Question

In cancer, mutations in stimulatory genes (such as in proto-oncogenes) are often dominant, whereas mutations in inhibitory genes (such as tumor-suppressor alleles) are often recessive. Why?

Answer 1

Mutations in proto-oncogenes are often dominant because a single mutated allele can lead to the production of a protein that actively promotes cell division, overriding the normal allele. Tumor suppressor gene mutations are typically recessive, as both alleles must be mutated for the gene to completely lose its function and fail to inhibit cell division.

Step-by-step explanation:

Mutations in Proto-oncogenes and Tumor Suppressor Genes

In the context of cancer development, mutations in stimulatory and inhibitory genes play pivotal roles. Proto-oncogenes, when mutated, can become oncogenes, which function like a malformed accelerator promoting continuous cell division. These mutations are often dominant because a single mutated proto-oncogene allele can produce a constitutively active protein, overriding the function of the unmutated allele and stimulating cell division abnormally.

Contrastingly, tumor suppressor genes are like the braking system, inhibiting unchecked cell division. Mutations here are generally recessive since both alleles need to be affected to lose function entirely. A single remaining functional tumor suppressor gene can still potentially halt inappropriate cell proliferation.

Thus, a dominant mutation in a proto-oncogene is often sufficient to contribute to cancer formation as it pushes the cell towards division. On the other hand, tumor suppressor genes typically require two recessive mutations to lose function and allow unrestricted cell growth, leading to tumorigenesis.