What are opsins?
Q: What are opsins?
A: Opsins are the universal photoreceptor molecules of all visual systems in the animal kingdom. They change from a resting state to a signalling state by absorbing light, which activates the G protein and produces physiological responses - this is known as phototransduction.
Q: How many groups of opsins are involved in vision?
A: Five groups of opsins are involved in vision.
Q: What is melanopsin?
A: Melanopsin is an opsin found in the mammalian retina that is involved in circadian rhythms and pupillary reflex, but not in image-forming.
Q: How many colours can be seen with two opsins?
A: Two opsins allow vision in two colours, which is usual for mammals.
Q: How many colours can be seen with four opsins?
A: Four opsins allows vision in full colour, and this is usual for teleost fish, reptiles and birds.
Q: Who has trichromacy (full colour vision)?
A: In mammals, only Old World monkeys, apes and humans have trichromacy (full colour vision).
Q: Why did mammals lose much of their colour vision capability during the Mesozoic period?
A: It is thought that mammals lost much of their colour vision capability during the long period in the Mesozoic when they lived as mostly nocturnal animals.
