What is a gene?

• A. An RNA molecule that carries genetic information.
• B. A structural unit of protein.
• C. A distinct sequence of DNA that codes for a particular protein.
• D. A chromosome segment that does not contain information.

Answer: (C)

A gene is a defined segment of DNA that contains the instructions to produce a product, usually a specific protein. The idea is that the gene provides the exact information needed to synthesize something with a biological function, and this product arises when the gene is transcribed and translated (or, in some cases, when it codes for a functional RNA rather than a protein). This makes the DNA sequence itself the essence of the gene, rather than the product being the gene, and it explains why a gene is a distinct hereditary unit.

The other statements miss that core idea. An RNA molecule carrying genetic information describes the product, not the DNA sequence that carries the instructions in typical gene definition. Saying a gene is a structural unit of protein confuses the product with the genetic unit. A chromosome segment that does not contain information is false because a gene is defined by containing information to make a product.