Current nucleotide sequencing focuses on DNA sequencing. As you will see
later in this chapter, direct RNA sequencing was de-selected by evolution. Instead,
RNA molecules are converted to cDNA and subject to DNA sequencing. Moreover,
DNA sequencing can be conducted by a number of sequencing technologies, each of
which uses a company- or inventer-defined procedure and sequencing mechanism. By
nature, both living organisms and non-living objects are constantly challenged by
evolution. DNA sequencing technologies are of no exception. For living organisms,
phenotypic variations resulted from genetic alterations are constantly tested by the
surrounding environment, which allows the fittest to propagate more efficiently than
the others. Similarly, using DNA sequencing technologies that we will discuss later in
this chapter as an example, each technology has its pros and cons against one another.
Also, their advantages and disadvantages co-evolve with, and depend on their
environmental backgrounds. Here, we review the evolution of DNA sequencing
technologies to appreciate the evolutionary process eventually leading to the
development of Next-Generation Sequencing technologies.
Keywords: Next-generation sequencing, NGS, Sanger sequencing, Single-molecule
sequencing.
