Genetics is a basic science. Genetics. Basic concepts. Genetic laws of G. Mendel

Basic terms genetics

Each organism, including humans, has species-specific and individual specific features, or signs. Signs may be:

High quality. Such signs indicate the presence or absence of some quality. For example, dwarfism, blood type, Rh factor, phenylketonuria. Often only one gene influences the manifestation of a qualitative trait.

Quantitative. Quantitative characteristics are changed, counted and expressed in numbers, e.g. live weight, height, IQ. They can be described by a curve normal distribution(Fig. 2.1). They are usually influenced by many gene pairs.

Figure 2.1.

The manifestation of traits is influenced by the environment (social, geographic, environmental) and heredity.

Heredity- the ability of living organisms to transmit properties and functions from parents to offspring. This transmission is carried out using genes. The ability to acquire new characteristics different from the parent ones is called variability.

Gene(translated as “genus, origin”) is a functionally indivisible unit of genetic material. The main function of a gene is to encode a protein, since the gene contains information about the sequence of amino acids in the protein. Some genes do not code for protein, but control the functioning of other genes. The function of a third of the genes is currently unknown. The term “gene” was proposed in 1909 by V. Ioganson.

Allele- one of the possible structural states of the gene. A person can simultaneously have two alleles of one gene - one allele on each of a pair of homologous chromosomes. In principle, among the many different people There can also be many such different gene states, providing the so-called genetic polymorphism. The location of a gene (alleles) on a chromosome is called locus.

Genotype- the totality of all the genes of an organism.

Phenotype- special case implementation of the genotype in specific environmental conditions; external manifestation of the genotype. The terms “genotype” and “phenotype” were also introduced by V. Ioganson in 1909. The phenotype is the result of the interaction between the genotype and the environment in which the individual develops. A phenotype is something that can be observed. Usually, sets of traits are used to describe a phenotype.

Under the norm of the genotype reaction refers to the severity of phenotypic manifestations of a particular genotype depending on changes in environmental conditions. It is possible to distinguish a range of reactions of a given genotype from minimum to maximum phenotypic values, depending on the environment in which the individual develops. Different genotypes in the same environment can have different phenotypes. Typically, when describing the range of reactions of a genotype to environmental changes, they describe situations where there is a typical environment, an enriched environment, or a depleted environment in the sense of a variety of stimuli influencing the formation of the phenotype.

Phenotypic differences between different genotypes become more pronounced if the environment is favorable for the manifestation of the corresponding trait. For example, if a person has a genotype that determines math skills, then he will demonstrate high abilities both in depleted and enriched environments. But in an enriched (favorable) environment, the level of mathematical achievement will be higher. In the case of another genotype, which determines low mathematical ability, changing the environment will not lead to significant changes in the level of mathematical achievement.

Genome- a set of genes characteristic of individuals of a given species. The original meaning of this term indicated that the concept of genome, in contrast to genotype, is genetic characteristics the species as a whole, rather than an individual. With development molecular genetics meaning this term has changed. Currently, the genome is understood as the totality of hereditary material of a specific representative of a species, an example is international project 1000 Genomes, which aims to sequence the genomes of 1000 people.

Dominant allele - an allele that masks the presence of another allele.

Recessive allele - an allele whose phenotypic manifestation is masked by another (dominant) allele. For a recessive allele to manifest, two alleles usually need to be present.

The organism is called homozygous, if there are identical copies (alleles) of genes. The body will heterozygous, if there are different copies of genes. If, for example, two different states of a gene are designated by the letters A and a, then homozygotes are designated AA and aa, and a heterozygote is designated Aa.

It has been established that the material carrier genetic information is DNA (deoxyribonucleic acid), which in humans has 46 chromosomes. Genes are located in chromosomes(colored bodies) and are giant DNA molecules stretched up to 2 meters long. The chromosomal theory of heredity was formulated in 1902. If you add up all the DNA of a person in one line, you get a length that is 1000 times greater than the distance from the Earth to the Sun.

Chromosomes are combined into pairs (chromosomes in pairs are called homologous). In total, a person has 23 pairs of chromosomes, and he receives one chromosome in a pair from his father, and the other from his mother (Fig. 2.2). The set of chromosomes contained in gametes is called a haploid set, and the cells of an organism developing from a zygote contain a diploid set of chromosomes.

Of the 23 pairs of chromosomes, 22 pairs are the same in men and women, they are called autosomes, and the 23rd pair is different for men and women. These are sex chromosomes. The chromosome carrying the “female” set of genes is the X chromosome, and the male one is the Y chromosome. Women always have two X chromosomes (XX karyotype), and men always have one chromosome - X, and the other - Y (karyotype XY) - fig. 2.3. Genes located on the sex X chromosome are characterized by specific transmission, which is called “criss-cross”. With this inheritance, the mother's trait appears in sons, and the father's trait appears in daughters.

Figure 2.2.


Figure 2.3.

In the late 40s of the 20th century, it was discovered that women’s cells contain peculiar chromatin clumps, called sex chromatin or Barr bodies after the researcher who discovered them. Men did not have such chromatin. It turned out that the Barr body is formed from one X chromosome. The formation of Barr bodies in humans is associated with maintaining the dosage ratio of genes in the genotype (gene balance). The Y chromosome contains few genes, and the X chromosome contains approximately 20% of all genes. It is thanks to this mechanism that the effect of the X chromosome, present in women in a double dose, is no stronger than in men who have only one X chromosome and, accordingly, one dose of genes. Any of the X chromosomes on the early stages embryogenesis, when the number of cells in the embryo is relatively small.

The material basis of heredity is DNA, which is a double helix. This type of it was discovered in the 50s of the 20th century John Watson And Francis Crick.

DNA consists of 4 types of nucleotides - bases. These include: A (adenine), T (thymine), C (cytosine), G (guanine). When forming a spiral, A connects to T, and G to C hydrogen bonds. The human genotype consists of 3 billion letters and combinations of nucleotides. If we compare the number of nucleotides with the number of letters, then the sum of nucleotides on a person’s 46 chromosomes, inherited from his father and mother, corresponds to the number of letters from the file of the newspaper “Moskovsky Komsomolets” for 30 years.

The property of DNA is to copy itself and retain changes. The mechanism of protein synthesis is very complex: in addition to DNA, RNA (ribonucleic acid) is also required.

RNA are polymers consisting of a phosphoric acid residue, ribose sugar, heterocyclic bases: adenine, guanine, uracil, cytosine. There are several types of RNA that have different structure and perform various functions.

Messenger (messenger) RNA(m-RNA) - a ribonucleic acid molecule containing information about the sequence of amino acids in a protein, ensures the rewriting (transcription) of genetic information from a DNA molecule. Figuratively, we can say that DNA is a blueprint, and RNA is a copy of the blueprint that is used in production.

Transfer RNA participates in the translation (translation) of the m-RNA nucleotide sequence into the amino acid sequence of the protein chain. Protein biosynthesis is carried out by protein organelles - ribosomes, which have ribosomal RNA (Fig. 2.4).

Figure 2.4.

Highlight the following types chromosomes depending on the ratio of the length of the short arm to the length of the entire chromosome (Fig. 2.5):

Telocentric (one pair of shoulders is missing - not found in humans);

Acrocentric (rod-shaped chromosomes with a very short, almost imperceptible second arm);

Submetacentric (with arms of unequal length, resembling the shape of the letter b);

Metacentric (Y-shaped chromosomes with arms of equal length).


Figure 2.5.

In each of the 23 pairs of chromosomes different quantities genes formed by a huge number of DNA bases (Table 2.1). There are chromosomal and cytoplasmic (mitochondrial) inheritance. Chromosomal heredity is determined by genes localized on chromosomes and the patterns of doubling, unification and distribution of chromosomes during cell division. Hereditary factors are found both in the cytoplasm and mitochondria. Cytoplasmic hereditary factors are distributed randomly between daughter cells; no patterns of inheritance were found here, that is, when genetic patterns are discussed, this refers to chromosomal heredity.

Table 2.1. Number of genes on chromosomes

Chromosome

Total bases

Number of genes

Number of protein-coding genes

X chromosome

Y chromosome

The process of fertilization involves two cells - the egg and the sperm. The egg is a large cell containing many mitochondria. The sperm, although it contains several mitochondria, loses them during or immediately after penetration into the egg due to the dissolution of the tail part. Therefore, only the sperm nucleus is involved in fertilization (with rare exceptions, the transfer of paternal mitochondria is also possible), that is, all mitochondria in the cells of a future person are of maternal origin (see Appendix B).

Mitochondrial DNA can persist in remains for many years. Her characteristics can serve as strong evidence of relationship. Yes, identification royal family Nicholas II on fossil remains was carried out on the basis of the analysis of mitochondrial DNA (Fig. 2.6).

Figure 2.6.

The mitochondrial genome has already been deciphered. It is represented by a circular DNA molecule containing 16,569 nucleotides. Mutations in mitochondria may cause hereditary diseases.

Karyotype is a set of characteristics (number, size, shape, etc.) of a complete set of chromosomes inherent in the cells of a given biological species (species karyotype), of a given organism(individual karyotype) or line (clone) of cells. A karyotype is sometimes also called a visual representation of the complete chromosome set (karyogram). When written, it indicates the number, size, and shape of chromosomes. For example:

46, XY - normal karyotype of a man;

46, XX - normal karyotype of a woman;

47, XX + 8 - karyotype with an extra chromosome in 8th position; 45, X0 - karyotype with a missing chromosome.

As a rule, karyotype abnormalities in humans are accompanied by multiple malformations; most of these anomalies are incompatible with life and lead to spontaneous abortions in the early stages of pregnancy. The proportion of miscarriages due to karyotype abnormalities during the first trimester of pregnancy is 50-60%. Karyotype disorders can also occur in the early stages of zygote fragmentation; the organism developed from such a zygote contains several cell lines (cell clones) with different karyotypes; such a multiplicity of karyotypes of the whole organism or its individual organs is called mosaicism.

Mendel's laws

The basic laws of heritability were described by the Czech monk Gregor Mendel (1822-1884). Mendel was engaged in the selection of peas and it was to the pea that he owed the discovery of the basic laws of heredity. Mendel carried out his work for 8 years, studied more than 10,000 pea plants, and presented the results of his work in an article in 1865. In this article, he summarized his work and formulated 3 basic laws of heredity.

Law of uniformity of first generation hybrids (Mendel's first law)

This law states that crossing homozygous individuals that differ in the trait under study produces genetically and phenotypically homogeneous offspring, all individuals of which are heterozygous. In Mendel's experiments, all first-generation hybrids had the phenotype of one of the parents (complete dominance). In experiments, he crossed green and yellow peas. And all the first generation hybrids were yellow. This trait (yellow color) was called dominant (Fig. 2.7).


Figure 2.7. Illustration of the first law Mendel

Law of segregation of second generation hybrids (Mendel's second law)

When crossing with each other among the second generation hybrids, the original parental forms are restored in certain proportions. In the case of complete dominance, this ratio is 3: 1. Three quarters of the hybrids carry a dominant trait, one quarter - a recessive one. When crossing hybrid yellow peas (descendants of green and yellow peas), three-quarters of the descendants were obtained yellow color, one quarter - green.

Law of independent combination (inheritance) of characteristics (Mendel's third law)

This law says that every couple different signs behaves in a number of generations independently of each other. So, the color and shape of peas are inherited independently. The color (yellow or green) has nothing to do with the shape (smooth or wrinkled) of the peas (Fig. 2.8).


Figure 2.8.

Modern genetics has established that Mendel's third law is satisfied only for traits whose genes are located on different chromosomes. If the genes for two traits are on the same chromosome, then these traits are inherited linked, i.e. are inherited as a connected pair of elements, and not as separate elements. For example, hair color and eye color are inherited in a linked manner. In practice, this means that most fair-haired people have light eyes, and conversely, most dark-haired people have dark eyes.

But even with linked inheritance, it is possible that the traits will still diverge in the next generation; this is due to crossing over - the process of a gene passing from one homologous chromosome to another in a pair.

Basic concepts of genetics

The subject of the study of genetics is two inseparable properties of all living organisms - heredity And variability. Variability is represented by the variety of forms within each species, breed, and even one litter. But at the same time, all representatives of the same species and one breed have undeniable similarity provided by heredity.

Each animal species has a characteristic set of chromosomes a certain shape, constituting karyotype

Sex cells contain half the set of chromosomes, called haploid, which is usually denoted - n. Egg formed by merger contains two sex cells twice large quantity chromosomes, the so-called diploid kit - 2n. Each pair of chromosomes in the diploid set is represented by homologous chromosomes, one of which is received from the father and the other from the mother. The diploid set of dogs is represented by 78 chromosomes.

All hereditary properties and characteristics are determined by well-defined material units independent of each other - genes. Each gene occupies strictly specific place on a strictly defined chromosome, called locus. Due to the pairing of chromosomes in cells, genes in the chromosome set are also presented in pairs. Genes located at the same locus are called allelic or alleles. Genes can undergo changes in their structure - mutate, as a result they change external manifestations trait for which this allele is responsible. Individuals who have received identical alleles of one locus from their father and mother are called homozygous, and different - heterozygous on this basis. Genes and alleles are usually designated by letters Latin alphabet, For example A, F, tfm and so on.

Interaction allelic genes

Being in a heterozygous state, the alleles interact with each other in a certain way. In the case when one of them completely suppresses the action of the other, it is called complete dominance. The dominant gene is usually designated capital letter Latin alphabet. At complete dominance heterozygous individuals Aa have the same appearance or phenotype, as well as homozygous for the dominant allele AA. This means that for manifestation dominant trait one dominant allele is sufficient, which is denoted as A -.

If heterozygous individuals differ in phenotype from homozygous ones and have an intermediate phenotype, then they speak of incomplete or intermediate dominance. For example, crossing a light sable collie with a tri-color collie will result in dark sable puppies.

At overdominance - in first generation hybrids it is observed heterosis - the phenomenon of superiority of offspring over parental forms in vitality, growth energy, and fertility. Thus, hybrids obtained by crossing wild gray rats - pasyuks with white laboratory rats, are similar in appearance to pasyuks, but are much larger and more fertile than the latter.

At co-dominance in a hybrid individual equally Both parental characteristics appear. Most antigenic factors are inherited according to the type of codominance. numerous systems blood groups.

In cases where the behavior of traits caused by one pair of alleles is analyzed, for example black B and brown b color, they talk about monohybrid cross. The crossing of individuals that differ in two pairs of characteristics is called dihybrid, three - trihybrid, for many - polyhybrid by crossing.

Mendel's laws

Back in the last century, Gregor Mendel showed the patterns of transmission of traits during crossing. He formulated the following laws:

Mendel's First Law is the law of uniformity of first generation hybrids.

Crossing with each other individuals homozygous for different alleles of the same locus leads to the birth of heterozygous offspring of the same phenotype. So when crossing homozygous blacks with each other BB and brown bb dogs, all puppies turn out black Bb.

Individuals belonging to the parent generation are designated Latin letter R. First generation hybrids - F 1 , second generation hybrids F 2 , hybrids of the third - F 3 etc.

II Mendel's Law - law of splitting states: when crossing hybrids of the first generation with each other, a split in phenotype occurs in the ratio 3:1, and by genotype 1:2:1. When crossing black heterozygous dogs with the genotype Bb in a litter you can expect the birth of three parts black, consisting of 1 part homozygotes BB and 2 parts heterozygotes Bb, and one part of brown puppies with the genotype bb.

Mendel also formulated rule purity of gametes, which states that genes that are in a heterozygous state do not mix with each other, but are transferred to the germ cells unchanged.

It is possible to determine which of the individuals with a dominant phenotype is homozygous and which is heterozygous only by conducting the so-called test cross with a homozygous recessive form. With such a crossing, if the individual under study is homozygous, there will be no splitting in the offspring. In the case of heterozygosity, a splitting in the ratio will be observed 1:1.

Another rule that was formulated by Mendel is called rules for independent segregation of alleles. It consists in the fact that in the second generation, each pair of alleles and traits determined by them behaves independently of other pairs of alleles and traits, respectively.

For the convenience of analyzing crosses, graphical notations have been introduced, the so-called "Punnet grid" in which the father's gametes are listed in the top row, and the mother's gametes in the left vertical row. At the intersection of rows and columns - the genotypes of the descendants.

As an example, let's look at crossing heterozygous black dogs.

The Punnett grid is convenient because it automatically identifies all possible genotypes and makes it convenient to count them. IN in this case it is clearly visible that in the offspring of these producers there will be a split both in genotype and phenotype.

The possible number of genotypes and phenotypes in the offspring depends on the number of pairs of analyzed traits. The table below allows you to determine the numerical ratios in the offspring of a polyhybrid cross.

Table 8. Numerical ratios in the offspring of a polyhybrid cross

Qualitative and quantitative characteristics.

All the characteristics that living organisms possess are usually divided into two categories - qualitative and quantitative. Quality - characteristics that have clearly distinguishable forms, for example, color or genetic abnormalities transmitted by individual genes. Environmental conditions have virtually no effect on the phenotypic manifestation of qualitative traits. To characterize a population based on qualitative characteristics, the concepts are used frequency of genes and genotypes.

However most of properties of the body are presented quantitative signs. They show mostly continuous variability and can be measured - height, coat length, weight. Quantitative characteristics, in to a greater extent than qualitative ones, depend on environmental conditions and are determined by many genes, the so-called polygenes, that is, a system of non-allelic genes that equally influence the formation of a given trait. The interaction of such genes in the process of trait formation is called polymeric. These genes are also called additive because their effects are additive.

Their distribution numerical values in the population approaches normal distribution curves. Their inheritance can be considered according to the polyhybrid crossing scheme.

The breeder has to deal mainly with continuous variability. Mendelian approach to study quantitative characteristics difficult, although they are subject to the same laws classical genetics, which are of high quality.

Interaction of nonallelic genes

Genes located in different loci can also influence each other. In this case, several types of such interaction can be distinguished.

Genes that do not express own action, but enhancing or weakening the effect of other genes are called modifier genes. The study of coloration in mammals has shown that, along with extreme forms with full development of pigment or its absence, a number of genotypically determined forms are observed. Thus, white spotting in dogs varies from a few white hairs at the site of the primary point of depigmentation to a completely white dog with a small tuft of colored hair in one of the pigment centers. Within the genotype determined by the white spot locus S, a lot of transitional forms can be identified.


Rice. 17. Different variants white spotting in dogs

Black and brindle dog colors have wide variability due to modifier genes.

If a trait is formed in the presence of two pairs of non-allelic genes, which, when acted together, do not produce the same effect that each of them causes independently, then such alleles are designated as complementary (complementary to each other). The interaction of gene loci is usually cited as an example of complementarity in dogs. IN And E, determining color.

Rice. 18. Complementary interaction of genes that determine the color of dogs: ratio - 9 black (B): 3 brown (R): 3 red (R): 1 fawn (P)

Locus genes IN are responsible for the synthesis of black ( IN ) or brown ( b ) pigment. Locus genes E are responsible for the distribution of these pigments. Allele E promotes the spread of black or brown pigment throughout the dog's body. Allele e prevent their synthesis in the coat. Dogs with genotype her - red or yellow. The black or brown pigment is concentrated only on the skin of the dog’s face.

The formation of a dog's color depends on the presence of both pairs of genes. Dogs with genotype HER or Her - black or brown depending on alleles B or b. At E-BB or E-Bb - the dog is black, with E-bb - brown.

Dogs with genotype herV- - red with a black nose. Dogs genotype bbee - usually fawn or light yellow with a light nose.

The complementary interaction of genes is due to special type paralysis of the hind limbs in Great Dane-St. Bernard crosses. Genetic analysis conducted by Stockard (1936), showed that with purebred breeding of both Great Danes and St. Bernards, paralysis does not develop.

A similar disease was noted in some crossbred bloodhound dogs (Petukhov et al., 1985).

In any pair of alleles, the dominant gene prevents (fully or partially) the expression of its recessive partner. But sometimes the effect of a dominant allele is suppressed by the action of a gene from another locus. An omnipotent gene that blocks the action of another gene or genes is called epistatic. And the phenomenon itself - epistasis. Genes whose action is suppressed are called hypostatic.

Thus, recessive dog color genes from the locus C do not allow the synthesis of pigments that determine the color of the coat. A dog homozygous for them is white.

The same mutant trait may appear in some individuals and not in others. related group. The ability of a given gene to express itself phenotypically is called penetrance. Penetrance is determined by the percentage of individuals in a population that have the mutant phenotype. With complete penetrance (100%), the mutant gene manifests its effect in each individual. With incomplete penetrance (less than 100%), the gene does not manifest itself phenotypically in all individuals.

In dogs, modifications to their tails in the form of shortening, various kinks and bends are quite common. It can be assumed that the diversity of this trait is due to its incomplete penetrance.

The degree of penetrance can vary greatly depending on environmental conditions.

Rice. 19. Scheme of dihybrid splitting with recessive epistasis: BB F 2 obtained 9 black: 3 brown: 4 white dogs. Thus, a deviation from the theoretically expected 9:3:3:1 split is observed, characteristic of recessive epistasis.

Often individuals that have the same genotype with respect to any hereditary trait are very different in its expressiveness, that is, the degree of manifestation of a given characteristic. The same gene in different individuals, depending on the influence of modifier genes and external environment may manifest itself phenotypically in different ways. The external environment and modifier genes can change gene expression that is, the expression of a feature.

Unlike penetrance, which refers to what proportion of individuals in a population exhibit a given trait, expressivity refers to the variability of a trait in those individuals that exhibit it. Thus, in dogs, the expressiveness of the development of dewclaws varies from fully developed digits on both hind limbs to their rudimentary presence on only one limb. A similar variation in expressivity is also characteristic of other inherited traits, in particular the above-mentioned tails.

The expressivity and penetrance of the gene apparently depend to a large extent on the influence of modifier genes and the developmental conditions of the individuals.

A fairly widespread phenomenon pleiotropy - the influence of one gene on the development of two or more traits. A classic “canine” example of pleiotropic influence is action Merle factor, (locus M ; dog color). Allele M in a heterozygous state Mm produces the “harlequin” spotting characteristic of Great Danes. Allele M in heterozygote mm in combination with tan it gives a “marbled” (blue-merle) color, typical of collies and shelties. In a homozygous state MM it leads to the birth of pure white puppies ( white-merle) with significant abnormalities of the sensory organs. Such puppies often die before birth, and if they are born alive, their viability is sharply reduced.

The phenomenon of pleiotropy is explained by the fact that genes with pleiotropic action control the synthesis of enzymes involved in numerous metabolic processes in the cell and in the body as a whole and, thus, simultaneously influencing the manifestation and development of many traits.

Some genes cause such strong deviations from the norm that they reduce the viability of the organism or even lead to its death. Such genes are called lethal, that is, deadly, or sublethal - reducing vitality. In most cases, lethal genes are completely recessive, so heterozygous carriers of these genes are phenotypically completely indistinguishable from normal individuals. In a homozygous state, such genes can disrupt the normal course of embryo development at any stage. The possibility of the presence of lethal genes can be indirectly judged by the decrease average number litters or by the loss of some expected part of the phenotypes in the split.

So, in the case of crossing the above-mentioned black merle dogs, heterozygous for the Merle factor, instead of the expected ratio, 3:1, it turns out 2:1 i.e. 2 marbled and 1 black dogs mm ? mm = MM: 2 mm: mm, Where MM white non-viable dog. White puppies are often not born at all, as they die long before birth.

Rice. 20. Inheritance of harlequin marbling in Great Danes. Gene M h (Merle factor) - dominant with a recessive lethal effect: 1 - crossing Great Danes with each other; 2 - analyzing crossing

The Merle factor belongs to the category of dominant lethal genes, of which there are significantly fewer than recessive ones. If desired, its carriers can be easily removed from breeding, since they have a characteristic phenotype. Some lethal genes cause major anomalies, others cause disorders physiological processes. The pathways for the deleterious effects of most lethal genes are unclear. There can be as many such genes as desired. It has been shown that each person is a carrier of an average of 4–9 “harmful” or lethal genes. Similar results can be expected for dogs. There are known lethal genes that, when manifested in the embryonic state, are also dangerous for the life of a pregnant bitch, for example, with hereditary contracture of the fetal muscles, as a result of which the bitch cannot give birth.

The interaction of genes, when when they are combined in one organism, completely new form the sign is called neoplasm.

Sometimes neoplasms lead to the appearance of signs of a wild phenotype. In this case they are called atavisms, that is, a return to the ancestral form or return to wild type.

Partial returns to the wild type are possible when crossing two individuals of the same breed if these producers originate from unrelated populations distant from each other. Apparently In a similar way The great similarity between mongrels living in very different places can also be explained.

Sex-linked traits

Sex-linked traits are called those that are formed under the influence of genes localized in X -chromosome. Most typical example The inheritance of a sex-linked trait is the inheritance of canine hemophilia. In dogs with hemophilia, the blood lacks a factor that, interacting with blood platelets (platelets), accelerates the conversion of prothrombin to thrombin. Canine hemophilia is similar to human hemophilia and is also caused by a sex-linked recessive gene. The gene that determines the development of hemophilia is located in X -chromosome and is recessive in relation to the normal allele. Consequently, hemophilia occurs only in homozygous females (carrying this gene in both X -chromosomes) and hemizygous males carrying the hemophilia gene in X -chromosome. Hemophilic puppies usually die in early age from external or internal bleeding. It is possible to preserve such a male to a mature state only if constant introduction specific drugs. Females inevitably die no later than the first estrus. Heterozygous females are completely normal in appearance and fertile. However, half of their male cubs suffer from hemophilia and half of their female cubs are heterozygous for this gene.

Parents:

female carrier of the hemophilia gene

X H X h

normal male

X H Y

Sex chromosome carrying the normal allele

X H

Xh - sex chromosome, carrying the hemophilia gene

Sex-linked traits also include congenital hypotrichosis, noted in dachshunds and miniature poodles; muscular dystrophy in retrievers; staggering syndrome associated with hypomyelination and found in chow chows and a number of other breeds; wrist subluxation ; and diaphragmatic hernia, described in golden retrievers.

Sex-limited traits

Some traits, completely independent of the location of the genes that cause them, appear only in individuals of one sex. These are the so-called limited by gender signs. These are, for example, defects in the development of the reproductive system, milk production, etc. One of these phenomena is cryptorchidism - failure of one or both testes to pass through the inguinal canal into the scrotum. Cryptorchidism is bilateral, right- or left-sided and can be caused by for various reasons: narrowness of the inguinal canal, short ligaments of the testes, underdevelopment of the testes. Undescended testes can be located in different places abdominal cavity. Cryptorchidism can be either congenital or acquired. Among its various forms, there is also a genetically determined one. However, due to the wide variability of this trait, it is impossible to draw unambiguous conclusions about its nature. And it is completely wrong to interpret it as a monogenic trait localized on the X chromosome.

Law homologous series N.I. Vavilova

The law was formulated by N.I. Vavilov in 1920. N.I. Vavilov discovered that all species and genera that are genetically close to each other are characterized by identical series of hereditary variability.

The law of homological series is based on the parallelism of genotypic variability in individuals with a similar set of genes.

This law is universal. Similar mutations were found in different types animals. Thus, manifestations of similar forms of anomalies were noted in dogs, cats, rabbits, pigs, humans, etc., which indicates the similarity of the structure of many enzymes and proteins and, accordingly, the similarity of genotypes. Thus, knowing the forms of hereditary changes in one species of animal, we can assume that they exist or may occur in another related species. Hereditary anomalies in farm animals and humans have been studied especially carefully. Significantly fewer anomalies have been described in dogs, but this only indicates that this species has been less studied. Thus, when a new abnormality is discovered in dogs, one should inquire whether it has been described in other animal species.

In the main breed-forming groups of dogs, there is homology in many characteristics. For example, leg length - achondroplasia occurs in shepherd dogs (Welsh corgis), terriers (Skye terriers, Seliham terriers, Dandy Diamond terriers), hounds (Basset), pointers, Great Danes (bulldogs), Tibetan dogs (Lhasa Apso, Shih Tsu), periodically Elements of achondroplasia are found in poodles. Similar dogs were not noted only in the group of greyhounds, since this sign is the opposite of acromegaly.

In all breed groups there are both giant and dwarf forms. In shepherd dogs (Komondor - Schipperke), mastiffs (mastiff - French bulldog), terriers (Airedale terrier - toy terrier), hounds (Bloodhound - Beagle), Spitz dogs (Alaska Malamute - Pomeranian Spitz), greyhounds (Irish Wolfhound - Italian Greyhound). Homologous variability in size from giants to dwarfs is also observed among narrow breed groups. For example, schnauzers (Riesen - Mittel - Zwerg), dachshunds (standard - dwarf - rabbit), poodles (standard - small - dwarf - toy poodle).

Characteristics showing homology are color and coat type.

From the book What if Lamarck is right? Immunogenetics and evolution by Steele Edward

Basic concepts of immunology AntigenAntigens are foreign proteins and carbohydrates that stimulate the formation of specific antibodies that bind to a given antigen, but not to other unrelated antigens. Self antigens are proteins or carbohydrates that

From the book Ecology [Lecture notes] author Gorelov Anatoly Alekseevich

1.1. Basic concepts of ecology

From the book The Human Genome: An Encyclopedia Written in Four Letters author Tarantul Vyacheslav Zalmanovich

MAIN MILESTONES OF GENETICS AND GENOMICS Inventas vitam juvat excoluisse per artes. Inventions improve life, art decorates it. Inscription on the Nobel medal, a phrase from Virgil’s “Aeneid” 1865 Discovery of heredity factors by G. Mendel (1822–1884) and development of the hybridological method,

author

Basic concepts Anticodon is a triplet of t-RNA nucleotides that determines its specificity and the region of attachment to mRNA. Secondary structure nucleic acids– order of laying of the polynucleotide strand. Nucleotide – monomer of nucleic acids. Primary structure

From the book Human Genetics with the Basics general genetics[Self Study Guide] author Kurchanov Nikolay Anatolievich

Basic concepts Bivalents are pairs of homologues united as a result of synapsis. Gametes are cells capable of merging with each other to form a diploid cell (zygote), giving rise to a new organism. Haploid set is a set of chromosomes containing half of the diploid

From the book Human Genetics with the Basics of General Genetics [Self-study Guide] author Kurchanov Nikolay Anatolievich

Basic concepts Allele is a variant of one gene. Autosomes are non-sex chromosomes of a karyotype. Hemizygote is the presence of only one allele in the genotype of a diploid organism. Gene (within the framework of classical genetics) is an elementary structure that encodes an individual

From the book Human Genetics with the Basics of General Genetics [Self-study Guide] author Kurchanov Nikolay Anatolievich

Basic concepts Gene mutations are changes in the nucleotide composition of the DNA of individual genes. Genomic mutations are changes in the number of chromosomes. Genotypic pre-adaptation is the influence of the environment, expressed by modifications, on the mutation process and recombination during

From the book Human Genetics with the Basics of General Genetics [Self-study Guide] author Kurchanov Nikolay Anatolievich

From the book Human Genetics with the Basics of General Genetics [Self-study Guide] author Kurchanov Nikolay Anatolievich

Basic concepts Vectors are structures capable of transferring foreign DNA into a recipient cell. Palindromes are short sections of DNA in which the writing of nucleotides from left to right in one chain is similar to the writing from right to left of another chain. Polymerase chain reaction(PCR) –

From the book Human Genetics with the Basics of General Genetics [Self-study Guide] author Kurchanov Nikolay Anatolievich

Basic concepts Assortativity - selective crossing: the genotype influences the choice of a marriage partner, i.e. individuals with certain genotypes mate more often than with random probability. Gene pool - the totality of alleles of all inhabiting the population

From the book Human Genetics with the Basics of General Genetics [Self-study Guide] author Kurchanov Nikolay Anatolievich

Basic concepts Altruism is behavior aimed at the well-being of relatives. Appetite behavior is the first stage instinctive behavior, which consists of an active search for special key stimuli. Drive - an urge to perform certain actions. Instinct -

From the book Human Genetics with the Basics of General Genetics [Self-study Guide] author Kurchanov Nikolay Anatolievich

Basic concepts Genocopies - similar phenotypes that arise during the expression of different genes. Carcinogenesis - the process of formation and formation of malignant tumors. Clinical polymorphism - the variety of phenotypic manifestations of various pathologies. Malignancy -

From the book Human Genetics with the Basics of General Genetics [Self-study Guide] author Kurchanov Nikolay Anatolievich

Basic concepts Evoked potentials (EP) are specific bioelectrical activity associated with a specific stimulus. GS correlations (genotype-environment correlations) are the phenomenon of non-random distribution of environments between different genotypes in humans. Related

From the book Human Genetics with the Basics of General Genetics [Self-study Guide] author Kurchanov Nikolay Anatolievich

Basic concepts Dysgraphia - a specific inability to write. Dyslexia - a specific inability to read. Impression - unusually strong emotionally charged childhood events that leave impressions for life. Emergent property -

From the book Human Genetics with the Basics of General Genetics [Self-study Guide] author Kurchanov Nikolay Anatolievich

Basic concepts Apoptosis is programmed cell death, which is implemented by a genetic “suicide” program. Genes “ household"(housekeeping genes) - genes associated with maintaining universal cellular functions. "Luxury" genes - associated with

From the book Human Genetics with the Basics of General Genetics [Self-study Guide] author Kurchanov Nikolay Anatolievich

Basic concepts Secondary sexual characteristics are morphophysiological characteristics of phenotypes of different sexes that are not related to the reproductive system. Hermaphroditism is a direction in the processes of sex differentiation, leading to the formation of organisms with characteristics of both

Introduction.

1. History of the development of genetics.

2. Basic concepts of genetics, methods of their study.

3. Gene identification. Main function of the gene.

4. The role and tasks of genetics.

Conclusion.

List of used literature.

Introduction.

My theme test work“Basic concepts and ideas of genetics.” Genetics is the science of heredity and variability of organisms. She takes leading place in modern biological science.

This topic interested me because modern society genetic issues are widely discussed in different audiences and with different points point of view, including ethical. Interest in human genetics is due to several reasons. Firstly, this is a person’s natural desire to know himself. Secondly, after many were defeated infectious diseases- plague, cholera, smallpox, etc., - the relative proportion of hereditary diseases has increased. Thirdly, once the nature of mutations and their significance in heredity were understood, it became clear that mutations can be caused by environmental factors that had not previously been given due attention. Began intensive study effects on heredity of radiation and chemical substances. Every year, more and more chemical compounds are used in everyday life, agriculture, food, cosmetics, pharmacological industries and other areas of activity, among which many mutagens are used.

In my work I want to talk about the history of the development of genetics, consider the basic concepts (heredity and variability), methods for studying them, and dwell on the carrier hereditary information(gene), voice the tasks of genetics and its role.

Human genetics, rapidly developing in recent decades, has provided answers to many of the questions that have long interested people: what determines the sex of a child? Why do children look like their parents? Which signs and diseases are inherited and which are not, why are people so different from each other, why are closely related marriages harmful?

Modern genetics is characterized by the deepening of all its sections to the molecular level of research, the development of a network of interdisciplinary approaches, especially in contact with physical and chemical biology, cybernetics, the penetration of genetic methodology and approaches into all biological sciences, as well as in anthropology and general pathology person.

Genetics is designed to reveal the laws of reproduction of living things through generations, the emergence of new properties in organisms, the laws individual development individuals and material basis historical transformations of organisms in the process of evolution. The first two problems are solved by gene theory and mutation theory. Clarification of the essence of reproduction for a specific variety of life forms requires the study of heredity in representatives at different stages evolutionary development. The objects of genetics are viruses, bacteria, fungi, plants, animals and humans. Against the background of species and other specificities in the phenomena of heredity for all living beings, general laws. Their existence shows the unity of the organic world.

History of the development of genetics.

Man has been raising domestic animals and growing crops for a long time. At the same time, he constantly improves them, leaving the best individuals for reproduction - the most useful for humans. As we penetrated into the essence of the phenomena of heredity and variability of organisms, methods and techniques for breeding new varieties and breeds were improved and improved.

The foundations of genetics were laid by the Czech scientist Gregor Mendel in experiments, the results of which were published in 1865. Since then, genetics has not stopped in its development. I.M. Sechenov, A.P. Bogdanov, N.K. Koltsov, G. Schade, Avery, McLeod, McCarthy, D. Watson - these are some of those great scientists who made a huge contribution to the science of heredity.

Genetics has gone through three well-defined stages in its development.

The first stage was marked by the discovery by G. Mendel (1865) of factors of heredity and the development of the hybridological method, i.e., the rules for crossing organisms and taking into account the characteristics of their offspring. Mendel first realized that, starting from the very simple case- differences in one single trait and gradually complicating the task, one can hope to unravel the whole tangle of patterns of inheritance of traits. This approach to setting up experiments allowed Mendel to clearly plan the further complexity of his experiments. Mendelian laws of heredity laid the foundation for the gene theory - greatest discovery natural sciences of the 20th century, and genetics has become a rapidly developing branch of biology. In 1901-1903 de Vries nominated mutation theory variability that played big role in the further development of genetics. The work of the Danish botanist V. Johannsen, who studied the patterns of inheritance in pure lines of beans, was important. He also formulated the concept of “population” (a group of organisms of the same species living and reproducing in a limited area), proposed calling Mendelian “hereditary factors” by the word gene, and gave definitions of the concepts “genotype” and “phenotype”. At the first stage, the language of genetics was formed, research methods were developed, fundamental principles were substantiated, and basic laws were discovered.

The second stage is characterized by a transition to the study of heredity phenomena in cellular level(cytogenetics). T. Boveri (1902-1907), W. Setton and E. Wilson (1902-1907) established the relationship between the Mendelian laws of inheritance and the distribution of chromosomes during cell division (mitosis) and maturation of germ cells (meiosis). The development of the study of the cell led to a clarification of the structure, shape and number of chromosomes and helped to establish that the genes that control certain characteristics are nothing more than sections of chromosomes. This served as an important prerequisite for the statement chromosome theory heredity. Crucial it was substantiated by studies conducted on American Drosophila flies

geneticist T. G. Morgan and his colleagues (1910-1911). They found that genes are located on chromosomes in a linear order, forming linkage groups. Morgan also established patterns of inheritance of sex-linked traits. It became possible to intervene in the mechanism of variability, the study of genes and chromosomes was further developed, the theory of artificial metagenesis was being developed, which allowed genetics from theoretical discipline go to applied.

The third stage in the development of genetics reflects the achievements molecular biology. And is associated with the use of methods and principles exact sciences- physics, chemistry, mathematics, biophysics and others. As well as the study of life phenomena at the molecular level. Objects genetic research became fungi, bacteria, viruses. At this stage, the relationships between genes and enzymes were studied and the “one gene - one enzyme” theory was formulated (J. Beadle and E. Tatum, 1940): each gene controls the synthesis of one enzyme; the enzyme, in turn, controls one reaction from a number of biochemical transformations that underlie the manifestation of external or internal sign body. This theory played important role in clarifying physical nature gene as an element of hereditary information.

In 1953, F. Crick and J. Watson, relying on the results of experiments by geneticists and biochemists and on X-ray diffraction data, created a structural model of DNA in the form double helix. The DNA model they proposed agrees well with biological function of this compound: the ability to self-duplicate genetic material and sustainably preserve it over generations - from cell to cell. These properties of DNA molecules also explained the molecular mechanism of variability: any deviations from the original structure of the gene, errors in self-duplication of the genetic material of DNA, once arising, are subsequently accurately and stably reproduced in the daughter strands of DNA. In the next decade, these provisions were experimentally confirmed: the concept of a gene was clarified, the genetic code and the mechanism of its action in the process of protein synthesis in the cell were deciphered. In addition, methods for artificially obtaining mutations were found and, with their help, valuable plant varieties and strains of microorganisms - producers of antibiotics and amino acids - were created.

Genetics is moving to the molecular level of research. It has become possible to decipher the structure of the gene, determine the material basis and mechanisms of heredity and variability. Genetics has learned to influence these processes and direct them to the right direction. Wide possibilities for combining theory and practice have emerged.

In the last decade, a new direction in molecular genetics has emerged - genetic engineering - a system of techniques that allows a biologist to construct artificial genetic systems. Genetic engineering is based on versatility genetic code: triplets of DNA nucleotides program the inclusion of amino acids in protein molecules all organisms - humans, animals, plants, bacteria, viruses. Thanks to this, it is possible to synthesize a new gene or isolate it from one bacterium and introduce it into the genetic apparatus of another bacterium that lacks such a gene.

Thus, the third modern stage the development of genetics opened up enormous prospects for targeted intervention in the phenomena of heredity and selection of plant and animal organisms, revealed the important role of genetics in medicine, in particular, in the study of the patterns of hereditary diseases and physical anomalies

person. The new biology, built on the principles of genetics, studies the simplest components of a living organism, neglecting the rest, and gradually rises to

macro level. This is what historical meaning genetics. Not only the methods of studying living organisms have changed, but also people’s ideas about such concepts as heredity, variability, etc. Today, humanity is already building entire programs (“Human Genome”) - the main goal of which is to read heredity in human DNA, study combinations of gene bundles, their dynamics, functional value. In general, the discovery of genetics is a breakthrough in biology. The revolution in it was prepared by the entire course of the powerful development of the ideas and methods of mendylism and the chromosomal theory of heredity. Modern molecular genetics is the true brainchild of the entire 20th century, which at a new level has absorbed the progressive results of the development of the chromosomal theory of heredity, mutation theory, gene theory, methods of cytology and genetic analysis.

Basic concepts of genetics, methods of studying them.

IN organic world There are amazing similarities between parents and children, between brothers and sisters, and other relatives. Why does a mother elephant give birth to only a baby elephant, an apple tree grows from an apple seed, and a chicken hatches from a chicken egg? Perhaps none biological problem did not give rise to such an abundance of fantastic hypotheses and fabrications as mysterious phenomenon heredity.

Heredity is an integral property of all living beings to preserve and transmit in a series of generations the structural, functional and developmental features characteristic of a species or population. Heredity ensures the constancy and diversity of life forms and underlies the transmission of hereditary inclinations responsible for the formation of the characteristics and properties of the organism. Thanks to heredity, some species (for example, the lobe-finned fish Coelacanth, which lived in the Devonian period) remained almost unchanged for hundreds of millions of years, reproducing a huge number of generations during this time.

At the same time, in nature there are differences between individuals of both different species and the same species, variety, breed, etc. This indicates that heredity is inextricably linked with variability.

Variability is the ability of organisms in the process of ontogenesis to acquire new characteristics and lose old ones. Variability is expressed in the fact that in any generation, individual individuals differ in some way from each other and from their parents. The reason for this is that the signs and properties of any organism are the result of the interaction of two factors: hereditary information received from parents, and the specific environmental conditions in which the individual development of each individual took place. Since environmental conditions are never the same even for individuals of the same species or variety (breed), it becomes clear why organisms that have the same genotypes (the set of all genes of the organism) often differ markedly from each other in phenotype (the set of all properties and characteristics of the organism). Thus, heredity ensures the preservation of the characteristics and properties of organisms over many generations, and variability causes the formation of new characteristics as a result of changes in genetic information or environmental conditions. It can be hereditary (ontogenetic, combinative, mutational, correlative) and non-hereditary (modification).

When studying heredity and variability, they consider not the entire organism as a whole, but its individual characteristics and properties. A trait is one of the main concepts in genetics. Inheritance and its change are the objects of the closest attention. For convenience of study, signs are conventionally divided into qualitative and quantitative.

Qualitative are morphological or biochemical characteristics, the manifestation of which can easily be characterized verbally (color, ear shape, etc.).

Many hereditary traits do not have a clear expression; they are studied by measurement and counting (weight, hair length, number of teeth, etc.). Such characteristics are called quantitative. Any hereditary trait is formed in the ontogenesis of an individual, therefore external conditions and other factors determine its full or partial manifestation.

When studying heredity and variability at different levels of organization of living matter (molecular, cellular, organismal, population) in genetics they use various methods modern biology:

The genealogical method consists of studying pedigrees based on Mendelian laws of inheritance and helps to establish the nature of inheritance of a trait (dominant or recessive).

The twin method is the study of differences between identical twins. This method is provided by nature itself. It helps to identify the influence of environmental conditions on the phenotype for the same genotypes.

Population method. Population genetics studies genetic differences between separate groups people (populations), explores patterns of geographic distribution of genes.

The cytogenetic method is based on the study of variability and heredity at the cellular and sublevel cellular structures. Row connection established serious illnesses with chromosomal abnormalities.

The biochemical method allows us to identify many hereditary human diseases associated with metabolic disorders. Anomalies of carbohydrate, amino acid, lipid and other types of metabolism are known.

The methods used by genetics can be divided into two groups - genetic methods proper and methods of related biological and medical disciplines, the use of which in genetics is determined by the hereditary characteristics being studied - biochemical, anatomical, physiological, mental, etc. The central place among the proper genetic methods is occupied by genetic analysis. The main principle of genetic analysis is the quantitative accounting of the studied traits in groups of individuals related to each other by certain degrees of kinship. In experimental genetics this is achieved using systems of crossings and hybridological analysis, in medical genetics- using genealogical analysis.

The methods of genetic analysis are varied, but mainly it is a system of all kinds of crosses, and any work goes through the following stages:

1. It is determined whether the trait is inherited and whether it has contrasting forms.

2. The number of genes that control the development of a given trait is determined.

3. It is determined whether there is interaction between these genes.

4. Determination of the linkage group (chromosome) and mapping of the gene on the chromosome.

5. Characteristics of genes.

Currently, the concept of genetic analysis includes gene cloning, determination of the DNA nucleotide sequence, elucidation of the intron-exon structure of the gene, and gene expression in ontogenesis.

TO special types Genetic analysis includes chromosomal analysis, in which the study of the formation of structural and functional characteristics of organisms is combined with an analysis of the structure and behavior of individual chromosomes. Due to the development of methods genetic engineering and biotechnology, the ability to analyze genetic structures and processes on molecular level expanded significantly. Genetic analysis widely uses statistical (biometric) methods, without which it is impossible to reliably establish the nature of the transmission of hereditary information.

Gene identification. Main function of the gene.

Genetics has made great strides in explaining the nature of heredity both at the level of the organism and at the level of the gene. The role of genes in the development of the body is enormous. Genes characterize all the characteristics of the future organism, such as eye and skin color, size, weight and much more. Genes are carriers of hereditary information on the basis of which an organism develops.

Despite the fact that much is now known about the structure of chromosomes, the structure and functions of DNA, give precise definition gene is still difficult. One possible definition of a gene considers the gene as a unit of function. We can say that a gene is a small section of a chromosome that has a specific biochemical function and has a specific effect on the properties of an individual.

A. Garrod's hypothesis. that "gene - enzyme", or, more correctly, "gene - protein", actually means that genes contain information about the sequence of amino acids in proteins and the product of gene activity is a specific protein. To put it even more precisely, the gene contains information for the synthesis not of the protein molecule as a whole, but only of the polypeptide molecule. Proteins, on the other hand, are often a combination of several polypeptides.

How is information about the sequence of DNA bases converted into the sequence of amino acids in proteins? There are only four various bases- A, T, G, C, and proteins contain 20 different amino acids. If one base determined the position of one amino acid in primary structure some protein, then this protein could only contain four types of amino acids. If each amino acid were encoded by two bases, then the number of possible pairs would be 42 = 16. This is also not enough to encode 20 amino acids. Only a code consisting of three bases could ensure the inclusion of all 20 amino acids in the protein, since the number of possible triplets here is 43 = 64. Thus, each amino acid must correspond to three consecutive DNA bases.

This relationship between bases and amino acids is known as the genetic code. The main features of the genetic code can be formulated as follows:

An amino acid is encoded by a triplet of bases in the polynucleotide chain of DNA.

The code is universal. In all living organisms, the same triplets code for the same amino acids.

An amino acid can be encoded by more than one triplet (the number of possible triplets is 64, and the number of amino acids is 20).

The code is non-overlapping, that is, each base can belong to only one triplet.

The protein synthesis mechanism in the cell reads the sequence of bases in one half of the DNA molecule in groups of three and then translates each “three” of bases into a specific amino acid and into a specific protein. The mechanism of protein synthesis in a cell is extremely complex. It involves the participation of another type of nucleic acid - ribonucleic acid (RNA) and a number of cellular structures outside the cell nucleus.

From all of the above, we can say that the main function of the gene is to encode the information necessary for the synthesis of a specific protein.

conclusions

The material substrate of heredity is deoxyribonucleic acid (DNA) molecules.

DNA molecules are capable of doubling with great fidelity.

DNA molecules are capable of forming an infinite variety of different shapes.

DNA is a chain of nucleotides, which include three components - a phosphorus, a carbohydrate and a nitrogen base (adenine, guanine, thymine or cytosine).

The DNA molecule consists of two polynucleotide chains connected through nitrogenous bases and has a complementary structure: bonds between the strands are formed only in adenine-thymine (A-T) and guanine-cytosine (G-C) pairs.

Genetic information is encoded by the sequence of bases in the DNA strand.

The main function of a gene is to encode information for the synthesis of a specific protein.

Amino acids for protein synthesis are encoded by triplets of bases in the DNA chain (genetic code).

Schemes of the relative location of linked genes are called genetic maps of chromosomes. They reflect what really exists linear order placement of genes on chromosomes and are important both in theoretical research, and during breeding work, since they allow you to consciously select pairs of traits during crossings, as well as predict the characteristics of inheritance and manifestations of various traits in the organisms being studied. Having genetic maps chromosomes, it is possible, by inheriting a “signal” gene that is closely linked to the one being studied, to control the transmission to offspring of genes that determine the development of difficult-to-analyze traits. Numerous facts absence (contrary to Mendel's laws) independent distribution traits in second generation hybrids were explained by the chromosomal theory of heredity

Basic provisions of the chromosomal theory of heredity:

1. Genes are located on chromosomes, different chromosomes contain an unequal number of genes, the set of genes for each of the non-homologous chromosomes is unique.

2. Genes on a chromosome are arranged linearly, each gene occupies a specific locus (location) on the chromosome.

3. Genes located on the same chromosome form a linkage group and are transmitted together (linked) to descendants; the number of linkage groups is equal to the haploid set of chromosomes.

4. Linkage is not absolute, since crossing over can occur in the prophase of meiosis and genes located on the same chromosome become separated. The strength of adhesion depends on the distance between genes in the chromosome: the greater the distance, the less strength clutch, and vice versa.

The role and tasks of genetics.

Genetics is a relatively young science. But she faces very serious problems for humans. So genetics is very important for solving many medical issues related primarily to various hereditary diseases nervous system(epilepsy, schizophrenia), endocrine system(cretinism), blood (hemophilia, some anemia), as well as the existence of a number of severe defects in the human structure: short-fingered, muscular atrophy and others. Using the latest cytological methods, cytogenetic in particular, extensive research is carried out genetic reasons various kinds diseases, thanks to which there is a new branch of medicine - medical cytogenetics.

Genetics began to play a special role in the pharmaceutical industry with the development of the genetics of microorganisms and genetic engineering. Undoubtedly, much remains unexplored, for example, the process of mutations or the causes of malignant tumors. It is precisely its importance for solving many human problems that causes the urgent need for the further development of genetics. Moreover, every person is responsible for the hereditary well-being of his children, while important factor is his biological education, since knowledge in the field of anomalies, physiology, and genetics will prevent a person from making mistakes.

Working on the topic “Basic concepts and concepts of genetics,” I came to the conclusion that genetics is aimed at:

1. Disclosure of the laws of reproduction of living things by generation;

2. Creation of new properties in organisms;

3. Identification of the laws of individual development of an individual;

4. Identification of the material basis of historical transformations of organisms in the process of evolution.

Genetics as a science solves the following main problems:

Studies methods of storing genetic information in different organisms (viruses, bacteria, plants, animals and humans) and its material carriers;

Analyzes ways of transmitting hereditary information from one generation of organisms to another;

Identifies the mechanisms and patterns of implementation of genetic information in the process of individual development and the influence of environmental conditions on them;

Studies the patterns and mechanisms of variability and its role in adaptive reactions and in the evolutionary process;

Finds ways to correct damaged genetic information.

Genetics is also the basis for solving a number of important practical problems. These include:

1) selection of the most effective types of hybridization and selection methods;

2) managing the development of hereditary characteristics in order to obtain the most significant results for a person;

3) artificial production of hereditarily modified forms of living organisms; 4) development of measures to protect wildlife from harmful mutagenic effects various factors external environment and methods of combating hereditary human diseases, pests of agricultural plants and animals;

5) development of genetic engineering methods in order to obtain highly efficient biological producers active compounds, as well as to create fundamentally new technologies in the selection of microorganisms, plants and animals.

Conclusion.

Finishing my work on the topic “Basic concepts and principles of genetics,” I came to the conclusion that genetics is a very fascinating and interesting science. I thoroughly enjoyed studying this topic. Even the superficial knowledge that I gleaned from scientific literature, make you feel the enormous power of genetics, which gives a person the power to determine his biological destiny. Previously, it seemed to me that we could all live quite calmly, not knowing the essence of the secrets of heredity, and that all this did not matter. But there are thousands and thousands of questions that have very important as for individuals, and for all humanity: why do children look like their parents? What are the causes of hereditary diseases and how to deal with them? How long can a person live? It is impossible to answer questions without knowing genetics without learning the secrets of heredity and learning to manage it. When a person reveals all these secrets and uses knowledge to his advantage, he will be able to participate in solving practical problems Agriculture, medicine, will learn to manage the evolution of life on our planet as a whole.

At the same time, we must not forget that for spiritual life and purposeful activity modern man The scientific worldview becomes extremely important. Among philosophical questions One of the main things of new natural science is understanding the essence of life, its place in the universe. And only modern molecular genetics has been able to show that life is a truly material, self-developing phenomenon, reflecting the influence of environmental conditions. She also proved that life has a systematic nature that cannot be broken down into its components. physical and chemical processes. However modern science does not yet fully know the essence of life.

As for human hereditary information, it is passed on from generation to generation. All biological features, which served as the basis for the emergence of a person with consciousness, are encoded in hereditary structures, and their transmission through generations is prerequisite for the existence of man on Earth as a rational being. Man like biological species- this is the highest and at the same time unique “achievement” of evolution on our planet. And so far no one can say with certainty or provide irrefutable evidence that this does not apply to the entire Universe.

Bibliography.

1. Naydysh V.M. Concepts modern natural science: Textbook., 2001.

2. General biology. Textbook for grades 10-11 schools with in-depth study biology. Edited by Professor A.O. Ruchinsky. Moscow, “Enlightenment” 1993.

3. R.G. Hare et al., Biology for university applicants. MN: graduate School, 1999

Abstract

biology lesson

in 9th grade on the topic

“The history of genetics. Basic concepts of genetics"

biology teacher

Koshlets Dmitry Yurievich

“History of genetics. Basic concepts of genetics"

Lesson objectives:

Educational : To acquaint students with the subject of genetics, some of its achievements, and implications for practice. Teach students to correctly reveal the essence of the basic concepts of genetics.

Developmental : continue the development of logical thinking.

Educating : to arouse students’ interest in the subject, the desire to learn more.

Teaching methods: Verbal (story), demonstrative (demonstration) thematic paintings, slides).

Lesson type : Learning new material.

Lesson structure:

    Organized start of lesson 1 min

    Learning new material 30 min

    Consolidation. 5 minutes

    Organization homework 3 min

    Organized end of lesson 1 min

Plan for learning new material:

    Genetics is the science of heredity and variability.

    Gregor Mendel is the founder of genetics.

    1900 – the birth of genetics as a science.

    Development of genetics in the 20th century.

    Heredity of organisms.

    Variability of organisms.

Literature for teachers:

General biology: Textbook for grades 10-11. Shk./D.K. Belyaeva, A.O. Ruvinsky et al. – 2nd ed. – M.: Education, 1992.- 271s

Literature for students:

Basics general biology: textbook for 9th grade students educational institutions/ under general Edited by Prof. I.N. Ponomareva. – M.: Ventana-Graff, 2003.-240 p.

During the classes:

Hello. Sit down!

From today's lesson we will begin to study the basics of the doctrine of heredity and variability.

Open your notebooks, write down today’s date and the topic of the lesson “History of the development of genetics. Basic concepts of genetics" (1 slide)

Genetics is a science that studies the heredity and variability of organisms, as well as the mechanisms for controlling these processes.

Over the course of several lessons we will talk about the material carriers of heredity - chromosomes and genes.

Judging by various archaeological data, already 6000 years ago people understood that some physical signs can be passed on from one generation to another. However, truly scientific knowledge heredity and variability began only many centuries later, when a lot of accurate information was accumulated about the inheritance of various characters in plants, animals and humans. The number of such observations, carried out mainly by plant and livestock breeders, especially increased during the period mid-18th century until the middle of the 19th century. However, clear ideas about the patterns of inheritance and heredity up to late XIX there was no century with one significant exception. This exception was the remarkable work of G. Mendel, who established in experiments on the hybridization of pea varieties the most important laws of inheritance of traits, which subsequently formed the basis of genetics. (listening to a report about G. Mendel)

Gregor Mendel (1822–1884):

Austrian naturalist, monk, founder of the doctrine of heredity;

1865 “Experiments on plant hybrids”;

Created scientific principles descriptions and studies of hybrids and their offspring;

Developed and applied algebraic system symbols and designations of features;

Formulated the basic laws of inheritance of traits over a series of generations, allowing predictions to be made;

He expressed the idea of ​​the existence of hereditary inclinations (or genes, as they later came to be called).

However, G. Mendel’s work was not appreciated by his contemporaries and, remaining forgotten for 35 years, did not affect the ideas about heredity and variability that were widespread in the 19th century.

The date of birth of genetics is considered to be 1900, when three botanists - G. de Vries (Holland), K. Correns (Germany) and E. Chermak (Austria), who conducted experiments on plant hybridization, independently came across the forgotten work of G. Mendel . They were struck by the similarity of his results with theirs, appreciated the depth, accuracy and significance of his conclusions and published their data, showing that they fully confirmed Mendel's conclusions. Further development genetics is associated with a number of stages, each of which was characterized by the prevailing areas of research at that time.

The name “genetics” was given to the developing science in 1906 by the English scientist W. Bateson, and soon such important genetic concepts as gene, genotype, and phenotype were developed, which were proposed in 1909 by the Danish geneticist W. Johansen.

Next stage development of science is associated with the name of Thomas Morgan (1866–1945). He established that genes are located on chromosomes and are located there linearly. The concept of the gene has been central to genetics ever since.

In the 40s The biochemical foundations of genetics were laid. Scientists have proven the role of nucleic acid molecules in the transmission of hereditary information, which led to the birth of molecular genetics. Decoding the structure of the DNA molecule, published in 1953, showed a close connection between this chemical compound with hereditary information in genes.

Fast development genetics during this period abroad, especially molecular genetics in the 2nd half of the 20th century, made it possible to reveal the structure of genetic material and understand the mechanism of its work.

So, trace the major discoveries in genetics over the course of a century.

1935 – experimental determination gene sizes.

1953 – structural model of DNA.

1961 – deciphering the genetic code.

1962 – first frog cloning.

1969 – chemically the first gene was synthesized.

1972 – the birth of genetic engineering.

1977 – the genome of bacteriophage X 174 was deciphered, the first human gene was sequenced.

1980 – The first transgenic mouse was produced.

1988 – The Human Genome Project was created.

1995 – formation of genomics as a branch of genetics, the bacterial genome was sequenced.

1997 – Dolly the sheep was cloned.

1999 – a mouse and a cow were cloned.

2000 – the human genome was read!

Notice how rapidly the development of genetic knowledge occurred.

As I already said, genetics deals with the study of two fundamental properties of living organisms - heredity and variability.

Heredity – the ability of organisms to transmit their characteristics and developmental characteristics to their offspring. Thanks to this ability, all living beings (plants, animals, fungi or bacteria) retain in their descendants character traits of its own kind.

This is ensured by the transfer of their genetic information. The carriers of hereditary information in organisms are genes.

Gene – a unit of hereditary information manifested as a sign of an organism. Genes consist of a series of nucleotides located on DNA strands arranged in a linear fashion, i.e. one after another.

In all organisms of the same species, each gene is always located in the same place on a specific chromosome. The location of a gene on a chromosome is called locus. Each gene that carries the makings of a single trait has two states that form a pair. Each member of this pair is called allele. Organisms that carry different (alternative) alleles of the same gene on identical (homologous) chromosomes are called heterozygous, and an organism with the same alleles on the same chromosomes is called homozygous.

Heterozygosity usually ensures higher viability of organisms, their good adaptability to changing environmental conditions and is therefore widely represented in natural populations various types.

The individual combination of all genes, including their alleles, in the chromosomes of the cells of an individual is called genotype(acts as a single interacting system of all genetic elements that control the manifestation of all characteristics of an organism) The set of characteristics of an organism formed in the process of interaction between the genotype and the external environment is called fe notype.

Each organism lives and develops in certain conditions environment experiencing the effect external factors. These factors (temperature, light, the presence of other organisms, etc.) can manifest themselves in the phenotype, i.e. the size or physiological properties body. Therefore, the manifestation of genotypic traits even in closely related organisms may be different. These differences between individuals within a species are called variability.

Variability – these are the properties of living organisms to exist in various forms, providing them with the ability to cope with changing conditions. Variability is the opposite property of heredity, but both are inextricably linked. They provide continuity of properties and the ability to adapt to changing new environmental conditions, causing the progressive development of life.

Page 72 write down the conclusion in your notebook!

The lesson is over!

To illustrate Mendel's first law - the law of uniformity of the first generation - let us reproduce the scientist's experiments on monohybrissimilar crossing of pea plants. The crossing of two organisms is calledhybridization; the offspring from crossing two individuals with different heredity is calledhybrid, and a separate individual -hybrid. Monohybrid is the crossing of two organisms that differ from each other in one pair of alternative (mutually exclusive) characteristics. Consequently, with such crossing, patterns of inheritance of only two variants of one trait can be traced, the development of which is determined by a pair of allelic genes. For example, a sign is the color of the seeds, mutually exclusive options are yellow or green. All other characteristics characteristic of these organisms are not taken into account and are not taken into account in the calculations.

If you cross pea plants with yellow and green seeds, then all the resulting hybrids will have yellow seeds. The same picture is observed when crossing plants with smooth and wrinkled seeds, namely, in hybrids the seeds will be smooth.

Consequently, in a first-generation hybrid, only one of each pair of alternative characters appears. The second symptom seems to disappear and does not develop. G. Mendel called the predominance of the trait of one of the parents in a hybrid dominance. A trait that appears in first-generation hybrids and suppresses the development of another trait was called dominant (from lat. dominantis - dominant); the opposite, i.e. suppressed, sign is recessive (from lat. recessus - retreat, deletion). The dominant trait is usually designated capital letter, for example "A". Recessive - lowercase - "a".

Genetics studies two fundamental properties of living organisms -heredity And variability. Usually heredity defined asthe ability of parents to transmit their characteristics, properties and developmental features next generation. Thanks to this, each species of animal or plant retains its characteristic features over generations. Ensuring the continuity of properties is only one of the aspects of heredity; the second side is the exact transfer of the type of development specific to each organism, i.e. formation during ontogenesis certain signs and the properties and metabolism inherent only to this type of organism.

Cells, throughwhich carry out the continuity of generations - specialized sexualsexual reproductionand body cells - somatic when asexual - do not carry the very signs and properties of future organisms, but only the makings of their development. These inclinations are called genes. The genome is section of a DNA molecule (or section of a chromosome) that determines the abilitydevelopment of a separate elementary trait or synthesis of one protein molecule.

From this position it follows that a trait caused by a particular gene may not develop. Indeed, the possibility of genes expressing themselves as traits largely depends on other genes, as well as on environmental conditions. Consequently, the subject of genetics is the study of the conditions for the manifestation of genes. In all organisms of the same species, each specific gene is located in the same place, orlocus,strictly defined chromosome. In a haploid set of chromosomes (for example, in prokaryotes or in the gametes of eukaryotic organisms) there is only one gene responsible for the development of this trait. The diploid set of chromosomes (in somatic cells in eukaryotes) contains two homologous chromosomes and, accordingly, two genes that determine the development of one particular trait.Genes located in the same loci of homologous chromosomes and responsible for the development of one trait are called allelic and (from Greek allelou - each other, mutually). Letter designations are used for genes. If two allelic genes are completely identical in structure, that is, they have the same nucleotide sequence, they can be designated as follows: AA. But as a resultmutationsone nucleotide in a DNA molecule may be replaced by another. The trait caused by this gene will also change somewhat; The genotype, including the original and mutant genes, will be designated as follows: AA 1.

A mutation that causes a change in the structure of a gene, i.e., the appearance of a variant of the original gene, also leads to the appearance of a variant of the trait. A gene can mutate repeatedly. As a result, several allelic genes arise. The set of such allelic genes that determine the diversity of variants of a trait is calleda series of allelic genes. The emergence of the tacoth series due to repeated mutation of one gene is calledmultiple allelism or multiple allelomorphism.

The set of all genes of one organism is called a genotype. However genotype - not a mechanical sum of genes. The possibility of manifestation of a gene and the form of its manifestation depend, as will be shown later, on environmental conditions. The concept of environment includes not only the conditions surrounding the cell, but also other genes. Genes interact with each other and, once in the same genotype, can greatly influence the manifestation of the action of neighboring genes. Thus, for each individual gene there is a genotypic environment. In this regard, the famous Russian geneticist M.E. L o bashev determined genotype as a system interacting genes.

Within the same species, all organisms are not alike. This variability is clearly visible, for example, within the species Homo sapiens, each representative of which has its own individual characteristics. Similar individual variability exists in organisms of any species of animals and plants.

Thus, variability- this is a property of organisms that is, as it were, the opposite of heredity. Variabilityconsists in changing hereditary inclinations - genes and, as a consequence, changing their manifestation in the process of development of organisms. There are different types of variability. Studying the causes, forms of variability and its

The basic concepts of genetics and their significance for evolution are also dealt with by genetics. At the same time, researchers deal not directly with genes, but with the results of their manifestation -signs or properties. Therefore, the patterns of heredityand variability is studied by observing the characteristics of organisms over a series of generations.

The totality of all the characteristics of an organism is called a phenotype . This includes not only external, visible signs (color of eyes, hair, shape of ear or nose, color of flowers), but also biochemical ones (shape of a structural protein or enzyme molecule, enzyme activity, concentration of glucose or urea in the blood, etc.), histological (shape and size of cells, structure of tissues and organs), anatomical (structure of the body and mutual arrangement organs), etc. In other words,signAny structural feature of an organism can be named at each level of organization, with the exception of the sequence of nucleotides in a DNA molecule. Underproperty understand any functional feature organism, which is based on a certain structural feature or group of elementary features . It should, of course, be remembered that the vast majority of “simple” signs are nothing more than a conventional designation of the distinctive features of organisms: Brown eyes or blue, tall or short, straight or curly hair, etc. Signs, no matter how simple they may seem outwardly, are determined by numerous and complex biochemical processes, each of which is caused by an enzyme protein - elementary (i.e., essentially simple) sign.

Thus, genetics is the science of the laws of heredity and variability - two opposite and at the same time inextricably linked processes characteristic of all life on Earth.



© 2023 netdenegnakino.ru - No for twos. Chemistry. Physics. Spelling. Geography