The disease Adrenoleukodystrophy (ALD) occurs when there is an accumulation of long fatty acid chains in the body. ALD results in neurodegeneration and problems with vision, hearing, and motor coordination. In Drosophila, the bubblegum gene is similar to the human gene that when mutant causes ALD. Mutations in bubblegum result in fly vision defects. Mutations in the curly gene result in curly wings. You want to study the linkage between bubblegum and curly so you do this cross: