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 Even in ancient prehistoric times, man noticed that children are most like their parents. Many peoples have proverbs similar to ours: "The apple falls not far from the apple tree".
Thanks to his acquaintance with this phenomenon, which may be foggy, not fully realized, prehistoric man could tame a dog and other animals, keeping offspring only from those individuals that seemed to him the most useful, and a prehistoric farmer trotted the seeds of the plants most suitable for him. Modern biological science has put the truth expressed in this proverb at the basis of a harmonious and complex
the doctrine of heredity, which received the title of genetics.
There is a long way from a popular proverb to a scientific theory. On this path, there is always a distortion of the first correctly noticed truth by numerous prejudices and mistakes that litter the ideas of people who are far from modern scientific achievements. The duty of scientists is to cleanse the worldview of their contemporaries from such delusions.
First of all, don't we very often see that the apple falls very far from the tree on which it was born? If you sow a seed from an apple tree strewn with fruits on poor soil and do not take care of a young tree, then the latter and newer may remain sterile. And vice versa, if you sow small seeds from miserable ears of corn on a rye field burnt out after a crop failure on fertile soil, you can get a brilliant harvest of magnificent ears with careful care. A heifer from (a high-milk mother can be completely spoiled by poor care, and good care and feeding can significantly increase the milk yield and meat content of even a "mongrel" cow. We say that only some hereditary inclinations, "genes" are transmitted from parents to children, which one way or another develop, depending on external conditions: thus, the hereditary inclinations of milk production in a cow, mother and daughter may be identical, but they can develop in a daughter in a completely different way, depending on different - better or worse - conditions of care and feeding.
The difference between hereditary inclinations and their manifestation in humans is especially clear in many cases. Here, the manifestation of inclinations depends mainly on difficult social conditions. Let us assume that the level of musical ability is determined by hereditary inclinations. But how could they in the old days manifest themselves in the development of a peasant child who, all his life, never left his remote village and never saw a single musical instrument? Perhaps, if he also had a good voice, he was known as a good singer, or, being a shepherd, he played well on a homemade pipe. Now, when teachers in elementary schools are already catching talents, children of such hereditarily gifted musically but never had the opportunity to show their musical talent, parents go to music schools, become outstanding pianists, violinists, composers. It seems that the apple falls very far from the apple tree, but in fact it falls on good soil, while the parent apple tree grew on poor soil.
 The clear dependence of the manifestation of hereditary inclinations on external conditions, and in humans - primarily on the social environment, forces many to completely deny the importance of heredity. But this is the other extreme and also a harmful prejudice. Only religious churchmen believe that all people are born the same and all people receive the same immortal soul. We know this is not the case.Some are inherited from birth and have high growth and heroic build, others are born and remain frail all their lives - regardless of external conditions, and often in spite of them, since it happens that heroes are brought up in the most unfavorable conditions, and frail ones do not acquire health even with the most thorough care.
The same must be said for abilities. There are many cultured people who have received the most careful education, who do not possess musicality at all and do not even get any pleasure from music, which gives the greatest pleasure to others at the very first contact with musical performance. One must have normal vision and a normally firm hand in order to become an excellent shooter after appropriate exercises, but not all people have normal vision and normal hand firmness. Not all practitioners are able to reach the highest degrees, because this requires not only exercises, but also the highest hereditary qualities. If everyone could become a champion in running, jumping, physical strength, but chess and other sports after long enough exercises, then there would be many more champions, and we see everywhere that the winner is one of hundreds of thousands and millions ... No, of course, champions are not only brought up by exercise, but they will also be born with the appropriate hereditary inclinations. And in the field of plant growing and animal husbandry, no one dares to deny the differences in hereditary inclinations, since such a denial would destroy all the foundations of agricultural selection.
The third widespread and all the more harmful prejudice concerns the reasons for the emergence of new hereditary inclinations. Until recently, it was widely believed among biologists that the hereditary inclinations of the offspring can be eliminated through appropriate care of the parents. However, at present, not a single scientifically educated agronomist will dare to assert that good fertilization of the field not only improves the yield of a certain wheat variety growing on it, but changes the wheat variety in the same direction, fixing the improvement caused by fertilization to the offspring. We train racehorses for equestrian competition in order to evaluate and select the best hereditary sires, rather than hoping that the results of training will be passed on to the offspring. And because parents have learned foreign languages or music, it is not at all easier for their children to learn these languages or learn music. Features that are acquired by parents during their lives cannot be inherited by their descendants. They say that syphilis acquired by parents is transmitted to descendants. But this is a misunderstanding: syphilis is an infectious disease caused by tissue parasites - spirochetes; from an infected mother, a spirochete can penetrate the tissues of an infant developing in her womb, but this is an infection of the child, not heredity.
If bad conditions for the development of the organism influenced the offspring in the same direction, then a class that has been in difficult conditions of existence for centuries would be doomed for a long time to a miserable existence even if these conditions change. However, history often shows us the opposite. During the Renaissance in Western Europe, the advancement of the middle classes was accompanied by an amazing flourishing of culture, which was built by the then Gorky, who for the first time had the opportunity to build. And in our time, the advancement of the working class is accompanied by the emergence of a huge number of new talents from families that previously could not fully reveal their abilities.
How are hereditary traits transmitted from parents to children? Every person, every animal, every plant begins its life in the form of one cell - "Zygotes"... This zygote is formed from the fusion of two germ cells - the mother's egg and the father's sperm.In the fertilized egg, from which a person develops, there is no head, no limbs, no organs or tissues whatsoever. But both the egg and the sperm are introduced into the human zygote by 24 small, microscopic bodies, called chromosomes. These 24 pairs of chromosomes, multiplying with each division of the egg, are preserved in all cells of the human body, and (when sex cells are formed in it, the elements of each pair of chromosomes diverge into different cells, so that in the gametes - eggs and sperm - only 24 chromosomes are again found , some of which are paternal and some are maternal, which explains why each person represents some mixture of the characteristics of the father and the characteristics of the mother.
Based on precise experiments carried out on various animals and plants, biologists have come to the conclusion that in these microscopic chromosomes, and only in them, are the hereditary inclinations of all the characteristics of organisms. We draw each chromosome as a thread, consisting of a number of heterogeneous segments - genes. In all likelihood, each segment has a structure close to molecular, only these are molecules of high complexity, consisting of thousands of atoms.
Until now, it remains a great scientific mystery how a complex human organism with all its subtle hereditary features develops from a fertilized egg with its 24 pairs of chromosomes - molecular aggregates. But the clearer are the patterns of inheritance of inclinations with various combinations of parental genes. Already on the basis of what has been said about the pairing of chromosomes during fertilization and about their discrepancy during the maturation of gametes, it can be understood that biologists in some cases can calculate with mathematical precision how hereditary inclinations should be combined in a marriage between parents that differ from one another in one way. or the genome, and how these genes diverge, are split in future generations.
 If one of the two parents is a "purebred" brunette (or brunette), and the other is blond (or blonde), then “all the children will be dark-haired. Although they receive the deposit of blond hair from the second parent, this deposit is suppressed by the development of the more active deposit of black hair received from the first parent. However, the children born of such a marriage are not purebred brunettes, since by hereditary inclinations they are only half brunettes and half blond. Half of their reproductive cells will carry the makings of blond hair, while the other half will carry the makings of black hair. If they marry blond, who never have the makings of black hair, then half of the children from such a marriage will be brunettes, and the other half will be blondes. If two "non-purebred" brunettes marry, then 25% of children will be purebred brunettes who have received a black hair color from each of their parents, 50% will not be purebred brunettes, like their parents, that is, with one gene of black hair coloring and one blond gene, and finally 25% will be blond, since they will receive one blond gene from each of the parents. And from the marriage of two blond parents, exceptionally blond children will be born, no matter what color the hair of the grandfathers and great-grandfathers was. This is the simplest case of Gregor Mendel's famous law of heredity.
The famous English novelist Herbert of Wales there is a novel translated into Russian language, — "Father of Christina Alberta"... The first page describes how a blonde woman had a daughter - a child with dark hair and dark eyes. The woman's husband is blond. An inexperienced reader will not pay any attention to this trifle, but the biologist will immediately understand the author's intention, which opens only in the middle of the book: the mother's husband is not at all the father of the child, since in this case only a brunette can be a father.If the mother of Christina Alberta sued her husband for alimony, the court, based on biology data, would have the right to refuse the claim.
We know a whole series of hereditary inclinations in humans, which are passed down from generation to generation, sometimes skipping over one or several generations (like the inclinations of blond hair hidden among brunettes), with the greatest regularity. These include: hair shape - curly, wavy, smooth; some features of blood, which sometimes characterize a person so accurately that in the armies of some countries they are entered in the passports of all military personnel (in case of emergency blood transfusion if injured in war); various deformities (six-fingered, short-fingered, cleft lip); visual impairments (color blindness), some nervous diseases, some peculiarities of taste, etc. Every year the number of human traits increases, the heredity of the inclinations of which becomes known to us. If now we already knew the heredity of some 20 widespread human traits, then we could, knowing the traits of the child and one of the parents, almost infallibly determine the other.
However, our information about heredity in humans is still very limited, and we know almost nothing about the hereditary transmission of such features that would be of real practical interest to us. We do not know by what patterns certain abilities are inherited, a predisposition to certain essential diseases like tuberculosis or schizophrenia, some connection with heredity is beyond doubt. There is only one organism, the heredity of which we have studied with the greatest completeness, and that is the small fruit fly, Drosophila. Thousands of individual hereditary inclinations - genes - have been studied in this fly over the past quarter of a century, and this study is based mainly on the entire modern theory of heredity and variability. From this fly, we have learned to change genes artificially - the easiest way is by irradiation with X-rays, however, without being able to foresee in advance what "mutations" will arise as a result of irradiation. But, knowing the genes of the flies we mate differing from each other, we can accurately predict which types will appear in the offspring and in what numerical ratios.
If someday we know as much about the heredity of man as we now know about the heredity of the Drosophila fly, then this may be of great practical importance. Each woman, choosing a spouse, will be able to determine in advance what physical characteristics and what abilities her children may have from this marriage and how in advance, with the help of appropriate care, prevention, to prevent the development of those diseases or disabilities that can be expected in some children on the basis of hereditary data ...
But, while our knowledge of human heredity is very limited, we must be very careful not to draw conclusions that are not justified by science. However, if we free ourselves from those prejudices that I spoke about above, then this will already be a great achievement, deeply penetrating into our everyday life. And as for the application of the data of the doctrine of heredity to the breeding of domestic animals and cultivated plants, here the successes of the biology of reproduction are already and now of great practical importance.
I. K. Koltsov
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