In laboratories around the world there is an intense desire to sequence more genomes.

All of the sequenced genomes listed in Genome Sizes were determined using the dideoxy method invented by Frederick Sanger and described in the page DNA Sequencing.

But now a great effort is being expended to find ways to sequence DNA more rapidly (and more cheaply).

Several new methods are being developed and one is already commercially available (the Genome Sequencer 20 System). Its method is called pyrosequencing or sequencing by synthesis.

It works like this.

After a primer is annealed to the end of the ssDNA, synthesis is ready to begin.

As is always true of DNA synthesis [Link], incoming nucleotides are added to the 3' end of the growing chain (left).

The nucleotides are supplied as four deoxynucleoside triphosphates. As each nucleotide is added, a molecule containing two phosphate groups — called pyrophosphate (PPi) is split off.

The sequencing run:

The diagram on the left shows the type of data produced in a single well. The height of the peak of light production gives the number of additions that occurred when a particular nucleotide was added (bottom).

Computer software then displays the template sequence (top) for each of the thousands of different fragments sequenced.

With this technology, as many as 20 million base pairs of genome sequence can be learned in an instrument run of less than 6 hours.

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7 March 2011