A gene that is not expressed. This can be a result of a mutation that leads to premature termination of transcription, a defect in the promoter, the blocking of translation by RNA interference, or a mutation that makes the product inactive. A silent mutation is one that does not (appreciably) alter the phenotype, e.g. a point mutation that changes a codon but not the amino acid that is encoded (because of multiple codon assignments to some amino acids).
Subjects: Medicine and Health.