The correct answer is option 1, operon. An operon is a group of genes that are regulated and coordinated together by a single DNA site. This DNA site, known as the operator, controls the expression of the genes within the operon. The operator acts as a switch, turning on or off the transcription and translation of the genes. This allows for the regulation of gene expression in response to various environmental conditions. Option 2, cistron, refers to a section of DNA that codes for a single polypeptide or protein. Option 3, polysome, refers to multiple ribosomes bound to a single mRNA molecule, involved in protein synthesis. Option 4, polypeptide, refers to a chain of amino acids linked together by peptide bonds, which is a product of gene expression.