Flies have a number of brain defects, the exact phenotype depending on the genetic background. In the original genetic background in which it was induced, fum1 produces the following phenotype; the β- and γ-lobes are sometimes fused across the sagittal midplane. When placed in a Canton S background, the mushroom body defects are similar to the phenotype in the original genetic background, and the ellipsoid body is open ventrally or flattened in some flies.
Beta lobes of mushroom bodies in dorsal brain are fused at the midline; penetrance incomplete.
