## **Core Concept**
The BRCA-1 gene is a tumor suppressor gene, and mutations in this gene significantly increase the risk of breast and ovarian cancers. The location of the BRCA-1 gene is crucial for genetic counseling and testing.

## **Why the Correct Answer is Right**
The BRCA-1 gene is located on the long arm of chromosome 17, specifically at position 21 (17q21). This gene plays a critical role in repairing damaged DNA and thereby maintaining the genetic stability of a cell. When either of the BRCA-1 or BRCA-2 genes is mutated, DNA damage may not be properly repaired, leading to increased genetic alterations that can result in cancer.

## **Why Each Wrong Option is Incorrect**
- **Option A:** Chromosome 13 is associated with other conditions, such as retinoblastoma (RB1 gene on 13q14), but not with BRCA-1.
- **Option B:** While chromosome 19 is involved in various genetic conditions, it is not the location of the BRCA-1 gene.
- **Option D:** Chromosome 22 is associated with conditions like 22q11.2 deletion syndrome but is not the site of the BRCA-1 gene.

## **Clinical Pearl / High-Yield Fact**
A crucial point to remember is that individuals with a family history of breast and ovarian cancers should undergo genetic testing for BRCA-1 and BRCA-2 mutations. The presence of a mutation significantly influences preventive and therapeutic strategies, including prophylactic surgery and enhanced screening.

## **Correct Answer:** C. 17q21.