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a mutation that results in the formation of the codon UAG, which results in the premature termination of a polypeptide chain. Compare: suppressor mutation.
Etymology: Ar, anbar, ambergris
a genetic alteration that causes the synthesis of a polypeptide chain to terminate prematurely because the triplet of nucleotides that normally codes for the next amino acid in the chain becomes uracil-adenine-guanine, the sequence that signals the end of the chain. This is one of three possible nonsense mutations.See also ochre mutation,opal mutation.