Regulation of gene expression via mechanisms that include suppression at transcriptional and posttranscriptional levels. Development requires the precise orchestration of complex patterns of gene expression that ultimately determine cell identity. Unique gene expression profiles are achieved through the integration of regulatory inputs from extrinsic and intrinsic factors that selectively activate or repress target genes. In multicellular organisms, gene silencing plays a major role in the regulation of gene expression, occurring at transcriptional and posttranscriptional levels.