6 myths about genes
The close relationship between pigs and humans, ethnicity embedded in the genes and other common misconceptions about genes
PostNauka debunks scientific myths and fights common misconceptions. We asked our experts to comment on the established ideas about the role of genes in the human body and the mechanisms of heredity.
Pig is genetically closest to humans
Mikhail Gelfand- Doctor of Biological Sciences, Professor, Deputy Director of the Institute for Information Transmission Problems of the Russian Academy of Sciences, member of the European Academy, laureate of the Prize. A.A. Baeva, member of the Public Council of the Ministry of Education and Science, one of the founders of Dissernet
It is not true.
This question is very easy to check: you just take the sequences of the genomes of humans and other mammals and see what they look like. No miracle happens there. Man is the most looks like a chimpanzee, then - the gorilla, other primates, then rodents. There are no pigs around.
If we consider this case, the result will be funny, because the closest relatives of the pig will be hippos and whales. This is the success of the molecular evolutionary biology because the whales have changed so much that morphological features it was quite difficult to figure out who they looked like.
A possible source of the myth could be that the pig lacks some of the proteins that make tissues recognizable by the human immune system. Pig organs are indeed the best among mammals adapted to transplant them to humans, especially if it is a genetically modified pig, in which some genes are additionally suppressed. Chimpanzees are more suitable, but no one will torture a chimpanzee to save a man.
In any case, "genetically" is not a very correct term. We can say, for example, that genetically cousins are closer to each other than fourth cousins. When you compare animals that don't interbreed, there's no genetics involved. Genetics is a science that tells what happens in the offspring when two individuals are crossed. The correct term would be "phylogenetically", i.e. that which reflects ancestry. And from the point of view of common origin, the pig is closer to dogs than to people.
Genes determine all individual traits of a person
Maria Shutova— candidate of biological sciences, Researcher laboratory of genetic bases of cellular technologies of the Institute of General Genetics of the Russian Academy of Sciences
This is true, but in part.
What matters is how these genes work, and many factors can influence this work. For example, individual differences in the DNA sequence, so-called single nucleotide polymorphisms, or SNPs. About 120 of these SNPs distinguish each of us from parents, from brothers and sisters. There are also a large number of genome modifications, which are called epigenetic, that is, supragenetic, which do not affect the DNA sequence, but affect the work of genes. In addition, one cannot deny the rather large influence of the environment on the expression of certain genes. The most obvious example is identical twins, whose genome is as close as possible to each other, but we can see clear differences, both physiological and behavioral. This illustrates quite well the influence of the genome, epigenetics, and external environmental factors.
You can try to evaluate the contribution of genetics and external factors to the manifestation of a particular trait. If we are talking about some disease-causing mutations that lead to very severe genetic syndromes like Down syndrome, then the contribution of genes is 100%. For the "minor" breakdowns associated with Parkinson's, Alzheimer's, different types of cancer, there are estimates of how often people with a particular mutation manifest the corresponding syndrome, and they can vary from a few percent to several tens of percent. If we are talking about complex traits that include the work of many genes at once, such as behavioral characteristics, then this, for example, is influenced by the level of hormones, which can be genetically determined, but the social environment also plays a big role. Therefore, the percentage is not very clear and highly dependent on the specific feature.
This myth is partially true: everyone knows that we differ from each other in the DNA sequence, there are many popular science articles about the connection of a certain polymorphism (mutation) with eye color, curls and the ability to run fast. But not everyone thinks about the contribution of supragenetic factors and the environment to the expression of any trait, and besides, this contribution is quite difficult to assess. Apparently, this is the reason for the emergence of such a myth.
Genome analysis can reveal ethnicity
Svetlana Borinskaya
It is not true.
Belonging to a particular ethnic group is determined by culture, not genes. The family influences which ethnic group (or groups, if the parents have different ethnicity) a person belongs to. But this influence is determined not by genes, but by upbringing, the traditions of the society in which a person grew up, the language he speaks, and many other cultural features.
Of course, from parents, everyone receives not only language and education, but also genes. Which parental genes the child will get is determined by the fusion of the sperm and the egg. It is at this moment that the individual's genome is formed - the totality of all hereditary information, which, in interaction with the environment, determines further development organism.
The processes of isolation of individual groups, interspersed with migrations and mixing of peoples, leave genetic "traces". If the number of marriages within a group exceeds the influx of genes from outside, then such a group accumulates gene variants that distinguish it from its neighbors in terms of spectrum and frequency of occurrence.
Such differences were revealed in the study of population groups living in different regions world and with different ethnicity. Therefore, genome analysis can show which group a person's relatives and ancestors belong to - if these more or less distant relatives have already been studied by population geneticists and if they indicated their ethnicity during the study. But this analysis does not indicate the nationality or ethnicity of the owner of the analyzed genome - this nationality may be the same as that of his relatives (especially if they are close relatives), but may be completely different.
nationality (or ethnicity) is not sewn into the genes, this phenomenon is not biological, but cultural. The times when it was believed that an ethnos has a biological nature are gone. Ethnicity, just like language, is not an innate feature - it is acquired (or not acquired) in communication with other people. The myth that "blood" or genes determine nationality (or any other traits formed under the influence of culture) is very dangerous. It has been used many times for manipulation. public consciousness, the consequences of which ranged from different depths of discrimination to genocide.
All mutations are harmful
Anton Buzdin— Doctor of Biological Sciences, Head of the Group for Genomic Analysis of Cell Signaling Systems, Institute of Bioorganic Chemistry named after A.I. Academicians M. M. Shemyakin and Yu. A. Ovchinnikov RAS
It is not true.
Many mutations are indeed harmful, but not all. In particular, some mutations occurred in our common ancestor with chimpanzees, which led to the fact that we humans appeared. Whether this mutation is useful is a question.
Mutations for the organism itself can be beneficial, neutral or harmful. Most of the mutations are neutral. Then come the harmful ones, and a very, very small part can be considered useful. In particular, the difference between people in the human population on our planet, of course, is determined by a combination of some normal variants of genes, which are now called normal, but they arose at one time as mutations. Then these mutations took hold, and some of them are beneficial.
Damage to some genes can have unexpected positive consequences. For example, a person becomes resistant to certain pathogens, such as the human immunodeficiency virus. The classic example is sickle cell anemia, when irregular shape hemoglobin. However, the presence of this mutation prevents infection with malaria, and therefore it has gained a foothold in Africa. People who do not have this mutation die, and those who have it get a chance to survive. On the one hand, this is a harmful mutation, but on the other hand, it is beneficial.
There are mutations that have changed the activity of certain metabolic enzymes, that is, proteins that are responsible for how our bodies metabolize milk, or fats, or alcohol, and so on. In different populations, there was a selection for some of these mutations, which are now considered normal variants (but once they were, of course, mutations), which led to the fact that, for example, the inhabitants of the north metabolize fat more actively than the inhabitants of the south . This is due, among other things, to survival in the conditions of the north. And Europeans and Asians are known to have different ethanol metabolism.
At different people different genes
Inga Poletaeva— Doctor of Biological Sciences, Leading Researcher, Laboratory of Physiology and Genetics of Behavior, Department of Higher Nervous Activity, Faculty of Biology, Lomonosov Moscow State University. M.V. Lomonosov
This is true, but in part.
All the genes that make up the genome of any species have a similar function, a similar structure, and deviations in the structure of these genes can relate only to minor changes in the structure of the proteins and regulatory elements that these genes determine. Another thing is that some regulatory moments of turning genes on and off may differ. This may be the reason for differences between organisms.
One example is the rapid maturation of the CNS: some children can speak at almost two years of age, while others know only a few words at this time. Nerve cells that need to develop and connect with each other in a network do this in different people at different speeds. There are also rare events - the so-called mutations, which can actually make their host different compared to most organisms of this species. The mutant gene is the basis for the synthesis of the abnormal protein.
Sometimes such mutations affect the regulatory regions of genes, and either a gene turns on at the wrong time, or some other violations of its work occur. Thus, there are genes that, due to their "breakdowns", can cause changes in the structure of the proteins they encode. And these changes can turn out to be very important for the fate of a given organism, while both physical and biochemical abnormalities are detected.
But genome each species of animal (and plant) is the same in its fundamental features. Close species have a small number of differences, unrelated species differ more. However, the mouse is considered a convenient object of modern genetics because it has a very large part of its genes similar to human genes, yeast and roundworms differ much more strongly.
The genomes of individuals of the same species can indeed differ slightly in nucleotide composition. As a rule, this does not affect the function of the gene or affects little. However, differences that do not affect the functions of genes are of interest to geneticists, since they allow us to trace genetic changes in populations.
In biology there was a paradigm "one gene - one enzyme". This is one of the first concepts in developmental biology. But now it is clear that this is a simplified view, because there are genes that have only a regulatory function and encode simple protein molecules. Such genes are not well studied in all cases, and they are no less, and perhaps even more important for tracking the work of this entire complex system of genetic control of the development of an organism.
People easily believe in the myth that genes differ from person to person because they have heard that there are genes that affect a lot, and that individual differences (and unexpected similarities) are facts. real life. However, between a gene (and even a protein that is “read” from this gene) and the signs of an organism that we encounter, there are many complex processes. This a complex system largely responsible for individual differences.
On the other hand, a person always wants to have an authoritative, close to peremptory and "scientific" opinion. In this regard, one has to hear phrases like "it has entered our genes." It’s not that easy to “enter” our genes, and into the genes of other organisms too.
Acquired traits are inherited
Svetlana Borinskaya- Doctor of Biological Sciences, Leading Researcher, Laboratory of Genome Analysis, Institute of General Genetics. N. I. Vavilov RAS
It is not true.
Biologists have thought so for a long time. The inheritance of acquired traits in the history of world science is primarily associated with the name of Jean Baptiste Lamarck (1744-1829). Lamarck's views on inheritance were also shared by Charles Darwin (1809-1882), who tried to combine them with his theory of the origin of species by natural selection. AT Russian history this idea is associated with the name of T.D. Lysenko (1898-1976). The discussion about the mechanisms of inheritance would have remained purely scientific, if not for the repression and destruction of geneticists who did not accept Lysenko's views. Therefore, the discussion of this topic, especially in Russia, is still often politicized.
The study of the molecular mechanisms of the operation of the hereditary apparatus showed that the level of activity of the genes that affect this trait is important for the formation of traits. And the level of gene activity is determined, firstly, by the nucleotide sequences inherited from parents, and secondly, by lifetime influences that change the activity of genes.
At the basis of lifetime changes in gene activity, among other mechanisms, there are those that make it possible to transfer changes in activity to offspring without the appearance of mutations in the gene. These mechanisms are called epigenetic, that is, "built on top" of the genetic ones. One of these mechanisms is methylation, the chemical modification of cytosine by attaching a methyl group to it with special enzymes. Methylation is preserved during cell division in the body, maintaining their tissue specificity.
For at least some traits, maintenance of methylation acquired in vivo by the parent has been shown in the offspring. For example, when developing fear in response to a certain smell, combined with an electric shock, a change in the methylation of the regulatory region in the olfactory receptor gene responsible for the perception of this smell was found in male mice, as a result of which the activity of the gene (and sensitivity to smell) increases.
In the children and grandchildren of these males, the level of methylation was also changed for the same gene, but not for the genes of other olfactory receptors. The press wrote that these descendants inherited a fear of smell, but this is not true. They inherited the ability to smell very low concentrations of a substance that proved dangerous to their mouse grandfather.
At the same time, epigenetic inheritance is reversible: methylation can be changed in vivo "in the opposite direction" in any generation. This distinguishes it from changes in traits under the influence of "classical" mutations that change nucleotide sequences, and not "supranucleotide" marks. What exactly traits can be transmitted epigenetically to offspring and what are the mechanisms of such epigenetic inheritance remains to be studied. And then, freed from politicized components, it will be possible to say "this is true, but in part."
Not certainly in that way! This statement was relevant even several decades ago. Then it was believed that the closest relative of man is anthropoid. This was confirmed by the so-called scale of ingenuity among animals. According to this scale, great apes were the closest. However, a number of experiments and experiments carried out at the present time, all move away from close relationship with man.
According to the theory of evolution, Homo sapiens is an underdeveloped ape that has one less chromosome than, for example, a chimpanzee, but has a similar structure of the skull and forelimbs. Currently, Charles Darwin's theory of the origin of man from apes is not confirmed, which allows the world's scientific minds to look for more and more new "relatives" of man.
Human resemblance to a dolphin
Researchers who studied the brain found that the encephalogram of bottlenose dolphins brings them closer to humans. The fact is that the brain of this species of dolphins is as similar as possible to the human one. The gray matter in these animals is slightly larger than in humans, and also contains more convolutions. According to the research of the Swiss professor A. Portman, the mental features of the dolphin took an honorable second place after the man (the third place among elephants, and the fourth place among monkeys).
What unites a person with pigs?
The anatomical structure of pigs allows us to call them the closest relatives of humans. The fact is that the embryo of this mammalian animal has a bookmark of a five-fingered limb and a muzzle that is very reminiscent of a human face. Piglet on a pig's muzzle and hooves on legs develop immediately before childbirth. In addition, already born pigs have the maximum physiology with humans. That is why pig organs (liver, kidneys, heart, spleen) are used in surgery for human transplantation.
Similarities between humans and rats
These rodents also amazingly copy a person at the anatomical level, but not as much as pigs. Rats have the same blood composition and tissue structure as humans. Curiously, these rodents are the only animals in the world that (like humans) have abstract thinking. Rats can make simple inferences, which allows them to be so tenacious. In addition, if a rat is enlarged to human size, and then the skeleton is straightened, one can see that the joints of humans and rats have the same anatomical structure, and the bones have an equal number of fragments.
Scientists have proven that pigs are much closer to us than monkeys. Some pig organs can be transplanted into humans. Why is it so, and not vice versa?
Whether we like it or not, we all have a lot in common with pigs. We are omnivorous mammals who gain weight easily and are susceptible to influenza. The very fact that pigs and humans are mammals means that we share some genes, which shows the similarity between human and pig DNA.
Scientists refer to the results of studies, according to which the DNA of a pig and a person are 98 percent similar, but in this state of affairs, many are misled, believing that a person is 98% a pig. The amount of genetic material we share with other species depends on what you're comparing.
All living organisms have genetic information encoded in deoxyribonucleic acid (DNA) divided into parts called genes. Information is transmitted from genes by a chemical called ribonucleic acid (RNA). Some RNA is translated into chains of amino acids that make up proteins, the building blocks of every living cell.
Scientists have discovered about 20,000 mammalian genes that code for proteins with similar basic functions. So if you compare some of the coding proteins in our DNA, you will find that we have a lot in common with a lot of mammals.
Pedigree of mammals based on molecular genetic data. It can be seen that the pig is farther from the person than the mouse, rabbit and porcupine.
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It is not so easy to transplant an animal organ into a human. The transplanted organ must match the recipient's age, physique and weight, genetic compatibility is required. Even a human donor is selected very carefully, what to say about a creature of another species.
However, the needs of medical practice dictate their own terms. It would be logical to assume that the organ donor would be the creature closest to humans - a chimpanzee, but transplantologists turned their eyes to ... a pig. People far from science even hurried to question Darwin's theory as a whole in connection with this.
Xenotransplantation: myths and reality
Speculation about the mass transplantation of pig organs to humans is greatly exaggerated. To date, medicine has not gone beyond the transplantation of mechanically functional tissues - heart valves, cartilage and tendons. Tissues before transplantation are treated with special chemicals and ultrasound to destroy antigens and avoid rejection of these tissues by the recipient's body. Even such transplants are very easy to damage during processing, making them unviable, what can we say about more complex formations - the heart, kidney or liver. Therefore, we are not yet talking about the transplantation of whole organs of a pig to a person.
Certain hopes are pinned on the creation of genetically modified pigs. If pig cells are forced to synthesize human glycoproteins on their surface by changing the genome, the human immune system will not perceive such organs as something alien. But this method is still at the stage of laboratory research, it is still far from mass application in medical practice.
Advantages of a pig as a donor
The choice of a pig as a possible organ donor is not at all explained by the genetic proximity of this animal to humans. The most genetically close animal still remains a chimpanzee. But the number of these monkeys in the world is measured in tens of thousands, which is clearly not enough for mass use. Pigs are slaughtered by the millions every year.
As for tissue compatibility, there are animals closer to humans - mice, but they do not fit in size, and pigs in this regard are quite comparable to humans.
People have been breeding pigs for a long time, these animals are well studied. It is unlikely that they will "present" some unknown terrible disease, which can be infected during transplantation. Pigs breed well and grow quickly, and their breeding and maintenance is relatively cheap.
All this makes them prefer pigs to monkeys, the use of which would turn organ transplants - already far from cheap - into a service available only to billionaires.
