Figure 1.

Photoreceptor morphology and retinal mosaics in invertebrates and vertebrates. A) Light is absorbed by specialized photoreceptor compartments (red), called rhabdomeres in invertebrates and discs in vertebrates. Adapted from (Arshavsky, 2003) with permission from AAAS. B) Stochastic (fly, human) or highly organized (fish) opsin expression in retinal mosaics. The fly R8 photoreceptors express either the short wavelength Rh5 (blue) or the medium wavelength sensitive Rh6 (green). Humans have three types of cones for short (blue), medium (green) and long wavelengths (red). Adapted from (Roorda and Williams, 1999). The zebrafish retina differs from the previous two mosaics, as it has a precisely arranged distribution of cones (UV and blue; adapted from (Allison et al., 2010)).