  Pyrosequencing is one of the important next-generation sequencing
technologies. We derive the distribution of the number of positive signals in
pyrograms of this sequencing technology as a function of flow cycle numbers and
nucleotide probabilities of the target sequences. As for the distribution of
sequence length, we also derive the distribution of positive signals for the
fixed flow cycle model. Explicit formulas are derived for the mean and variance
of the distributions. A simple result for the mean of the distribution is that
the mean number of positive signals in a pyrogram is approximately twice the
number of flow cycles, regardless of nucleotide probabilities. The statistical
distributions will be useful for instrument and software development for
pyrosequencing and other related platforms.
