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The target DNA is repeatedly duplicated during Sanger sequencing, resulting in pieces of various lengths. The ends of the fragments are marked by fluorescent "chain terminator" nucleotides, which make it possible to determine the sequence.

Sanger sequencing, often known as the chain termination method, is a common method for sequencing DNA regions up to 900,000 base pairs in length. The British scientist Fred Sanger and his associates invented Sanger sequencing in 1977.

Sanger sequencing was employed in the Human Genome Project to identify the sequences of a large number of relatively short pieces of human DNA. (These pieces weren't always 900 bp or smaller, but utilising repeated rounds of Sanger sequencing, researchers were able to "walk" along each fragment.) The sequences of bigger DNA regions and, finally, complete chromosomes, were assembled from the fragments by aligning them based on overlapping areas.

Sanger sequencing is still widely used for the sequencing of individual pieces of DNA, such as fragments used in DNA cloning or produced through a polymerase chain reaction, even though genomes are now routinely sequenced using other techniques that are quicker and less expensive (PCR).