Conservation and non-conservation of genetic pathways in eye specification.

In this review we highlight two genetic pathways important for eye morphogenesis that are partially conserved between flies and vertebrates. Initially we focus on the ey paradigm and establish which aspects of this genetic hierarchy are conserved in vertebrates. We discuss experiments that evaluate the non-linear relationship amongst the genes of the hierarchy with a concentration on vertebrate functional genetics. We specifically consider the Six genes and their relationship to sine oculis, as tremendous amounts of new data have emerged on this topic. Finally, we highlight similarities between Shh/Hh directed morphogenesis mediated by basic Helix-Loop-Helix factors in vertebrate retinal cell specification and in specification of fly photoreceptors.