This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Disease of Infancy & Childhood, Subject name: Pathology
In cystic fibrosis mutation occurs at? 
Select and explain. 
A. One gene, B. Two gene, C. Three gene, D. Four gene
A: One gene
Answer: A: One gene 
Explanation: Ans. (a) One gene(Ref: Robbins 9th/pg 466-470)Cystic Fibrosisis an Autosomal recessive disease, caused by mutation in Cystic Fibrosis Transmembrane conductance Regulator (CFTR) gene on chr7q31.2, which leads to abnormal function of ion transport channel.