Why do humans and pigs have many similarities? Achievements of modern genomics: the similarity of a pig to a person
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.
Genetically, the pig is closest to humans.
It is not true.
This question is very easy to test: you just take the genome sequences of humans and other mammals and see who they look more like. No miracle happens there. Man most of all, then - gorilla, other primates, then rodents. The pig is not there or near.
If we consider this case, the result will be funny, because the closest relatives of the pig are hippos and whales. This is the success of molecular evolutionary biology, because whales have changed so much that it was rather difficult to understand what they look like based on morphological features.
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. Pork organs are indeed the best among mammals to be transplanted 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 allow chimpanzees to be tortured in order to save a person.
In any case, "genetically" is not a very correct term. One 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, then there is no genetics. Genetics is the science that tells what happens in the offspring when two individuals are crossed. The correct term would be "phylogenetically", that is, that which reflects the origin. And from the point of view of common origin, the pig is closer to dogs than to humans.
Mikhail Gelfand
Doctor of Biological Sciences, Professor, Skoltech Life Sciences Center, Deputy Director of the Institute for Information Transmission Problems of the Russian Academy of Sciences, member of the European Academy, laureate of the A. A. Baeva, member of the Public Council of the Ministry of Education
Genes determine all the individual traits of a person
This is true, but in part.
How these genes work is important, and this work can be influenced by many factors. For example, individual differences in the DNA sequence, the so-called single nucleotide polymorphisms, or SNPs. About 120 such 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 to each other as possible, 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 assess the contribution of genetics and external factors to the manifestation of a particular trait. If we are talking about some kind of disease-causing mutations that lead to very severe genetic syndromes like Down's syndrome, then the contribution of genes is one hundred percent. For "minor" breakdowns associated with Parkinson's, different types of cancer, there are estimates of how often people with a certain mutation show 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 features, then this, for example, is affected by the level of hormones that can be genetically laid down, but the social environment also plays an important role. Therefore, the percentage is not very clear and strongly depends 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 external environment to the expression of any trait; moreover, this contribution is rather difficult to assess. Apparently, this is the reason for the emergence of such a myth.
Maria Shutova
PhD in Biology, Researcher, Laboratory of Genetic Foundations of Cell Technologies, Institute of General Genetics, Russian Academy of Sciences
Genome analysis can reveal ethnicity
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 are of different ethnicity) a person attaches himself 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 features of the culture.
Of course, everyone receives from their parents not only language and upbringing, 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 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 the outside, then in such a group gene variants accumulate, which, in terms of the spectrum and frequency of occurrence, distinguish it from its neighbors.
Such differences were revealed when studying population groups living in different regions of the world and having different ethnicity. Therefore, the analysis of the genome can show to which group the relatives and ancestors of a person belong - if these more or less distant relatives have already been studied by population genetics and if during the study they indicated their ethnicity. But this analysis does not indicate the nationality or ethnicity of the owner of the analyzed genome - this nationality can be the same as that of his relatives (especially if they are close relatives), but it can be completely different.
An international consortium of scientists announces another advancement in deciphering the genetic code of animals. This time, the genome of the domestic pig (Sus scrofa domesticus) and its close relative, the wild boar (Sus scrofa), has been fully sequenced. The first details of the new study have been published in the journal Nature.
"It is very important that we were able to uncover the pig genome and make this information publicly available," said research co-author Ronnie Green of the University of Nebraska. pigs as a model for biomedical research on human diseases ".
Pig DNA consists of 2.6 billion base pairs and contains almost 22 thousand genes. The researchers compared individual sections of the pig's genetic code with the genomes of humans, mice, dogs, horses and cows. This made it possible to discover new details of the evolution of pigs and reveal interesting features of their physiology.
By comparing the genetic code of ten wild boar species from different regions of Europe and Asia, the researchers also reconstructed a picture of the migration of their ancient ancestors across Eurasia. It turned out that the European and Asian lines separated almost a million years ago.
“These branches diverged so long ago that we can now speak of them as subspecies,” says Lawrence Schook of the University of Illinois. “We found the same difference between Eastern and Western domestic pig breeds. that pigs were independently domesticated in western Eurasia and East Asia. "
Scientists have found that some groups of genes of domestic pigs underwent fairly rapid evolutionary changes. This is especially true of genes responsible for immunity and sense of smell. For example, they have found 39 genes encoding the interferon protein, which resists viruses. This is twice as much as in humans.
Interestingly, with a well-developed sense of smell, pigs have a bad taste. So, they have very few genes responsible for the receptors for bitter taste. This allows them to happily eat what a person finds disgusting. Significant differences were also found in the receptors that distinguish between sweet and salty foods.
Scientists speculate that these features may explain why pigs were chosen by humans as pets. They can be fed with what people will not eat.
As for the modern demand for pigs, a stunning similarity in the anatomy of individual organs and tissues of pigs and humans played a role. Thanks to this, pigs have become the main object for the study of human diseases. And in this respect, the data obtained in the course of DNA sequencing is a real treasure for such work.
"We have found a large number of genes that are associated with diseases in humans such as obesity, diabetes, Parkinson's and Alzheimer's," says work manager Martien Groenen of Wageningen University.
The latest research will benefit not only doctors, but also farmers. The wild cousins of domestic pigs (boars) are still found in abundance in the wild today. This means that researchers can look in the wild for genes that can be used for breeding purposes to give pets new qualities.
For example, using genetic tools can improve the quality of pork produced, feed efficiency and animal resistance to disease.
It is not so easy to transplant an animal organ into a person. The transplanted organ must be appropriate for the age, body type and weight of the recipient; genetic compatibility is required. Even a human donor is selected very carefully, what can we 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 creature closest to man - the chimpanzee - will become the organ donor, but the transplantologists turned their eyes to ... the pig. People far from science even hastened to question the theory of Darwin as a whole in this regard.
Xenotransplantation: Myths and Reality
The 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. Before transplantation, tissues are treated with special chemicals and ultrasound in order to destroy antigens and avoid rejection of these tissues by the recipient's body. Even such grafts are very easy to damage during processing, making them unviable, what can we say about more complex formations - the heart, kidney or liver. Therefore, the question of transplanting whole pig organs to humans is not yet discussed.
Some hopes are pinned on the creation of genetically modified pigs. If, by changing the genome, the pig cells are forced to synthesize human glycoproteins on their surface, the human immune system will not perceive such organs as something alien. But this method is still at the stage of laboratory research, and is still far from widespread use in medical practice.
Benefits of a pig as a donor
The choice of a pig as a possible organ donor is not due to the genetic affinity of this animal to humans. The closest genetically to animals is still the chimpanzee. But the number of these monkeys in the world is measured in tens of thousands, clearly not enough for mass use. Pigs are slaughtered by the millions every year.
As for tissue compatibility, that is, animals that are closer to humans are 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 that can be contracted during transplantation. Pigs reproduce well and grow quickly, and their breeding and maintenance is relatively cheap.
All this makes people prefer pigs over monkeys, the use of which would turn organ transplants - already far from cheap - into a service available only to billionaires.
Scientists have proven that pigs are much closer to us than monkeys. Some pig organs can be transplanted into humans. Why so, and not vice versa?
Whether we like it or not, we all got a lot in common with pigs. We are omnivorous mammals that gain weight easily and are susceptible to influenza. The very fact that pigs and humans are mammals means that we share some genes, in which the DNA of humans and pigs is similar.
Scientists refer to the results of studies according to which the DNA of pigs and humans are 98 percent similar, but in this state of affairs, many are misled into believing that a person is 98% a pig. The amount of genetic material we share with other species depends on what you are comparing.
All living organisms have genetic information encoded in deoxyribonucleic acid (DNA), split into pieces called genes. Information is transmitted from genes using 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 large number 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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