Format
Total number of nucleotides available for mutations ("coverage")
in the MB study from Parsons et al.,
broken down by gene, screen (Discovery or Prevalence),
and mutation type, composed of the wild type nucleotide
and its context. The object is a data frame, with the
variables: Gene, Screen, WTNuc (wild type nucleotide),
Context, and Coverage. The two possible values
for Screen are Disc ("Discovery") and Prev ("Prevalence").
The nucleotides availables for indels are all the successfully
sequenced nucleotides in a gene; the corresponding rows
have a "" entry for WTNuc and an "All" entry for "Context."
The nucleotides availables for other
mutations are excluding nucleotides which can only give rise to
synonymous mutations.