Figure 2. Genetic study of phenotype-genotype association.

The traditional phenotype-genotype association study follows the principle of “one gene, one protein, one phenotype (disease)” and uses either forward (top-down) genetics or reverse (bottom-up) genetics strategy to identify the genetic variability responsible for the phenotype or disease. This “one gene, one enzyme, one drug” principle has guided the traditional drug research with identification of “one pure drug target” as the ideal drug with pure therapeutic efficacy and the least side-effect or toxicity.