Final answer:
For mutations to have an evolutionary effect, they must occur in gametes and be passed on to offspring. Germline mutations are important since they can be transmitted to offspring, while somatic mutations cannot. Mutations can have different effects on an organism's phenotype, and genetic diversity resulting from sexual reproduction also contributes to evolution.
Step-by-step explanation:
To have an evolutionary effect, mutations must occur in the gametes (egg, sperm) and be passed on to offspring. Germline mutations occur in gametes and are especially significant because they can be transmitted to offspring, while somatic mutations occur in other cells of the body and cannot be passed on to offspring. Mutations can have various effects on an organism's phenotype, from small to large. Sexual reproduction and crossing over in meiosis also contribute to genetic diversity, which is essential for evolution.