The FOP method is based on the proportion of optimal codons to a gene’s total number of codons.
It is calculated as the gene’s ratio of optimal codons to synonymous codons.
The ratio of optimal codons number to the total number of codons (both optimal and non-optimal) provides the Fop index.
It is essential to understand that the Fop index is context-dependent as values rely on the genetic code of the particular species. Because the genetic code is not perfectively universal, the Fop index may not universally apply across species.
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