Why are all people different, geneticists explained

(ORDO NEWS) — If we compare any two people, then all the differences between them, according to scientists, fit on average 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

The genome is information stored in the cells of the body about its structure, transmitted by inheritance. It can be thought of as a text written down with just four special chemical compounds, nucleotides – adenine, thymine, guanine and cytosine.

Combining in a certain sequence, they form individual genes, which can be considered “sentences”, as well as entire “paragraphs” – DNA molecules. There are approximately 3.2 billion “letters” of nucleotides in our genome.

The basic order of “letters” in the complete human genome was determined by scientists in 2001. Today, the genomes of hundreds of thousands of people, as well as the genomes of hundreds of animal and plant species, bacteria and viruses, have already been read, or, as scientists say, “sequenced”.

“People, like all living beings, have special species properties programmed by DNA. The genetic “code” sets the development of an organism and the boundaries in which its characteristics can change.

However, many factors affect the manifestation of a particular gene, ranging from random chemical events and interaction with other genes and ending, for example, with the dietary habits of the individual,” said Konstantin Krutovsky, professor and head of the Scientific and Educational Center for Genomic Research at the 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 the 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 sex: in women, these are two identical X chromosomes, and in men, they are both. Moreover, the Y chromosome is about two times shorter than the X chromosome and has much fewer genes.

Variants of one gene from the mother and from the father may differ slightly, and may be very significant. This is due to mutations that occur mainly when DNA is copied. On average, human genomes differ by one in a thousand nucleotides, and in the total volume of the genetic “text” these 0.1% make up about three million differences.

In addition to the replacement of individual “letters”, there are other types of mutations: insertions or omissions of individual nucleotides, gene fragments 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 most rare cases they turn out to be somehow useful for survival. Along with non-lethal 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, which is vitamin C, due to mutations.

We have a gene for its synthesis, but, like monkeys, it does not works, so people have to actively get vitamin C from food in order to stay healthy,” explained the head of the genome analysis laboratory of the Institute of General Genetics. N.I. Vavilov RAS Svetlana Borinskaya.

Our ancestors and their relatives

The highest genetic diversity among modern earthlings is among the inhabitants of Africa. It was there that the modern species of Homo sapiens was formed about a hundred thousand years ago, scientists say.

“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 not only the number of differences is important, but also , in which parts of the genes they appeared,” Krutovsky noted.

The DNA of the nuclear genome of modern humans (Homo sapiens) and Neanderthals (Homo neanderthalensis) is approximately 99.5% identical, and that of humans and chimpanzees is 98.8%. Modern man and Neanderthal, according to scientists, “dispersed” on the evolutionary tree about 700-760 thousand years ago. The ancestors of the Neanderthals left Africa much earlier than ours, having settled in Europe and parts of Asia.

In parallel with modern man and Neanderthals for 40 thousand years, another close extinct subspecies of people lived in Asia, called the Denisovans (Homo denisovans) after the name of 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 a third species or subspecies of Homo sapiens. She 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.

Subtleties of inheritance

What should be the genetic differences between groups in order to be considered different species? As 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 closely related species are often rather arbitrary.

According to geneticists, we can assume that a new species appears at the moment when, due to accumulated mutations, related populations of animals lose the ability to freely interbreed and produce fertile offspring.

“Our ancestors interbred with Neanderthals, about 2% of the genetic material went to modern people from them.

Although the ancestors of the Neanderthals separated from the sapiens line more than half a million years ago, the ability to produce fertile offspring apparently remained,” Krutovsky explained.

Sexual reproduction, providing “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 be individuals in the population that 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, geneticists noted.


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