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

Question

Nowadays, it is possible to detect the mutated gene causing cancer by allowing a radioactive probe to hybridize its complementary DNA in a clone of cells, followed by detection using autoradiography because:

K SURESH KUMAR · Accepted Answer

## CORE INFORMATION
✓ **Answer**: Option A
## CONCEPT FRAMEWORK
 **Primary Concept**: Molecular Biology techniques for gene detection
 **Related Topics**: DNA hybridization, PCR, autoradiography, cancer genetics
 **Prerequisites**: Understanding of DNA structure, complementary base pairing, radioactive labeling, PCR amplification.
## SOLUTION PATHWAY
**Given Information**:
  A radioactive probe hybridizes to complementary DNA in a clone of cells.
  Detection is done using autoradiography.
  The goal is to detect a mutated gene causing cancer.
**Method & Steps**:
 1. **Understanding the process**: Autoradiography detects the presence of radioactivity.  The radioactive probe only binds to its complementary DNA sequence.  If a mutated gene is present, the probe will bind to it.
  Reasoning: The intensity of the signal on the autoradiogram is directly proportional to the amount of target DNA present.
  Formula/Rule: No specific formula is needed here; it's a conceptual understanding.
 2. **Role of PCR**: To detect a small amount of mutated DNA among a large amount of normal DNA, the mutated DNA needs to be amplified. PCR (Polymerase Chain Reaction) is a technique specifically designed for DNA amplification. 
  Working: PCR exponentially increases the number of copies of a specific DNA sequence, making it detectable by autoradiography.
  Key Point: Without PCR amplification, the amount of mutated DNA might be too low to be detected by autoradiography.
 3. **Final Step**: The radioactive probe hybridizes to the amplified mutated DNA. Autoradiography visualizes this hybridization, revealing the presence and location of the mutated gene.
  Result: Option A is correct because PCR amplification is crucial for detecting the mutated gene.
  Verification:  Options B, C, and D are incorrect.  While DNA extraction (B) is a preliminary step, it's not the reason autoradiography works.  Radioactive probes don't inhibit cell growth (C), and autoradiography doesn't visualize cell growth (D); it visualizes the presence of radioactivity.
 ## OPTION ANALYSIS
[A] ✓:  PCR amplifies the mutated DNA, making it detectable by the radioactive probe and autoradiography.  A high concentration of the target sequence is needed for the signal to be strong enough for detection.
[B] :x: DNA extraction is a necessary preliminary step but not the reason autoradiography is effective in detecting the mutated gene.  The amount of mutated DNA after extraction might still be too low to be detected.
[C] :x: Radioactive probes are designed to bind to complementary DNA, not inhibit cell growth.  Their radioactivity is used for detection, not as a cytotoxic agent.
[D] :x: Autoradiography detects radioactivity, not cell growth.  It visualizes the location of the radioactive probe bound to the DNA.
 ## LEARNING AIDS
 **Common Mistakes**:
  1.Confusing the role of the radioactive probe: Students might think the probe directly affects cell growth or that autoradiography is solely a cell-growth visualization technique.
  [How to avoid]: Focus on the probe's function as a hybridization tool for detecting specific DNA sequences.
  2.Overlooking the need for amplification: Students might assume that a small amount of mutated DNA is enough for detection without amplification.
  [How to avoid]: Understand that PCR is often necessary to increase the amount of target DNA to detectable levels.
 **Quick Tips**:
  1.Remember the key steps: PCR amplification → hybridization → autoradiography.
  2.Think of it like a detective story: The radioactive probe is the clue, PCR is the magnifying glass, and autoradiography is the way to see the clue.

K SURESH KUMAR · Answer

The correct Option is "mutated DNA is amplified using PCR"

K SURESH KUMAR · Answer

mutated DNA is extracted from the cells

K SURESH KUMAR · Answer

radioactive probes inhibit the growth of mutated cells

K SURESH KUMAR · Answer

autoradiography can visualize the growth of mutated cells

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