A scientist makes three artificial mRNA strands:
(x) 5' AAAUUUAAAUUUAAAUUUAAAUUUAAA 3'
(y) 5' UUUCCCUUUCCCUUUCCCUUUCCCUUU 3'
(z) 5' AUAUAUAUAUAUAUAUAUAUAUAUAU 3'
When he analyzes the polypeptides produced, he finds that:
x produces a polypeptide that is 50% phenylalanine and 50%lysine.
y produces a polypeptide that is 50% phenylalanine and 50% proline.
z produces a polypeptide that is 50% isoleucine and 50% tyrosine.
Based on these results only, the best conclusion to make is that
AAA codes for lysine