colour vision

Question 1

visible light is part of which spectrum?

Answer 1

electromagnetic

Question 2

what components make up visible light?

Answer 2

wave and particle

Question 3

wavelength of visible light

Answer 3

400-750/800nm

Question 4

what determines the colour of light?

Answer 4

frequency

Question 5

3 retinal cones

Answer 5

red, green, blue

Question 6

what is the basis of colour vision?

Answer 6

comparing between cones in two dimensions
ratio of activity across photoreceptors

comparing the activity of neighbouring cones with differing spectral sensitivity

Question 7

what cones do we make comparisons between?

Answer 7

red vs green
yellow vs blue
yellow is a mixture of red and green

Question 8

mechanism for red green comparison

Answer 8

colour opponent centre: surround
balance of inhibitory and excitatory input on the central cone

Question 9

mechanism for blue: yellow comparison

Answer 9

colour opponent ON and OFF bipolars, were red and green synapse with the same bipolar cell

Question 10

If blue is connected to on bipolar cell and yellow to off…

Answer 10

excited in blue light

Question 11

If yellow is connected to on bipolar cell and blue to off…

Answer 11

most excited in yellow light

Question 12

what type of polarisation occurs with colour vision

Answer 12

graded polarisation

Question 13

opsin protein

Answer 13

• 7 transmembrane domain G protein coupled receptor
• Binds retinaldehyde
• Translates isomerisation of retinal into a ‘biological’ signal
• Determines spectral sensitivity

Question 14

what is retinaldehyde most sensitive to when not bound to an opsin protein?

Answer 14

UV light

Question 15

what happens to retinaldehyde when bound to an opsin protein? What causes this change?

Answer 15

its wavelength sensitivity shifts towards the visual light spectrum by adjusting its amino acid structure

Question 16

long wave cone sensitivity and colour

Answer 16

564nm red

Question 17

middle wave cone sensitivity and colour

Answer 17

533nm green

Question 18

short wave cone sensitivity and colour

Answer 18

433nm blue

Question 19

what determines the wavelength of light that retinaldehyde is most sensitive to?

Answer 19

the amino acid structure of the protein opsin

Question 20

where are the characteristics of the protein opsin determined?

Answer 20

amino acid sequence encoded in our genome

Question 21

why can our cone opsin proteins be different from one another?

Answer 21

we dont all have the same amino acid sequence surrounding retinaldehyde as each other, genetic differences

Question 22

in what ways may cone opsins not work equally well across individuals?

Answer 22

not enough wavelength sensitivity difference between your red and green cone opsins

one of your red or green opsins is malfunctional
In these cases you may loose ability to discriminate between red and green

Question 23

why do red-green discrimination errors occur more in males than females?

Answer 23

Human Long wavelength sensitive and melanopsin wavelength sensitive opsins are X linked (expressed on our X chromosome)

• If gene on men’s X chromosome is faulty it will be expressed

Question 24

why is yellow, green colour discrimination less common in

Answer 24

not x linked

Question 25

what could adding cone types allow?

Answer 25

1. Improved spectral resolution within human visible range 2. Extend to UV

Question 26

how many cone opsins do most mammals have? what does this cause

Answer 26

two red green colour blindness

Question 27

how many cone opsin receptors do chickens have?

Answer 27

four, they have an additional blue visual receptor

Question 28

why are mammals the worst at colour vision?

Answer 28

we only have photoreceptors in our eyes most mammals only have 2 cone opsin genes

Question 29

inter-individual and species differences in cones:

Answer 29

number of cone classes their spectral sensitivity

Question 30

sensory requirements causing differences in species vision capacity

Answer 30

nature of the environment they are living in land or water

Question 31

ocean surface species have how many cone opsins

Answer 31

>4

Question 32

what wavelength does water transmit more effectively than others?

Answer 32

blue

Question 33

what range of wavelengths do you get at very deep water

Answer 33

very narrow range, appears blue to us

Question 34

how many cone opsins do deep sea species have? what so these encode?

Answer 34

two, encoding 'blue' sensitive pigments

Question 35

why do almost all mammals have only 2 cone opsins

Answer 35

many mammals are nocturnal, so would have less use for cone opsins at the same time in evolution would've lost photoreceptors in other parts of the body

Question 36

what are primates the only group to do?

Answer 36

re-evolve a 3rd cone opsin gene

Question 37

how many cone opsins did ancestral vertebrate have?

Answer 37

at least 4 cone opsins

Question 38

What determines species differences in vision capacity

Answer 38

sensory requirements (nature of environment they are living in evolutionary history

Question 39

what cone opsin may people lack?

Answer 39

the green cone opsin

Question 40

what cone opsin is always x linked in mammals?

Answer 40

the green cone opsin/ long wavelength sensitive opsin

Question 41

how many and what cone opsins does a mouse have?

Answer 41

two cone opsins green and UV sensitive

Question 42

how did new world monkeys develop trichromatic vision?

Answer 42

Stable polymorphism on the x chromosome involving two variants of cone opsin gene same cone opsin gene, but with different amino acids which means it can shift between being sensitive mostly to green or red spectrum

Question 43

why are new world monkeys colourblind?

Answer 43

the polymorphism allele is X linked so they can only have one version of the allele

Question 44

what evidence suggests that trichromatic development in primates is under positive selection

Answer 44

it has developed multiple times in new world monkeys

Question 45

what is the advantage of having females with heterozygous alleles for cone opsins in new world monkeys?

Answer 45

females in the group may lead tasks using colour discrimination. E.g., food selection

Question 46

how did old world monkey's develop trichromatic vision?

Answer 46

Duplication of the green cone opsin gene on X chromosome, so X chromosome accumulation of mutations to shift its spectral sensitivity- so one’s spectral sensitivity is more red and one is more green

Question 47

do male or female old world monkeys have trichromatic vision?

Answer 47

both

Question 48

what is the advantage of red/green colour discrimination in primates?

Answer 48

important in discrimination of colour in fruit and vegetation

Question 49

what is needed for red green discrimination further than cone opsin genes

Answer 49

retina/brain capable of comparing their activation

Question 50

Engineer female mouse X chromosome green opsin to express human red opsin (result)

Answer 50

* Wild type mice cannot distinguish red from green panel to claim reward * transgenic mice gradually learn to do this

Question 51

Engineer female mouse X chromosome green opsin to express human red opsin (conclusion)

Answer 51

Red-green discrimination arises from existing centre:surround organisation All it requires is that the centre has an over representation of one cone class vs the surround