Editing Stop codon (section)

=== ''opal'' or ''umber'' mutations ({{mono|UGA}}) ===
The third and last stop codon in the standard genetic code was discovered soon after, and corresponds to the nucleotide triplet "UGA".<ref>{{cite journal |pages=449–50 |doi=10.1038/213449a0 |title=UGA: A Third Nonsense Triplet in the Genetic Code |year=1967 |last1=Brenner |first1=S. |last2=Barnett |first2=L. |last3=Katz |first3=E. R. |last4=Crick |first4=F. H. C. |journal=Nature |volume=213 |issue=5075 |pmid=6032223|bibcode=1967Natur.213..449B |s2cid=4211867 }}</ref>

To continue matching with the theme of colored minerals, the third nonsense codon came to be known as '''"[[opal]]"''', which is a type of silica showing a variety of colors.<ref name="Lewin2011"/> Nonsense mutations that created this premature stop codon were later called opal mutations or [[umber]] mutations.