Make a Parity rule 2 (PR2) plot, where the AT-bias [A3/(A3 +T3)] at the third codon position of the four-codon amino acids of entire genes is the ordinate and the GC-bias [G3/(G3 +C3)] is the abscissa. The center of the plot, where both coordinates are 0.5, is where A = U and G = C (PR2), with no bias between the influence of the mutation and selection rates.
# NOT RUN {# read DNA from fasta filefasta <- fasta.read("virus.fasta", "host.fasta")
fasta.v <- fasta[[1]]
fasta.h <- fasta[[2]]
# }# NOT RUN {PR2.plot(fasta.v)
# }