Q.57 Consider the following pathway controlling time to flowering in wheat:
If batch 𝑃 of wheat seed is vernalized before sowing and batch 𝑄 is not vernalized, then which of the
following statements is most likely to be correct?
(A) 𝑃 will have lower 𝑉𝑅𝑁2 transcript and will flower later than 𝑄
(B) 𝑃 will have lower 𝑉𝑅𝑁2 transcript and will flower earlier than 𝑄
(C) 𝑃 will have higher 𝑉𝑅𝑁2 transcript and will flower later than 𝑄
(D) 𝑃 and 𝑄 will have equal VRN2 transcript and will flower at the same time

Introduction

Flowering time in wheat is tightly regulated by environmental cues, especially cold temperature (vernalization). Vernalization ensures that wheat plants flower only after experiencing prolonged cold, preventing premature flowering before winter. This process is genetically controlled mainly by VRN genes, particularly VRN1 and VRN2.

The given question tests conceptual understanding of how vernalization affects gene expression and flowering time.

Understanding the Given Pathway

From the diagram:

• Cold temperature (vernalization) ⟶ suppresses VRN2

• VRN2 ⟶ represses VRN1

• VRN1 ⟶ promotes flowering

• When VRN1 is inactive ⟶ plant remains in vegetative growth

Key Gene Functions

• VRN2: Floral repressor

• VRN1: Floral promoter

• Vernalization: Reduces VRN2 expression, allowing VRN1 to be expressed

Question Recap

Two batches of wheat seeds are compared:

• Batch P: Vernalized before sowing

• Batch Q: Not vernalized

Which statement is most likely correct?

Correct Answer

✅ Option (B):

P will have lower VRN2 transcript and will flower earlier than Q

Explanation of the Correct Answer

• Vernalization represses VRN2, which normally inhibits flowering.

• Lower VRN2 allows VRN1 expression, triggering flowering.

• Therefore, batch P (vernalized):

  • Has lower VRN2 transcript levels

  • Activates flowering sooner

• Batch Q (non-vernalized):

  • Retains high VRN2 levels

  • Remains longer in vegetative growth

Hence, batch P flowers earlier than batch Q.

Explanation of All Options

Option (A):

❌ P will have lower VRN2 transcript and will flower later than Q

• Although VRN2 is lower in P (correct part),

• Lower VRN2 actually promotes flowering, not delays it

• ❌ Incorrect flowering outcome

Option (B):

✅ P will have lower VRN2 transcript and will flower earlier than Q

• Matches known vernalization biology

• Correct gene regulation and flowering response

• ✔️ Correct answer

Option (C):

❌ P will have higher VRN2 transcript and will flower later than Q

• Vernalization reduces, not increases, VRN2

• ❌ Incorrect gene expression and timing

Option (D):

❌ P and Q will have equal VRN2 transcript and will flower at the same time

• Vernalization causes distinct molecular differences

• ❌ Equal transcript levels are biologically incorrect

Concept Summary for Exams

• Vernalization ⟶ ↓ VRN2 ⟶ ↑ VRN1 ⟶ flowering

• VRN2 = repressor | VRN1 = activator

• Vernalized wheat flowers earlier