Transcriptional and post-transcriptional mechanisms of phenotype modification including as involving chromatin organization, enhancer sequences, mRNA degradation, etc.
Control of gene expression in eukaryotes begins with control of transcription and ends with differences in terms of what enzymes are active and indeed what proteins are present among the otherwise differentiated cells making up the same organism.
Gene expression thus is controlled at the level of organism development, in terms of the maintenance of homeostasis, with regard to the structure of chromatin (euchromatin versus heterochromatin), and in terms of temporary protein activation or inactivation (including allosteric regulation).
Control also is exerted in terms of rates of initiation of translation and in terms of mRNA degradation (where faster degradation, like less initiation of translation, results in less gene expression per mRNA). Lastly, but nevertheless crucially important, there is control that is effected at the level of transcription, particularly in terms of transcription initiation.
Note that developmental biology, cellular differentiation, and to a lesser extent organism physiology in general (i.e., maintenance of homeostasis) all have initiation of transcription as important control points in control of gene expression. Thus, see in particular transcriptional control of gene expression.
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