DNA Sequencing

Abstract

DNA sequencing is the determination of base order in a DNA molecule. Methods for determining base order involve either chemical degradation or, more commonly, enzymatic synthesis of the region that is being sequenced. Automation of the DNA sequencing process is accelerating the progress of the Human Genome Project.

Keywords: human genome project; biotechnology; automated sequencing; gene

Figure 1.

Schematic view of Maxam–Gilbert reaction products. G, A, R, Y and C represent the specific chemical reactions that identify the relative positions of guanine (G), adenine (A), purine (‘R’; G and A), pyrimidine (‘Y’; C and T) and cytosine (C) bases, respectively. In this example the fragment is labelled at the 5′ end. Reading from the bottom towards the top of the gel, the banding pattern corresponds to the sequence 5′ GGTACGCCTGA 3′.

Figure 2.

Data produced using Sanger sequencing reaction. G, A, T and C represent the sequencing reaction products resulting from inclusion of ddGTP, ddATP, ddTTP or ddCTP. Since enzymatic synthesis proceeds 5′ to 3′, the smaller fragments identify bases that are closer to the primer (5′ end of the sequence information). (a) Schematic view of Sanger reaction products. The DNA sequence identified by this pattern of bands is indicated. (b) Photograph of corresponding sequence data.

Figure 3.

(a) Raw sequence data collected on an automated DNA sequencer (Perkin‐Elmer ABI PRISM Model 377). The four colours indicate the relative position of the bases in the DNA fragment. Each four‐colour vertical line corresponds to a different sequence reaction. The smaller fragments (nearer the cathode) identify bases that are closer to the primer (5′ end of the sequence information). (b) Portions of a representative, analysed sequence determined by the automated sequencer.

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Further Reading

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How to Cite close
Hardin, Susan H(Apr 2001) DNA Sequencing. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1038/npg.els.0003147]