Somatic Mutations: The DNA Changes That Accumulate in Your Body Over a Lifetime

Somatic mutations are DNA changes occurring in non-reproductive (somatic) cells after fertilization. Unlike germline mutations, they are not passed to offspring — they affect only the cell lineage in which they occur. ## Accumulation Every cell division carries a small probability of replication errors (~1–1.4 mutations per division per genome in humans). Over a lifetime, somatic mutations accumulate — an average human cell acquires roughly 40 mutations per year. Most are in non-coding regions and functionally neutral. ## Cancer Connection When somatic mutations hit critical genes — oncogenes (accelerators) or tumor suppressor genes (brakes) — they can drive uncontrolled cell growth. Cancer typically requires multiple "driver" mutations accumulating in the same cell lineage, which is why cancer risk increases dramatically with age. ## Genetic Mosaicism Somatic mutations mean that no two cells in your body have exactly the same genome — you are a genetic mosaic. This is usually invisible but can manifest as visible patches (e.g., heterochromia, mosaic skin pigmentation) when mutations occur early in development. ## Mycelial Biology In long-lived fungal networks, somatic mutations accumulate across genetically distinct hyphal sectors (sectoring), creating mosaicism within a single mycelial organism — relevant to understanding Mycelial Biology: Identity, Immortality, and Emergent Intelligence.