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

Question

If DNA replication were conservative, what density distribution would be observed after **two** generations in $^{14}$N medium, following growth in $^{15}$N medium?

Mr. NARESH KUMAR K · Accepted Answer

## CORE INFORMATION
✓ **Answer**: [Option B]
## CONCEPT FRAMEWORK
	**Primary Concept**: DNA replication mechanism
	**Related Topics**: Isotope labeling, density gradient centrifugation
	**Prerequisites**: Understanding of the semi-conservative model of DNA replication
## SOLUTION PATHWAY
**Given Information**:
		- Initial growth in $^{15}$N medium (heavy nitrogen)
		- Transition to $^{14}$N medium (light nitrogen)
		- Conservative replication model
**Method & Steps**:
	1. **First generation after transfer to $^{14}$N**:
		Reasoning: In conservative replication, the original double helix remains intact, and an entirely new double helix is formed.
		Formula/Rule: N/A (conceptual understanding)
		- Result: After one generation, there would be one heavy molecule (from $^{15}$N) and one light molecule (from $^{14}$N).
	2. **Second generation**:
		Working: The heavy double helix remains intact, and the light DNA strands replicate to form new light strands.
		Key Point: The original heavy DNA does not contribute to the new strands.
		- Result: After the second generation, we have:
			- One molecule of $^{15}$N (heavy) and two molecules of $^{14}$N (light).
	3. **Final density distribution**:
		Result: Therefore, after two generations, there would be two distinct bands: one heavy and one light.
		Verification: This is consistent with the expected outcomes of conservative replication.
## OPTION ANALYSIS
[A] :x: One intermediate band - This is incorrect as conservative replication does not produce intermediate density.
[B] ✓: Two distinct bands: one heavy and one light - This is the correct outcome of conservative replication after two generations.
[C] :x: One light band - This is incorrect as we still retain the heavy DNA.
[D] :x: A mixture of heavy, intermediate, and light bands - This is incorrect because there are no intermediate bands in conservative replication.
## LEARNING AIDS
	**Common Mistakes**:
		1. Confusing conservative and semi-conservative replication: Remember that in conservative replication, the original strands remain intact.
		2. Incorrectly predicting the density bands: Visualize the outcomes based on the initial and subsequent growth mediums.
	**Quick Tips**:
		1. Use diagrams to visualize DNA replication processes and density outcomes.
		2. Remember that conservative replication keeps the original strands intact while producing entirely new strands.

Mr. NARESH KUMAR K · Answer

One intermediate band

Mr. NARESH KUMAR K · Answer

The correct Option is "Two distinct bands: one heavy and one light"

Mr. NARESH KUMAR K · Answer

One light band

Mr. NARESH KUMAR K · Answer

A mixture of heavy, intermediate, and light bands

NEET Botany Molecular Basis of Inheritance Replication MCQs

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