**Core Concept**
Cystic fibrosis (CF) is a genetic disorder caused by mutations in the CF transmembrane conductance regulator (CFTR) gene. This gene is responsible for encoding a protein that functions as a chloride channel in epithelial cells, playing a crucial role in maintaining proper fluid balance and electrolyte transport across cell membranes.

**Why the Correct Answer is Right**
The CFTR gene is located on the long arm of chromosome 7 (7q31.2) in humans. This specific location is significant because it affects the expression and function of the CFTR protein, leading to the characteristic symptoms of cystic fibrosis, such as respiratory complications and digestive issues. The mutation in the CFTR gene disrupts the normal functioning of the chloride channel, resulting in abnormal chloride transport and subsequent dehydration of airway secretions.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because chromosome 1 is not associated with cystic fibrosis. Chromosome 1 contains genes involved in various other diseases, but not CF.
* **Option B:** This option is incorrect because chromosome 5 is not linked to cystic fibrosis. Chromosome 5 contains genes related to other conditions, but not CF.
* **Option D:** This option is incorrect because chromosome 19 is not associated with cystic fibrosis. Chromosome 19 contains genes involved in various other diseases, but not CF.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that cystic fibrosis is an autosomal recessive disorder, meaning that individuals must inherit two copies of the mutated gene (one from each parent) to express the disease. This genetic background is crucial for diagnosis and genetic counseling.

**Correct Answer: C. 7**