This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pathology
Chromosome defective in cystic fibrosis is - 
Select and explain. 
A. Chromosome 5, B. Chromosome X, C. Chromosome 7, D. Chromosome 1
C: Chromosome 7
Answer: C: Chromosome 7 
Explanation: The primary defect in cystic fibrosis results from abnormal function of an epithelial chloride channel protein encoded by the cystic fibrosis transmembrane conductance regulator (cfTR) gene on chromosome band 7q31.2.