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Introduction to genomics. The human genome, the main features of the organization. Methods for studying the human genome

The value of the human genome study program for practical medicine.

The 21st century is the era of genomics - the time when the DNA sequence in the human genome is determined almost completely, the time when the role of thousands of human genes in health and disease is analyzed. The time is coming for personalized medicine - when the study of small variations in many genes will lead to the identification of a person's individual predisposition to a particular pathology.

The most important events of genetics of the 20th century, initiating the study of the genome:

The discovery of the DNA double helix (J. Watson, Fr. Crick, 1953)

Development of a DNA sequencing method - 1997

Isolation of human embryonic stem cells (1998)

A decisive advance in molecular biology was the development of DNA sequencing methods in 1977.

The International Human Genome Project was officially launched in 1990. Scientists from 6 countries - the USA, Great Britain, France, Germany, Japan and China - made a huge contribution. By 2001, 90% was sequenced with an accuracy of 99.99%. By 2003, 99% of the human genome had been sequenced. There are about 400 holes left.

During the implementation of the Human Genome Project, the DNA sequence of all chromosomes and mitochondrial DNA was determined.

Twenty-two autosomal chromosomes, two sex chromosomes X and Y, and human mitochondrial DNA contain together approximately 3.1 billion base pairs.

Full sequencing revealed that the human genome contains 20-25 thousand active genes, which is significantly less than expected at the beginning of the project (about 100 thousand) - that is, only 1.5% of all genetic material encodes proteins. The rest (97%) is non-coding DNA, which is often referred to as junk DNA. The human genome is an aggregate of hereditary material enclosed in a human cell.

In general, the word "genome" refers to the total DNA content of a given species, including not only genes, but all other DNA as well. In humans, for example, protein-coding sequences account for only 1.25% of the entire genome. What does the human genome represent?

Introns account for up to 20-25%. But a significant part of intergenic DNA is occupied by regulatory sequences.

Gene classifications:

Genes active and repressed

The bulk of genes that are actively functioning in most cells of the body during ontogenesis are genes that provide the synthesis of general-purpose proteins (ribosome proteins, histones, tubulins, etc.), tRNA and rRNA. Such genes are called constitutive. The work of another group of genes that control the synthesis of specific proteins depends on various regulatory factors. They are called regulated genes. Changing conditions can lead to the activation of "silent" genes and repression of active ones. Differentiated expression of the mammalian genome leads to the development of a wide variety of tissue types.

Coding proteins and RNA

Protein coding sequences (many of the sequences composing exons) make up less than 1.5% of the genome.

In addition to protein-coding genes, the human genome contains thousands of RNA genes, including transport RNA (tRNA), ribosomal RNA, microRNA (microRNA), and other non-protein-coding RNA sequences.

Structural genes, characterized by unique sequences of nucleotides that encode their protein products, which can be identified by mutations that disrupt the function of the protein.

Household genes and luxury genes.

All genes are divided into genes for "housekeeping" and genes for "luxury".

Housekeeping genes encode what any cell always needs, regardless of tissue. Housekeeping genes are genes needed to maintain vital bodily functions and are expressed in virtually all tissues and cells at a relatively constant level. Household genes function everywhere, at all stages of an organism's life cycle.

According to various estimates, there are 10-20 thousand of such genes in humans. These are histone genes, tRNA, rRNA, etc.

Genes for "luxury", which are obviously 2-3 times more, are genes that are expressed in the cells of certain tissues and at a certain time. For example, all genes for protein hormones are genes for "luxury".

Regulatory sequences are nucleotide sequences that do not encode specific proteins, but regulate the action of a gene (inhibition, increase in activity, etc.)

There are many different sequences found in the human genome that are responsible for gene regulation. Regulation refers to the control of gene expression (the process of constructing messenger RNA along a portion of the DNA molecule). Typically, these are short sequences located either next to the gene or within the gene. Sometimes they are located at a considerable distance from the gene (enhancers).

Silencer is a DNA sequence to which repressor proteins (transcription factors) bind. The binding of repressor proteins to silencers leads to a decrease or complete suppression of RNA synthesis.

Insulators

The human genome consists of 23 pairs of chromosomes found in the nucleus, as well as mitochondrial DNA in the form of 2-6 circular molecules. Human chromosomes. The chromosomes range in size from 45 million to 280 million bp.

The chromosome is not homogeneous. In it, areas of euchromatin (not dense areas) and heterochromatin (more dense) alternate. Differential staining along the length of the chromosome reveals a number of colored (heterochromatin) and unstained (euchromatin) bands. The character of the transverse striation obtained in this case makes it possible to identify each chromosome in the set, since the alternation of stripes and their sizes are strictly individual and constant for each pair.

EUCHROMATIN, a chromosome substance that retains a despiralized (diffuse) state in a quiescent nucleus and coils during cell division. Contains most of the body's structural genes. Heterochromatin - extended stretches of repetitive and highly condensed sequences that do not encode any proteins.

Classification of heterochromatin:

Optional (Depending on the stages of the cell cycle, the type of cells, the same region of the chromosome can be in the state of both hetero- and euchromatin. Such regions of the chromosomes are called facultative heterochromatin.

Constitutive (near-centromeric, telomere) Areas that are always compacted. These sections of chromosomes contain tandemly repeating DNA (located one behind the other "head to tail").

Nearcentromeric heterochromatin consists of short tandem repeats up to 20 bp in length, organized into long blocks (100-200 tandems each). The blocks form rows ranging from 250 thousand to 5 million bp. This type of DNA is called satellite, alpha-satellite. Make up 3% of the genome. In the locations of satellite DNA, maximum compaction is possible; all four levels of DNA packing are present even in interphase. On satellite DNA, crossing over occurs between homologous chromosomes.

Telomeres (from ancient Greek phElpt - end and mEspt - part) - minisatellites - end portions of chromosomes. In most eukaryotes, telomeres consist of short tandem repeats and contain thousands of 6-nucleotide repeats: in humans - TTAGGG, (for comparison, in all insects - TTAGG, in plants - TTTAGGG). They are repeated 250 to 1500 times.

Several proteins are associated with telomeres, forming a protective "cap" - a telomere complex that protects telomeres from the action of nucleases and adhesion and, apparently, it is he who preserves the integrity of the chromosome and protects the entire chromosome from destruction. Telomeric regions of chromosomes are characterized by the absence of the ability to connect with other chromosomes or their fragments and perform a protective function.

In each cycle of telomere division, cells are shortened due to the inability of DNA polymerase to synthesize a copy of DNA from the very end. DNA polymerase can start strand synthesis only from an RNA primer. After the completion of DNA synthesis, the RNA primers on the lagging strand are removed, and the gaps are filled with DNA polymerase. However, this gap cannot be filled at the end of the chain. Therefore, 3 "DNA regions remain single-stranded, and 5" underreplicated. Therefore, EVERY ROUND OF REPLICATION WILL LEAD TO A REDUCTION OF THE ENDS OF THE CHROMOSOME. This phenomenon is called terminal underreplication and is one of the most important factors in biological aging. So, in a newborn, telomere length varies about 15 thousand bp in chronic diseases, it decreases to 5 kb. Scientists from Cardiff University have found that the critical length of a human telomere, at which chromosomes begin to connect to each other, is 12-13 telomere repeats.

With such a critical shortening of telomeres, the structure of chromosomes is disrupted, adjacent genes can be damaged and chromosomal aberrations begin to form, which often lead to malignancy. To prevent this from happening, special molecular mechanisms block cell division, and the cell goes into a state of rest - an irreversible stop of the cell cycle. As a result, the cell can die or stop dividing. This occurs in most normal somatic cells that have a limited ability to reproduce. Many stimuli can bring a cell to such a state of rest - telomere dysfunction, DNA damage caused by mutagenic effects of the environment, endogenous processes, strong mitogenic signals (overexpression of the Ras, Raf, Mek, Mos, E2F-1 oncogenes, etc.) , chromatin disorders, stress, etc.

However, in embryonic, germ and stem cells there is a special enzyme - telomerase, capable of restoring telomeric sequences, which are shortened with each act of replication.

Terminal underreplication defense mechanisms.

There is a special enzyme - telomerase (RNA + protein), which, using its own RNA matrix, completes telomere repeats and lengthens telomeres. In most differentiated cells, telomerase is blocked, but active in stem and germ cells.

It is believed that reactivation of telomerase is an important stage in malignant processes, since it allows cancer cells to “ignore” the proliferation limit. Telomere dysfunction contributes to chromosomal fusions and aberrations, which most often leads to malignant neoplasms. Active telomerases are found in 90% of cancerous tumors, which allows cancer cells to proliferate. Therefore, at present, among the drugs used to treat cancer, there is also a telomerase inhibitor.

For the discovery of the protective mechanisms of chromosomes against terminal underreplication using telomeres and telomerase in 2009, the Nobel Prize in Physiology or Medicine was awarded to an Australian working in the USA, Elizabeth Blackburn, American Carol Greider and her compatriot Jack Shostak (Jack Szostack).

In addition, telomere DNA has come under intense scrutiny in recent years due to the discovery of a link between telomere shortening and aging.

Other classes of tandem repeats are genes for RNA, such as ribosomal. These genes are localized in the NOR of 5 pairs of acrocentric chromosomes.

Another group of repeats are dispersed repeating sequences that are scattered throughout the genome individually, rather than in tandem. They are mobile (mobile) genetic elements - retrotransposons. 15% of the genome is occupied by long dispersed elements - LINEs, 12% - by short SINEs. These sequences produce enzymes called endonucleases that can cut into DNA and insert their own sequences there. The incorporation of MGE into DNA can disrupt gene function. In humans, about 30 retrotranspositions are known to cause disease. Why doesn't the genome get rid of such dangerous areas? Repetitive sequences and MGE are an important source of genome remodeling.

Systematization of these sequences, understanding of the mechanisms of work, as well as issues of mutual regulation of a group of genes by a group of corresponding enzymes are currently only at the initial stage of study. The mutual regulation of gene groups is described using gene regulation networks. The study of these issues is at the intersection of several disciplines: applied mathematics, high performance computing and molecular biology. Knowledge comes from comparisons of genomes of different organisms and from advances in the organization of artificial gene transcription in the laboratory.

All genes are subdivided by function into structural and functional.

Structural genes carry information about the structure of proteins and RNA.

Among the functional genes are:

modulator genes that enhance or weaken the work of structural genes (suppressors (inhibitors), activators, modifiers);

genes that regulate the work of structural genes (regulators and operators).

genome underreplication protein

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The initial stages of studying the human genome can be considered the development of methods for determining the sequence of nucleotides or DNA sequencing (Gilbert W., Berg P., Senger F.), for which in 1980 the Nobel Prize in chemistry was awarded. Four years later, work began on the full sequencing of the human genome (Human Genome Projekt, funded by the US Congress - $ 3 billion). By 2003, a complete decoding of the nucleotide sequence of the human genome was completed. The last to be sequenced was the largest human chromosome (No. 1). Now anyone can theoretically sequenced their entire genome in a few minutes, which will cost them $ 1,500.

Currently, it is believed that there are 20-25 thousand structural genes in the human genome, and only 1% of all DNA is in exons. It is enough for people to look at each other to understand that there is genetic variability in the species of Homo sapiens. The structure of genomes of different races and nationalities is 99.9% identical, and the individual variability is 0.1%. The differences between human genotypes are mainly due to mutations. This variability is called genetic polymorphism, which is understood as small differences in the nucleotide sequence, giving a normal phenotype. Polymorphisms include, for example, single nucleotide substitutions - SNPs, which occur every 300-400 bp. in the human genome. Most of these SNPs are located in non-coding regions. SNPs are easy to identify due to their stability, and they can be used as markers for mapping genes responsible for multifactorial diseases such as diabetes and atherosclerosis. Currently, 4.0 million SNPs have been identified, among which 2.6 million are significant intragenic SNPs.

The next stage in the study of the human genome was the ENCODE program “Encyclopedia of DNA Elements”. The human genome or the number of nucleotides in the haploid set of a cell has 3 billion base pairs, of which 10-20% are coding sequences, and 80-90% are non-coding sequences, and therefore the main part of DNA does not carry information about the structure of proteins that make up the basis of any living organism. Non-coding sequences are represented by repetitions of different lengths, and for half of them the functions are not yet known, but it is assumed that they contain information about the program of individual development, which is called the score of the “symphony of life”. It is she who regulates the work of genes, RNA processing, the accuracy of matrix processes, conjugation and crossing over. Non-coding DNA can provide for the compartmentalization of genomes of different species, or it can create the basis for greater genetic variation. The transcribed part of the genome is only 10%, of which 25% falls on RNA synthesis, and 5% is translated to proteins.

According to ENCODE data, DNA sequences that do not carry information about the protein structure encode different types of RNA - tRNA, rRNA and regulatory RNA: small interfering RNA (si RNA) and microRNA (microRNA, mi RNA). All small regulatory RNAs affect gene expression at different levels - RNA synthesis and post-transcriptional modifications, pre-RNA splicing, RNA stabilization, translation, they are involved in genomic imprinting, DNA methylation, and chromatin remodeling. The action of such RNAs is based on the phenomenon of RNA interference, the essence of which is to suppress gene expression at the level of transcription or translation.

The aforementioned si RNAs work as cofactors of RNAase complexes, which cause the degradation of certain i-RNAs that are not needed by the cell. RNA interference can be used to knock down genes. Distinguish between the concepts of "knockout" and "knockdown" of genes. When a gene is knocked out, mutations are induced that damage and turn off the gene. When a gene is knocked down, degradation of the i-RNA synthesized from it is caused by si-RNA. The introduction of siRNA into patient cells is part of an innovative strategy to reduce gene activity in the treatment of certain cancers, hepatitis and other diseases.

Micro RNA - mi RNA class of non-coding hairpin RNAs, which are about 22 nucleotides in length. The structure of mi-RNA is encoded in the genome; mi-RNA genes are located in the regions of inverted repeats of introns of protein-coding genes, in exons or intergenic regions. They can temporarily turn off the translation of proteins due to their hybridization with the complementary region of m-RNA, forming an RNA-RNA double helix, which is not normally characteristic of cells.

In addition, other classes of regulatory RNAs have been discovered, which include - small nuclear RNAs (snRNA) involved in mRNA splicing; telomerase RNA; small nucleolar RNA (snoRNA) and ribozymes - cRNA, involved in the modification of other RNA; long non-coding RNAs - lincRNAs (long noncocling RNAs) with an as yet unknown function, containing approximately more than 200 n; piRNA (piwi - interacting RNA) are short molecules 24–30 nucleotides long, encoded in the centromeric and telomeric regions of the chromosome, possibly participating in the organization of chromatin. It turned out that the piRNA nucleotide sequences are complementary to mobile genetic elements and can suppress the MGE activity at the level of transcription and replication. The piRNA genes are active only in germ cells during embryogenesis.

All types of regulatory RNAs are synthesized from ¾ of our genome, i.e. approximately 80.4% of genomic sequences are involved in some way in regulatory processes.

It turned out that in patients with hereditary pathology, the same SNP substitutions are located in the genes of regulatory RNA, and not in the structural genes of proteins.

3. Methods for studying mutations in humans.

Depending on the type of mutation that is supposed to be detected in a person, either cytogenetic or molecular genetic methods are used. With the help of cytogenetic methods, it is possible to identify chromosomal and genomic mutations in patients, and with the help of molecular genetic methods, gene mutations.

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There is a point of view, which is shared by a considerable number of specialists, that all human diseases, with the exception of injuries, are associated with genetic defects. Obviously, this is an extreme point of view, nevertheless, it reflects the importance of genetic factors in determining the state of human health. Genetic defects are of different significance and condition.

Although diabetes and muscular dystrophy are commonly considered a disease, and cleft palate or color blindness are hereditary defects, these are all the result of mutations in the genetic material. It has also been shown that the predisposition to the disease also depends on the genetic constitution.

Genetic defects or mutations in the DNA sequence are expressed in the replacement of one nucleotide with another, loss of an entire fragment or its transfer to another position in the genome, etc. Such changes can lead to changes in the structure (and function) of the protein encoded by this DNA fragment or to a change in regulatory sites of genes that are fatal to cells. When we talk about hereditary diseases, we mean mutations that appear in the germ cells and are passed on to the offspring.

Mutations also accumulate in somatic cells throughout life, which can cause disease, but they are not inherited. Previously, it was believed that all mutations are harmful. This is due to the fact that it was with such mutations that cause diseases that the study of human genetic characteristics began. But now, when almost the entire nucleotide text of a person has been read, it has become clear that most of the mutations are neutral. Harmful mutations leading to a gross violation of the development of the organism are eliminated by selection - their carriers do not survive or do not give offspring.

A huge breakthrough in understanding how inherited genes affect the physical and psychological characteristics of a person has occurred in recent decades thanks to discoveries made in the study of the human genome. Established and diagnosed as a number of genetic diseases, and a predisposition to them, and at the earliest stages of embryo development. Great hopes for expanding the possibilities of modern medicine are associated with the implementation of the Human Genome project.

Implementation of the research project "Human Genome"

The Human Genome scientific project is an international program whose ultimate goal was to determine the nucleotide sequence (sequencing) of all human genomic DNA, as well as to identify genes and their localization in the genome (mapping). In 1988, the US Department of Energy and the US National Institutes of Health presented an extensive project that included the sequencing of the genomes of humans, as well as bacteria, yeast, nematodes, fruit flies, and mice, organisms that have been widely used as model systems in the study of human genetics. ...

For the implementation of this project, Congress allocated $ 3 billion. (one dollar for each nucleotide in the human genome). Nobel laureate James Watson was appointed director of the project. Other countries joined the project - England, France, Japan, etc.

In 1989, on the initiative of Academician A.A. Baev, a scientific council was organized in our country under the Human Genome Program. In 1990, the International Organization for the Study of the Human Genome (HUGO) was established, with Academician A.D. Mirza-bey. Regardless of the contribution and nationality of individual program participants, from the very beginning, all the information they received in the course of work was open and accessible to all program participants.

Twenty-three human chromosomes were shared among the participating countries. Russian scientists had to investigate the structures of the 3rd and 19th chromosomes. However, soon funding for the work on this project was greatly reduced, and our country did not take real participation in sequencing. Nevertheless, the work on the genomic project in our country did not stop: the program was revised and focused on the development of bioinformatics - mathematical methods, computing technology, software, improving the methods of describing and storing genomic information that would help to understand and comprehend the decoded information.

It took 15 years to decode the human genome. However, the continuous development of sequencing technology made it possible to complete the project 2 years earlier. The private American company Celera, headed by J. Venter (formerly a biologist at the US National Institutes of Health), played a significant role in the intensification of the work. Whereas in the early years of the project, several million nucleotide pairs per year were sequenced around the world, at the end of 1999 Celera was decoding at least 10 million nucleotide pairs per day. For this, work was carried out around the clock in automatic mode by 250 robotic installations, the information was immediately transmitted to data banks, where it was systematized, annotated and posted on the Internet.

During work in 1995, Venter et al. Developed and published a completely new approach to genome sequencing, called the method of random sequencing of the whole genome (better known as random sequencing by cleavage), which made it possible to assemble a complete genome from partially sequenced DNA fragments using a computer model ...

This method was the first to completely sequenced the genome of a self-replicating free-living organism - the bacteria Haemophilus in-fluenzae Rd. The bacterial DNA copies were cut into pieces of arbitrary length from 200 to 1,600 bp. These fragments were sequenced several hundred from each end. In addition, longer fragments of 15–20 kbp were sequenced. The resulting sequences were entered into a computer, which compared them, sorted them into groups and by similarity.

Non-repeating sequences were identified first, followed by repeating sequences of fragments. Long chunks helped to establish the order of frequently repeated, almost identical sequences. Then the gaps between the resulting master pieces of DNA were filled in. The genome sequencing of Haemophilus influenzae took one year and a sequence of 1,830,137 bp was determined. and 1,749 genes located on 24,304 fragments.

It was an undeniable success that proved that the new technology could be used to quickly and accurately sequenced entire genomes. In 1996, the genome of the first eukaryotic cell, a yeast cell, was mapped, and in 1998 the genome of a multicellular organism, the round earthworm Caenorhabolits elegans, was sequenced for the first time.

In February 2001, a working version of the human genome (90% complete) was simultaneously published in the journals "Nature" - the results of HUGO and "Science" - the results of research by Celera. Analysis of the resulting variant of the human genome revealed about 25 thousand genes. Earlier it was assumed that this number should reach 140 thousand (based on the postulate "one gene encodes one protein"). At present, it seems possible that one gene can encode 5-6 proteins. The variety of proteins encoded by the same gene is provided by several mechanisms: through alternative splicing, post-translational transformations of proteins - phosphorylation, acetylation, methylation, glycosylation, and many others.

In 2003, the final version of the complete human genome sequence was published. All this information is available on the Internet at several sites. However, some elements of the genome still do not lend themselves to sequencing by modern technologies, and our knowledge of the genome remains incomplete. It turned out that only 30% of the genome encode proteins and are involved in the regulation of gene action.

What are the functions of the rest of the genome and whether they exist at all remains completely unclear. About 10% of the genome is made up of so-called Alu-elements about 300 bp in length. They appeared out of nowhere in the course of evolution only in primates. Once in humans, they multiplied to half a million copies and distributed along the chromosomes in the most bizarre way.

As for the coding regions of DNA, in a purely molecular-computer analysis they were called genes according to purely formal criteria: the presence of punctuation marks necessary for reading information and synthesizing a specific gene product. At the same time, the timing and action of most potential genes are still unclear, and it may take at least a hundred years to determine their functions.

ON THE. Voinov, T.G. Volova

Human genetics is a science that combines genetics and medicine. It is devoted to the laws of inheritance, change, human evolution. Genetics of races ...

From Masterweb

03.04.2018 20:00

Human genetics is a science that combines genetics and medicine. It is devoted to the laws of inheritance, change, human evolution. This science considers both individuals, whose condition is fully consistent with the norm, and those with various individual signs of physiology, psychology, inherited from birth, as well as pathological conditions. Genetics also considers behavioral aspects. The main task of scientists is to determine what is formed under the influence of the environment, and what is the manifestation of the genotype.

General idea

Human genetics is based on general laws - these are universal, they can be applied to a wide variety of species and individuals, and humans are no exception. Currently, more than 3,000 human signs have been identified. They affect morphology, biochemistry, physiology. 120 of them are related to gender. Scientists were able to identify and investigate 23 types of genetic linkage. It was possible to draw up a chromosome map on which many genes are fixed.

Particularly noteworthy are the studies carried out within the framework of the refinement of human genetics, devoted to small populations, that is, such societies in which there are no more than one and a half thousand people. Scientists have found that for such a group of people, the frequency of internal marriages exceeds 90%, therefore, in just one century, all participants become second cousins ​​to each other. Research has shown that these conditions increase the risk of recessive mutations. About eight percent of them are lethal, some are associated with the structure of the eyes or skeleton. Mutations are often observed already at the stage of fetal formation, which leads to its premature death - even before childbirth or immediately after birth.

Features and numbers

Investigating human genetics, it was possible to reveal that the haploid set is a combination of genes in an amount of at least 100,000, but for some this number reaches a million. One genome is the source of mutations from one to ten. An increase in the probability of mutations by 0.001% for a particular individual means practically nothing, but when assessing the health of a population, the picture changes - the number of patients is measured in hundreds and thousands. By analyzing the information received, scientists were able to assess how important the mutagenic influence of the world around us is. It is by examining it on a population scale that one can realize the magnitude of the problem.

Studying the human genome in genetics, it was possible to establish that some specific features are inherent in humans, due to which scientific progress slows down. In particular, the karyotype has a huge number of chromosomes, in addition, few children are usually born in a marriage. And during pregnancy, a woman predominantly carries only one child. Exceptions are possible, but rare. The complexity of the study of human genetics is associated with the duration of growing up and the slow change of generations, as well as the impossibility of forming a marriage base, organizing experimental crossbreeding, and using artificial technologies to activate mutations.

The study of human genetics is not only a forced struggle with difficulties and problems, but also a number of specific advantages. Mutations are inherent in humans; at present, their diversity is only growing. In addition, the physiology and anatomy of the species have been studied in detail. The population as a whole is large, which means that scientists can choose among the existing ones such marriage schemes that are most consistent with the goals of the scientific work being carried out.

Do not stand still

The tasks of human genetics are to study how inheritance occurs, in what forms genetic traits appear in various individuals. Nowadays, scientists know for sure that the set of signs changes quite significantly from person to person. This is due to the relevance of all types of inheritance: by dominant, recessive gene, autosomal, codominant, in linkage with the sex chromosome. To achieve the maximum accuracy of research, it is necessary to use specific methods - those are designed specifically for the study of humans. Work continues on new methods and ways that will provide more information on this topic.

For decades now, scientists have not only been gathering new information. In human genetics, analytical approaches are used that involve the analysis of already known data, taking into account new information received. This ongoing analytical process allows for the broadening of the catalog of human traits passed down between generations.

Man and Science

The study of human genetics involves the study of the mechanisms of inheritance and the characteristics of variability inherent in humans as a species. An alternative term for science is anthropogenetics. Science is devoted to the differences and communities of people explained by the hereditary factor. Currently, it is customary to put medical genetics in a separate category. This area is devoted to inherited diseases, methods of their treatment and prevention. The relevance of research is closely related to the large accumulated base of information on this issue. It was possible to obtain fairly clear information about the morphology and physiology, biochemistry of man. All this information is relevant in the study of the genetic specificity of members of the population.

Features of the study of heredity, human genetics is a science closely related to the characteristics of society, ethics, human biology. At the same time, it is taken into account that a person has the ability to think abstractly, to perceive data. These traits are considered undeniable advantages that are not inherent in other objects studied by genetics.

Research: how is it organized?

The following methods are used in human genetics: cytogenetics, statistics, population research, ontogenetics, genealogy, modeling. The twin approach to the study of man is widespread. An interesting and giving a lot of useful information is dermatoglyphics. In human genetics, the method of hybridization is used, using somatic cells as a material for work. Approaches that allow working at the molecular level are also relevant.

In addition to the main ones, auxiliary techniques are used - they are designed to obtain additional information. These involve the use of methods of microbiology, biochemistry, immunology and other related disciplines.

Genealogy

This method of human genetics is based on the study of traits, properties inherited from person to person. To study it is necessary to have access to the individual's pedigree. For the first time such an approach was developed by Galton, and to simplify its application, Yust later suggested using conventional symbolism. Genealogy involves the formation of a pedigree and the subsequent analysis of information.

Within the framework of this method of human genetics, it is necessary to first collect comprehensive data about the family. Further, the information is recorded graphically using standard symbols. As part of an analytical study of the collected database, it is assessed whether a particular trait can be called familial, and also determine by what mechanism it is transmitted. Scientists investigate what are the genotypes of close relatives, calculate the risks of the appearance of the analyzed trait in future generations. For different mechanisms of inheritance, individual characteristics are inherent, and their features are visible when analyzing the pedigree.

About details

For analytical work in this method of studying human genetics, it is first necessary to form an idea of ​​the rules for monogenic transmission of properties by inheritance. Mendelian features investigated in this way are discrete, deterministic, and splittable. To assess discreteness, it is necessary to analyze morphology, physiology, biochemistry, immunology, and clinical criteria.

Particularly detailed information on the systematization of traits can be found in the works of Cusick, who published a catalog of mendelian human traits. Genealogy as a method of research is comparable to the hybridological method, and the differences are explained by social characteristics and human biology. Currently, this approach is widely used in research on mutations, sex-linked inheritance, as well as in medical genetic counseling.

Twin way

This method of studying human genetics assumes the presence of twin pairs. The objects are examined, scientists reveal what are the similarities between them, what are the differences. Twins are considered only those children who were born and at the same time were born to the same mother. Distinguish between mono- and dizygotic forms. In the first case, the source material is one zygote, while the genotypes are the same, the sex is the same. With two zygotes, the genotypes of the twins are different, and the sex may or may not be the same.

When the twins method is used to study human genetics, zygosity is first detected using a polysymptomatic approach. People are assessed for similarity by traits for which inheritance is established, and the influence of the environment on them is minimal. When it is possible to determine exactly the zygosity, the individuals are compared for a specific trait.

A concordant pair is identified if some feature is present in both twins. In its absence, one of the twins speaks of a discordant pair. If the twins method is used to study human genetics, it is taken into account that the information obtained most accurately makes it possible to assess the role of inheritance, how strongly the environment affects the correction of a certain trait. Scientists can establish what traits are inherited, why genes differ in penetrance. Within the framework of the study, it is possible to assess how effectively external factors affect the individual - from medication to approaches to education.

Cytogenetics

Human medical genetics involves the study of cellular structures under a microscope. In this study, attention is paid to chromosomes. The main task of a specialist is to identify sex chromatin, to carry out karyotyping. This process is required to identify metaphase chromosomes.

A karyotype is a diploid chromosome set characteristic of a particular species. An idiogram is a karyotype fixed in the form of a diagram. Karyotyping is effective if there are individual lymphocytes. First, a certain number of cells capable of division are removed, metaphase plates, a hypotonic solution are obtained. Systematization is carried out by one of two methods - Parisian or Denver.

The Denver version assumes taking into account the shape, size of the chromosome, and the method of solid staining is used in the work. There are seven categories of chromosomes. The complexity of the approach is that it is not easy to identify individual chromosomes within a group.

The Paris method of classification involves staining metaphase chromosomes. Each has a unique pattern, and the discs allow for clear differentiation.

Prenatal diagnosis

Genetics and human health are closely related. To prevent the birth of a child suffering from pathological abnormalities, prenatal diagnosis is used. This measure is considered to be the primary way to prevent inherited diseases. There are several approaches to diagnostics, the choice in favor of a specific one depends on the specifics of the family and the condition of the expectant mother.

An indirect method of studying human genetics with the basics of medical genetics involves studying pregnant women to determine risk groups. The blood is checked for alpha-fetoprotein, the parameters of hCG and estriol are detected. It is known, for example, that Down's disease is often observed with increased hCG and decreased estriol. From the indicators of alpha-fetoprotein, one can conclude how high the likelihood of pathologies of the neural tube, skin, the risks of chromosomal diseases is.

Alternative option

Direct approaches to prenatal diagnosis have been developed within the framework of human genetics. These are invasive and non-surgical. Non-invasive - examining the condition of the fetus using ultrasound. This can be used to identify multiple pregnancies, certain diseases and defects.

Direct invasive methods include chorion biopsy, placentobiopsy, amniocentesis, cordocentesis, fetoscopy. To study the condition, samples of the skin of the fetus can be taken. Materials and samples obtained for further work are studied using the approaches of cytogenetics, biochemistry, molecular composition and genetic characteristics are checked. The findings are used to advise future parents on heredity issues. Human genetics at the stage of prenatal diagnosis reveals the risk of chromosomal diseases and molecular abnormalities. In addition, it is these methods that are used to identify the sex of the unborn child and assess the likelihood of fetal malformations.

Modeling and genetics

If the genealogical method of studying human genetics makes it possible to estimate the probability of inheriting traits based on their observation in previous generations, then modeling is an approach in which hereditary variability is used to form a model of an object. Vavilov's laws are applied, indicating that genetically close species, genera have similar series of variability that is inherited. Phylogenetically close individuals give an unambiguous answer to external factors, including provoking mutations.

By resorting to mutant lines inherent in animals, it is possible to form models of the inheritance of a number of diseases inherent in both animals and humans. Scientists receive new methods for studying the ways of formation of diseases, methods of their inheritance. Currently, there are new approaches to diagnosis based on the achievements of genetics. The data obtained from the study of animals are applied to humans after certain amendments have been made.

Biochemistry and statistics

The ontogenetic method, which is relevant for the study of human genetics, involves studying using biochemistry approaches to identify metabolic problems and failures that are individual for a particular object, if such are explained by mutation. In the body of the object, intermediate products of metabolic reactions can be observed, and their detection in organic liquids has been widely used in approaches to the diagnosis of pathological conditions.

Population statistics and research is an approach in modern genetics that involves the study of the genetic population composition. Having collected a sufficiently voluminous database, it is possible to estimate how high the chance of the appearance of an individual with a given phenotype in the studied group of people is. You can calculate the frequency of gene alleles, genotypes.

Another approach that is applicable today is molecular genetics. This is the same genetic engineering that many have heard about, although not every person can imagine what the essence of the work of scientists is. Engineering is about isolating genes and creating their clones, forming recombinant molecules and placing them in a living cell. The templates obtained from the synthesis of new nucleic acid chains are used for replication. Molecular genetics actively uses the sequencing approach and some other high-tech methods.

Human genetics and characteristics

Heredity is ensured by the presence of genes whose carriers are chromosomes. The subject receives a set of genes from the mother, father. Transmission between generations is realized through germ cells. In the body, the gene is represented twice, transmitted by the mother and father. Genes can be identical, they can differ. In the first case, they speak of homozygosity, in the second, heterozygosity. The probability of the first option is extremely low, since there are too many genes. If there is a common line of ancestors, the chance of homozygosity is higher, since the father and mother pass on identical genes to the child. In practice, this is rare due to the institution of marriage relations and current laws. The philological foundation of the uniqueness of the personality, its uniqueness is explained by the diversity of the genetic set in each specific case.

Population human genetics is one of the most important branches of science. The human population differs significantly from other species, since it is a product of history, natural selection, and the development of society. Genetic reproduction is both a biological and a social process, associated with demography and inseparable from it and the reproduction of the population. The transfer of data between generations and the distribution of genetic sets, migrations and interrelationships with the human environment, provide for the movement of genetic material. It is safe to say that genetics and demography are closely related aspects; population genetics is in fact demographic, and the scientists involved in it study the results of processes inherent in demography.

Nuances and features

A long-term study of genetics and demographic changes allows us to conclude with confidence that the gene pool is constant over time, although it is represented in each specific generation by an abundance of unique genotypes. Permanence is provided by fertility and mortality, the movement of carriers of genetic information. The population gene pool can change, since different carriers of the material participate in the reproduction process with different degrees of activity. This feature is an element of natural selection, under the influence of which the structure of the gene pool changes, and the community is more consistent with the conditions of the environment in which a person lives.

In the human population, the change in the gene pool is to some extent due to mutations, gene drift and migration. Natural mutation is a process, the rate of which is considered to correspond to the normal change in the gene pool. The genotypes formed in such a process may be completely new, previously uncharacteristic of the community. Regular gene migration smooths out the differences between populations, leads to the loss of originality, uniqueness, explained by the local specifics of the environment.

Gene migration is due to the migration of carriers of genetic material. Currently, there is no way to unambiguously assess and describe the role of migration in the development of mankind. A number of consequences of migration are obvious, the main percentage of the world's population is the product of a mixed population.

Stability and progress

The chance that there will be no mutations, migrations, genetic selection is extremely small, but even if we imagine that this is possible, there is still the possibility of changing the gene pool. This is due to gene drift, that is, the process of genetic adjustment at the population level. In particular, a small population can lead to drift. As a rule, drift is characteristic of endogamous societies, whose distinctive feature is a small number of carriers of genotypes, while the potential diversity of sets of traits is extremely large.

The paucity of the population allows only a small percentage of possible sets of features to be realized in each new generation. Consequently, the gene pool of each new generation appears as a product of a random selection of a certain number of genes passed on from their parents.

In demographic genetics, gene drift is considered to be an environment-independent process. Exploring small human populations, one can see how the level of development of culture, society, economy affects the population size, how it affects the nature of interaction with the environment. The drift of genes, determined by the number of people in a society, depends on the specifics of the society and the environment in which it exists.

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Medical genetics is a direction devoted to heredity, hereditary pathologies and health, treatment and prevention of genetic diseases, as well as the problems of hereditary transmission of predisposition to diseases.

What is genetics?

An important part of medical genetics is clinical genetics, whose task is to detect and prevent hereditary pathology.

It is difficult to overestimate the role of genetics in modern medicine. As it turned out, it is huge, and even the considerable knowledge that has been accumulated in this area to date is, according to scientists, only the tip of the iceberg.

So, the doctors conducting, it was found that many types of cancer are hereditary, in particular:

• leukemia;
• most childhood cancers;
• and etc.

New technologies, gifts of scientific and technological progress, opened up new possibilities for genetics, and from a predominantly theoretical discipline, it became applied. Deciphering the human genome opened up the possibility of interfering with the genome, excluding some genes and activating others - this is the direction in which medical genetics is developing.

One of the important areas in which genetics is engaged is reproduction. Such a popular method of treating infertility as IVF, which has become firmly established in medical practice, also became possible thanks to the development of medical genetics. In addition, when a genetic diagnosis is always carried out, if the patient has indications.

Methods of foreign genetics

There are the following methods of human genetics:

• Genealogical. The method consists in tracking and studying pedigrees, it allows you to determine the patterns by which certain traits are inherited, including those that are responsible for hereditary diseases.
• Twin. The method studies the influence of the environment on the human genotype by comparing identical twins living in different conditions.
• Cytogenetic. A method consisting in a microscopic examination of chromosomes. With its help, chromosomal diseases are determined (for example, one of the variants of Down's syndrome).
• Sequestration. A method consisting in the study of human DNA at the molecular level.
• Dermatoglyphic. The method is based on the study of the relief of the skin of the fingers, palms and feet. With its help, a number of hereditary pathologies are diagnosed.
• Biochemical. It is used to study hereditary metabolic diseases, which are based on enzymatic disorders.
• Population statistical method - study of the patterns of hereditary traits in large groups of the population.

Genetic diagnostics abroad

A geneticist consultation includes genetic diagnostics. Genetic analysis allows us to determine not only the possibility of hereditary diseases, but also a predisposition to a number of common diseases.

For genetic analysis, blood is taken (5 ml), in addition, a thorough examination of the patient's history is carried out - this is necessary in order to correctly interpret the results obtained.

Most often, people turn to the genetic center or or any other country if they have certain suspicions of a possible hereditary pathology, if one of the family members (including a born child) has such a pathology, and during pregnancy, if there are certain indications.

Genetic diagnostics in pregnant women, with reasonable suspicions of the possibility of hereditary pathology, is carried out, including by invasive methods:

Treatment of genetic diseases abroad

Genetics abroad, thanks to the availability of state-of-the-art equipment and trained specialists, has great opportunities in the diagnosis of hereditary pathologies of all types. Patients apply to the Department of Genetics as directed by a doctor in the presence of certain indications (for example, families planning a child, in the presence of a confirmed genetic pathology in children already born) or of their own free will.

Regardless of whether it is a large institute of genetics, a genetics center or a genetics department, the patient will receive qualified assistance in full.

Each IVF medical diagnostic center also has the ability to carry out genetic diagnostics according to modern standards, which is why there are practically no children born with the help of artificial insemination who suffer from hereditary diseases.

The cost of treatment in genetics centers abroad

If you need advice on genetics, the UNIMED website invites you to fill out a contact form and contact us. We will provide you with comprehensive information, including regarding the possible cost of genetic diagnosis and treatment. Also on this portal you can find out the official and other countries.