[Campbell Biology P.831] Based on the principles of the ABC hypothesis, if a genetic mutatio... | Practice Question

Based on the principles of the ABC hypothesis, if a genetic mutation caused gene C to be expressed in all four whorls, while gene A and B expression remained normal assuming A and C are mutually antagonistic, and B combines with A or C to specify petals or stamens, respectively , what would be the expected arrangement of floral organs from the outermost whorl inward?

  • A: Sepal-Petal-Stamen-Carpel
  • B: Carpel-Stamen-Stamen-Carpel
  • C: Petal-Petal-Stamen-Stamen
  • D: Sepal-Sepal-Carpel-Carpel

Explanation

In the standard ABC model, gene A is expressed in whorls 1 and 2, gene B in whorls 2 and 3, and gene C in whorls 3 and 4. Genes A and C are mutually antagonistic. If gene C is expressed in all four whorls, it will suppress gene A's function in whorls 1 and 2. Therefore: Whorl 1: C A suppressed -> Carpel; Whorl 2: B + C A suppressed -> Stamen; Whorl 3: B + C normal -> Stamen; Whorl 4: C normal -> Carpel. The resulting arrangement is Carpel-Stamen-Stamen-Carpel.