What is the probability that a single point mutation occurri

What is the probability that a single point mutation occurring in the codon TTT will cause an amino acid change? Assume the universal genetic code and equal likelihood of each possible point mutation.

Solution

TTT codes for Lysine. TTC also codes for lysine.

The probability that will cause aminoacid change is 1/3 * 1/3 * 1/2 = 1/18.