Discuss evidence that the genetic code is almost universal, and cite some exceptions.

Codons that code for particular amino acids are nearly universal across all life. This means that the same codon (3 nucleotide sequence) that codes for aspartic acid or glutamate are the same in a bacteria as in a human being. This has been used to suggest that all life on earth evolved from one ancestral organism. The only exception in some organisms is very slightly such as of a difference of one or two amino acids coded by a particular codon. An example is yeast. In the universal genetic code CUG codes for leucine, however in budding yeast, it codes for serine amino acid.