Define tumor-suppressor genes. Why is a mutation in a single copy of a tumor- suppressor gene expected to behave as a recessive gene?

Tumor-suppressor genes are a type of genes that play a critical role in regulating the cell cycle and preventing the formation of tumors. They act as a safety mechanism that controls cell growth and division, ensuring that cells with damaged DNA do not replicate uncontrollably and develop into cancerous tumors. When functioning properly, tumor-suppressor genes produce proteins that inhibit cell division and promote the repair or elimination of damaged cells.

In humans, genes are inherited in pairs, with one copy coming from each parent. They can be dominant or recessive, depending on how they affect an individual's traits. A dominant gene is one that masks the effects of another gene, while a recessive gene shows its effect only when both copies are mutated or non-functional. In other words, an individual must inherit the mutated gene from both parents for the recessive trait to manifest.

A mutation in a single copy of a tumor-suppressor gene is expected to behave as a recessive gene because it usually takes more than one mutation in the gene for it to become non-functional and lead to abnormal cell growth. When one copy of the tumor-suppressor gene is mutated, the other (non-mutated) copy can still produce enough functional protein to regulate the cell cycle and prevent the formation of tumors. Thus, an individual with just one mutated copy of a tumor-suppressor gene would typically not develop cancer, as the normal function of the gene is maintained by the non-mutated copy. In this case, the mutated gene is recessive because its effect is masked by the presence of a functional (dominant) copy of the gene. So, to summarize: 1. Tumor-suppressor genes regulate the cell cycle and prevent tumor formation. 2. Genes are inherited in pairs and can exhibit dominant or recessive inheritance patterns. 3. A mutation in a single copy of a tumor-suppressor gene behaves as a recessive gene because the other non-mutated copy still maintains its normal function and can prevent tumor formation.