Final answer:
Gene expression is the process by which a gene is used to make a protein.
Step-by-step explanation:
When a gene is expressed, a protein is produced.
Gene expression is the process by which a gene is used to make a protein. It involves the transcription of DNA into mRNA and the translation of mRNA into a protein. Once a gene is expressed, the protein product of that gene is usually made, which is why gene expression and protein synthesis are often considered the same process.