The vertebrate mitochondrial DNA (mtDNA) genetic code

    Differences between the vertebrate mtDNA code and the "Universal" code are indicated in red. Note that AUA and AUG (AUR) are both Met codons, UGA codes for Trp rather than being a Stop codon such that Trp is now two-fold degenerate (UGR), and AGA and AGG (AGR) codons are read as Stops instead of Arg. The mtDNA code thus has four Stops.There are currently 27 alternative codes to the "Universal" code, in various evolutionary lineages.