Evolution and genetics of colour vision Flashcards
What are visual pigments?
Photon-absorbing molecules that enable photoreceptors to produce electrical signals in response of light
What do visual pigments consist of?
They consist of an opsin that is covalently bound to a chromophore
What are opsins?
They are protein molecules that regulate spectral sensitivity of the visual pigment
What is a chromophore?
It is an 11-cis retinal, this confers light sensitivity by absorbing photons causing it to change to trans retinal
How does spectral sensitivity differ from one visual pigment to another?
This depends on the AA sequences of the opsins
What has sequence analysis suggested about opsins?
It suggests that the the earliest mammels had 5 vertibrate opsin families - one rod opsins family and 4 cone opsins family meaning tetrachromatic.
The cone opsins are very ancient.
The rod opsins family emerges after divergence of cone opsins
Summarise the divergence of the opsin gene families.
The first split in the ancestral vertebrate gave rise to two classes, short-wave sensitive and long-wave sensitive.
Subsequent dupilications and dibergence derived four opsin gene families from the original SWS - SWS1, SWS2, Rh1, Rh2 (rod opsin)
How has these opsin gen families been conserved?
The 5 families have been inherited by all extant vertibrates, but some families have been lost in different lineages.
E.g. The line to modern mammals has lost 2 of the 4 cone opsins, retaining the LWS and SWS1 (plus Rh1 rod) - making them trichromatic.
However, in birds all 4 cone opsin classes are retained (if only it is needed as it is metabolically expensive)
What is spectral tuning of opsin gene families?
Each opsin within in a family can be tuned by AA substitutions
Peak spectral sensitivity can be shifted (by a few nm) by single AA substitutions at certain key positions
