<prompt> Stop codons are all except -UAGUAAUGAUGG  <response>: Ans. is d i.e., UGG Out of 64 codons, 3 are stop codons. The three stop codons are UGA, UAG, UAA. Exception is mitochondrial DNA - in mitochondria, UGA is not a stop codon. It codes for Tryptophan. Instead AGA and AGG act as stop codons in mitochondrial DNA. 61 codons code for 21 aminoacids. Hence more than one codon code for a single aminoacid. This is called as degeneracy of Codon. Exceptions are Methionine and Tryptophan. Both Methionine and Tryptophan are coded by only one codon each Methionine is coded by AUG and Tryptophan is coded by UGG Hence UGG is not a stop codon. It codes for Tryptophan 