Biology I / The Origin of Life and the RNA World
Practice question · Numerical answer

A hypothetical genetic code uses 4 bases and codons of length 2. How many distinct codons does it have?

Hints
  1. Each position can hold any of the 4 bases, independently.
  2. Compute 4 to the power 2.
Show the answer

16

Why

42=164^2 = 16 distinct codons, not enough for 20 amino acids, which is precisely why life uses triplets. Doublets would have forced a smaller amino-acid alphabet.

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