**Core Concept**
Tumor suppressor genes are genes that regulate cell growth and division by preventing the uncontrolled proliferation of cells, which can lead to cancer. These genes function by preventing mutations in oncogenes or by repairing DNA damage.

**Why the Correct Answer is Right**
The retinoblastoma (Rb) gene is a classic example of a tumor suppressor gene. It regulates cell cycle progression by inhibiting the activity of the E2F family of transcription factors, which are involved in the transition from the G1 to the S phase of the cell cycle. When the Rb gene is mutated or inactivated, it allows for uncontrolled cell growth and tumor formation. The Rb gene is particularly significant because its mutation is associated with retinoblastoma, a type of eye cancer that primarily affects children.

**Why Each Wrong Option is Incorrect**
* **Option A:** The Myc gene is an oncogene, which means it promotes cell growth and proliferation. Its overexpression is associated with various types of cancer, but it is not a tumor suppressor gene.
* **Option B:** The Fos gene is also an oncogene that is involved in cell growth and differentiation. It is a member of the AP-1 transcription factor complex and plays a role in the regulation of genes involved in cell proliferation and survival.
* **Option C:** The Ras gene is an oncogene that is involved in signaling pathways that regulate cell growth and differentiation. Mutations in the Ras gene are associated with various types of cancer, but it is not a tumor suppressor gene.

**Clinical Pearl / High-Yield Fact**
Tumor suppressor genes like Rb are critical for preventing cancer, and their inactivation is a key step in the development of many types of cancer. Understanding the role of tumor suppressor genes is essential for the development of targeted cancer therapies.

**✓ Correct Answer:** D. Rb