The 454 Sequencing™ process uses a sequencing by synthesis approach to generate sequence data. In sequencing by synthesis, a single-stranded DNA fragment is copied with the use of an enzyme making the fragment double stranded. Starting at one end of the DNA fragment, the enzyme sequentially adds a single nucleotide that is the match of the nucleotide on the single strand. Nucleotides are paired one by one as the enzyme moves down the single stranded fragment to extend the double-helix ladder structure.