## **Core Concept**
The BRCA1 gene is a tumor suppressor gene, and its mutations are associated with an increased risk of breast and ovarian cancers. The location of the BRCA1 gene on a specific chromosome is crucial for genetic counseling and testing.

## **Why the Correct Answer is Right**
The BRCA1 gene is located on the long arm (q) of chromosome 17, specifically at position 21. The correct chromosomal location is essential for understanding the genetic basis of breast and ovarian cancer susceptibility. The BRCA1 protein plays a critical role in maintaining genomic stability through its involvement in DNA repair mechanisms, particularly in the repair of double-strand breaks through homologous recombination.

## **Why Each Wrong Option is Incorrect**
- **Option A:** Chromosome 13 is associated with other genetic conditions, such as retinoblastoma (RB1 gene on 13q14), but not with the BRCA1 gene.
- **Option B:** Chromosome 11 has several important genes related to various diseases, but the BRCA1 gene is not located here.
- **Option D:** Chromosome 22 is known for its involvement in certain conditions like 22q11.2 deletion syndrome, but it does not carry the BRCA1 gene.

## **Clinical Pearl / High-Yield Fact**
A crucial clinical pearl is that mutations in the BRCA1 and BRCA2 genes significantly increase the risk of breast and ovarian cancers. Women with a family history of these cancers should undergo genetic testing for BRCA1 and BRCA2 mutations. The identification of a BRCA1 or BRCA2 mutation can guide preventive measures, such as mastectomy or salpingo-oophorectomy, and screening strategies.

## **Correct Answer:** . 17.