Answer:
If the two mutations are on different genes, mating together, the progeny will have the function restored.else if the mutation is the same, the function shall remain and wingless progeny will be visible.
Explanation:Just to explain shall use an example.Suppose there are two different mutations . The genes be called as 1 and 2.Also assume that they make proteins 1 and 2.Now the two proteins shall perform two different functions but the end wingless character is maintained.Now suppose fly 1 has mutation 1 and protein 1 is not being synthesized .But yet it is being synthesized in fly 2, that has a mutation in protein 2.when the two are mated protein 1 comes from fly 2 and protein 2 comes from Fly 1, as a result the two proteins and their functional copies are available and hence all functions completed and the fly develops a wing.The essential thing to understand is that if two flies have two different mutations both will have the two proteins from the other fly and the function of the protein will be completed.