**Core Concept**
The BRCA-1 gene is a tumor suppressor gene that plays a crucial role in maintaining genomic stability, particularly in the repair of DNA double-strand breaks. It is located on the long arm (q) of chromosome 17.

**Why the Correct Answer is Right**
The correct answer is D. 17q 21 because the BRCA-1 gene is situated on the long arm (q) of chromosome 17, at the q21 band. This location is critical for its function in repairing DNA damage and preventing the development of breast and ovarian cancers. The BRCA-1 gene encodes a protein that interacts with other proteins, such as BRCA-2, to form a complex that recognizes and repairs DNA double-strand breaks.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the BRCA-1 gene is not located on the short arm (p) of chromosome 13. Chromosome 13 is associated with other genetic disorders, such as retinoblastoma.
**Option B:** This option is incorrect because the BRCA-1 gene is not located on the long arm (q) of chromosome 13. Chromosome 13 is not directly associated with the BRCA-1 gene.
**Option C:** This option is incorrect because the BRCA-1 gene is not located on the short arm (p) of chromosome 17. The correct location is on the long arm (q) of chromosome 17.

**Clinical Pearl / High-Yield Fact**
The BRCA-1 gene mutation is a significant risk factor for breast and ovarian cancers. Patients with a family history of these cancers should be screened for BRCA-1 mutations, and those who test positive should consider prophylactic mastectomy and salpingo-oophorectomy.

**✓ Correct Answer: D. 17q 21**