Small homozygous mutant somatic clones in the adult brain lead to ellipsoid body (EB) and mushroom body (MB) defects. These defects were often not cell-autonomous. A severe fusion of β and/or β' lobes can be seen, comprising of both cas- and cas+ cells. No obvious defects are seen with clones in the lobula, the medulla and the antennal lobes. Large clones are very rarely seen in the EB and never seen in the MB suggesting these clones are lethal.