What is a gene?

• A. A unit of heredity that occupies a locus on a chromosome and codes for a functional product.
• B. A sequence of amino acids.
• C. A type of lipid found in membranes.
• D. A segment of RNA that stores genetic material.

Answer: (A)

A gene is a unit of heredity that sits at a specific location on a chromosome and contains the instructions to make a functional product. In most organisms, that product is a protein or a molecule of RNA, and the gene’s information is read by cellular machinery to produce it. This definition emphasizes that genes are discrete pieces of DNA (or RNA in some viruses) with a definable position that influence inherited traits by directing production of a gene product. The other choices mix up what a gene is: a sequence of amino acids describes a protein, not the hereditary unit; a lipid is a type of membrane molecule; and an RNA segment that stores genetic material describes a piece of a genome in some viruses, not the gene itself.