**Core Concept:** Cystic Fibrosis (CF) is an autosomal recessive genetic disorder caused by mutations in the CFTR gene, which encodes the cystic fibrosis transmembrane conductance regulator (CFTR) protein. The CFTR protein is involved in the regulation of chloride ion transport in epithelial cells, particularly in the lungs and pancreas.

**Why the Correct Answer is Right:** The correct answer is **D** chromosome 7 because the mutation in the CFTR gene, which causes cystic fibrosis, is located on this chromosome. The CFTR gene is responsible for producing the CFTR protein, which regulates chloride ion transport in epithelial cells. When the CFTR gene is mutated, it leads to the production of a faulty protein, resulting in impaired chloride ion transport and other downstream effects in organs like the lungs and pancreas.

**Why Each Wrong Option is Incorrect:** Option **A** (chromosome 17) and option **B** (chromosome 1) are incorrect because the CFTR gene is not located on these chromosomes. Option **C** (chromosome 12) is incorrect because the gene causing the Marfan syndrome, which is not related to cystic fibrosis, is located on chromosome 15, not 7.

**Clinical Pearl:** Understanding the genetic basis of cystic fibrosis is crucial for healthcare professionals, as it helps in genetic counseling, prenatal diagnosis, and identifying potential carriers. Cystic fibrosis can be inherited through different combinations of parental alleles, including homozygous (two mutated copies) or heterozygous (one mutated and one normal copy) states.

**Correct Answer:** **D** chromosome 7