Table 1.

Five groups of visual pigments generated by gene duplication.

Visual pigment	Description	Approximate range of the wavelength of maximum absorption (in nanometers)
RH1	Also called rhodopsin. These pigments are expressed mostly in rods.	480–510
RH2	The amino acid sequences of these pigments are most closely related to those of RH1 pigments.	450–530
SWS1	Short-wavelength-sensitive type 1 pigment. This group includes ultraviolet-, violet-, and blue-sensitive visual pigments.	360–440
SWS2	Short-wavelength-sensitive type 2 pigment.	400–450
M/LWS	Middle- and long-wavelength-sensitive pigments.	510–560

Sources: Yokoyama 1994, 2000, Ebrey and Koutalos 2001.