What kinds of mutations are there?
There are almost as many ways to change DNA as you can imagine. Individual rungs of the DNA ladder can be replaced by other rungs. This is called a substitution mutation, and is generally the most common, but that does not mean it is the only thing that occurs. Rungs can be deleted, or inserted—one at a time, or in bigger chunks. Individual rungs or whole sections of the DNA ladder can be duplicated. Duplications of DNA are thought to be a major way that new genes are created, for instance. The copy of a gene, if it gets mutated further, can begin to take on new functions.
