## **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 is crucial for genetic counseling and testing. Chromosomal location of genes can be critical in understanding genetic disorders.

## **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 17q21. This gene plays a significant role in repairing damaged DNA and thereby acts as a tumor suppressor. Mutations in this gene can lead to an increased risk of breast and ovarian cancers.

## **Why Each Wrong Option is Incorrect**
- **Option A:** Chromosome 12 is not associated with the BRCA1 gene. While chromosome 12 does carry several important genes, BRCA1 is not one of them.
- **Option B:** Chromosome 13 is known for carrying the RB1 gene, which is associated with retinoblastoma, not the BRCA1 gene.
- **Option D:** Chromosome 22 is associated with several conditions, including 22q11.2 deletion syndrome, but it is not the location of the BRCA1 gene.

## **Clinical Pearl / High-Yield Fact**
A crucial clinical pearl is that individuals with a family history of breast and ovarian cancers should undergo genetic testing for BRCA1 and BRCA2 mutations. The BRCA1 gene is particularly significant because mutations in this gene can increase the risk of breast cancer by up to 72% and ovarian cancer by up to 44% by age 80.

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