Pyrosequencing is a DNA sequencing method based on the sequencing by synthesis principle. During the sequential addition of nucleotides onto a growing DNA strand, pyrophosphate (PPi) is released. A cascade of enzymatic reactions is then initiated by PPi, giving off chemiluminescent signals that can be detected and used to recognize the newly added nucleotide. One type of nucleotide is added and identified at a time, until full DNA molecule is sequenced.