Data | Select Preferences | Include Codon Positions
Use this menu item to specify the codon positions you would like to include in the nucleotide sequence analysis. You can include any combination of 1st, 2nd, 3rd positions and non-coding sites. The specified options are used only if you conduct a nucleotide-by-nucleotide site analysis. If relevant, you will be given this choice in the dialog box that appears in response to a requested analysis (e.g., distance computation or phylogenetic reconstruction). Thus, you have the flexibility to select or change appropriate options at the time of the analysis.