This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General pathology, Subject name: Pathology
Cystic fibrosis is due to mutation long arm of chromosome? 
Select and explain. 
A. 7, B. 9, C. 11, D. 21
A: 7
Answer: A: 7 
Explanation: Robbins and Cotran pathologic basis of disease South Asia edition the primary defect in cystic fibrosiscresults from abnormal function of an epithelial chloride channel protein encoded by the cystic fibrosis trans membrane conductance regulator gene (CFTR) on chromosome 7q 31.2..