Biology how to complete task number 6 of the Unified State Exam. Crossbreeding

The sixth building of the Unified State Exam in biology is tasks. For people just starting out in biology, or test prep in particular, they are terrifying. Very in vain. Once you figure it out, everything will become simple and easy. 🙂

Refers to the basic level, with a correct answer you can get 1 primary point.

To successfully complete this task, you should know the following topics given in the codifier:

Topics in the codifier for task No. 6

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

Patterns of heredity, their cytological basis. Patterns of inheritance established by G. Mendel, their cytological basis (mono- and dihybrid crossing). T. Morgan's laws: linked inheritance of traits, disruption of gene linkage. Genetics of sex. Inheritance of sex-linked traits. Gene interaction. Genotype as an integral system. Human genetics. Methods for studying human genetics. Solving genetic problems. Drawing up crossing schemes.

“Solve the Unified State Exam” divides tasks into two large groups: monohybrid crossing and dihybrid crossing.

Before solving problems, we suggest compiling a small dictionary of terms and concepts in order to understand what is required of us.

Theory for crossing tasks

Traits are divided into two types: recessive and dominant.

« A dominant trait suppresses a recessive one" is a stable phrase. What does suppress mean? This means that in the choice between a dominant and recessive trait, the dominant one will necessarily appear. Anyway. A dominant trait is indicated by a capital letter, and a recessive trait is indicated by a small letter. Everything is logical. In order for a recessive trait to appear in the offspring, it is necessary that the gene carries the recessive trait from both the female and the male.

For clarity: let’s imagine a sign, for example, the color of a kitten’s fur. Let us have two options for the development of events:

Black wool
White wool

Black wool is dominant over white. In general, tasks always indicate what dominates what; applicants are not required to know everything, especially about genetics.

Black wool will then be indicated by a capital letter. The most commonly used are A, B, C and further in alphabetical order. White wool, respectively, in small letters.

A - black wool.

a- white wool.

If the fusion of gametes results in the following combinations: AA, Aa, aA, then this means that the fur of the descendants of the first generation will be black.

If the fusion of gametes results in the combination aa, then the wool will be white.

What kind of gametes the parents have will be stated in the task conditions.

Gametes, or germ cells, are reproductive cells that have a haploid (single) set of chromosomes and participate, in particular, in sexual reproduction.

Zygote- a diploid cell formed as a result of fertilization.

Heterozygote - two genes that determine one trait are different (Aa)

Homozygote - two genes that determine one trait - identical (AA or aa)

Dihybrid cross- crossing of organisms that differ in two pairs of alternative characteristics.

Monohybrid cross- crossing, in which the crossed organisms differ in only one characteristic.

Analysis cross- crossing a hybrid individual with an individual homozygous for recessive alleles.

Gregor Mendel - the “father” of genetics

So, how to distinguish these types of crossing:

When crossing a monohybrid, we are talking about one trait: color, size, shape.

In a dihybrid cross we are talking about a pair of traits.

In an analytical cross, one individual can be absolutely anything, but the other’s gametes must carry exclusively recessive traits.

Alleles- different forms of the same gene, located in the same regions of homologous chromosomes.

It doesn't sound very clear. Let's figure it out:

1 gene carries 1 trait.

1 allele carries one trait value (it can be dominant or recessive).

Genotype- the totality of genes of a given organism.

Phenotype- a set of characteristics inherent in an individual at a certain stage of development.

Problems often ask you to indicate the percentage of individuals with a certain genotype or phenotype or to indicate the breakdown by genotype or phenotype. If we simplify the definition of phenotype, then phenotype is the external manifestation of characteristics from the genotype.

In addition to all sorts of concepts, you need to know the laws of Gregor Mendel, the father of genetics.

Gregor Mendel crossed peas with fruits that differed in color and smoothness of the skin. Thanks to his observations, the three laws of genetics emerged:

I. Law of uniformity of first generation hybrids:

In a monohybrid crossing of different homozygotes, all descendants of the first generation will be identical in phenotype.

II. Law of splitting

When crossing descendants of the first generation, a splitting of 3:1 in phenotype and 1:2:1 in genotype is observed.

III. Law of independent cleavage

When a dihybrid crossing of two different homozygotes occurs in the second generation, phenotypic cleavage is observed in a ratio of 9:3:3:1.

When the skill of solving genetic problems is acquired, the question may arise: why do I need to know Mendel’s laws if I can already solve the problem perfectly well and find splitting in particular cases? Attention answer: in some tasks you may need to indicate by what law the splitting occurred, but this applies more to tasks with a detailed answer.

Having gained some grounding in theory, you can finally move on to the tasks. 😉

Analysis of typical tasks No. 6 Unified State Exam in biology

Types of gametes in an individual

How many types of gametes are produced in an individual with the aabb genotype?

We have two pairs of allelic chromosomes:

First pair: aa

Second pair: bb

These are all homozygotes. You can make only one combination: ab.

Types of gametes in crossing

How many types of gametes are formed in diheterozygous pea plants during dihybrid crossing (the genes do not form a linkage group)? Write down the number in response.

Since plants are diheterozygous, this means that for both traits, one allele is dominant and the other is recessive.

We obtain genotypes AaBb and AaBb.

Gametes in problems are designated by the letter G, without commas, in circles; the gametes of one individual are indicated first, then a semicolon (;) is placed, and the gametes of another individual are written, also in circles.

Crossing is indicated by an "x".

Let's write out the gametes; to do this, we'll go through all the combinations:

The gametes of the first and second individuals turned out to be the same, so their genotype was also the same. This means we have 4 different types of gametes:

Calculation of the proportion of diheterozygotes

When crossing individuals with genotypes AaBb with AaBb (genes are not linked), the proportion (%) of heterozygotes for both alleles (diheterozygotes) in the offspring will be….

Let's create a Punnett lattice. To do this, we write out the gametes of one individual in a column, the gametes of another in a row, and we get a table:

Let's find diheterozygotes in the table:

Total zygotes: 16

Diheterozygotes:4

Let's calculate the percentage: =

Application of Mendel's laws

The rule of uniformity of the first generation will appear if the genotype of one of the parents is aabb, and the other is

According to the rule of uniformity, monohybrid homozygotes must be crossed, one with a dominant trait, and the other with a recessive trait. This means that the genotype of the other individual must be AABB.

Answer: AABB.

Phenotype ratio

The genotype of one of the parents will be AaBb if, during an analyzing dihybrid crossing and independent inheritance of traits, a split in phenotype is observed in the offspring in the ratio. Write your answer as a sequence of numbers showing the ratio of the resulting phenotypes, in descending order.

Analyzing dihybrid cross, which means that the second individual has a recessive dihomozygote: aabb.

Here you can do without a Punnett grid.

Generations are designated by the letter F.

F1: AaBb; Aabb; aaBb; aabb

All four variants of phenotypes are different, so they relate to each other as 1:1:1:1.

What is the probability of having healthy boys in a family where the mother is healthy and the father is sick with hypertrichosis, a disease caused by the presence of a gene linked to the Y chromosome?

If a trait is linked to the Y chromosome, it means that it is not reflected in any way on the X chromosome.

The female sex is homozygous: XX, and the male is heterozygous: XY.

Solving problems with sex chromosomes is practically no different from solving problems with autosomes.

Let's make a table of genes and traits, which should also be compiled for problems about autosomal chromosomes, if the traits are indicated and this is important.

The letter above the Y indicates that the gene is linked to that chromosome. Traits can be dominant or recessive, they are designated by capital and small letters, they can relate to both the H chromosome and the Y chromosome, depending on the task.

♀ХХ x ХY a

F1: XX-girl, healthy

XY a - boy, sick

The boys born to this couple will be 100% sick, which means 0% healthy.

Blood groups

What ABO blood group does a person with genotype I B I 0 have? Write down the number in response.

Let's use the table:

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

Problems 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 Unified State Exam.

The sixth type of task 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 outlines theoretical foundations of genetics necessary for successful preparation for task C6, as well as solutions to problems of all types are considered and examples are given for independent work.

Basic terms of genetics

Gene- this is a section of a 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 one gene, encoding an alternative manifestation of the same trait. Alternative signs are signs that cannot be present in the body at the same time.

Homozygous organism- an organism that does not split according to one or another characteristic. Its allelic genes equally influence the development of this trait.

Heterozygous organism- an organism that produces splitting according to certain characteristics. Its allelic genes have different effects on the development of this trait.

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

Recessive gene is responsible for a trait whose development is suppressed by a dominant gene. A recessive trait occurs 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 hybrid uniformity

This law was derived based on the results of monohybrid crosses. For the experiments, two varieties of peas were taken, differing from each other in one pair of characteristics - the color of the seeds: one variety was yellow in color, the second was green. The crossed plants were homozygous.

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

Yellow color of seeds
- green color of seeds

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

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

Mendel's second law - the law of segregation

Plants were grown from seeds obtained by crossing a homozygous plant with yellow colored seeds with a plant with green colored seeds and obtained by self-pollination.



	(plants have a dominant trait, - recessive)

Statement of the law: in the offspring obtained from crossing first-generation hybrids, there is a split in phenotype in the ratio , and in genotype -.

Mendel's third law - the law of independent inheritance

This law was derived from data obtained from dihybrid crosses. Mendel considered the inheritance of two pairs of characteristics in peas: color and seed shape.

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

Yellow color of seeds, - green color of seeds,
- smooth form, - wrinkled form.



	(yellow smooth).

Mendel then grew plants from seeds and obtained second-generation hybrids through self-pollination.

The Punnett grid is used to record and determine genotypes

Gametes

There was a split into phenotypic classes in the ratio. All seeds had both dominant traits (yellow and smooth), - the first dominant and second recessive (yellow and wrinkled), - the first recessive and 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 characteristics (seed shape).

Statement of the law: when crossing organisms that differ from each other in 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 is true only if the genes are in different pairs of homologous chromosomes.

Law (hypothesis) of “purity” of gametes

When analyzing the characteristics of hybrids of the first and second generations, Mendel established that the recessive gene does not disappear and does not mix with the dominant one. Both genes are expressed, which is only possible if the hybrids form two types of gametes: some carry a dominant gene, others carry 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 proven after studying the processes occurring in meiosis.

The hypothesis of the "purity" of gametes is the cytological basis of Mendel's first and second laws. With its help, it is possible to explain the splitting by phenotype and genotype.

Analysis 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 one could conclude: the original organism is homozygous for the trait being studied.

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

Inheritance of blood groups (AB0 system)

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). In the human population, there are three genes encoding red blood cell antigen proteins that determine people's blood types. The genotype of each person contains only two genes that determine his blood type: group one; second and ; third and fourth.

Inheritance of sex-linked traits

In most organisms, sex is determined during fertilization and depends on the number 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, while the male sex has a set of sex chromosomes. The female sex is called homogametic (forms one type of gametes); and the male one is heterogametic (forms two types of gametes). In birds and butterflies, the homogametic sex is male, and the heterogametic sex is female.

The Unified State Exam includes tasks only for traits linked to the - chromosome. They mainly concern two human characteristics: blood clotting (- normal; - hemophilia), color vision (- normal, - color blindness). Tasks on the inheritance of sex-linked traits in birds are much less common.

In humans, the female sex can be homozygous or heterozygous for these genes. Let's consider possible genetic sets in a woman using hemophilia as an example (a similar picture is observed with color blindness): - healthy; - healthy, but is a carrier; - sick. The male sex is homozygous for these genes, because -chromosome does not have alleles of these genes: - healthy; - is ill. Therefore, most often men suffer from these diseases, and women are their carriers.

Typical USE tasks in genetics

Determination of the number of gamete types

The number of gamete types is determined using the formula: , where is the number of gene pairs in the heterozygous state. For example, an organism with a genotype does not have genes in a heterozygous state, i.e. , therefore, and it forms one type of gametes. 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.

Mono- and dihybrid crossing problems

For monohybrid crossing

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

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

	(black)	(white)

	(black) : (white)

For dihybrid crossing

Dominant genes are known

Task: Crossed normal-sized tomatoes 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, red fruit color dominates yellow, and normal growth dominates dwarfism.

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

Let's analyze the inheritance of each trait separately. All descendants have normal growth, i.e. no segregation for this trait is observed, therefore the initial forms are homozygous. Segregation 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 were red saucer, red funnel, white saucer and white funnel. Determine the dominant genes and genotypes of the parental forms, as well as their descendants.

Solution: Let's analyze the splitting for each characteristic separately. Among the descendants of plants with red flowers are, with white flowers -, i.e. . That's why it's red - white color, and the parental forms are heterozygous for this trait (since there is cleavage in the offspring).

There is also a split in flower shape: half of the offspring have saucer-shaped flowers, the other half have funnel-shaped flowers. 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 types are possible in children?

Solution:



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

Solving problems on the inheritance of sex-linked traits

Such tasks may well appear in both Part A and Part C of the Unified State Examination.

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 a blood type married a woman with brown eyes and a 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 can have a genotype or, the first - only. Since the child has the first blood group, therefore, he received the gene from both his father and mother, therefore his father has the genotype.

	(father)	(mother)

	(was born)

Task: A 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, better control of the right hand dominates over left-handedness, therefore - right-handed, - left-handed. The genotype of the man (since he received the gene from a left-handed mother), and women - .

A colorblind man has the genotype, and his wife has the genotype, 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 ()

Problems to solve independently

Determine the number of gamete types in an organism with genotype.
Determine the number of gamete types in an organism with genotype.
Crossed tall plants with short plants. B - all plants are medium in size. What will it be?
Crossed a white rabbit with a black rabbit. All rabbits are black. What will it be?
Two rabbits with gray fur were crossed. In with black wool, - with gray and with white. Determine the genotypes and explain this segregation.
A black hornless bull was crossed with a white horned cow. We got black hornless, black horned, white horned and white hornless. Explain this split if black color and lack of horns are dominant characteristics.
Drosophila flies with red eyes and normal wings were crossed with fruit flies 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?
A blue-eyed brunette married a brown-eyed blonde. What kind of children can be born if both parents are heterozygous?
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 characteristic?
The mother and father have the same blood type (both parents are heterozygous). What blood type is possible in children?
The mother has a blood type, the child has a blood type. What blood type is impossible for the father?
The father has the first blood group, the mother has the second. What is the probability of having a child with the first blood group?
A blue-eyed woman with a blood type (her parents had a third blood group) married a brown-eyed man with a blood type (his father had blue eyes and a first blood group). What kind of children can be born?
A hemophilic man, right-handed (his mother was left-handed) married a left-handed woman with normal blood (her father and mother were healthy). What children can be born from this marriage?
Strawberry plants with red fruits and long-petioled leaves were crossed with strawberry plants with white fruits and short-petioled leaves. What kind of offspring can there be if red color and short-petioled leaves dominate, while both parent plants are heterozygous?
A man with brown eyes and a blood type married a woman with brown eyes and a blood type. They had a blue-eyed child with a blood type. Determine the genotypes of all individuals indicated in the problem.
Melons with white oval fruits were crossed with plants that had white spherical fruits. The offspring produced the following plants: with white oval, white spherical, yellow oval and yellow spherical fruits. Determine the genotypes of the original plants and descendants, if in a melon the white color dominates over the yellow, the oval shape of the fruit dominates over the spherical.

Answers

type of gametes.
types of gametes.
type of gametes.
high, medium and low (incomplete dominance).
black and white.
- black, - white, - gray. Incomplete dominance.
Bull: , cow - . Offspring: (black hornless), (black horned), (white horned), (white hornless).
- Red eyes, - white eyes; - defective wings, - normal. Initial forms - and, offspring.
Crossing results:
A)
- Brown eyes, - blue; - dark hair, - blond. Father mother - .

- brown eyes, dark hair
- brown eyes, blond hair
- blue eyes, dark hair
- blue eyes, blond hair
- right-handed, - left-handed; - Rh positive, - Rh negative. Father mother - . Children: (right-handed, Rh positive) and (right-handed, Rh negative).
Father and mother - . Children may have a third blood group (probability of birth - ) or first blood group (probability of birth - ).
Mother, child; he received the gene from his mother, and from his father - . The following blood groups are impossible for the father: second, third, first, fourth.
A child with the first blood group can only be born if his mother is heterozygous. In this case, the probability of birth is .
- Brown eyes, - blue. Female Male . Children: (brown eyes, fourth group), (brown eyes, third group), (blue eyes, fourth group), (blue eyes, third group).
- right-handed, - left-handed. Man Woman . Children (healthy boy, right-handed), (healthy girl, carrier, right-handed), (healthy boy, left-handed), (healthy girl, carrier, left-handed).
- red fruits, - white; - short-petioled, - long-petioled.
Parents: and. Offspring: (red fruits, short-petioled), (red fruits, long-petioled), (white fruits, short-petioled), (white fruits, long-petioled).
Strawberry plants with red fruits and long-petioled leaves were crossed with strawberry plants with white fruits and short-petioled leaves. What kind of offspring can there be if red color and short-petioled leaves dominate, while both parent plants are heterozygous?
- Brown eyes, - blue. Female Male . Child:
- 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.

The problem of successfully passing the Unified State Exam begins to worry schoolchildren a year, or even two, before they graduate from 11th grade. And it’s not surprising - the Unified State Exam is not just a condition for being awarded a school certificate at graduation, but also a kind of key that opens the door to a successful adult life. It is no secret that admission to higher educational institutions in the country requires the mandatory availability of Unified State Examination certificates in several specialized subjects. And the Unified State Exam 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 branches of medicine, veterinary medicine, agronomy or the chemical industry, but in 2019 the Unified State Examination certificate in biology will also be considered for admission to the faculties of physical education, psychology, paleontology, landscape design and etc.

Biology is a subject that many schoolchildren like, because many topics are close and understandable to students, and most laboratory work is related to knowledge of the world around them, which arouses genuine interest in children. But when choosing the Unified State Exam 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 required Unified State Examination certificates, which allows you to apply for budget or contract education at a particular university in the Russian Federation, can be found on the website of the educational institution you are interested in.

Dates

Like all other subjects, in 2019 the Unified State Examination in biology will be taken on the days established by the State Examination Calendar. The draft of this document should be approved in November. As soon as the exam dates are known, we will be the first to tell you when the tests for biology and other subjects will take place.

You can get an approximate idea of when exams may be scheduled by reviewing the previous year's calendar. So, in 2018, biology was taken on the following days:

Main date

Reserve day

Early

Basic

Individuals readmitted to take the test were also given their test dates in April and June.

Innovations for 2019

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

The main innovation for the 2018-2019 academic year will be the replacement of the 2-point task of the 2nd line (multiple choice) with a 1-point task involving working 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 structure of the CMM will remain unchanged, which should please 11th graders, because in the preparation process they will be able to rely on numerous 2018 materials available on the Internet.

Structure of KIMs in biology

So, knowing already what changes will occur in the Unified State Examination in Biology, let’s take a closer look at the types of tasks and their distribution on the ticket. CMM, as before, will include 28 tasks, divided into two parts:

The proposed CMM format allows you to assess the graduate’s knowledge in 7 main blocks:

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

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

It is prohibited to bring additional materials and equipment with you, or use them during the Unified State Exam in Biology!

Performance evaluation

For correctly completing 21 tasks of the 1st block, the examinee can score a maximum of 38 primary points, and for completing 7 tasks of the second - another 20, which is a total of 58 points, which will correspond to a 100-point USE result.

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

Although the results of the Unified State Exam have long been no longer equated with certain grades on a 5-point scale, many still want to know how they coped with the task. It will be possible to convert the 2019 result into a school grade using the following approximate correspondence table:

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

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

Secrets of preparation

Biology is a difficult science; it requires attentiveness and understanding, and not just rote memorization. Therefore, preparation is needed methodically and constantly.

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

Practice in solving problems of a certain type is required. By systematically solving the options presented on the FIPI website, students form a strategy for completing tasks and gain confidence in their own abilities, which is an indispensable assistant in achieving success.

The date of the Unified State Exam in Biology in 2019 will be known only in January 2019.

What is tested in the exam?

To complete the exam work, a Unified State Exam participant needs to be able to:

work with diagrams, pictures, graphs, tables and histograms,

explain the facts

generalize and formulate conclusions,

solve biological problems,

work with biological information, with images of biological objects.

The knowledge and skills of graduates, formed while studying the following sections of the biology course, are tested:

"Plants".

“Bacteria. Mushrooms. Lichens."

"Animals".

"Man and his health."

"General Biology".

The examination work is dominated by tasks on general biology, which examine general biological patterns that appear at different levels of the organization of living nature. These include:

cellular, chromosomal and evolutionary theories;

laws of heredity and variability;

ecological patterns of biosphere development.

We invite you to watch this useful video right now:

Genetics, its tasks. Heredity and variability are properties of organisms. Genetics methods. 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 make assumptions about the existence of certain hereditary factors that determine, for example, the development of hereditary diseases, but these assumptions were not supported by relevant evidence. Even the theory of intracellular pangenesis formulated by H. de Vries in 1889, which assumed the existence in the cell nucleus of certain “pangenes” that determine the hereditary inclinations of the organism, and the release into protoplasm of only those of them that determine the type of cell, could not change the situation, as well as the theory of “germ plasm” by A. Weissman, according to which characteristics acquired during the process of ontogenesis are not inherited.

Only the works of the Czech researcher G. Mendel (1822-1884) became the foundation stone of modern genetics. However, despite the fact that his works were cited in scientific publications, his 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 patterns of heredity and variability and methods of controlling them.

The tasks of genetics at the present stage are the study of qualitative and quantitative characteristics of 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 hereditary human diseases and methods for “correcting” them, creating a new generation of drugs according to the type DNA vaccines, the construction, using genetic and cellular engineering, of organisms with new properties that could produce the medicines and food products needed by humans, as well as the complete deciphering of the human genome.

Heredity and variability - properties of organisms

Heredity is the ability of organisms to transmit their characteristics and properties over a series of generations.

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

Signs- these are any morphological, physiological, biochemical and other characteristics of organisms by which some of them differ from others, for example, eye color. Properties also called any functional features of organisms, which are based on a certain structural feature or group of elementary features.

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

The material carrier of heredity is DNA. In eukaryotes, there are two types of heredity: genotypic And cytoplasmic. The carriers of genotypic heredity are localized in the nucleus and will be discussed further, while the carriers of cytoplasmic heredity are the circular DNA molecules located in mitochondria and plastids. Cytoplasmic heredity 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 changes can have a significant impact on the development of the organism, for example, leading to the development of blindness or a gradual decrease in mobility. Plastids play an equally important role in plant life. Thus, in some areas of the leaf, chlorophyll-free cells may be present, which leads, on the one hand, to a decrease in plant productivity, and on the other hand, such variegated organisms are valued in decorative landscaping. Such specimens reproduce mainly asexually, since sexual reproduction often produces ordinary green plants.

Genetics methods

1. The hybridological method, or the method of crossings, consists of selecting parental individuals and analyzing the offspring. In this case, the genotype of an organism is judged by the phenotypic manifestations of genes in descendants obtained through a certain crossing scheme. This is the oldest informative method of genetics, which was most fully first used by G. Mendel in combination with the 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 organism’s chromosomes. The study of these features allows us to identify various developmental pathologies.

3. The biochemical method allows you to determine the content of various substances in the body, especially 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 DNA sections under study. They make it possible 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, genetic load, and also outline the prospects for the development of a population.

6. The method of hybridization of somatic cells in culture makes it possible to determine the localization of certain genes in chromosomes during the fusion of cells of different organisms, for example, a mouse and a hamster, a mouse and a human, etc.

Basic genetic concepts and symbolism

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

Some genes can influence the manifestation of several traits at once. This phenomenon is called pleiotropy. For example, the gene that causes the development of the hereditary disease arachnodactyly (spider fingers) also causes curvature of the lens and pathologies 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 certain 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 located on the other chromosome and suppresses the development of the trait encoded by the recessive gene. Dominant alleles are usually designated in capital letters of the Latin alphabet (A, B, C, etc.), and recessive alleles are designated in 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 alleles on both homologous chromosomes is called homozygous for this 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 this gene, or heterozygous(Aa, AaBb, etc.).

A number of genes may 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. This phenomenon is called multiple allelism. However, even in this case, each chromosome of a pair carries only one allele, that is, all three gene variants cannot be represented in one organism.

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

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

Phenotype- a set of characteristics 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, the patterns of their inheritance can only be established by analyzing two or more traits in the offspring. Crossing, in which inheritance is considered and an accurate quantitative count of the offspring is carried out according to one pair of alternative characteristics, is called monohybrid m, in two pairs - dihybrid, according to a larger number of signs - polyhybrid.

Based on the phenotype of an individual, it is not always possible to determine 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, they use test cross- a crossing in which an organism with a dominant trait is crossed with one homozygous for a recessive gene. In this case, an organism homozygous for the dominant gene will not produce splitting in the offspring, whereas in the offspring of heterozygous individuals there is an equal number of individuals with dominant and recessive traits.

The following conventions are most often used to record crossing schemes:

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

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

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

$×$ — crossing sign;

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

F a - offspring from an analyzing cross.

Chromosomal theory of heredity

The founder of genetics, G. Mendel, as well as his closest followers, did not have the slightest 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. Satton 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 chromosomes. These assumptions became the cornerstone of the chromosomal theory of heredity.

In 1906, English geneticists W. Bateson and R. Punnett discovered a violation of Mendelian segregation 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 if we consider that by that time it was already known that the number of known characteristics 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, experiments by T. Morgan's group began on a new experimental object - the fruit fly Drosophila. The results of these experiments made it possible by the mid-20s of the 20th century to formulate the basic principles of the chromosomal theory of heredity, to determine the order of genes in chromosomes and the distances between them, i.e., to draw up the first maps of chromosomes.

Basic provisions of the chromosomal theory of heredity:

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.
Each gene occupies a strictly defined place on the chromosome - a locus.
Genes are arranged linearly on chromosomes.
Disruption of gene linkage occurs only as a result of crossing over.
The distance between genes on a chromosome is proportional to the percentage of crossing over between them.
Independent inheritance is typical only for genes on 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 neurospora fungus, came to the conclusion that each gene controls the synthesis of an enzyme, and formulated the principle of “one gene - one enzyme” .

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

In the process of research, 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.

Structure of a prokaryotic gene. The structural gene of prokaryotes has a complex structure, since it includes regulatory regions and coding sequences. The regulatory regions include the promoter, operator, and terminator. Promoter called the region of the gene to which the enzyme RNA polymerase is attached, which ensures the synthesis of mRNA during transcription. WITH operator, located between the promoter and the structural sequence, can bind repressor protein, which does not allow RNA polymerase to begin reading the 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. Reading of information ends at a section of the gene called terminator.

Coding sequence A structural gene contains information about the amino acid sequence of the corresponding protein. The coding sequence in prokaryotes is called cistronome, and the totality of coding and regulatory regions of a prokaryotic gene is operon. In general, prokaryotes, which include E. coli, have a relatively small number of genes located on a single circular 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 transmitted from one cell to another. They may carry information about sex characteristics, pathogenicity and antibiotic resistance.

Structure of a 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 terminator. In addition, in eukaryotic genes significant regions ( exons) alternate with insignificant ones ( introns), which are completely transcribed into mRNA and then excised during their maturation. The biological role of introns is to reduce the likelihood of mutations in significant regions. The regulation of genes in eukaryotes is much more complex than that described for prokaryotes.

Human genome. In each human cell, the 46 chromosomes contain about 2 m of DNA, tightly packed into a double helix, which consists of approximately 3.2 $×$ 10 9 nucleotide pairs, which provides about 10 1900000000 possible unique combinations. By the end of the 80s of the twentieth century, the location of approximately 1,500 human genes was known, but their total number was estimated at approximately 100 thousand, since humans have approximately 10 thousand hereditary diseases alone, not to mention the number of various proteins contained in cells .

In 1988, the international Human Genome project was launched, which by the beginning of the 21st century ended with a complete decoding of the nucleotide sequence. He made it possible to understand that two different people have 99.9% similar nucleotide sequences, and only the remaining 0.1% determine 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 encode a much larger number of proteins, for example tens of thousands of protective proteins - immunoglobulins.

97% of our genome is genetic “junk” that exists only because it can reproduce well (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 the genes of the Drosophila fly, and up to 99% of our genes are similar 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 discover, but also to determine the location of some genes responsible for the development of hereditary diseases, as well as drug target genes.

Decoding the human genome has not yet given 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 manufacture it or at least correct errors in it. Nevertheless, the era of molecular medicine is already on the threshold; all over the world, so-called gene preparations are being developed that can block, delete 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 genes in mitochondria and plastids 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 the full set of proteins necessary for their own functioning, they are capable of significantly influencing some of the body's characteristics. Thus, variegation in plants of chlorophytum, ivy and others is inherited by a small number of descendants even when crossing two variegated plants. This is due to the fact that plastids and mitochondria are transmitted mostly with the cytoplasm of the egg, therefore such heredity is called maternal, or cytoplasmic, in contrast to genotypic, which is localized in the nucleus.

The biology exam is selective and only those who are confident in their knowledge will take it. The Unified State Exam in biology is considered a difficult subject, since it tests the knowledge accumulated over all years of study.

The Unified State Exam (USE) tasks in biology are of different types; solving them requires solid knowledge of the main topics of the school biology course. Based demo versions teachers developed over 10 test tasks for each topic.

Topics that need to be studied when completing assignments, see from FIPI. Each task has its own algorithm of actions that will help in solving problems.

There are no changes to the KIM Unified State Examination 2020 in biology.

Structure of Unified State Examination tasks in biology:

Part 1– these are tasks from 1 to 21 with a short answer; approximately 5 minutes are allotted for completion.

Advice: Read the wording of the questions carefully.

Part 2– these are tasks from 22 to 28 with a detailed answer; approximately 10-20 minutes are allotted for completion.

Advice: express your thoughts in a literary manner, answer the question in detail and comprehensively, define biological terms, even if this is not required in the assignments. The answer should have a plan, not write in continuous text, but highlight points.