English > About genomes (glossary) > First-generation DNA sequencers

About genomes (glossary)

First-generation DNA sequencers

In first-generation DNA sequencers, the DNA sequencing technology using the Sanger method was modified in three ways: dideoxynucleotides were labeled with four fluorochromes, electrophoresis and fluorescence detection were automated using robot technologies, and base identification was automated using information technologies. The modified technology was already mature when the International Human Genome Project entered its final stage in 2003. As of 2014, sequencing 96 specimens with a first-generation sequencer takes approximately 2 hours, and the accuracy attained when sequencing more than 1,000 nucleotides is greater than 99.9%. The DNA Sequencing Center has used dozens of first-generation DNA sequencers.

First-generation DNA sequencers

Although the technology behind first-generation DNA sequencers has almost been perfected, the maximum number of specimens that can be sequenced at one time is limited to 96 samples. In addition, DNA molecules must be prepared individually for sequencing by cloning and PCR amplification, and this preparation requires much time and labor. One sequencing run takes 2 hours. If DNA sequencing is continuously performed for 10 days, 120 operations can be performed for 11,000 specimens; consequently, 11 million bases can be sequenced. This number is much higher than the number of bases that could have been sequenced using the technologies available during the initial stage of DNA sequencing, as with those technologies, it would have taken years to sequencing 1,000 bases. Therefore, the use of a first-generation DNA sequencer for sequencing may be appropriate depending on the type of sequencing project. When high accuracy is required and a large number of bases must be read, a first-generation DNA sequencer is an essential device. At present, the Advanced Genomics Center possesses seven first-generation DNA sequencers, which are mainly used for terminal sequencing of bacterial artificial chromosomes (BAC) and high-accuracy sequencing of a specific region of genome. These seven sequencers are used at near maximum capacity.