Definition:
Gene expression is the process by which information from a gene is used in the synthesis of a functional gene product. These products are often proteins, but in non-protein coding genes such as rRNA genes or tRNA genes, the product is a functional RNA. The process of gene expression is used by all known life – eukaryotes: including multi-cellular organisms, prokaryotes: (bacteria and archaea) and viruses – to generate the macromolecular machinery for life.
Maria Konovalenko 