COMPONENTS OF PHENOTYPIC VARIANCE

Genetic variance (VG)

Environmental variance (Ve)

Genetic–environmental interaction variance (VGE)

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There are two types of photoreceptors:

Rods 

Cones

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Rods 

• Have low acuity or resolution

• are sensitive to low-intensity light

• receptors for night vision (scotopic vision)

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Cones 

• Higher visual acuity

• responsible for vision in bright light (photopic vision) Participate in color vision

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Inputs from eye to CNS: 

• Input from the rods 

• Input from the cones

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Duplicity Theory 

The existence of these two kinds of input, each working maximally under different conditions of illumination

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Axons of retinal ganglion cells 

Received and transduced information and carried to the CNS