Sequencing

For decades, Sanger sequencing has been the gold standard in DNAsequencing, ultimately resulting in the first draft of the human genome in 2001.  Since then the sequencing landscape underwent a drastic change with the development of technologies that are capable of generating thousands to millions of shorter or longer reads in a massive parallel manner.  In technologies currently on the market, target DNA is sequenced by copying the complementary strand one base at the time. In Roche 454 and Ion Torrent the read out is based on the release of pyrophosphate (pyrosequencing) or a proton, respectively, whereas ABI SOLiD by Applied Biosystems deploys ligation based sequencing.  Illumina directly measures the incorporation of fluorescently labeled nucleotides. With each of the above mentioned technologies, the complete sequence of individual human genomes has been identified each at a cost only marginally to the cost of the first human draft sequence.  Even a company has been set up (Complete Genomics) with one single goal: sequencing and selling human genomes with its own proprietary technology.

Development doesn’t stop there. Pacific Biosciences is penetrating the market with instruments allowing for very long reads starting from non-amplified DNA or RNA (single-molecule sequencing). Sequencing technologies that read the physical or chemical properties of the DNA without enzymatic steps involved are eagerly awaited.

Most of the currently available high-end instrumentation has been developed with high-throughput applications in mind (e.g. genome sequencing).  However, compartimentalisation and sample barcoding are also available to make more efficiently use of the sequencing monster’s capacity.  By clever experimental design, samples from different projects and from different applications can be combined.  However, this puts more stress on the experimental design.

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