A change in the sequence of DNA is called a gene mutation.This change will be copied to an mRNA strand and translated into a protein.This could lead to a different sequence of amino acids and this may affect the secondary, tertiary and quaternary structures of the protein leading to a protein that functions differently or does not function at all.If the change in the amino acid results in a codon being changed into a stop codon then it is unlikely the protein would function as the polypeptide would be truncated.Gene mutations occur spontaneously during DNA replication where the wrong nucleotide could be incorporated or a nucleotide could be omitted.