How do germ-line and somatic mutations differ in terms of heritability?

• A. Germ-line mutations occur in somatic tissues and are not heritable.
• B. Germ-line mutations occur in sperm, eggs, and their progenitor cells and are heritable.
• C. Somatic mutations are inherited by offspring.
• D. Somatic mutations occur in all cells and are always lethal.

Answer: (B)

Mutations are heritable only if they occur in the reproductive cell lineage. Germ-line mutations happen in sperm, eggs, or their precursor cells, so the mutation is passed to the zygote and is present in every cell of the offspring. Somatic mutations occur after fertilization in non-reproductive body cells, so they affect only the individual and are not transmitted to offspring. That’s why germ-line mutations are heritable, while somatic mutations are not. For context, a germ-line mutation can underlie inherited cancer predispositions, whereas a somatic mutation might cause a tumor in one person but wouldn’t be found in their children. The other statements misstate where germ-line mutations occur or the inheritance pattern of somatic mutations.