What is a gene?

• A. An organelle in the nucleus
• B. A lipid that forms membranes
• C. A sequence of DNA that codes for a protein and thus determines a trait
• D. A protein that speeds up reactions

Answer: (C)

Genes are units of heredity: specific stretches of DNA that carry the instructions to make a product that influences a trait. Usually that product is a protein, produced when the gene is transcribed into mRNA and translated into a polypeptide, though some genes code for RNA molecules that have their own roles. This is why a gene is best described as a DNA sequence that codes for a protein and thus helps determine a trait.

The other options describe things that aren’t genes: an organelle in the nucleus isn’t a gene, lipids that form membranes aren’t genetic carriers, and a protein that speeds up reactions is an enzyme, not a gene.