Q.33 ‘B’ gene of ABCD flower model is made silenced in a plant. Which of the whorl is
absent in the plant.
(A). Sepals
(B). Carpels
(C). Stamens
(D). Petals
Choose the correct answer from the options given below:
1. (B) and (D) only.
2. (B) and (C) only.
3. (A) and (B) only.
4. (C) and (D) only.
ABC Model Flower Development: B Gene Silencing Effects
In the ABC model of flower development, silencing the ‘B’ gene disrupts petal and stamen formation across whorls 2 and 3, respectively. The correct answer is option 4: (C) and (D) only, meaning stamens and petals are absent.
ABC Model Basics
The ABC model explains floral organ identity in four whorls: sepals (whorl 1, A genes), petals (whorl 2, A+B), stamens (whorl 3, B+C), and carpels (whorl 4, C). A and C genes antagonize each other, ensuring precise expression.
B genes (like APETALA3, PISTILLATA) activate only in whorls 2-3, partnering with A or C for petal/stamen development.
Effect of B Gene Silencing
Silencing B genes transforms whorl 2 into sepals (A alone) and whorl 3 into carpels (C alone). Whorls 1 (sepals) and 4 (carpels) remain unchanged.
Thus, petals and stamens are absent, matching mutants like apetala3 or pistillata.
Option Analysis
| Option | Whorls Affected | Explanation | Correct? |
|---|---|---|---|
| 1. (A) and (B) only | Sepals, Carpels | Wrong: Sepals (A only) and carpels (C only) persist without B. | No |
| 2. (B) and (C) only | Carpels, Stamens | Wrong: Carpels (whorl 4, C) unaffected; stamens missing. | No |
| 3. (A) and (B) only | Sepals, Carpels | Wrong: Same as option 1; neither depends on B. | No |
| 4. (C) and (D) only | Stamens, Petals | Correct: Stamens (B+C → C = carpels); petals (A+B → A = sepals). | Yes |
Exam Tip
For NEET-style questions, recall: B mutants yield sepal-carpel-carpel-carpel flowers. Practice with diagrams for whorl-gene mapping.
1 Comment
Ankita Pareek
May 1, 2026Correct option is C and D because in ABCD model A makes sepal,A+B makes petal ,B+C makes stamen and C makes carpel
In given question if B gene made silenced petals and stamens will not form in whorl.