Primate Colour Vision

Question 1

What is colour vision?

Answer 1

Ability to distinguish object based on wavelength of the light

Question 2

What detects colour?

Answer 2

Photoreceptor cells aka cones working with neural mechanisms

Question 3

What are the four types of opsins?

Answer 3

SWS1 = short wavelengths

SWS2

RH2 = medium wavelengths

LWS = long wavelengths

Question 4

Give the brief history of colour vision in the amniotes

Answer 4

Early amniotes had all four opsins

Sauropsids had all four opsins but diapsids lost SWS2

Synapids had all four opsins but primitive mammals lost RH2

Monotremes lost SWS1 so they only have SWS2 and LWS

Marsupials have SWS1, LWS and possibly RH2

Eutherians have SWS1 and LWS

Question 5

What are the different states of colour vision?

Answer 5

Monochromacy = only have 1 type of cone cells and only see around 100 colours e.g. owl monkey and achromat primates

Dichromacy = have two types of cone cells and see around 10,000 colours e.g. colour blind primates

Trichromacy = have three types of cone cells and can see 10 million colours e.g. most primates especially great apes

Tetrachromacy = have four types of cone cells and can see 100 million colours e.g. mostly reptiles, amphibians and some humans although rare

Pentachromacy = have five types of cone cells and can see 10 billion colours e.g. some species of butterflies and pigeons

Question 6

Are primate neural signals pooled?

Answer 6

No

Each cone has its own optic nerve fibre

In non-primates they often have pooled siganls which means multiple cones are linked to one optic nerve fibre

Question 7

Give some features of dichromacy

Answer 7

Most new world monkeys

Gene for S opsin is located on chromosome 7

Gene for L opsin is located on X chromosome

Similar to red-green colour blind humans

Question 8

Give some features of trichomacy

Answer 8

In all catarrhines and howler monkeys (very recent event in howler monkeys) but it is due to convergent evolution

L opsin on X chromosome due to duplication event

Gradual evolution into the varients M (green) and L (red)

All individuals are trichomatic

Question 9

Give some features of polymorphic trichromacy

Answer 9

1 autosomal S opsin gene

Individuals of same sex and same species can differ:

Heterozygous females are capable of colour vision but homozygous females and all males are dichromats

50-66% of females usually trichromatic