Which statement describes a mutation?

• A. A non-heritable change in phenotype due to environmental factors.
• B. A heritable change in the DNA sequence that can alter a gene's function.
• C. A temporary change in a trait that is not inherited.
• D. A random change in phenotype without genetic basis.

Answer: (B)

Mutations are heritable changes in the DNA sequence that can alter a gene's function. They involve the genetic code itself, and if they occur in germ cells, they can be passed to offspring, introducing variation in traits. These changes can range from single-nucleotide substitutions to larger insertions, deletions, or rearrangements, and they can affect how a protein works or how a gene is regulated. This is different from changes caused by the environment that affect appearance without changing the DNA, or from temporary, non-genetic trait changes. A classic example is a single base change in a gene that alters the protein’s shape and function, which can then be inherited.