The process in which a gene's sequence is converted into a mature gene product (protein or RNA). This includes the production of an RNA transcript and its processing, as well as translation and maturation for protein-coding genes. [ http://www.ncbi.nlm.nih.gov/pubmed/31580950 GOC:txnOH-2018 http://www.ncbi.nlm.nih.gov/pubmed/25934543 ]