This is generally what the public thinks mutations are.
Geneticists recognize a different type of mutation.
Most of these affect a single character such as a loss of melanin in cells leading to albinism or a loss of a tiny protein that pins muscle bundles to the cell membrane resulting in Duchenne muscular dystrophy. Also, unlike public belief, most mutations don't show up in the individual allegedly mutated by exposure to some physical or chemical agent nor even among the children of the exposed individual. The reason for this absence has to do with our biparental inheritance. Most newly induced mutations result in the loss of a function. Most of those functions can be done by either of the two genes each parent contributes.