Evolution of human colour vision as 'visual purple' receptor proteins, are encoded by Rh1, OPN2 and RHO genes. They are characterized by extreme sensitivity to light and enable monochromatic human vision in low light or dim conditions. They are broken down into retinal and opsin when exposed to these conditions. Humans have 3 types of photopsin proteins found in the cone cells. Long Wavelength Sensitive Opsin (Red cone opsin) – Encoded by the OPN1LW gene with a λmax of 560 that is found in the yellow-green electromagnetic spectrum despite its name. Its sensitivity to the colour red is still known to be higher than the
Evolution of human colour vision hypothesized that T285A was one of the first two mutations because absolute max values would be between 532-538 which is close to the absolute value found in human middle wavelength opsins. Normal human trichromats require a mixture of three primary colours for every day colour vision. Protanopes, deuteranopes and tritanopes are all dichromats, meaning they use a mixture of two primary colours to match any specific colour that they see. Thus, they are missing one of the three wavelength sensitive cones. Trichromats with all three cone pigments intact can generally see minimum wavelength differences between <1 and <3 for wavelengths