Final answer:
Point mutations, specifically substitutions, typically cause the most significant changes.
Step-by-step explanation:
Point mutations are single base pair changes in DNA that can have significant effects at the protein level. The most common type of point mutation is a substitution, where one base is replaced by another. Transition substitution refers to a purine or pyrimidine being replaced by a base of the same kind, while transversion substitution refers to a purine being replaced by a pyrimidine, or vice versa.