HTT and Alzheimer disease: To establish fly eye models for AD, HD, SCA1, and SCA3, we expressed the respective disease‐causing genes in the developing eyes using the GMR‐GAL4 driver; Aβ1‐42 for AD, Htt‐Q128 for HD, Ataxin1‐Q82 for SCA1, and Ataxin3‐Q78 for SCA3.