1 Vision The Evolution of Vision Carroll Chapter 8, pgs. 193-203 䇾Looks are deceiving: All animals share a tool kit of organ and body-building genes䇿 Eye diversity • Wide range of eye types in animals Eye Cup of Flatworms Nautilus Scallop2 Compound Eye of Insects and Crustaceans Squid Vertebrate Eye diversity • Did they all evolve independently? • Or did they evolve form a common ancestor? • First is less likely and later is more likely. • What䇻s the evidence? Is there a prototype eye? Photoreceptor and pigment cell The prototype eye3 Is there a prototype eye? Do organisms share genes for the prototype eye? Pax-6 Gene Eye development in squid, fruit fly, planarian, ribbon worm, ragworm, mouse, human, etc. Pax-6 protein sequence Figure 8.2 in Carroll LQRNRTSFTNDQIDSLEKEFERTHYPDVFARERLAAKIDLPEARIQVWFSNRRAKWRREE LQRNRTSFTQEQIEALEKEFERTHYPDVFARERLAAKIDLPEARIQVWFSNRRAKWRREE LQRNRTSFTQEQIEALEKEFERTHYPDVFARERLAAKIDLPEARIQVWFSNRRAKWRREE Fruit Fly Mouse Human OK but one unit of a prototype eye doesn䇻t account for most types of eyes. So explain that! Evolution uses parts from a toolbox to make more complex structures Photoreceptor and pigment cell Make more than one!4 Any other lines of evidence? Common photosensitive proteins and common cell types Figure 8.4 in Carroll Photoreceptive protein Opsins Photoreceptive protein Opsins Cell types Rhabdomeric Ciliary Photoreceptive protein Opsins Cell types Rhabdomeric Ciliary Photoreceptive protein Opsins Cell types Rhabdomeric Ciliary5 But what about the evolution of the structure of the eye? Single Lens Eye Anatomy But what about the evolution of the structure of the eye? Cumulative selection Diversity of Molluskan eyes Figure 8.5 in Carroll Log in to PRS. Evolution of Mollusk Eye6 Evolution of Mollusk Eye Evolution of Mollusk Eye Evolution of Mollusk Eye Evolution of Mollusk Eye Evolution of Mollusk Eye Development of vertebrate eye7 Vertebrate Vision Sensory physiology and biomechanics Single Lens Eye Anatomy Fig. 46-9 Lens in vertebrate eye changes shape to focus8 Molecular mechanism of photoreceptive cells Location of photoreceptive cells Carroll Figure 4.2 Photoreceptors in Retina Rod and Cone Receptor Cells Rods and Cones are tuned to bands of light spectrum. Tuning based on differences in opsins.9 How do rod cells detect light? Rhodopsin Fig. 46-10 Fig. 46-10 Rod cell䇻s signal transduction pathway Light and the synapse10 How could you genetically modify an animal to maximize its color resolution? 1. Induce genes to produce a greater number of cone cells in the fovea. 2. Clone in genes for opsins capable of detecting a greater range of light wavelengths. 3. Clone in genes to produce ommatidia like those found in the compound eye of insects. 4. Answers 1 and 2 are both correct. Fig. 46-9 Fig. 46-9 Phosphenes Artificial Vision11 Camera <> Visual Cortex Interface Edge Detection Edge