For a long time, the question of how, as a result of random changes (mutations) in the genome of living things, new information appears, remained open. However, scientists were still able to figure out how the expansion and replenishment of the genome occurs. One of the most important mechanisms for obtaining new information is the process of gene duplication
In the photo: Bald eagle. He sees the world in a wider range of colors than a person.
Alexander Markov, Doctor of Biological Sciences, Leading Researcher of the Paleontological Institute of the Russian Academy of Sciences, talks about him.
How do new discoveries in the field of genetics allow us to understand the mechanism of the appearance of new genes and new properties in the body?
- One of the most typical arguments of people who deny evolution sounds like this: we cannot imagine how new information can arise as a result of random mutations in the genome. It seems to many intuitively that random changes made, for example, to some text, cannot create new information. They can only bring noise or chaos. Meanwhile, science today is already very well aware of how, in the course of evolution, new information appears in the genome, new genes, new functions, new characteristics in an organism, and so on. And one of the most important mechanisms for the emergence of new genetic information is the duplication of genes and the subsequent division of functions between them. The idea is very simple: there was one gene, now two as a result of a random mutation. At first, the genes are the same. And then, as a result of the accumulation of random mutations in two copies of this gene, they become slightly different, and there is a chance that they will share functions among themselves.
Give an example of the emergence of a new gene
- Now there are many well-studied examples. In general, this idea itself is quite old, back in the 1930s, the great biologist, geneticist John Haldwin suggested that duplication, that is, duplication of genes, plays an important role in the emergence of evolutionary innovations. And in recent years, in connection with the development of molecular genetics, the reading of genomes, many convincing examples have appeared, good illustrations of how this actually happens. One of the brightest, is associated with the evolution of color vision in mammals, or rather, even more broadly, in terrestrial vertebrates. When terrestrial vertebrates first appeared, came to land in the Devonian period, they still had the so-called tetrochromatic vision, which arose at the level of fish. What does it mean? Color vision is determined by light-sensitive proteins of the retina - there are such cone cells,which are responsible for color vision and in these cones there are light-sensitive proteins called opsins. The fish from which the vertebrates evolved, and the first terrestrial vertebrates, had four such opsins. Each opsin is tuned to a specific wavelength.
Can we say that fish see exactly four colors?
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- This does not mean that a given opsin only reacts to a given wave, it means that a given wavelength excites this opsin the most, and the more the wavelength differs, the weaker it reacts. The tetrachromatic color vision system is a very good system, it gives a very clear distinction of the shades of the entire spectrum, and in many modern vertebrates it has been preserved, for example, in birds. Birds are great at distinguishing colors, apparently better than we are. Many can see in the ultraviolet range, some species have UV patterns on their plumage. And perhaps the birds found the system of color transmission of our televisions and monitors extremely poor. Because we use a trichromatic system, mixing three colors - our vision is arranged the same way. The bird has four, not three.
That is, people in comparison with birds see the world more primitive
- From the point of view of birds, we are a little color blind. In humans, as I said, the trichromatic system is three opsins, tuned to three different waves. One for blue, another for green and the third, shifted towards yellow. But the most interesting thing is that other mammals, besides humans and monkeys, have dichromatic vision, they only have two opsins. They do not have a third, which is closest to the red end of the spectrum, and they therefore distinguish blue from green, but they do not distinguish green from red. How did it come about? Why did mammals lose two opsins?
It is known that the ancestors had four, and mammals have two opsins. Apparently, the loss of two opsins was associated with the fact that mammals switched to a nocturnal lifestyle at the dawn of their history. Why did they switch to a nocturnal lifestyle? This was due to the vicissitudes of a long competition between the two main evolutionary lines of terrestrial vertebrates. These lines, they are called synapsid and diapsid. The synapsid line is animal-like lizards, animal-like reptiles. And this group was dominant among terrestrial vertebrates in ancient times, in the Permian period, more than 250 million years ago. Then, in the Triassic period, they had strong competitors, representatives of the diapsid line. In modern animals, all reptiles, crocodiles, lizards and birds belong to the diapsid line. In the Triassic period, active predators appeared, running fast, including on two legs. Diapsid reptiles, crocodiles began to crowd out our ancestors of synapsid or animal-toothed reptiles. And this competition ended at first not in favor of our ancestors. At the end of the Triassic period, fast-running diapsid reptiles appeared, they gave birth to a new group, a new group came from them - dinosaurs, which for a very long time became the dominant daytime predators and herbivores on the entire planet. They occupied all daytime niches, animal niches in the large size class. At the end of the Triassic period, fast-running diapsid reptiles appeared, they gave birth to a new group, a new group came from them - dinosaurs, which for a very long time became the dominant daytime predators and herbivores on the entire planet. They occupied all daytime niches, animal niches in the large size class. At the end of the Triassic period, fast-running diapsid reptiles appeared, they gave birth to a new group, a new group came from them - dinosaurs, which for a very long time became the dominant daytime predators and herbivores on the entire planet. They occupied all daytime niches, animal niches in the large size class.
The synapsid line was forced to go into the night, underground, they crushed. In the Permian period there were giant synapsid reptiles, by the end of the Triassic period one little thing remained. At the same time, at the end of the Triassic period, the process of the so-called mammalianization of synapsid reptiles was completed, that is, roughly speaking, the first mammals appeared. All the other synapsid reptiles became extinct, and one group became mammals and they survived. But they survived, becoming small and nocturnal. Throughout the Jurassic and Cretaceous periods, mammals were nocturnal - they looked like some kind of shrews, mice. Since they were nocturnal, color vision became almost useless for them. Because the cones still don't work at night, natural selection could not support four descriptive, tetrochromatic vision,because that vision was not needed.
Natural selection cannot look into the future, it works like this: either you use the gene, or you lose it. If the gene is not needed here and now, then the mutations that arise and spoil it are not eliminated by selection, and the gene sooner or later fails.
The loss of genes is probably aimed at preserving any forces in the body, at maximum economy, maximum efficiency, that is, nothing should work idle in our body
- In principle, yes, of course, this is economy - excess protein is not synthesized. I must say that in general, a lot of excess proteins are synthesized in the body, which have become unnecessary, but have not yet had time to die off, this does not happen so quickly, but in the end it happens. At first, it was thought that both opsin genes were lost by the ancestors of mammals or the first mammals very quickly and practically at the same time. Now in the genome of the platypus - and this is a representative of the most primitive mammals, there is one of the lost genes. That is, the platypus has three more opsins, while more advanced mammals have only two. The genes were lost, thus in turn. The common ancestor of mammals still had three opsins, and placentals and marsupials, excluding the oviparous platypus and echidna, only two opsins.
How, then, did our ancestors, monkeys, regain their trichromatic vision? And here the gene duplication mechanism just worked. When the era of dinosaurs ended and mammals were able to become diurnal again, they remained with their dichromatic vision, because there was nowhere to take the lost genes.
And this continues in most groups of mammals, although it would be useful for them to distinguish colors, but there is nowhere to take the gene. But the ancestors of the monkeys of the Old World were lucky. They had one of the remaining two opsin genes undergoing duplication, duplication, and natural selection quickly tuned two copies of the resulting gene to different wavelengths. It only took three mutations to do that - replacing three amino acids in a protein, a pretty minor change. A small operation, due to which the wavelength to which one of the opsins reacts has shifted to the red side. This is enough for us to be able to distinguish between red and green. This made it possible for the ancestors of the first monkeys of the Old World to switch to eating fruits and fresh foliage in tropical forests: it is very important to distinguish red from green,ripe fruits from unripe and young leaves from old leaves.
But this only happened to the monkeys of the Old World. This is a happy event - the duplication of the gene occurred in the ancestors of the monkeys of the Old World after America separated from Africa and sailed away, between them was the Atlantic Ocean. American monkeys were unlucky and most of them were left with dichromatic vision. And they still live like this. Of course, it would also be useful for them to distinguish red from green fruits, but what can you do if there is no gene.
It turns out that the monkeys of the New World do not distinguish between red and green, make mistakes, eat anything?
- It turns out like this. Maybe that's why the monkeys of the Old World became people, and the monkeys of the New World did not.
Author: Olga Orlova