In genetics and biochemistry, sequencing means to determine the primary structure (or primary sequence) of an unbranched biopolymer. Sequencing results in a symbolic linear depiction known as a sequence which succinctly summarizes much of the atomic-level structure of the sequenced molecule.
In genetics terminology, sequencing is determining the nucleotides of a DNA or RNA strand. Currently, all sequencing is performed using the chain termination method, created by Frederick Sanger. This technique can only be used to identify fairly short sequences at a time (around 300-1000 base pairs on ABI machine), and therefore strategies to have been devised to scale the method up to sequence genes and genome. Two of the mainstream chain termination strategies are chromosome walking and shotgun sequencing.
Other techniques under development, which may offer many benefits over these, include:
Methods for performing protein sequencing include:
Though polysaccharides are also biopolymers, it is not so common to talk of 'sequencing' a polysaccharide, because a symbolic linear depiction cannot capture their tendency to branch and to bond to one another in different ways.