Several types of mutation are identified and described in the chapter. These include (1) promoter mutation, (2) splice site mutation, (3) missense mutation, (4) frameshift mutation, and 5) nonsense mutation. Match the following mutation descriptions with the type(s) of mutations listed above. More than one mutation type might match a description.

A mutation that produces about 5% of the wild-type amount of an mRNA.

Key Concepts

Promoter Mutation

A promoter mutation occurs in the DNA sequence that regulates the transcription of a gene. This type of mutation can affect the binding of RNA polymerase and transcription factors, potentially leading to reduced levels of mRNA. If the mutation significantly impairs promoter function, it may result in a drastic decrease in mRNA production, such as the 5% of wild-type levels mentioned.

Nonsense Mutation

A nonsense mutation is a type of point mutation that introduces a premature stop codon in the mRNA sequence. This leads to the truncation of the protein, often resulting in a nonfunctional product. If a nonsense mutation occurs early in the coding sequence, it can severely reduce the amount of functional mRNA and protein, potentially aligning with the description of producing only 5% of the wild-type mRNA.

Splice Site Mutation

A splice site mutation affects the regions of pre-mRNA that are necessary for proper splicing, which is the process of removing introns and joining exons. This can lead to the inclusion of intronic sequences or the exclusion of exonic sequences in the final mRNA. Such alterations can disrupt the normal mRNA structure and function, potentially resulting in a significant reduction in the amount of mature mRNA produced.