Patent ID: 7592504

Claim:
A method for determining whether a phenotype resulting from introduction of an siRNA into a cell is due to silencing of an intended target gene, or due to off-target effects, comprising: a) providing a cell exhibiting a silenced phenotype in which a target nucleic acid has been silenced by exogenously introduced siRNA, wherein said cell is selected from the group consisting of a plant cell, a yeast cell, an insect cell, or a cell from C. elegans; b) providing a synthetic nucleic acid sequence which encodes an identical protein to that encoded by the silenced target nucleic acid of step a), whereby codon sequences in said synthetic nucleic acid are altered from those of the silenced target nucleic acid so as to reduce the nucleic acid sequence identity between said target and synthetic nucleic acids; c) introducing the synthetic nucleic acid of step b) into the cell of step a) and assessing whether the silenced phenotype has been reversed indicating that said siRNA is acting specifically on its target or whether part or all of said silenced phenotype is maintained indicating that said siRNA is acting via an off-target mechanism.