Rods are rods and cones cones, and (never) the twain shall meet.
More than 100 photopigment G protein-coupled receptors (opsins) have been sequenced and organized into six classes. Rod photoreceptors in various species have been found to express an opsin from one of the two rhodopsin classes, while cones express an opsin from one of the four remaining classes. It has now been discovered that salamander short-wavelength sensitive cones and green rods express the same opsin, while manifesting other features that classically distinguish rods from cones.
Pugh
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Department of Ophthalmology, School of Medicine, F.M. Kirby Center, University of Pennsylvania, Philadelphia, PA 19104, USA.
D000221:Adaptation, Ocular / Q000502:physiology; D000557:Ambystoma; D000818:Animals; D003623:Dark Adaptation / Q000502:physiology; D017949:Retinal Cone Photoreceptor Cells / Q000378:metabolism*; D017948:Retinal Rod Photoreceptor Cells / Q000378:metabolism*; D017299:Rod Opsins / Q000096:biosynthesis; D014562:Caudata
D017299:Rod Opsins