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The facts accumulated to date by medical genetics allow us to present the whole variety of relationships between heredity and the environment in a generalized form.

Imagine a situation where the contribution of heredity to the development of a trait, including a pathological one, is zero. This would mean that the trait is completely formed by the external environment, without any involvement of the genotype. In other words, the medium would act "on nothing." In fact, the environment always affects one or another material substrate, which is the result of the action of genes. Imagine the opposite situation, that is, when the contribution of heredity is 100%. This would mean that the genetic information about the trait is realized outside the influence of the environment. In fact, the contribution of each of the components to the formation of a sign or property, and therefore, the disease will be different for various types of pathology.

An organism is a unity of external and internal, an integral system of complex interconnected parts. Any organism has an infinite number of signs, although in the empirical description of both a healthy and a sick organism we record only a limited list of properties. Based on the most common genetic and molecular biological concepts, many chains of disparate events of development of both normal and pathological signs can be connected. Both normal and pathological signs of the organism are the result of the interaction of hereditary (internal) and environmental (external) factors. That is why a common understanding of pathological processes is possible only taking into account the results of the interaction of heredity and the environment. Thus, an individual’s genetic program, directly or indirectly, can participate in the development of pathology.

There are forms of hereditary pathology, the clinical manifestations of which are almost independent of the influence of the environment. However, this does not mean that everything in a person comes down only to his biology, his genetics. However, today it is completely obvious that outside the phenomenon of heredity, no processes of cell activity, development of an individual and evolution of organisms are possible.

The fact that a person is social in nature, largely determines the nature of the disease. The increase in the proportion of noncommunicable diseases (such as atherosclerosis, coronary heart disease, oncological pathology, mental and other diseases) in the structure of morbidity, mortality and disability is perhaps the most convincing evidence of this. The social nature of man in many ways becomes a determining factor in the implementation of pathological genotypes. Conducting medical and hygienic measures aimed at preventing the influence of harmful environmental factors, creating conditions conducive to the implementation of normal genotypes and preventing the development of pathological ones, therapy of a number of hereditary diseases can reduce the severity of hereditary defects, and in some cases, complete correction of the hereditary disease.

Currently, not only microsocium forms specific conditions for the implementation of the genotype.
Broad socio-economic transformations significantly change the genetic structure of populations. Changes in population and demographic indicators, such as blood relationship, population density, intensity and direction of migration, marriage system, family size, and others, inevitably affect both the spectrum and the prevalence of hereditary pathology.

Socio-economic activity of a person leads to the appearance in the biosphere of new chemical compounds and physical factors with teratogenic and mutagenic effects. The extent of environmental pollution by chemical compounds and radiation sources is amazing. Currently, about 7 million artificially created chemical compounds are in the human environment. A resident of a large industrial city contacts almost 50 thousand of them during the day. Despite the lack of rigorous evidence of the relationship between the degree of environmental pollution with the occurrence of genetically determined diseases and congenital anomalies, it can be stated that their number is increasing. Environmental degradation may create a background conducive to the realization of a hereditary predisposition to multifactorial diseases. In connection with the anthropogenic nature of pathological environmental factors, qualitatively new problems arise in the protection of the human gene pool.

A number of environmental causes are capable of causing disease in any genotype. Most often, this situation is realized in the absence of species protection from exposure to external agents, but even in this case, the nature of the lesion, the magnitude and variety of clinical manifestations, and other characteristics of the disease are largely determined by the genetic constitution of the body. On the other hand, even with a strict genetic determination of pathology, environmental conditions, constitutional features, the whole genotype as a whole can have a significant modifying effect on the nature, frequency and degree of manifestation of a pathological gene. Such high plasticity of the genotype creates great opportunities for the treatment, prevention of hereditary diseases, the development of effective medical and pedagogical training programs, rehabilitation and adaptation of patients.
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    Nowadays, the structure of diseases caused by adverse environmental factors has undergone significant changes due to the manifestation of various pathways of xenobiotics into the human body. During evolution, the bulk of toxic products entered the body through the gastrointestinal tract and rendered harmless in the liver. Currently, the majority of foreign products
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  10. Malformations of the maxillofacial apparatus. The role of genetic factors in their development
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