AAAS: THE LIVING ENVIRONMENT: HEREDITY - Gene mutations can be caused by such things as radiation and chemicals
Gene mutations can be caused by such things as radiation and chemicals. When they occur in sex cells, the mutations can be passed on to offspring; if they occur in other cells, they can be passed on to descendant cells only. The experiences an organism has during its lifetime can affect its offspring only if the genes in its own sex cells are changed by the experience.