A change in the sequence of nucleotides is called a mutation. There are many different kinds of mutations, such as insertions, deletions, and substitutions. If a single nucleotide is inserted or deleted, then it may have the effect of changing more than a single amino acid. If there is a substitution then may be only one amino acid is changed or there is no change at all, if the nucleotide that is changed is in the third position of a codon, since most amino acids are coded by multiple codons, differing only in the third position.