Cystic Fibrosis Transmembrane Conductance Regulator

[abery]

I'm having some trouble with the following multiple choice question:

16) What is the evidence that the Cystic Fibrosis Transmembrane conductance Regulator (CFTR) gene is defective in individuals with Cystic Fibrosis (apart from the name):

a) The CFTR gene has a phenylalanine codon deletion in CF patients
b) The CFTR gene has a BamHI RFLP in its coding region in CF patients
c) The CFTR gene is tightly linked to the CF phenotype
d) a and b
e) a and c

To me it seems that options a) and c) are both possibilities, as affected individuals have a mutation that removes phenylalanine, and the gene is experimentally linked to the phenotype.

The correct answer is supposedly b. Maybe a and are not evidence?

Any help would be greatly appreciated!

[canalon]

a) but is that phenylalanine essential, or even important? If the deletion is in frame that might not be a massive problem.
c) Everyone does have a version of CFTR! So its presence in case of CF is irrelevant. What would be interesting would be a link between a mutation and the CF phenotype.

so we come to b) I am not sure but there is a TAG in the restriction site, that might be bad if it is in sequence.