This document discusses genetic variation within species and the role of mutations. It defines key terms like species, genes, and genetic variation. Genetic variation arises from factors like independent assortment, crossing over, and mutations during DNA replication or meiosis. Mutations are a permanent change in genetic material and are the only source of new genetic variation. Mutations can occur naturally during DNA copying or be caused by environmental mutagens like radiation, viruses, transposons, or chemicals. Mutations may result in cell death, malfunction, or sometimes provide a selective advantage that improves an organism's chances of survival, especially in a changing environment. Examples of selective advantages are provided for Daphnia and bacteria.