Which feature best distinguishes proto-oncogenes from tumor suppressor genes in terms of their role in carcinogenesis?

Explanation

## Distinguishing Proto-oncogenes from Tumor Suppressor Genes ### Genetic Basis of Activation **Key Point:** Proto-oncogenes follow a **dominant** inheritance pattern in carcinogenesis, whereas tumor suppressor genes follow a **recessive** pattern. ### Mechanistic Differences | Feature | Proto-oncogenes | Tumor Suppressor Genes | |---------|-----------------|----------------------| | **Alleles required** | One mutated allele (monoallelic) | Both alleles inactivated (biallelic) | | **Type of mutation** | Gain-of-function | Loss-of-function | | **Normal function** | Promote cell growth, proliferation | Inhibit growth, enforce checkpoints | | **Activation mechanism** | Point mutations, translocations, amplification | Deletion, mutation, methylation | | **Inheritance pattern** | Dominant (one hit sufficient) | Recessive (two hits needed) | ### Clinical Pearl **High-Yield:** The **two-hit hypothesis** (Knudson) applies specifically to tumor suppressor genes (e.g., RB, p53, BRCA1). A single activating mutation in a proto-oncogene (e.g., RAS, MYC) is sufficient to drive transformation in the appropriate cellular context. ### Examples - **Proto-oncogenes:** RAS (point mutations), MYC (translocations in lymphoma), HER2 (amplification in breast cancer) - **Tumor suppressors:** p53 (Li-Fraumeni syndrome), RB (retinoblastoma), BRCA1/BRCA2 (hereditary breast/ovarian cancer) **Mnemonic:** **POTS** = Proto-Oncogenes = One allele Transformed (dominant); **TSG** = Tumor Suppressors = Gene (recessive, needs both alleles gone)