A strain of Drosophila known as dunce produces one-half the amount of cAMP phosphodiesterase found in wild-type flies, which causes a learning defect
Another strain of Drosophila known as rutabaga produces a defective adenylyl cyclase protein (one of the AC types expressed in most cells) and also causes a learning defect. A dunce–rutabaga double mutant fly has relatively normal learning. Explain these curious observations.
What will be an ideal response?
Answer: cAMP accumulates to higher levels and persists longer in dunce fly cells because of the lower level of cAMP phosphodiesterase, which reduces cAMP levels by converting it to AMP. Elevated cAMP levels cause the dunce fly learning defect. Rutabaga fly cells make less cAMP because of the adenylyl cyclase defect. cAMP deficiency causes a learning defect. When these mutations are combined, the limited cAMP produced as a result of rutabaga accumulates to normal levels, because it is converted only very slowly to AMP by the low cAMP phosphodiesterase levels resulting from dunce.
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