The genetically programmed repression of transcription. Silencing may be the net effect of regulatory events that increase transcription and those which repress it (the analogue model), or it may be an all-or-none phenomenon in which the gene exists with its promoter and enhancer sites open and its coding region available to transcription or tightly folded and packaged into heterochromatin (the digital or binary switch model). In the latter view, the switch is operated by two similarly acting sequences: a locus control region (LCR) and a silencer. Both are cis-acting, function bi-directionally and their actions are position and distance dependent. The LCR promotes unfolding of the chromatin and allows a promoter to act; the silencer has the opposite effect. The switch is apparently set in each cell cycle during the S-phase.