**Core Concept**
The BRCA1 gene is a tumor suppressor gene that plays a crucial role in maintaining genome stability by facilitating DNA repair through homologous recombination. Mutations in the BRCA1 gene are associated with an increased risk of breast and ovarian cancers.

**Why the Correct Answer is Right**
The BRCA1 gene is located on the long arm of chromosome 17, specifically at the 21q21 locus. This location is critical for its function, as it allows for proper expression and regulation of the gene. The BRCA1 protein interacts with other proteins, including BRCA2, to facilitate DNA repair and prevent genetic instability.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specify the correct chromosome. The BRCA1 gene is not located on chromosome 1.
**Option B:** This option is incorrect because it is a different chromosome altogether. The BRCA1 gene is not located on chromosome 5.
**Option C:** This option is incorrect because it specifies a different arm and locus. The BRCA1 gene is located on the long arm of chromosome 17, not the short arm.

**Clinical Pearl / High-Yield Fact**
The BRCA1 gene is just one of several genes associated with an increased risk of breast and ovarian cancers. Other genes, such as BRCA2 and TP53, also play critical roles in maintaining genome stability and preventing cancer.

**Correct Answer:** D. 17