The present invention discloses a method for modulating the quality of a selected phenotype that is displayed by an organism or part thereof and that results from the expression of a polypeptide-encoding polynucleotide by replacing at least one codon of that polynucleotide with a synonymous codon that has a higher or lower preference of usage by the organism or part thereof to produce the selected phenotype than the codon it replaces. The present invention is also directed to the use of a codon-modified polynucleotide so constructed for modulating the quality of a selected phenotype displayed by an organism or part thereof.
