Linked from
The 15 pages that link to Codon, each with the reason it gives.
CysteineRelated: The UGU and UGC codons specify cysteine during protein synthesis.
LysineRelated: The codons AAA and AAG specify lysine during translation.
RNA editingRelated: Editing within a coding region can change codons and the resulting protein.
ArginineRelated: Six codons in the standard genetic code specify arginine.