. Explain how mutations in the photoreceptor genes
result in different vision defects.
The human eye is a sensory organ that gives a sense of vision. Cells present in eyes convert light energy into electrical signals. These signals are carried to the brain by optic nerves. There are cells known as photoreceptor cells present in the eye that help in visual transduction. Rods, cones and photosensitive ganglion that is present in the retina are photoreceptor cells that help in the conversion of light energy into electrical signals. There are certain photoreceptor proteins also known as opsin present in these cells that help in visual perception, regulation of circadian rhythms for example rhodopsin, melanopsin, photopsin, etc. these photoreceptor cells are not present on the blind spot.
Rods and cones help in the visual responses whereas photosensitive ganglion help in circadian rhythm and pupillary reflexes. The two optic nerve is formed by the axons of these ganglion cells.
Rods can function even in low intensity of light. The number of rod cells is high in nocturnal animals. They can sense low light levels and can respond even with a single photon. Cons function best at bright light. There are 3 types of cone cells present based on the wavelength of light they absorb. Short cones absorb the light of short wavelength like blue, medium cone cells absorb the light of medium wavelength like green and long cones absorb the light of long wavelength like red. As these are the primary colors, we can see a different combination of these colors.
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