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Question #45836
The Question
A phenotypically normal couple has a child with a rare autosomal dominant disorder. Pedigree analysis confirms no history of this disorder in either parent's extended family. Genomic analysis of the father's germinal epithelium reveals a localized mutation in the replication machinery, causing it to fail at excising incorrectly paired nucleotides immediately after their addition during S-phase. Which of the following correctly identifies the compromised enzymatic domain and the genetic phenomenon observed in the pedigree?
Options
- A.
5' → 3' exonuclease domain of DNA-dependent DNA polymerase; Autosomal recessive carrier unmasking
- B.
3' → 5' exonuclease domain of DNA-dependent DNA polymerase; De novo germline mutation
- C.
3' → 5' exonuclease domain of DNA-dependent DNA polymerase; De novo somatic mutation
- D.
5' → 3' polymerase domain of DNA-dependent DNA polymerase; Autosomal recessive carrier unmasking
Check Your Answer
Correct Answer
Step-by-Step Solution
Explanation
How the Examiner Thinks
Regulatory_Failure
Understand how NOT, EXCEPT, and logical constraints are used to manipulate exam results.
Concepts Behind This Question
DNA Polymerase Directionality|Okazaki Fragment Logic|Pedigree Analysis Traps
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: This question tests two distinct high-yield concepts.
First, students must differentiate the directionality of DNA polymerase exonuclease activities (3' → 5' for proofreading vs. 5' → 3' for primer removal).
Second, it exploits a common pedigree misconception: students reflexively associate 'unaffected parents with an affected child' as autosomal recessive inheritance, ignoring the explicit 'autosomal dominant' constraint which necessitates identifying a de novo germline mutation.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Principles of Inheritance and Variation - Class 12 |
| Concept | Pedigree Analysis Traps |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |