English > About genomes (glossary) > Third-generation and subsequent types of DNA sequencers

About genomes (glossary)

Third-generation and subsequent types of DNA sequencers

In second-generation DNA sequencers, the template DNA must be amplified before the sequencing reaction, and bias and/or error may occur during the amplification (although if a sufficient amount of DNA is available, amplification can be omitted). Since excess fluorochromes must be removed after each step following the synthesis of each base or hybridization of each oligonucleotide, a cycle consisting of DNA synthesis, fluorescence detection, removal, and cleaning must be repeated 100 times to read 100 bases, and this process is time consuming. Third-generation DNA sequencers use a single DNA molecule as the template without needing to amplify the DNA. One device that is currently used, PACBIO RS (Pacific Biosciences of California, Inc.) can continuously read several thousand bases within a short period. The Advanced Genomics Center introduced this device in 2012. At present, the Center has been performing preparatory work required before the device can be operated.

Third-generation and subsequent types of DNA sequencers

Almost all the devices mentioned above rely on the elongation of DNA molecules by a DNA polymerase. Therefore, the accuracy and speed of DNA sequencing depend on the biochemical features of the DNA polymerase used. Consequently, reaction conditions, time, and accuracy are restricted. To overcome these disadvantages, a DNA sequencer has been developed that performs DNA sequencing by detecting the physicochemical features of each nucleotide in a DNA molecule without using an enzyme. This type of sequencer may be called a fourth-generation sequencer.

The aim behind the development of sequencing technology is to generate a larger amount of sequence data within a shorter period of time at a lower cost. The media topicalized the development of a device before the end of 2012 that could realize the “$1,000 genome” (a term signifying a project in the U.S. aiming at developing technology that would enable the sequencing of the entire human genome at a cost of $1,000). In contrast, the processing of sequence data requires huge amounts of computational and human resources. In particular, human resources are insufficient for this task worldwide, and this tendency is predicted to continue in the future. Therefore, appropriate personal development policies are expected to be created and executed.