A mutation changes a DNA sequence. Copying errors and DNA damage can lead to mutations if not repaired. UV radiation and some chemicals, including chemicals in tobacco smoke, can damage DNA. Mutation is not directed toward what an organism needs. Many changes have no detectable effect; effects depend on the sequence and context. Safety: No biological samples or mutation experiments; never look at the Sun. Stop: Stop at paper DNA. Do not expose anything to UV, smoke, radiation or chemicals.

Materials: Paper; Pencil 1. Copy a short illustrative DNA sequence: A C G T A C. Make a second version A C A T A C. Circle the changed position and name the change: G replaced by A. These letters are not a real gene and do not specify an actual trait. 2. Make cause cards: copying mistake; UV radiation; certain chemicals in smoke. Make effect cards: no detectable effect; reduced reproduction; increased reproduction in a particular environment. Draw possible, not guaranteed, links from causes to effects. 3. Use these explicitly fictional outcome cards: change P has no measured effect; Q reduces seed production; R helps a plant reproduce in salty soil but not in ordinary soil. Sort neutral, harmful and beneficial relative to the stated environment. Explain why the letters alone did not reveal these outcomes. 4. Write that mutations create new sequence variants, while recombination reshuffles existing ones. Add: in sexually reproducing animals, a change must enter an egg or sperm lineage to be passed to offspring; a skin-cell change is not automatically inherited. Explain how a helpful inherited variant can become more common through reproduction. Done: Keep the sequence comparison, cause/effect sort and inheritance statement. Proof: Keep both sequences and outcome cards. Note help locating the changed base or explaining inheritance. Stop: Stop at paper DNA. Do not expose anything to UV, smoke, radiation or chemicals.