If the adenine in the 15th position of the sequence is changed to a guanine, the person does not have CF. However, if the thymine in the 14th position is changed to a cytosine the person does have CF. What are some reasons this might occur?

Mutation is a sudden heritable change in the genome of an organism.

Substitution is a form of mutation whereby a base pair is been substitued for by another base pair resulting in a serious damage.

Codon are three alphabeth coding for a particular amino acid.

When substitution occurs in a base pair and the replacement forms a protein that has the same function as the one that was removed there will be no observable in the phenotype. Hence, If the adenine in the 15th position of the sequence is changed to a guanine, the person may not have cystic fibrosis.

But when a particular base pair is substituted for and an entirely new protein or amino acids results with a different functions and structure it could lead to a serious damage or healthy issue. Hence, If the adenine in the 15th position of the sequence is changed to a guanine, the person does have cystic fibrosis.