6 myths about genes
Post-science debunks scientific myths and fights against common misconceptions. We asked our experts to comment on the well-established ideas about the role of genes in the human body and the mechanisms of heredity.
Genetically, the pig is closest to a personThat's not true.
This question is very easily verified:
you just take the genome sequences of humans and other mammals and see who they look more like. No miracle is happening there. Man is most like a chimpanzee, then a gorilla, other primates, then rodents. There is no pig there or near.
If we consider this case, the result will be funny, because the closest relatives of the pig will be hippos and whales. This is a success of molecular evolutionary biology, because whales have changed so much that it was quite difficult to understand from morphological signs who they looked like.
A possible source of the myth may be that the pig does not have some proteins that make the 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 let a chimpanzee be tortured to save a person.
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 do not interbreed with each other, there is no genetics here. Genetics is the science that tells what happens in the offspring when two individuals are crossed. The correct term would be "phylogenetically", that is, something that reflects the origin. And from the point of view of common origin, a pig is closer to dogs than to people.
Michael Gelfand
Doctor of Biological Sciences, Professor, Deputy Director of the Institute of Information Transmission Problems of the Russian Academy of Sciences, member of the European Academy, laureate of the A.A. Baev Prize, member of the Public Council of the Ministry of Education and Science, one of the founders of the Dissernet.
Genes determine all individual traits of a personThis is true, but in part.
The important thing is how these genes work, and many factors can influence this work.
For example, individual differences in the DNA sequence, the so-called single nucleotide polymorphisms, or SNP. About 120 such SNPs distinguish each of us from our parents, from brothers and sisters. There are also a large number of modifications of the genome, which are called epigenetic, that is, supra-genetic, which do not affect the DNA sequence, but affect the work of genes. In addition, it is impossible to 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 to each other as possible, but we can see obvious differences, both physiological and behavioral. This illustrates quite well the influence of the genome, epigenetics and environmental factors.
You can try to assess 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 one hundred percent. For more "minor" breakdowns associated with Parkinson's, Alzheimer's, and various types of cancer, there are estimates of how often people with a certain mutation manifest the corresponding syndrome, and they can vary from several 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, for example, the level of hormones that can be genetically laid down, but the social environment also plays a big role. Therefore, the percentage is not very clear and strongly depends on the specific attribute.
This myth is partially true: everyone knows that we differ from each other in DNA sequence, there are many popular scientific 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 supergenetic factors and the external environment to the expression of any sign, besides, this contribution is quite difficult to assess. Apparently, this is the reason for the emergence of such a myth.
Maria Shutova
Candidate of Biological Sciences, Researcher at the Laboratory of Genetic Foundations of Cellular Technologies of the Institute of General Genetics of the Russian Academy of Sciences
Genome analysis can reveal ethnicityThat's 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 will relate to. But this influence is determined not by genes, but by upbringing, traditions of the society in which a person grew up, the language he speaks, and many other cultural features.
Of course, everyone gets not only language and upbringing from their parents, but also genes. Which parental genes the child will get is determined by the fusion of sperm and egg. It is at this moment that the individual's genome is formed – the totality of all hereditary information that, in interaction with the environment, determines the further development of the 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 gene variants accumulate in such a group 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 of the world and having 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 it may be completely different.
Nationality (or ethnicity) is not sewn to the genes, this phenomenon is not biological, but cultural. The times when it was believed that the ethnos has a biological nature are gone. Ethnicity, as well as language, is not an innate trait – it is acquired (or not acquired) in communication with other people. The myth that "blood" or genes determine nationality (or any other signs formed under the influence of culture) is very dangerous. It has been used more than once to manipulate public consciousness, the consequences of which ranged from varying degrees of discrimination to genocide.
Borinskaya Svetlana
Doctor of Biological Sciences, Leading Researcher at the Genome Analysis Laboratory of the N. I. Vavilov Institute of General Genetics of the Russian Academy of Sciences
All mutations are harmfulThat's not true.
Many mutations are really harmful, but not all.
In particular, our common ancestor with chimpanzees had some mutations that led to the fact that we humans appeared. Whether this mutation is considered useful is a question.
Mutations for the body itself can be beneficial, neutral or harmful. Most of the mutations are neutral. Then the harmful ones come, 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 became fixed, and some of them are useful.
Spoiling some genes can have unexpected positive consequences. For example, a person becomes resistant to certain pathogens, such as the human immunodeficiency virus. A classic example is sickle cell anemia, when an irregular form of hemoglobin is formed. However, the presence of this mutation prevents infection with malaria, and therefore it has become entrenched in Africa. People who don't have this mutation die, and those who do have it get a chance to survive. On the one hand, this is a harmful mutation, but on the other – a useful one.
There are mutations that have changed the activity of certain metabolic enzymes, that is, proteins that are responsible for how milk, or fats, or alcohol, and so on, are metabolized in our body. In different populations, selection took place according to some such mutations, which are now considered normal variants (but once they were, of course, mutations), which led to the fact that, for example, fat metabolism occurs more actively in the inhabitants of the north than in 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.
Anton Buzdin
Doctor of Biological Sciences, Head of the Group of Genomic analysis of cell Signaling Systems at the Institute of Bioorganic Chemistry named after Academicians M. M. Shemyakin and Yu . A . Ovchinnikov of the Russian Academy of Sciences
Different people have different genesThis is true, but in part.
All the genes that make up the genome of a species have a similar function, a similar structure, and deviations in the structure of these genes can only concern insignificant changes in the structure of proteins and regulatory elements that these genes determine.
Another thing is that some regulatory moments of switching genes on and off may differ. This may be the reason for differences between organisms.
One example is the speed of maturation of the central nervous system: some children can speak at almost two years old, while others at this time know only a few words. Nerve cells that need to develop and connect to each other in a network do this in different people at different speeds. There are also rare events – so-called mutations that can really make their host different compared to most organisms of this species. A mutant gene is the basis for the synthesis of an abnormal protein.
Sometimes such mutations affect regulatory regions of genes, and either some gene is switched 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 encoded by them. And these changes can be very important for the fate of this organism, while physical and biochemical deviations are detected.
But the genome of each animal (and plant) species is the same in its fundamental features. Close species have a small number of differences, unrelated species differ more. However, the mouse is therefore considered a convenient object of modern genetics because it has a very large part of the genes similar to human genes, yeast and roundworms differ much more.
The genomes of individuals of the same species may indeed differ slightly in nucleotide composition. As a rule, this does not affect the function of the gene or affects a little. However, differences that do not affect the functions of genes are interesting for geneticists, because they allow them to trace genetic changes in populations.
In biology, there was a paradigm of "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 the organism.
People easily believe in the myth that genes differ from one person to another, because they have heard that there are genes on which a lot depends, and that individual differences (and unexpected similarities) are facts of real life. However, there are many complex processes between the gene (and even the protein that is "read" from this gene) and the signs of the organism that we encounter. This complex system is largely responsible for individual differences.
On the other hand, a person always wants to have an authoritative, close to categorical and "scientific" opinion. In this regard, we have to hear phrases like "this has entered our genes." It's so easy to "not enter" our genes, and the genes of other organisms, too.
Inga Poletaeva
Doctor of Biological Sciences, Leading Researcher at the Laboratory of Physiology and Genetics of Behavior of the Department of Higher Nervous Activity of the Faculty of Biology of Lomonosov Moscow State University
Acquired traits are inheritedThat's not true.
That's what biologists thought 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 shared by Charles Darwin (1809-1882), who tried to combine them with his theory of the origin of species by natural selection. In 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 hereditary apparatus has shown that the level of activity of genes that affect this trait is important for the formation of traits. And the level of gene activity is determined, firstly, by the sequences of nucleotides inherited from parents, and secondly, by lifetime influences that change the activity of genes.
At the heart of lifetime changes in gene activity, among other mechanisms, there are those that make it possible to transmit changes in activity to offspring without the appearance of mutations in the gene. These mechanisms are called epigenetic, that is, "superstructured", super-genetic. One of such mechanisms is methylation, chemical modification of cytosine by "hanging" on it with special enzymes of the methyl group. Methylation persists during cell division in the body, maintaining their tissue specificity.
At least for some signs, maintenance of methylation, acquired in life by the parent, in the offspring is shown. For example, when developing fear in response to a certain smell combined with an electric shock, a change in the methylation of the regulatory site in the gene of the olfactory receptor responsible for the perception of this smell was detected 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 methylation level 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 turned out to be dangerous for their mouse grandfather.
At the same time, epigenetic inheritance is reversible: methylation can be changed in life "in the opposite direction" in any generation. This distinguishes it from changes in traits under the influence of "classical" mutations that change the sequences of nucleotides, and not "supranucleotide" labels. Exactly which traits can be transmitted epigenetically to offspring and what are the mechanisms of such epigenetic inheritance have yet to be studied. And then, freed from politicized components, it will be possible to say "this is true, but in part."
Borinskaya Svetlana
Doctor of Biological Sciences, Leading Researcher at the Genome Analysis Laboratory of the N. I. Vavilov Institute of General Genetics of the Russian Academy of Sciences
Portal "Eternal youth" http://vechnayamolodost.ru04.03.2015