This type of mutation is not a major
change in a DNA sequence. But they usually occur at a key position within the gene. For example, a single point mutation in the protein coding region of a gene may have a deleterious effect on the creation of that protein.

The word spelling analogy may give a feel for this change. A single change in a letter in some words may change the word into something that is not recognized. For example , if "butler" is change to "butter", the meaning of that word is entirely different, even though only a single letter, l to t, has been modified.