The Drosophila gene eyeless (ey) encodes a transcription factor with both a 
paired domain and a homeodomain. It is homologous to the mouse Small eye (Pax-6) 
gene and to the Aniridia gene in humans. These genes share extensive sequence 
identity, the position of three intron splice sites is conserved, and these 
genes are expressed similarly in the developing nervous system and in the eye 
during morphogenesis. Loss-of-function mutations in both the insect and in the 
mammalian genes have been shown to lead to a reduction or absence of eye 
structures, which suggests that ey functions in eye morphogenesis. By targeted 
expression of the ey complementary DNA in various imaginal disc primordia of 
Drosophila, ectopic eye structures were induced on the wings, the legs, and on 
the antennae. The ectopic eyes appeared morphologically normal and consisted of 
groups of fully differentiated ommatidia with a complete set of photoreceptor 
cells. These results support the proposition that ey is the master control gene 
for eye morphogenesis. Because homologous genes are present in vertebrates, 
ascidians, insects, cephalopods, and nemerteans, ey may function as a master 
control gene throughout the metazoa.