced. The incorporation of ddNTPs to the growing strand prevents the addition of subsequent dNTPs, thus stopping the actively elongating DNA molecule, and resulting in a labeled ddNTP at the end of each DNA fragment. As such, this technique is also known as chain termination. As with Maxam-Gilbert sequencing, the sequence of nucleotides can be determined by separating the DNA products by size. Current sequencing methods based on Sanger sequencing involve the use of fluorescently labeled ddNTPs where each base is labeled with a unique fluorophore.
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