What does genes have to do with it?
Scientists have explained why all people are different
If we compare any two people, then all the differences between them, according to scientists, fit into an average of only 0.1% of genetic information. However, as experts emphasize, these small differences in DNA are key to the survival of our entire species. Leading Russian geneticists told RIA Novosti about the mechanisms that program our personal development and the history of all mankind.
Code of life
A genome is information stored in the cells of an organism about its structure that is inherited. It can be represented as a text written with only four special chemical compounds, nucleotides — adenine, thymine, guanine and cytosine.
Combining in a certain sequence, they form individual genes that can be considered "sentences", as well as whole "paragraphs" — DNA molecules. There are about 3.2 billion "letters"-nucleotides in our genome.
Scientists determined the basic order of the "letters" in the complete human genome in 2001. Today, the genomes of hundreds of thousands of people, as well as the genomes of hundreds of species of animals and plants, bacteria and viruses have already been read, or, as scientists say, "sequenced".
"Humans, like all living beings, have special species properties programmed by DNA. The genetic "code" sets the development of the organism and the boundaries in which its signs can change. However, the manifestation of a particular gene is influenced by many factors, ranging from random chemical events and interactions with other genes to, for example, dietary habits of a person," said Konstantin Krutovsky, professor and head of the Scientific and Educational Center for Genomic Research at Siberian Federal University (SFU) and Professor at the University of Göttingen.
All genes are divided into groups and packed into separate blocks, chromosomes located inside cells. A person has 23 pairs of chromosomes, and in each pair he receives one chromosome from his mother, and one from his father.
Sources of differences
Special X- and Y-chromosomes determine gender: women have two identical X-chromosomes, and men have both. Moreover, the Y chromosome is about twice as short as the X chromosome and has much fewer genes.
Variants of the same gene from the mother and from the father may differ slightly, or they may differ very significantly. This is due to mutations that occur mainly when copying DNA. On average, human genomes differ by one in a thousand nucleotides, and in the total volume of the genetic "text" these 0.001% give about three million differences.
In addition to replacing individual "letters", there are other types of mutations: insertion or omission of individual nucleotides, fragments of genes or large fragments of chromosomes, exchange between chromosomes and their doubling.
Sometimes mutations do not manifest themselves in any way, sometimes they lead to the development of pathologies, and in the rarest cases they turn out to be useful for survival in one way or another. Together with non-fatal mutations, new properties arise that may be useful for adaptation, or may be neutral.
"An interesting selective-neutral property, for example, is that our monkey ancestors lost the ability to produce ascorbic acid, that is, vitamin C, due to mutations. We have a gene for its synthesis, but, like monkeys, it does not work, so people have to actively get vitamin C from food to stay healthy," explained Svetlana Borinskaya, head of the genome analysis laboratory at the N.I. Vavilov Institute of General Genetics of the Russian Academy of Sciences.
Our ancestors and their relatives
The inhabitants of Africa have the highest genetic diversity among modern earthlings. It was there that the modern look was formed Homo sapiens about a hundred thousand years ago, scientists believe.
"The common ancestor of great apes and humans lived 5-7 million years ago. Now, at the genome level, the differences with our closest relative in the animal world, the chimpanzee, are ten times greater than between two people. But it is important not only the number of differences, but also in which parts of the genes they appeared," Krutovsky said.
The DNA of the nuclear genome of modern humans (Homo sapiens) and Neanderthals (Homo neanderthalensis) are approximately 99.5% identical, and in humans and chimpanzees — 98.8%. Modern man and Neanderthal, according to scientists, "diverged" on the evolutionary tree about 700-760 thousand years ago. The ancestors of the Neanderthals came out of Africa much earlier than ours, settling in Europe and parts of Asia.
In parallel with modern man and Neanderthals, another close extinct subspecies of humans lived in Asia for 40 thousand years, called "Denisovans" (Homo denisovensis) after the Denisova cave in Altai. It was there that the material from which their DNA was isolated was first discovered.
This branch, according to scientists, can be considered the third species or subspecies of Homo sapiens. It is a sister group of Neanderthals and separated from them about 500-600 thousand years ago. The DNA of modern humans and Denisovans is approximately 97.7% identical.
The subtleties of inheritance
What should be the genetic differences between groups so that they can be considered different species? As the scientists explained, there is no answer to this question: the very concept of "species" was introduced for the convenience of description and classification, and the boundaries between close species are often quite conditional.
According to geneticists, it can be assumed that a new species appears at a time when, due to accumulated mutations, related animal populations lose the ability to freely interbreed and produce fertile offspring.
"Our ancestors interbred with Neanderthals, about 2% of the genetic material was inherited by modern people from them. Although the ancestors of Neanderthals separated from the Sapiens lineage more than half a million years ago, the ability to produce fertile offspring apparently persisted," Krutovsky explained.
Sexual reproduction, which ensures the "mixing" of genes, guarantees the genetic diversity of mankind. Scientists believe that its preservation and development is a key factor in the survival and prosperity of our species.
With unfavorable transformations of the habitat, it is necessary that there are individuals in the population who can successfully adapt, although they used to live like everyone else or even worse. It is they who will give rise to the next generation, in which everyone will also be different, the geneticists noted.
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