Gene for retinoblastoma is found on which chromosome

**Core Concept**
The retinoblastoma gene (RB1) is a tumor suppressor gene that plays a crucial role in regulating cell growth and division. Alterations in this gene can lead to the development of retinoblastoma, a malignant tumor of the retina.

**Why the Correct Answer is Right**
The RB1 gene is located on the long arm of chromosome 13 (13q14), and mutations in this gene can result in the loss of its tumor suppressor function. This leads to uncontrolled cell growth and tumor formation. The RB1 gene encodes a protein that binds to E2F transcription factors, preventing them from initiating the cell cycle. Mutations in RB1 can disrupt this interaction, allowing cells to proliferate uncontrollably.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as the RB1 gene is not located on chromosome 1.
**Option B:** This option is incorrect as the RB1 gene is not located on chromosome 9.
**Option C:** This option is incorrect as the RB1 gene is not located on chromosome 21.
**Option D:** This option is incorrect as the RB1 gene is not located on chromosome 18.

**Clinical Pearl / High-Yield Fact**
Retinoblastoma is a rare but aggressive form of cancer that primarily affects children under the age of 5. Early detection and treatment are critical for improving outcomes.

**Correct Answer:** D.