The patterns of inheritance of various traits in the human body are investigated by a branch of biology - human genetics. It is closely related to physiology, medicine, ecology and is designed to solve the problems of identifying and early diagnosis of pathologies, the causes of which are aberrations in the gene pool of human populations - chromosomal, gene and genomic mutations. The population-statistical method is one of the most tested forms of detecting and predicting syndromes - hereditary human diseases, and this article will be devoted to its study.
Features of the application of the method
In his work, medical genetics resorts to various forms of research on the human chromosome apparatus, using data from the exact sciences, statistics, and clinical medicine. It is no accident that the theoretical basis of population genetics and its laws were formulated using mathematical analysis. The population-statistical method is used not only to identify hereditary pathologies, but also to determine the frequency of occurrence of genes that carry these disorders, both in a homozygous recessive state and (which is more common) in a heterozygous, not manifested phenotypic form.
Population concept
To establish the mathematical laws of the distribution of specific hereditary inclinations in the gene pool, in genetics they resort to the concept of the human population. What methods are most demanded by modern science for its study? We will name three most important:
1. The population-statistical method.
2. Genealogical.
3. The twin.
Under the gene pool understand the genotypes of all people living in a given place. This may be the population of a whole country, a specific nationality or a human group that lives quite isolated, for example, residents of a village lost in the mountains of Afghanistan or a tribe in the Amazonian jungle.
The genotypic characteristic of a population includes the totality of all genes and external characteristics of its individuals. The population-statistical research method is used to study both sporadic pathologies and those that have a distinct genealogical form of manifestation.
The first group arises as a result of situational teratogenic factors. The other group includes an extensive list of developmental anomalies that are systematically recorded in a particular family, nationality, nationality over a fairly long period of time. For example, polydactyly, color blindness, hemophilia. To study the mechanism of transmission of pathological hereditary inclinations controlling these diseases, the population-statistical method is used.
Factors affecting the appearance of diseases with a hereditary predisposition
Medicine has proved the multifactorial nature (both genetic and environmental) of pathologies, which are manifested in a series of several human generations. A genetic analysis of hypertension, type I diabetes mellitus, bronchial asthma, schizophrenia and other diseases with a hereditary predisposition requires the study of thousands of pedigrees.
In each case, the population-statistical method of genetics is able to identify the level of reaction of the human group to the influence of environmental factors (radiation, trace elements of drinking water, climate) and to determine how many genes it is determined.
Are human diseases related to the genetic heterogeneity of the population
What are the results of a comparative analysis of different ethnic groups living in the same external conditions? The differing reaction of such populations to similar abiotic factors is evidence of their genetic heterogeneity.
The clinical, genealogical and population-statistical method for studying human genetics proved that the level of manifestation of pathology in families is comparable with its frequency of occurrence in the population. They are used in the study of the genetic predisposition of rheumatism, allergies, as well as in clinical studies of the population affected by multifactorial diseases: multiple sclerosis, Alzheimer's disease, autism.
Mathematical substantiation of inheritance of characters
Before considering the features of the genetics of human populations, we study its theoretical basis, presented in the form of a mathematical law. Its essence is as follows: the genotype frequencies for any of the genes can be calculated using the square equation of the sum of two numbers. However, the population in question must be quite large, it is impossible for the genes to drift and the forces of natural selection to act, and crosses occur spontaneously.
Using the population-statistical method for studying human genetics and the results of clinical observations, one can predict the frequency of phenotypic manifestations of defective genes and the likelihood of having a baby with a pathology.
How the probability of manifestation of pathology is calculated
Here is an example of the inheritance of phenylketonuria, a gene disease based on impaired metabolism of the essential amino acid phenylalanine. In European populations, the frequency of the pathological f gene is 1: 10000; patients are recessive homozygotes with the ff genotype.
Using the capabilities of the population-statistical method and mathematical calculations, it is possible to establish the frequency of the abnormal gene. It equals 0.01. Then the probability of the trait expressed in the phenotype will be 0.99. Hence, carriers of the recessive gene having the Ff genotype are 0.02. That is, in the considered population, approximately 2% of living people have a recessive phenylketonuria gene in their genotype.
As you can see, the population-statistical method is used to calculate the frequency of the genes of the panmictic population responsible for the manifestation of hereditary pathologies.
Features of human populations
The evolution of human civilization, which forms a biological taxon, can be represented as the development of individual communities, living for a long period of time in similar environmental conditions. They included similar climatogeographic parameters, a single method of nutrition, and common pathogens.
All this contributed to the consolidation in the gene pool of populations of groups of normal allelic gene pairs and, in the early stages of anthropogenesis, served as the basis for the action of hereditary varieties and natural selection.
What are genetics studying by the population-statistical method at present? First of all, this is the effect on the human genome of forced isolation, closely related marriages, and environmental degradation. It was they that led to the burden of the gene pool of humanity by pathological genes and served as the reason for creating a wide network of medical and genetic consultations designed to identify a hereditary predisposition to the manifestation of various diseases.