Mutation

A mutation is a change or error in the DNA sequence of an organism. Mutations can range from a single nucleotide change to large segments of a chromosome being altered, and they can occur spontaneously or due to environmental factors like radiation or chemicals.

• Not all mutations are harmful. Many are neutral (no effect on the organism), some are deleterious (cause diseases or dysfunction), and a rare few can be beneficial and provide raw material for evolution.
• Only mutations in germ cells (sperm or eggs) are passed to offspring. Mutations in body (somatic) cells can affect the individual (e.g., causing cancer) but won't be inherited by that person's children.
• Common causes of mutations include DNA copying errors during cell division, exposure to mutagens such as UV light or chemicals, and certain viral insertions. Cells do have DNA repair mechanisms, but if errors escape repair, they become permanent mutations.

• If asked for the ultimate source of genetic variation in populations, the answer is mutation -- it creates new alleles (new genetic variants) that evolution can act upon.
• Questions might test understanding of different mutation types: e.g., point mutation (single base change) vs frameshift (caused by insertion/deletion), or ask which types of mutations can be inherited (germline mutations).
• Be cautious with wording: sometimes students confuse "mutation" with "natural selection." Remember, mutation creates variation randomly; natural selection then sorts that variation (favoring beneficial mutations).