What is meant by a gene?

• A. A length of DNA that codes for a single protein/polypeptide
• B. A unit of inheritance that influences a trait
• C. A protein that binds DNA
• D. A lipid molecule associated with chromatin

Answer: (B)

A gene is a unit of inheritance that directs the transmission of traits from one generation to the next. It is typically a specific stretch of DNA (or, in some cases, RNA) that contains the information to produce a product, usually a protein or a functional RNA molecule. This makes the statement that a gene is a unit of inheritance that influences a trait the best description, because it captures both the hereditary role and the functional output that links genotype to phenotype.

The other idea—that a gene is simply a length of DNA that codes for a single protein—is too narrow. Not all genes encode a single protein, and some genes produce RNA products with important functions rather than proteins. The remaining options describe a protein that binds DNA or a lipid, neither of which defines what a gene is.