A nonsense mutation is a mutation in which an amino acid–specifying codon is changed into a termination codon or stop codon. A stop codon is a codon that does not code for any amino acid and serves to terminate the process of protein synthesis as ribosomes encounter it on the mRNA.
There are three stop codons: UAA, UAG, UGA. A nonsense mutation introduces a stop codon in place of an amino acid encoding codon. It results in the formation of truncated protein which is shorter than the normal protein. Truncated proteins are mostly nonfunctional.
