Distribution of nucleotide frequency in codons. Pie chart representation of mean frequencies of the four nucleotides at 1st, 2nd and 3rd positions of codons in dengue virus (left). The chart on the right shows nucleotide context pattern (based on mean dinucleotide frequencies) in the coding sequences of dengue virus. The number after each nucleotide and nucleotide pair represents its proportion compared to the total nucleotide counts for that codon position (left) or total counts of dinucleotides in the coding sequences (right). The nucleotide frequency as well as the dinucleotide frequency varies in highly correlated manner (Pearson correlation > 0.93), hence the mean value represents the nucleotide composition pattern of coding sequences of DENV within as well as between the four serotypes.