What is the probability that a single point mutation occurri

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

Solution

ATA, ATC and ATT codes for isoleucine and ATG codes for methionine

TTA, CTA codes for leucine and GTA codes for valine

AAA codes for lysine, AGA codes for arginine and ACA codes for threonine.

Thus, 7 point mutations out of 9 possible point mutations will change the amino acid code by ATA.

Thus, the probability that a single point mutation occurring in the codon ATA will cause an amino acid change is = 7/9 = 0.77