[Campbell Biology P.902] If an Arabidopsis plant carries both the ein ethylene-insensitive s... | Practice Question

If an Arabidopsis plant carries both the ein ethylene-insensitive single mutation and the eto ethylene-overproducing mutation, what would be the most likely phenotype regarding the triple response, and why?

  • A: It would show a constitutive triple response because the overproduced ethylene would bypass the insensitivity.
  • B: It would show a normal wild-type phenotype because the overproduced ethylene would compensate for the insensitivity.
  • C: It would fail to undergo the triple response, similar to a single *ein* mutant, because the plant cannot perceive the ethylene signal.
  • D: It would exhibit a more severe triple response than a single *eto* mutant due to synergistic effects.

Explanation

The ein mutation causes ethylene insensitivity, often due to a non-functional ethylene receptor. This means the plant cannot 'see' or respond to ethylene, regardless of how much is present. The eto mutation causes overproduction of ethylene, but if the plant cannot perceive it due to the ein mutation, the triple response will still not occur. Therefore, the ein phenotype failure to respond is epistatic, and the double mutant would show a phenotype similar to a single ein mutant.