Which type of mutation can result in abnormal retention of intron or exclusion of exons?
A. promoter mutation
B. polyadenylation mutation
C. replication mutation
D. splice site mutation
The correct answer and explanation is:
The correct answer is D. splice site mutation.
A splice site mutation refers to changes that occur at the sequences in the DNA that mark the borders of introns and exons. In the process of RNA splicing, introns (non-coding regions) are typically removed from the precursor mRNA (pre-mRNA), and exons (coding regions) are joined together to form the mature mRNA. This process is critical for the accurate expression of genes.
When a splice site mutation occurs, it can disrupt the normal splicing process, leading to two potential outcomes:
- Abnormal retention of introns: If the mutation occurs at a splice site, it can prevent the introns from being properly removed. As a result, the mature mRNA retains these non-coding regions, which can lead to incorrect or dysfunctional protein production.
- Exclusion of exons: Conversely, a mutation at a splice site can lead to the exclusion of essential exons. This can cause parts of the protein to be missing or incorrectly translated, which may impair its function.
These types of mutations are often associated with various genetic disorders. For example, mutations in splice sites have been implicated in diseases like thalassemia and cystic fibrosis, where the improper splicing of genes leads to defective or absent proteins that disrupt normal biological functions.
In contrast, the other types of mutations listed in the options are not typically associated with splicing abnormalities:
- A. Promoter mutation affects the binding of RNA polymerase and thus the initiation of transcription.
- B. Polyadenylation mutation affects the process by which a poly-A tail is added to the mRNA, which is important for mRNA stability and translation but does not directly influence splicing.
- C. Replication mutation refers to errors that occur during DNA replication and typically affect the DNA sequence, not splicing.
Splice site mutations are therefore a primary cause of abnormal mRNA processing, including intron retention or exon exclusion.