Author: Carol Clark
Title: A clear, molecular view of how human color vision evolved
Title: A clear, molecular view of how human color vision evolved
Source: Emory Health Sciences
Date: December 18 2014
URL: http://www.sciencedaily.com/releases/2014/12/141218210100.htm
The Summary
Many genetic mutations occurred in visual pigments over the past millions of years. These mutations were required for humans to evolve and change from a primitive mammal with a dim, and not clear view of the world into a a larger ape/chimpanzee able to see all of the colors in the spectrum of light. In todays world, after extensive amounts of research done by Emory Health Sciences, scientists have produced a vivid picture of the evolution of human color vision over the past millions of years. PLOS Genetics published the process for how humans switched from ultraviolet vision to violet vision (ability to see blue light). Shozo Yokoyama who is a leading author of the publications explains that they, at Emory Health Sciences have traced the evolutionary pathways going back over 90 million years. Yokoyama and various other scientists have been studying adaptive evolution of vision in humans and other vertebrates by studying ancestral molecules. Firstly scientists have to estimate and synthesize proteins and pigments of an ancestral species. After this the scientists then conduct experiments on them by combining microbiology with theoretical computation, biophysics, quantum chemistry and genetic engineering. Five classes of opsin genes encode visual pigments for dim-light and color vision. Bits and pieces of the opsin genes change and vision adapts as the environment of a species changes. Around 90 million years ago our ancestors had UV-sensitive and red-sensitive color but 30 million years ago, they evolved four classes of opsin genes, allowing them to see the full-color spectrum of visible light. For the PLOS genetic papers researchers focused on the seven genetic mutations involved in losing UV vision and achieving the current function of a blue-sensitive pigment. They traced the progression from 90-30 million years ago. 5,040 possible pathways for the amino acid were discovered for changes required to bring about the genetic changes. Experiments were carried out for each of these 5,040 possible pathways. Scientists discovered that of the 7 genetic changes needed, each of them individually has no effect. It was only when several of the changes were combine in a particular order that the evolutionary pathway could be completed. Thus just as an animal's environment drives natural selection, so do changes in the animal's molecular environment. About 80 percent of the 5,040 pathways the researchers traced stopped in the middle, because a protein became non-functional. The other 20 percent remained possible pathways. Yokoyama described how our ancestors only used one of these paths and he discovered this path. The three specific amino acid changes that led to human ancestors developing a green-sensitive pigment were uncovered. Yokoyama tried to construct an extensive evolutionary tree for dim-light vision. At specific branches of the tree, his lab engineered ancestral gene functions, in order to connect changes in the living environment to the molecular changes.
Description of its Relevance
This article is relevant to the current unit we are studying as it concerns the study of evolution. Specifically the evolution from humans ultraviolet vision to violet vision (ability to see blue light). The article discusses molecular genetics, and how as well as an animal's environment driving natural selection, so does changes in the animals molecular environment. The article discusses genetic mutations. It describes how many genetic mutations in visual pigments, spread over millions of years, were required for humans to evolve from a primitive mammal with a dim, shadowy view of the world into a greater ape able to see all the colors in a rainbow. A genetic mutation, as we learned in the last chapter is a mutation is a permanent change of the nucleotide sequence of the genome of an organism. 
Your article says that the evolution of seeing colors, came from the fact that specific proteins became non-functional. My question is, how can a protein for seeing blue colors become non-functional if we can still see blue colors. You also say that our ancestor chose a path where they can see other light, yet we can see blue light. How does that work?
ReplyDeleteHi Divya, it was not that a specific protein became non-functional, but our primitive mammalian ancestors were previosuly nocturnal and had UV-sensitive and red-sensitive color, giving them a bi-chromatic view of the world. Our ancestors then evolved four classes of opsin genes, giving them the ability to see the full-color spectrum of visible light. Thus, it was not a specicifc protein becoming non-functional but it was an evolution of opsin genes.
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