Not every gene is active in every cell. Gene expression is the multi-step process by which information in a gene is converted into a functional product—protein or non-coding RNA. Transcription produces RNA; translation produces protein; both steps are tightly regulated.

Promoters, enhancers, transcription factors, and chromatin state control whether a gene is transcribed. Alternative splicing, RNA editing, and microRNAs further refine the output. Expression patterns differ across tissues, developmental stages, and environmental conditions.

Measuring expression with RNA sequencing or microarrays reveals which genes respond to signals or disease. Dysregulated expression contributes to cancer and many other disorders. Therapeutic approaches increasingly target the regulatory machinery that governs expression rather than the genes themselves.

• Process converting gene information into product
• Includes transcription and translation
• Highly regulated in space and time
• Measurable with modern omics methods