Since every letter in a gene is part of a word in the recipe book, it’s important that every letter is in the correct place. A mutation changes the order of the letters in the DNA sequence.
This is important as it can change the protein that is made. If we changed the C in the word CAT to a T, the sentence: “the cat sat on the mat” wouldn’t make much sense any more – TAT is still a word, but it’s not the right word for this sentence. In much the same way if we change one of the nucleotides in a codon – the word is altered and we’ll get the wrong amino acid being added to the protein. Or, if the word gets altered to the special stop codon, the protein will stop being made and be too short. This shortening is called a truncation.
There are two main ways that DNA may be mutated.