58. Following are certain statements regarding the activities of homeotic genes of classes A, B and C involved in floral organ identity:
A. Activity of A alone specifies sepals
B. Activity of B alone specifies petals
C. Activities of B and C form stamens
D. Activity of C alone specifies carpels
Which one of the following combinations of above statements is correct?
(1) A, B and C (2) A, B and D
(3) B, C and D (4) A, C and D
The correct answer is:
(2) A, B and D
Explanation:
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Statement (A) Activity of A alone specifies sepals — Correct. Class A gene function alone specifies sepals in the first whorl.
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Statement (B) Activity of B alone specifies petals — Incorrect. Petal identity requires combined activity of Class A and B genes, not B alone.
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Statement (C) Activities of B and C form stamens — Correct. Combined B and C gene activities specify stamens in the third whorl.
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Statement (D) Activity of C alone specifies carpels — Correct. Class C gene function alone specifies carpels in the fourth whorl.
Therefore, statements A, C and D individually are correct, but B is wrong as B alone does not specify petals.
Hence, the combination representing the correct statements is option (4) A, C and D.
Introduction
Floral organ identity in Arabidopsis is determined by the combinatorial activity of three classes of homeotic genes in the ABC model. Each gene class acts in specific floral whorls to shape distinct organs—sepals, petals, stamens, and carpels. Understanding these gene combinations is critical for elucidating mechanisms of flower development.
Detailed Roles of Class A, B, and C Genes
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Class A genes alone specify sepals in the first whorl.
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Class A + B genes together specify petals in the second whorl.
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Class B + C genes jointly specify stamens in the third whorl.
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Class C genes alone specify carpels in the fourth whorl.
This genetic interplay ensures proper organ specification with spatial fidelity.
Analysis of Statements
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Statement (B) claiming B alone specifies petals is inaccurate because petal identity requires both A and B gene activity.
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Statements A, C, and D accurately describe individual gene class roles in the floral organ specification process.
Summary Table: Class Gene Functions and Floral Organs
| Gene Class | Floral Whorl(s) | Organ Identity |
|---|---|---|
| A | 1 | Sepals |
| A + B | 2 | Petals |
| B + C | 3 | Stamens |
| C | 4 | Carpels |
Conclusion
The ABC model specifies that Class A alone governs sepals, Class C alone controls carpels, and Class B functions only in combination with A or C to specify petals and stamens respectively. Therefore, statements A, C, and D are correct, corresponding with option (4).
2 Comments
Kajal
November 12, 2025A,C and D
Mohd juber Ali
November 17, 2025Satament 2 incorrect bcs B+A= petals not B alone specific
So option A C D CORRECT