The problem of successful passing the exam begins to bother schoolchildren a year or even two before they finish the 11th grade. And no wonder - the exam is not just a condition that you will be awarded school certificate at the graduation party, but also as a kind of key that opens the door to a successful adult life. It's no secret that admission to higher educational establishments countries requires the mandatory availability of USE certificates in several specialized subjects. And the USE in Biology 2019 is especially important for future doctors, psychologists, veterinarians and many others.

First of all, this subject is necessary for children who want to succeed in studying various industries medicine, veterinary medicine, agronomy or the chemical industry, but in 2019 the USE certificate in biology will also be quoted for admission to the faculties of physical education, psychology, paleontology, landscape design, etc.

Biology is a subject that many students like, because many topics are close and understandable to students, and laboratory works mostly associated with the knowledge of the world, which causes genuine interest in children. But when choosing the USE in biology, it is important to understand that a fairly large amount of material is submitted for the exam, and for admission to various faculties, a certificate in chemistry, natural science or physics is often also required.

Important! A complete list of the required USE certificates that allow you to apply for budget or contract education at a particular university of the Russian Federation can be found on the website of the educational institution you are interested in.

Dates

Like all other subjects, in 2019 USE year in biology will be taken on the days set by the GIA calendar. The draft of this document should be approved in November. As soon as the dates of the exams are known, we will be the first to tell you when the tests in biology and other subjects will take place.

You can roughly understand when exams can be scheduled by reading last year's calendar. So, in 2018, biology was taken on such days:

	Main date	Reserve day
Early
Basic

For persons re-admitted to surrender, their dates for testing in April and June were also set.

Innovations 2019

Although fundamental changes will not affect the USE in biology, there will still be some changes in the 2019 tickets.

The main innovation of 2018-2019 school year will be the replacement of the 2-point task of the 2nd line (multiple choice) with a 1-point task involving work with a table. Thus, the maximum number of primary points in the subject will now be 58 (1 point less than it was in 2018).

Otherwise, the KIM structure will remain unchanged, which should please 11th graders, because in the preparation process it will be possible to rely on the numerous materials of 2018 available on the Internet.

Structure of KIMs in biology

So, knowing already what changes will occur in the exam in biology, let's take a closer look at the types of tasks and their distribution in the ticket. KIM, as before, will include 28 tasks divided into two parts:

The proposed CIM format allows you to evaluate the knowledge of a graduate in 7 main blocks:

The distribution of tasks by difficulty levels will be as follows:

In 2019, 3.5 hours (210 min.) will be allotted for the completion of the examination paper in biology, taking into account the fact that the examinee must spend on each task of the 1st block on average no more than 5 minutes, and for each building of the 2nd block – from 10 to 20 minutes.

Bring with you Additional materials and equipment, as well as to use them in USE time biology is forbidden!

Evaluation of work

For the correct completion of 21 tasks of the 1st block, the examinee can score a maximum of 38 primary points, and for the completion of 7 tasks of the second - another 20, which is 58 points in total, which will correspond to a 100-point result of the Unified State Examination.

The first block of work, during which the examinee fills in the table of answers, is checked by an electronic method, and the second block is evaluated by two independent experts. If their opinion differs by more than 2 points, the 3rd expert is involved in checking the work.

Although USE results no longer equate to certain marks on a 5-point scale, many still want to know how they coped with the task. Convert 2019 result to school grade it will be possible according to such an approximate correspondence table:

To obtain a certificate, it will be enough to score 16 primary (or 36 test calls) points, although such a result will not allow you to join the fight for budget place in the University.

At the same time, the passing score in universities ranges from 65 to 98 points (not primary, but already test). Naturally, the passing threshold of Moscow universities is as close as possible to the upper limit of the range, which makes 11th graders take preparation more seriously and focus on a 100-point mark, rather than the minimum threshold.

Secrets of preparation

Biology is not an easy science, it requires attentiveness and understanding, and not just mechanical memorization. Therefore, preparation is necessary methodical and constant.

Basic training includes the study of terminology, without its knowledge it is difficult to navigate in biology as a science. To facilitate memorization, reinforce the theory with illustrative material, look for pictures, graphs, diagrams that will become the basis for the associative work of memory. You also need to familiarize yourself with the demo version of KIMs in order to understand the structure of the biology exam.

It takes practice to solve tasks of a certain type. By systematically solving the options presented on the FIPI website, students form a strategy for completing tasks and gain self-confidence, which is an indispensable assistant in achieving success.

date conducting the exam in biology in 2019 will be known only in January 2019.

What is tested in the exam?

To complete the examination paper, the USE participant needs to be able to:

• work with diagrams, drawings, graphs, tables and histograms,
• explain the facts
• summarize and formulate conclusions,
• solve biological problems
• work with biological information, with the image of biological objects.

The knowledge and skills of graduates, formed during the study of the following sections of the biology course, are checked:

1. "Plants".
2. "Bacteria. Mushrooms. Lichens.
3. "Animals".
4. "Man and his health".
5. "General Biology".

IN examination work dominated by tasks general biology, which considers general biological patterns that manifest themselves in different levels wildlife organizations. These include:

• cellular, chromosome and evolutionary theories;
• laws of heredity and variability;
• ecological laws of development of the biosphere.

It is such a useful video that we suggest you watch right now:

Among the tasks in genetics at the exam in biology, 6 main types can be distinguished. The first two - to determine the number of types of gametes and monohybrid crossing - are most often found in part A of the exam (questions A7, A8 and A30).

Tasks of types 3, 4 and 5 are devoted to dihybrid crossing, inheritance of blood groups and sex-linked traits. Such tasks make up the majority of C6 questions in the exam.

The sixth type of tasks is mixed. They consider the inheritance of two pairs of traits: one pair is linked to the X chromosome (or determines human blood groups), and the genes of the second pair of traits are located on autosomes. This class of tasks is considered the most difficult for applicants.

This article sets out theoretical basis genetics necessary for successful preparation for task C6, as well as solutions to problems of all types are considered and examples for independent work are given.

Basic terms of genetics

Gene- This is a section of the DNA molecule that carries information about the primary structure of one protein. A gene is a structural and functional unit of heredity.

Allelic genes (alleles)- different variants of the same gene encoding an alternative manifestation of the same trait. Alternative signs - signs that cannot be in the body at the same time.

Homozygous organism- an organism that does not give splitting for one reason or another. Its allelic genes equally affect the development of this trait.

heterozygous organism- an organism that gives splitting according to one or another feature. Its allelic genes affect the development of this trait in different ways.

dominant gene is responsible for the development of a trait that manifests itself in a heterozygous organism.

recessive gene is responsible for the trait, the development of which is suppressed by the dominant gene. A recessive trait appears in a homozygous organism containing two recessive genes.

Genotype- a set of genes in the diploid set of an organism. The set of genes in a haploid set of chromosomes is called genome.

Phenotype- the totality of all the characteristics of an organism.

G. Mendel's laws

Mendel's first law - the law of uniformity of hybrids

This law is derived on the basis of the results of monohybrid crossing. For experiments, two varieties of peas were taken, differing from each other in one pair of traits - the color of the seeds: one variety had a yellow color, the second - green. Crossed plants were homozygous.

To record the results of crossing, Mendel proposed the following scheme:

Yellow seed color
- green seed color

(parents)
(gametes)
(first generation)	(all plants had yellow seeds)

The wording of the law: when crossing organisms that differ in one pair of alternative traits, the first generation is uniform in phenotype and genotype.

Mendel's second law - the law of splitting

From seeds obtained by crossing a homozygous plant with yellow seed color with a plant with green seed color, plants were grown, and by self-pollination was obtained.

	(plants have a dominant trait, - recessive)

The wording of the law: in the offspring obtained from crossing hybrids of the first generation, there is a splitting according to the phenotype in the ratio, and according to the genotype -.

Mendel's third law - the law of independent inheritance

This law was derived on the basis of data obtained during dihybrid crossing. Mendel considered the inheritance of two pairs of traits in peas: seed color and shape.

As parental forms, Mendel used plants homozygous for both pairs of traits: one variety had yellow seeds with a smooth skin, the other green and wrinkled.

Yellow seed color - green color of seeds,
- smooth shape, - wrinkled shape.

	(yellow smooth).

Then Mendel grew plants from seeds and obtained second-generation hybrids by self-pollination.

	The Punnett grid is used to record and determine genotypes. Gametes

In there was a splitting into phenotypic class in the ratio . all seeds had both dominant traits (yellow and smooth), - the first dominant and the second recessive (yellow and wrinkled), - the first recessive and the second dominant (green and smooth), - both recessive traits (green and wrinkled).

When analyzing the inheritance of each pair of traits, the following results are obtained. In parts of yellow seeds and parts of green seeds, i.e. ratio . Exactly the same ratio will be for the second pair of characters (seed shape).

The wording of the law: when crossing organisms that differ from each other by two or more pairs of alternative traits, genes and their corresponding traits are inherited independently of each other and combined in all possible combinations.

Mendel's third law holds only if the genes are on different pairs of homologous chromosomes.

Law (hypothesis) of "purity" of gametes

When analyzing the characteristics of hybrids of the first and second generations, Mendel found that the recessive gene does not disappear and does not mix with the dominant one. In both genes are manifested, which is possible only if the hybrids form two types of gametes: one carries a dominant gene, the other a recessive one. This phenomenon is called the gamete purity hypothesis: each gamete carries only one gene from each allelic pair. The hypothesis of gamete purity was proved after studying the processes occurring in meiosis.

The hypothesis of "purity" of gametes is the cytological basis of Mendel's first and second laws. With its help, splitting by phenotype and genotype can be explained.

Analyzing cross

This method was proposed by Mendel to determine the genotypes of organisms with a dominant trait that have the same phenotype. To do this, they were crossed with homozygous recessive forms.

If, as a result of crossing, the entire generation turned out to be the same and similar to the analyzed organism, then it could be concluded that the original organism is homozygous for the trait under study.

If, as a result of crossing, a splitting in the ratio was observed in the generation, then the original organism contains the genes in a heterozygous state.

Inheritance of blood groups (AB0 system)

The inheritance of blood groups in this system is an example of multiple allelism (the existence of more than two alleles of one gene in a species). There are three genes in the human population that code for erythrocyte antigen proteins that determine people's blood types. The genotype of each person contains only two genes that determine his blood type: the first group; second and ; third and fourth.

Inheritance of sex-linked traits

In most organisms, sex is determined at the time of fertilization and depends on the set of chromosomes. This method is called chromosomal sex determination. Organisms with this type of sex determination have autosomes and sex chromosomes - and.

In mammals (including humans), the female sex has a set of sex chromosomes, the male sex -. The female sex is called homogametic (forms one type of gametes); and male - heterogametic (forms two types of gametes). In birds and butterflies, males are homogametic and females are heterogametic.

The USE includes tasks only for traits linked to the -chromosome. Basically, they relate to two signs of a person: blood clotting (- normal; - hemophilia), color vision (- normal, - color blindness). Tasks for the inheritance of sex-linked traits in birds are much less common.

In humans, the female sex may be homozygous or heterozygous for these genes. Consider the possible genetic sets in a woman on the example of hemophilia (a similar picture is observed with color blindness): - healthy; - healthy, but is a carrier; - sick. The male sex for these genes is homozygous, tk. - chromosome does not have alleles of these genes: - healthy; - is ill. Therefore, men are most often affected by these diseases, and women are their carriers.

Typical USE tasks in genetics

Determination of the number of types of gametes

The number of gamete types is determined by the formula: , where is the number of gene pairs in the heterozygous state. For example, an organism with a genotype has no genes in a heterozygous state; , therefore, and it forms one type of gamete. An organism with a genotype has one pair of genes in a heterozygous state, i.e. , therefore, and it forms two types of gametes. An organism with a genotype has three pairs of genes in a heterozygous state, i.e. , therefore, and it forms eight types of gametes.

Tasks for mono- and dihybrid crossing

For a monohybrid cross

Task: Crossed white rabbits with black rabbits (black color is a dominant trait). In white and black. Determine the genotypes of parents and offspring.

Solution: Since splitting is observed in the offspring according to the trait being studied, therefore, the parent with the dominant trait is heterozygous.

	(black)	(white)
	(black) : (white)

For a dihybrid cross

Dominant genes are known

Task: Crossed tomatoes of normal growth with red fruits with dwarf tomatoes with red fruits. All plants were of normal growth; - with red fruits and - with yellow ones. Determine the genotypes of parents and offspring if it is known that in tomatoes the red color of the fruit dominates over yellow, and normal growth over dwarfism.

Solution: Denote dominant and recessive genes: - normal growth, - dwarfism; - red fruits, - yellow fruits.

Let us analyze the inheritance of each trait separately. All offspring have normal growth, i.e. splitting on this basis is not observed, so the original forms are homozygous. Splitting is observed in fruit color, so the original forms are heterozygous.

		(dwarfs, red fruits)
	(normal growth, red fruits) (normal growth, red fruits) (normal growth, red fruits) (normal growth, yellow fruits)

Dominant genes unknown

Task: Two varieties of phlox were crossed: one has red saucer-shaped flowers, the second has red funnel-shaped flowers. The offspring produced red saucers, red funnels, white saucers and white funnels. Determine the dominant genes and genotypes of parental forms, as well as their descendants.

Solution: Let us analyze the splitting for each feature separately. Among the descendants, plants with red flowers are, with white flowers -, i.e. . Therefore, red - white color, and parental forms are heterozygous for this trait (because there is splitting in the offspring).

Splitting is also observed in the shape of the flower: half of the offspring have saucer-shaped flowers, half are funnel-shaped. Based on these data, it is not possible to unambiguously determine the dominant trait. Therefore, we accept that - saucer-shaped flowers, - funnel-shaped flowers.

	(red flowers, saucer-shaped)	(red flowers, funnel-shaped)
	Gametes

red saucer-shaped flowers,
- red funnel-shaped flowers,
- white saucer-shaped flowers,
- white funnel-shaped flowers.

Solving problems on blood groups (AB0 system)

Task: the mother has the second blood group (she is heterozygous), the father has the fourth. What blood groups are possible in children?

Solution:

	(the probability of having a child with the second blood type is , with the third - , with the fourth - ).

Solving problems on the inheritance of sex-linked traits

Such tasks may well occur both in part A and in part C of the USE.

Task: a carrier of hemophilia married a healthy man. What kind of children can be born?

Solution:

	girl, healthy () girl, healthy, carrier () boy, healthy () boy with hemophilia ()

Solving problems of mixed type

Task: A man with brown eyes and blood type marries a woman with brown eyes and blood type. They had a blue-eyed child with a blood type. Determine the genotypes of all individuals indicated in the problem.

Solution: Brown eye color dominates blue, therefore - brown eyes, - Blue eyes. The child has blue eyes, so his father and mother are heterozygous for this trait. The third blood group may have the genotype or, the first - only. Since the child has the first blood type, therefore, he received the gene from both his father and mother, therefore his father has a genotype.

	(father)	(mother)
	(was born)

Task: The man is colorblind, right-handed (his mother was left-handed), married to a woman with normal vision (her father and mother were completely healthy), left-handed. What kind of children can this couple have?

Solution: In a person, the best possession of the right hand dominates over left-handedness, therefore - right-handed, - lefty. Male genotype (because he received the gene from a left-handed mother), and women -.

A color-blind man has the genotype, and his wife -, because. her parents were completely healthy.

R
	right-handed girl, healthy, carrier () left-handed girl, healthy, carrier () right-handed boy, healthy () left-handed boy, healthy ()

Tasks for independent solution

1. Determine the number of types of gametes in an organism with a genotype.
2. Determine the number of types of gametes in an organism with a genotype.
3. They crossed tall plants with short plants. B - all plants are medium in size. What will be?
4. They crossed a white rabbit with a black rabbit. All rabbits are black. What will be?
5. They crossed two rabbits with gray wool. B with black wool, - with gray and white. Determine the genotypes and explain this splitting.
6. They crossed a black hornless bull with a white horned cow. They received black hornless, black horned, white horned and white hornless. Explain this split if black and the absence of horns are dominant traits.
7. They crossed Drosophila with red eyes and normal wings with Drosophila with white eyes and defective wings. The offspring are all flies with red eyes and defective wings. What will be the offspring from crossing these flies with both parents?
8. A blue-eyed brunette married a brown-eyed blonde. What kind of children can be born if both parents are heterozygous?
9. A right-handed man with a positive Rh factor married a left-handed woman with a negative Rh factor. What kind of children can be born if a man is heterozygous only for the second sign?
10. The mother and father have a blood type (both parents are heterozygous). What blood group is possible in children?
11. The mother has a blood group, the child has a blood group. What blood type is impossible for a father?
12. The father has the first blood type, the mother has the second. What is the probability of having a child with the first blood type?
13. A blue-eyed woman with a blood type (her parents had a third blood type) married a brown-eyed man with a blood type (his father had blue eyes and a first blood type). What kind of children can be born?
14. A right-handed hemophilic man (his mother was left-handed) married a left-handed woman with normal blood (her father and mother were healthy). What kind of children can be born from this marriage?
15. Strawberry plants with red fruits and long-leaved leaves were crossed with strawberry plants with white fruits and short-leaved leaves. What offspring can there be if red color and short-leaved leaves dominate, while both parental plants are heterozygous?
16. A man with brown eyes and blood type marries a woman with brown eyes and blood type. They had a blue-eyed child with a blood type. Determine the genotypes of all individuals indicated in the problem.
17. They crossed melons with white oval fruits with plants that had white spherical fruits. The following plants were obtained in the offspring: with white oval, with white spherical, with yellow oval and with yellow spherical fruits. Determine the genotypes of the original plants and descendants, if the white color of the melon dominates over the yellow, the oval shape of the fruit is over the spherical.

Answers

1. gamete type.
2. gamete types.
3. gamete type.
4. high, medium and low (incomplete dominance).
5. black and white.
6. - black, - white, - grey. incomplete dominance.
7. Bull:, cow -. Offspring: (black hornless), (black horned), (white horned), (white hornless).
8. - Red eyes, - white eyes; - defective wings, - normal. Initial forms - and, offspring.
   Crossing results:
   A)
9. - Brown eyes, - blue; - dark hair, - light. Father mother - .
   

   	- brown eyes, dark hair - brown eyes, blonde hair - blue eyes, dark hair - blue eyes, blonde hair

10. - right-handed, - left-handed; Rh positive, Rh negative. Father mother - . Children: (right-handed, Rh positive) and (right-handed, Rh negative).
11. Father and mother - . In children, a third blood type (probability of birth -) or a first blood group (probability of birth -) is possible.
12. Mother, child; He received the gene from his mother, and from his father -. The following blood types are impossible for the father: second, third, first, fourth.
13. A child with the first blood group can only be born if his mother is heterozygous. In this case, the probability of birth is .
14. - Brown eyes, - blue. Female Male . Children: (brown eyes, fourth group), (brown eyes, third group), (blue eyes, fourth group), (blue eyes, third group).
15. - right-handed, - lefty. Man Woman . Children (healthy boy, right-handed), (healthy girl, carrier, right-handed), (healthy boy, left-handed), (healthy girl, carrier, left-hander).
16. - red fruit - white; - short-stalked, - long-stalked.
    Parents: and Offspring: (red fruit, short stem), (red fruit, long stem), (white fruit, short stem), (white fruit, long stem).
    Strawberry plants with red fruits and long-leaved leaves were crossed with strawberry plants with white fruits and short-leaved leaves. What offspring can there be if red color and short-leaved leaves dominate, while both parental plants are heterozygous?
17. - Brown eyes, - blue. Female Male . Child:
18. - white color, - yellow; - oval fruits, - round. Source plants: and. Offspring:
    with white oval fruits,
    with white spherical fruits,
    with yellow oval fruits,
    with yellow spherical fruits.

For this task you can get 1 point on the exam in 2020

Knowledge test educational material on the topic "Genetics. Heredity ”offers task 6 of the Unified State Examination in biology. All test options contain a fairly extensive amount of material, divided into several subtopics. Part of the tickets is devoted to genetic terms. Do you want to pass the test successfully? Repeat before the exam - what is the genotype and phenotype, genome and codon, gene pool and genetic code, what are the paired genes of homologous chromosomes called, and how is an organism whose genotype contains different alleles of one gene. Surely in one of the ticket options there will be questions devoted to the works of the famous scientist Gregor Johann Mendel: how he called those signs that do not appear in first-generation hybrids or what the concept of “hereditary factor” he introduced is called today.

Task 6 of the USE in biology also contains many tasks for sex-linked inheritance. “Can a hemophilic father have a daughter with hemophilia?”, “What is the probability of a hemophilic boy being born in a woman with a hemophilia gene and a healthy man.” Practice before the exam to solve problems for compiling the gene pool - there are also a lot of them in task No. 6 of the Unified State Examination in biology. Typical examples of such tasks are: “Compose the genotype of a color-blind person” or “Compose the genotype of the brown-eyed daughter of a color-blind father if she has normal color vision.” In each of these tasks, various variants of the genotype will be given as answer options, you must choose the only correct one.

Genetics, its tasks. Heredity and variability are properties of organisms. Methods of genetics. Basic genetic concepts and symbolism. Chromosomal theory of heredity. Modern ideas about the gene and genome

Genetics, its tasks

Advances in natural science and cell biology in the 18th-19th centuries allowed a number of scientists to speculate about the existence of certain hereditary factors that determine, for example, the development of hereditary diseases, but these assumptions were not supported by appropriate evidence. Even the theory of intracellular pangenesis formulated by H. de Vries in 1889, which assumed the existence of certain “pangens” in the cell nucleus that determine the hereditary inclinations of the organism, and the release into the protoplasm of only those of them that determine the cell type, could not change the situation, as well as the theory of "germ plasm" by A. Weisman, according to which the traits acquired in the process of ontogenesis are not inherited.

Only the works of the Czech researcher G. Mendel (1822-1884) became the foundation stone modern genetics. However, despite the fact that his works were cited in scientific publications, contemporaries did not pay attention to them. And only the rediscovery of the patterns of independent inheritance by three scientists at once - E. Chermak, K. Correns and H. de Vries - forced the scientific community to turn to the origins of genetics.

Genetics is a science that studies the laws of heredity and variability and methods of managing them.

The tasks of genetics at the present stage are the study of qualitative and quantitative characteristics hereditary material, analysis of the structure and functioning of the genotype, deciphering the fine structure of the gene and methods for regulating gene activity, searching for genes that cause the development of human hereditary diseases and methods for their "correction", creating a new generation of drugs similar to DNA vaccines, constructing using gene and cellular engineering organisms with new properties that could produce the necessary medications and food, as well as a complete decoding of the human genome.

Heredity and variability - properties of organisms

Heredity- is the ability of organisms to transmit their characteristics and properties in a number of generations.

Variability- the property of organisms to acquire new characteristics during life.

signs- these are any morphological, physiological, biochemical and other features of organisms in which some of them differ from others, for example, eye color. properties They also call any functional features of organisms, which are based on a certain structural feature or a group of elementary features.

Organisms can be divided into quality And quantitative. Qualitative signs have two or three contrasting manifestations, which are called alternative features, for example, blue and brown eyes, while quantitative ones (milk yield of cows, wheat yield) do not have clearly defined differences.

The material carrier of heredity is DNA. There are two types of heredity in eukaryotes: genotypic And cytoplasmic. Carriers of genotypic heredity are localized in the nucleus, and further we will talk about it, and carriers of cytoplasmic heredity are circular DNA molecules located in mitochondria and plastids. Cytoplasmic inheritance is transmitted mainly with the egg, therefore it is also called maternal.

A small number of genes are localized in the mitochondria of human cells, but their change can have a significant impact on the development of the organism, for example, lead to the development of blindness or a gradual decrease in mobility. Plastids play at least important role in plant life. So, in some parts of the leaf, chlorophyll-free cells may be present, which, on the one hand, leads to a decrease in plant productivity, and on the other hand, such variegated organisms are valued in decorative gardening. Such specimens are reproduced mainly asexually, since ordinary green plants are more often obtained during sexual reproduction.

Genetic methods

1. The hybridological method, or the method of crosses, consists in the selection of parent individuals and the analysis of offspring. At the same time, the genotype of an organism is judged by the phenotypic manifestations of genes in offspring obtained by a certain crossing scheme. This is the oldest informative method of genetics, which was most fully applied for the first time by G. Mendel in combination with statistical method. This method is not applicable in human genetics for ethical reasons.

2. The cytogenetic method is based on the study of the karyotype: the number, shape and size of the body's chromosomes. The study of these features makes it possible to identify various developmental pathologies.

3. The biochemical method makes it possible to determine the content of various substances in the body, in particular their excess or deficiency, as well as the activity of a number of enzymes.

4. Molecular genetic methods are aimed at identifying variations in the structure and deciphering the primary nucleotide sequence of the studied DNA sections. They allow you to identify genes for hereditary diseases even in embryos, establish paternity, etc.

5. The population-statistical method makes it possible to determine the genetic composition of a population, the frequency of certain genes and genotypes, the genetic burden, and also to outline the prospects for the development of a population.

6. The method of hybridization of somatic cells in culture allows you to determine the localization of certain genes in chromosomes when cells of various organisms merge, for example, mice and hamsters, mice and humans, etc.

Basic genetic concepts and symbolism

Gene- This is a section of a DNA molecule, or chromosome, that carries information about a certain trait or property of an organism.

Some genes can influence the manifestation of several traits at once. Such a phenomenon is called pleiotropy. For example, the gene that determines the development of the hereditary disease arachnodactyly (spider fingers) also causes the curvature of the lens, the pathology of many internal organs.

Each gene occupies a strictly defined place in the chromosome - locus. Since in the somatic cells of most eukaryotic organisms the chromosomes are paired (homologous), each of the paired chromosomes contains one copy of the gene responsible for a particular trait. Such genes are called allelic.

Allelic genes most often exist in two variants - dominant and recessive. Dominant called an allele that manifests itself regardless of which gene is on the other chromosome, and suppresses the development of a trait encoded by a recessive gene. Dominant alleles are usually denoted by capital letters of the Latin alphabet (A, B, C, etc.), while recessive alleles are indicated by lowercase letters (a, b, c, etc.). recessive alleles can only be expressed if they occupy loci on both paired chromosomes.

An organism that has the same allele on both homologous chromosomes is called homozygous for that gene, or homozygous(AA, aa, AABB, aabb, etc.), and an organism that has different gene variants on both homologous chromosomes - dominant and recessive - is called heterozygous for that gene, or heterozygous(Aa, AaBb, etc.).

A number of genes can have three or more structural variants, for example, blood groups according to the AB0 system are encoded by three alleles - I A, I B, i. Such a phenomenon is called multiple allelism. However, even in this case, each chromosome from a pair carries only one allele, that is, all three gene variants in one organism cannot be represented.

Genome- a set of genes characteristic of the haploid set of chromosomes.

Genotype- a set of genes characteristic of a diploid set of chromosomes.

Phenotype- a set of signs and properties of an organism, which is the result of the interaction of the genotype and the environment.

Since organisms differ from each other in many traits, it is possible to establish the patterns of their inheritance only by analyzing two or more traits in the offspring. Crossing, in which inheritance is considered and an accurate quantitative account of offspring is carried out for one pair of alternative traits, is called monohybrid m, in two pairs - dihybrid, according to more signs - polyhybrid.

According to the phenotype of an individual, it is far from always possible to establish its genotype, since both an organism homozygous for the dominant gene (AA) and heterozygous (Aa) will have a manifestation of the dominant allele in the phenotype. Therefore, to check the genotype of an organism with cross-fertilization, analyzing cross A cross in which an organism with a dominant trait is crossed with a homozygous for a recessive gene. In this case, an organism homozygous for the dominant gene will not produce splitting in the offspring, while in the offspring of heterozygous individuals an equal number of individuals with dominant and recessive traits is observed.

The following conventions are most often used to write crossover schemes:

R (from lat. parent- parents) - parent organisms;

$♀$ (alchemical sign of Venus - a mirror with a handle) - maternal individual;

$♂$ (alchemical sign of Mars - shield and spear) - paternal individual;

$×$ is the cross sign;

F 1, F 2, F 3, etc. - hybrids of the first, second, third and subsequent generations;

F a - offspring from analyzing crosses.

Chromosomal theory of heredity

The founder of genetics G. Mendel, as well as his closest followers, had no idea about the material basis of hereditary inclinations, or genes. However, already in 1902-1903, the German biologist T. Boveri and the American student W. Setton independently suggested that the behavior of chromosomes during cell maturation and fertilization makes it possible to explain the splitting of hereditary factors according to Mendel, i.e., in their opinion, genes must be located on the chromosomes. These assumptions have become the cornerstone chromosome theory heredity.

In 1906, the English geneticists W. Batson and R. Pennet discovered a violation of Mendelian splitting when crossing sweet peas, and their compatriot L. Doncaster, in experiments with the gooseberry moth butterfly, discovered sex-linked inheritance. The results of these experiments clearly contradicted Mendelian ones, but given that by that time it was already known that the number of known features for experimental objects far exceeded the number of chromosomes, and this suggested that each chromosome carries more than one gene, and the genes of one chromosomes are inherited together.

In 1910, the experiments of the T. Morgan group began on a new experimental object - the Drosophila fruit fly. The results of these experiments made it possible by the mid-20s of the 20th century to formulate the main provisions of the chromosome theory of heredity, to determine the arrangement of genes in chromosomes and the distance between them, i.e., to compile the first maps of chromosomes.

The main provisions of the chromosome theory of heredity:

1. Genes are located on chromosomes. Genes on the same chromosome are inherited together, or linked, and are called clutch group. The number of linkage groups is numerically equal to the haploid set of chromosomes.
2. Each gene occupies a strictly defined place in the chromosome - a locus.
3. Genes are arranged linearly on chromosomes.
4. Disruption of gene linkage occurs only as a result of crossing over.
5. The distance between genes on a chromosome is proportional to the percentage of crossing over between them.
6. Independent inheritance is characteristic only for genes of non-homologous chromosomes.

Modern ideas about the gene and genome

In the early 40s of the twentieth century, J. Beadle and E. Tatum, analyzing the results of genetic studies conducted on the neurospore fungus, came to the conclusion that each gene controls the synthesis of an enzyme, and formulated the principle "one gene - one enzyme" .

However, already in 1961, F. Jacob, J. L. Monod and A. Lvov managed to decipher the structure of the Escherichia coli gene and study the regulation of its activity. For this discovery they were awarded in 1965 Nobel Prize in physiology and medicine.

In the course of the study, in addition to structural genes that control the development of certain traits, they were able to identify regulatory ones, the main function of which is the manifestation of traits encoded by other genes.

The structure of the prokaryotic gene. The structural gene of prokaryotes has a complex structure, since it includes regulatory regions and coding sequences. Regulatory regions include promoter, operator, and terminator. promoter called the region of the gene to which the RNA polymerase enzyme is attached, which ensures the synthesis of mRNA during transcription. WITH operator, located between the promoter and the structural sequence, can bind repressor protein, preventing RNA polymerase from starting reading hereditary information from the coding sequence, and only its removal allows transcription to begin. The structure of the repressor is usually encoded in a regulatory gene located in another part of the chromosome. The reading of information ends at a section of the gene called terminator.

coding sequence structural gene contains information about the sequence of amino acids in the corresponding protein. The coding sequence in prokaryotes is called cistronome, and the set of coding and regulatory regions of the prokaryotic gene - operon. In general, prokaryotes, which include E. coli, have a relatively small number of genes located on a single ring chromosome.

The cytoplasm of prokaryotes may also contain additional small circular or open DNA molecules called plasmids. Plasmids are able to integrate into chromosomes and be transferred from one cell to another. They can carry information about sexual characteristics, pathogenicity, and antibiotic resistance.

The structure of the eukaryotic gene. Unlike prokaryotes, eukaryotic genes do not have an operon structure, since they do not contain an operator, and each structural gene is accompanied only by a promoter and a terminator. In addition, significant regions in eukaryotic genes ( exons) alternate with insignificant ( introns), which are completely transcribed into mRNAs and then excised during their maturation. The biological role of introns is to reduce the likelihood of mutations in significant areas. Eukaryotic gene regulation is much more complex than that described for prokaryotes.

The human genome. In each human cell, there are about 2 m of DNA in 46 chromosomes, densely packed into a double helix, which consists of about 3.2 $×$ 10 9 nucleotide pairs, which provides about 10 1900000000 possible unique combinations. By the end of the 1980s, the location of about 1,500 human genes was known, but their total number was estimated at about 100,000, since only about 10,000 hereditary diseases in humans, not to mention the number of various proteins contained in cells .

In 1988, the international project "Human Genome" was launched, which by the beginning of the 21st century ended with a complete decoding of the nucleotide sequence. He made it clear that two different person 99.9% have similar nucleotide sequences, and only the remaining 0.1% define our individuality. In total, approximately 30-40 thousand structural genes were discovered, but then their number was reduced to 25-30 thousand. Among these genes there are not only unique ones, but also repeated hundreds and thousands of times. However, these genes code for much large quantity proteins, for example, tens of thousands of protective proteins - immunoglobulins.

97% of our genome is genetic "garbage" that exists only because it can reproduce well (the RNA that is transcribed in these regions never leaves the nucleus). For example, among our genes there are not only "human" genes, but also 60% of genes similar to those of the fruit fly, and up to 99% of our genes are related to chimpanzees.

In parallel with the deciphering of the genome, chromosome mapping also took place, as a result of which it was possible not only to detect, but also to determine the location of some genes responsible for the development of hereditary diseases, as well as drug target genes.

The deciphering of the human genome does not yet have a direct effect, since we have received a kind of instruction for assembling such a complex organism as a person, but have not learned how to make it or at least correct errors in it. Nevertheless, the era of molecular medicine is already on the threshold, all over the world there is a development of so-called gene preparations that can block, remove or even replace pathological genes in living people, and not just in a fertilized egg.

We should not forget that in eukaryotic cells DNA is contained not only in the nucleus, but also in mitochondria and plastids. Unlike the nuclear genome, the organization of mitochondrial and plastid genes has much in common with the organization of the prokaryotic genome. Despite the fact that these organelles carry less than 1% of the cell's hereditary information and do not even encode a complete set of proteins necessary for their own functioning, they can significantly affect some features of the body. Thus, variegation in plants of chlorophytum, ivy and others is inherited by an insignificant number of descendants, even when two variegated plants are crossed. This is due to the fact that plastids and mitochondria are transmitted mostly with the cytoplasm of the egg, so this heredity is called maternal, or cytoplasmic, in contrast to the genotypic, which is localized in the nucleus.

For this task you can get 1 point on the exam in 2020

Checking the knowledge of educational material on the topic “Genetics. Heredity ”offers task 6 of the Unified State Examination in biology. All test options contain a fairly extensive amount of material, divided into several subtopics. Part of the tickets is devoted to genetic terms. Do you want to pass the test successfully? Repeat before the exam - what is the genotype and phenotype, genome and codon, gene pool and genetic code, what are the paired genes of homologous chromosomes called, and how is an organism whose genotype contains different alleles of one gene. Surely in one of the ticket options there will be questions devoted to the works of the famous scientist Gregor Johann Mendel: how he called those signs that do not appear in first-generation hybrids or what the concept of “hereditary factor” he introduced is called today.

Task 6 of the USE in biology also contains many tasks for sex-linked inheritance. “Can a hemophilic father have a daughter with hemophilia?”, “What is the probability of a hemophilic boy being born in a woman with a hemophilia gene and a healthy man.” Practice before the exam to solve problems for compiling the gene pool - there are also a lot of them in task No. 6 of the Unified State Examination in biology. Typical examples of such tasks are: “Compose the genotype of a color-blind person” or “Compose the genotype of the brown-eyed daughter of a color-blind father if she has normal color vision.” In each of these tasks, various variants of the genotype will be given as answer options, you must choose the only correct one.