Proto-oncogenes stimulate cells to progress through the cell cycle and begin mitosis. In cells that stop dividing, transcription of proto-oncogenes is inhibited by regulatory molecules. As is typical of all genes, proto-oncogenes contain a regulatory DNA region followed by a coding DNA region that specifies the amino acid sequence of the gene product. Consider two types of mutation in a proto-oncogene, one in the regulatory region that eliminates transcriptional control and the other in the coding region that renders the gene product inactive. Characterize both of these mutant alleles as either gain-of-function or loss-of-function mutations and indicate whether each would be dominant or recessive.

Step by step solution

01

Understand the role of proto-oncogenes in cell cycle and mitosis

Proto-oncogenes are genes that stimulate cells to progress through the cell cycle and begin mitosis. They are necessary for normal cell division. In cells that stop dividing, transcription of proto-oncogenes is inhibited by regulatory molecules.

02

Analyze the first mutation in the regulatory region of the proto-oncogene

The first mutation occurs in the regulatory region of the gene, which eliminates transcriptional control. This means that the gene is not controlled by the regulatory molecules, and it will continue to be transcribed, even in cells that should stop dividing. As a result, the gene product will stimulate cell division continually, which is not the normal function of the proto-oncogene. This mutation is considered a gain-of-function mutation since it causes the gene to have a stronger or different function than it normally has. In this case, the mutated proto-oncogene would be considered dominant, as the different function overrides the normal function of the non-mutated allele.

03

Analyze the second mutation in the coding region of the proto-oncogene

The second mutation occurs in the coding region of the gene, rendering the gene product inactive. In this case, the mutation leads to a non-functional gene product, which means it fails to perform its normal function of stimulating cell division. This mutation is considered a loss-of-function mutation since it results in a gene product with less or no function. Loss-of-function mutations are typically recessive because both copies of the gene need to be mutated to lose the normal function. So, in this case, the mutated proto-oncogene would be considered recessive, as the normal function of the non-mutated allele is still present and sufficient for proper cell division stimulation.

04

Summarize the findings

To summarize, we have characterized the two types of mutations in a proto-oncogene: 1. Mutation in the regulatory region: Gain-of-function mutation and is dominant. 2. Mutation in the coding region: Loss-of-function mutation and is recessive. These conclusions are based on the effect of the mutations on the gene's normal function and the subsequent impact on cell division.

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