The Question is from neet-botany molecular-basis-of-inheritance , and it was created by the author Mr. NARESH KUMAR K

Question

A mutation in a eukaryotic gene results in the production of a truncated protein lacking its C-terminal region.  Analysis reveals a mutation within an intron of the gene.  Which of the following is the MOST likely explanation?

Mr. NARESH KUMAR K · Accepted Answer

## CORE INFORMATION
✓ **Answer**: A
## CONCEPT FRAMEWORK
 **Primary Concept**: Eukaryotic gene expression and splicing
 **Related Topics**: Introns, exons, splicing enhancers, spliceosomes, premature termination codons, polyadenylation
 **Prerequisites**: Understanding of basic molecular biology, including transcription, translation, and RNA processing.
## SOLUTION PATHWAY
**Given Information**:
  * A mutation in a eukaryotic gene's intron.
  * Results in a truncated protein lacking the C-terminal region.
  * The mutation is within an intron, not an exon.
**Method & Steps**:
 1. Consider the role of introns in eukaryotic gene expression. Introns are non-coding sequences within a gene that are removed during RNA processing (splicing).
  Reasoning: The mutation is in an intron, so it directly affects splicing.
  Formula/Rule: None directly applicable, this is a conceptual understanding question.
 2. Analyze the effect of the mutation on the final protein product. A truncated protein suggests that some part of the coding sequence (exon) is missing from the mature mRNA.
  Working: The C-terminal region is missing. This indicates that a portion of the mRNA corresponding to the 3' end of the gene is absent.
  Key Point:  Intron mutations primarily affect splicing, not translation directly.
 3. Evaluate the given options. Option A is the most likely explanation because a mutation in a splicing enhancer sequence could prevent the correct recognition and removal of an intron, leading to exon skipping (inclusion of the intron or exclusion of an exon).
  Result: Option A is the most likely explanation.
  Verification: The other options are less likely because the mutation is in an intron.  A new promoter in an intron would likely lead to an additional transcript, not a truncated protein.  A mutation in the polyadenylation signal would affect mRNA termination, but not necessarily result in a truncated protein. A premature stop codon within the intron would not be translated.
 ## OPTION ANALYSIS
A ✓: The mutation disrupted a splicing enhancer sequence, leading to exon skipping. This explains the truncated protein.  The splicing machinery fails to remove the affected exon, or incorrectly joins exons, resulting in a truncated protein.
B :x: The mutation created a new promoter within the intron. This would likely lead to transcription of the intron, resulting in a longer mRNA, not a shorter one.
C :x: The mutation disrupted the polyadenylation signal, preventing proper termination.  This would affect the 3' end of the mRNA but wouldn't necessarily result in a truncated protein. The protein might be full length but unstable.
D :x: The mutation created a premature stop codon within the intron. Introns are not translated into proteins, therefore a premature stop codon within an intron would not be expressed.
 ## LEARNING AIDS
 **Common Mistakes**:
  1.Assuming the mutation directly affects the coding sequence: The key is understanding that intron mutations primarily affect splicing.
  2.Overlooking the role of splicing enhancers: Splicing enhancers are crucial for proper spliceosome assembly and function.
 **Quick Tips**:
  1.Focus on the effect of the mutation on splicing and the resulting mRNA.
  2.Remember that introns are removed during RNA processing.

Mr. NARESH KUMAR K · Answer

The correct Option is "The mutation disrupted a splicing enhancer sequence, leading to exon skipping."

Mr. NARESH KUMAR K · Answer

The mutation created a new promoter within the intron.

Mr. NARESH KUMAR K · Answer

The mutation disrupted the polyadenylation signal, preventing proper termination.

Mr. NARESH KUMAR K · Answer

The mutation created a premature stop codon within the intron.

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