2-aminopurine is the analog of adanine but sometimes pairs with cytosine. The incorporation of a base analog will to a base pair substitution in that appears in daughter cells in a later generation. Exposure to direct UV light induces covalent linking between adjacent thymine nucleotides on a DNA strand forming a thymine dimer. These dimers cause the strand to buckle, disrupting normal base pairing. This prevents proper replication and transcription.
Bacteria have enzymes to fix the damage created by UV light.
An enzyme cuts the DNA at two point and removes the damaged portion. DNA polymerase synthesizes a new DNA segment using the healthly strand as a template. DNA ligase joins the new fragment to the old strand. Mutation Rate Mutations are random events and there is no way of knowing when a mutation will occur. Genes do, however mutate spontaneously at a characteristic rate, making it possible to assign probabilities to certain mutation events.