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Question #47751
The Question
During the diagnostic PCR amplification of a target gene, a technician observes the expected DNA band along with several unexpected, faster-migrating discrete bands on an Ethidium Bromide-stained agarose gel. Assuming the primers are highly specific and no DNA contamination occurred, what is the most likely molecular cause of these smaller fragments, and what diagnostic error might they induce?
Options
- A.
Premature dissociation of Taq polymerase due to suboptimal extension conditions; misidentification as a micro-deletion mutation.
- B.
Incomplete denaturation of the template DNA at 94°C; misidentification as a gene duplication event.
- C.
Excessive intercalation of Ethidium Bromide causing DNA fragmentation during electrophoresis; misidentification as a nonsense mutation.
- D.
Use of an excessively high annealing temperature causing non-specific amplification; misidentification as an allelic variant.
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
Heat Shock Thermal Gradient|Competent Cell Preparation|CaCl2 Treatment
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Distinguishing between biological mutations (true micro-deletions) and procedural PCR artifacts (incomplete extension).
The trap relies on the student's understanding of PCR stringency and enzyme processivity.
Option D is a classic 'Half-Truth' trap: while annealing temperature issues do cause extra bands, a HIGH temperature increases specificity (fewer bands), whereas a LOW temperature decreases specificity (more bands).
Students who memorize 'temperature = extra bands' without understanding the thermodynamic directionality will incorrectly choose D.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Biotechnology : Principles and Processes - Class 12 |
| Concept | Heat Shock Thermal Gradient |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |