What produces a nonsense mutation?

A nonsense mutation is a genetic mutation in a DNA sequence that leads to the appearance of a stop codon where previously there was a codon specifying an amino acid. DNA is a chain of many smaller molecules called nucleotides. During protein formation, DNA (or RNA) nucleotide sequences are read three nucleotides at a time in units called codons, and each codon corresponds to a specific amino acid or stop codon, which is also called nonsense codon because it does not code for an amino acid and instead signals the end of protein synthesis. Therefore, nonsense mutations occur when a premature nonsense or stop codon is introduced in the DNA sequence. When the mutated sequence is translated into a protein, this premature stop codon results in the production of a shortened, and likely nonfunctional, protein.