Summary: Heredity, ideas about the genetic code, personality genes. Collection of tasks for preparing for the exam How and where are the hereditary properties of organisms encoded

Earlier, we emphasized that nucleotides have an important feature for the formation of life on Earth - in the presence of one polynucleotide chain in a solution, a second (parallel) chain is formed spontaneously on the basis of a complementary compound of related nucleotides. The same number of nucleotides in both chains and their chemical affinity is an indispensable condition for the implementation of such reactions. However, in protein synthesis, when information from mRNA is implemented into the protein structure, there can be no talk of observing the principle of complementarity. This is due to the fact that not only the number of monomers is different in the mRNA and in the synthesized protein, but also, which is especially important, there is no structural similarity between them (on the one hand, nucleotides, on the other, amino acids). It is clear that in this case there is a need to create a new principle for the exact translation of information from polynucleotide into the structure of the polypeptide. In evolution, such a principle was created and the genetic code was based on it.

The genetic code is a system for recording hereditary information in nucleic acid molecules, based on a certain alternation of nucleotide sequences in DNA or RNA, forming codons corresponding to amino acids in a protein.

Genetic code has several properties.

Tripletness.

Degeneracy or redundancy.

Unambiguity.

Polarity.

Non-overlap.

Compactness.

Universality.

It should be noted that some authors also offer other properties of the code related to the chemical characteristics of nucleotides included in the code or to the frequency of occurrence of individual amino acids in body proteins, etc. However, these properties follow from the above, therefore we will consider them there.

a. Tripletness. The genetic code, like many complexly organized systems, has the smallest structural and smallest functional unit. A triplet is the smallest structural unit of a genetic code. It consists of three nucleotides. A codon is the smallest functional unit of a genetic code. As a rule, triplets of mRNA are called codons. In the genetic code, the codon performs several functions. Firstly, its main function is that it encodes a single amino acid. Secondly, the codon may not encode an amino acid, but, in this case, it performs a different function (see below). As can be seen from the definition, a triplet is a concept that characterizes elementary structural unit   genetic code (three nucleotides). Codon - characterizes elementary semantic unit   genome - three nucleotides determine the attachment of one amino acid to the polypeptide chain.

The elementary structural unit was first deciphered theoretically, and then its existence was confirmed experimentally. Indeed, 20 amino acids cannot be encoded with one or two nucleotides since the latter are only 4. Three out of four nucleotides give 4 3 \u003d 64 variants, which over-covers the number of amino acids present in living organisms (see table 1).

The nucleotide combinations presented in table 64 have two features. Firstly, of the 64 triplet variants, only 61 are codons and encode any amino acid, they are called semantic codons. Three triplets do not encode

Table 1.

Codons of messenger RNA and their corresponding amino acids

amino acids a are stop signals indicating the end of translation. There are three such triplets - UAA, UAG, CAA, they are also called "meaningless" (nonsense codons). As a result of a mutation, which is associated with the replacement in a triplet of one nucleotide by another, a meaningless codon can arise from a sense codon. This type of mutation is called nonsense mutation. If such a stop signal was formed inside the gene (in its information part), then during protein synthesis in this place the process will be constantly interrupted - only the first (before the stop signal) part of the protein will be synthesized. A person with such a pathology will feel a lack of protein and there will be symptoms associated with this shortage. For example, this kind of mutation was detected in the gene encoding the hemoglobin beta chain. A shortened inactive hemoglobin chain is synthesized, which is rapidly destroyed. As a result, a hemoglobin molecule lacking a beta chain is formed. It is clear that such a molecule is unlikely to fully fulfill its responsibilities. There is a serious disease that develops according to the type of hemolytic anemia (beta-zero thalassemia, from the Greek word "Talas" - the Mediterranean Sea, where this disease was first discovered).

  The mechanism of action of stop codons differs from the mechanism of action of semantic codons. This follows from the fact that for all codons encoding amino acids, the corresponding tRNAs were found. No tRNAs were found for nonsense codons. Therefore, tRNA is not involved in the process of stopping protein synthesis.

  CodonAUG   (sometimes GUG in bacteria) not only encode the amino acid methionine and valine, but alsobroadcast initiator .

b. Degeneracy or redundancy.

61 out of 64 triplets encode 20 amino acids. Such a three-fold excess of the number of triplets over the number of amino acids suggests that two types of coding can be used in the transfer of information. Firstly, not all 64 codons can be involved in the coding of 20 amino acids, but only 20 and, secondly, amino acids can be encoded by several codons. Studies have shown that nature used the latter option.

His preference is obvious. If out of 64 triplet variants only 20 participated in the coding of amino acids, then 44 triplets (out of 64) would remain non-coding, i.e. meaningless (nonsense codons). Earlier, we indicated how dangerous it is for a cell to turn a coding triplet as a result of a mutation into a nonsense codon - this significantly disrupts the normal functioning of RNA polymerase, ultimately leading to the development of diseases. Currently, three codons in our genome are meaningless, and now imagine what would happen if the number of nonsense codons increases by about 15 times. It is clear that in such a situation, the transition of normal codons to nonsense codons will be immeasurably higher.

The code in which one amino acid is encoded by several triplets is called degenerate or redundant. Almost every amino acid has several codons. So, the amino acid leucine can be encoded in six triplets - УУА, УУГ, ЦУУ, ЦУЦ, ЦУА, ЦУГ. Valine is encoded in four triplets, phenylalanine in two and only tryptophan and methionineencoded by one codon. The property that is associated with the recording of the same information by different characters is called degeneracy.

The number of codons destined for one amino acid correlates well with the frequency of occurrence of the amino acid in proteins.

And this is most likely not accidental. The higher the frequency of occurrence of an amino acid in a protein, the more often the codon of this amino acid is presented in the genome, the higher the probability of its damage by mutagenic factors. Therefore, it is clear that a mutated codon is more likely to encode the same amino acid with its high degeneracy. From these positions, the degeneracy of the genetic code is a mechanism that protects the human gene from damage.

It should be noted that the term degeneracy is used in molecular genetics in another sense. So the main part of the information in the codon falls on the first two nucleotides, the base in the third position of the codon is of little importance. This phenomenon is called the “degeneracy of the third base”. The latter feature minimizes the effect of mutations. For example, it is known that the main function of red blood cells is the transfer of oxygen from the lungs to tissues and carbon dioxide from tissues to the lungs. This function is carried out by the respiratory pigment - hemoglobin, which fills the entire cytoplasm of the red blood cell. It consists of the protein part - globin, which is encoded by the corresponding gene. In addition to protein, the hemoglobin molecule includes heme containing iron. Mutations in globin genes lead to the appearance of various hemoglobin variants. Mutations are most often associated with replacing one nucleotide with another and the appearance of a new codon in the gene, which can encode a new amino acid in the hemoglobin polypeptide chain. In a triplet, as a result of a mutation, any nucleotide can be replaced - the first, second or third. Several hundred mutations are known that affect the integrity of globin genes. Near 400 of them are associated with the replacement of single nucleotides in the gene and the corresponding amino acid substitution in the polypeptide. Of these, only 100 replacements lead to hemoglobin instability and various diseases from mild to very severe. 300 (approximately 64%) mutation substitutions do not affect hemoglobin function and do not lead to pathology. One of the reasons for this is the “degeneracy of the third base” mentioned above, when replacing the third nucleotide in a triplet encoding serine, leucine, proline, arginine, and some other amino acids leads to the appearance of a synodon codon encoding the same amino acid. Phenotypically, such a mutation will not occur. In contrast, any replacement of the first or second nucleotide in a triplet in 100% of cases leads to the appearance of a new variant of hemoglobin. But even in this case, severe phenotypic disorders may not exist. The reason for this is the replacement of the amino acid in hemoglobin with another similar to the first one in physicochemical properties. For example, if an amino acid with hydrophilic properties is replaced by another amino acid, but with the same properties.

Hemoglobin consists of the iron-porphyrin heme group (oxygen and carbon dioxide molecules are attached to it) and the protein, globin. Adult Hemoglobin (HBA) contains two identical -chains and two -chains. Molecule -chain contains 141 amino acid residues, -chain - 146, - and -chains differ in many amino acid residues. The amino acid sequence of each globin chain is encoded by its own gene. Gene encoding the chain is located in the short arm of chromosome 16, -gene - in the short arm of 11 chromosomes. Substitution in the gene encoding The hemoglobin chain of the first or second nucleotide almost always leads to the appearance of new amino acids in the protein, impaired hemoglobin functions and severe consequences for the patient. For example, replacing “C” in one of the CAU triplets (histidine) with “U” will result in the appearance of a new UAU triplet encoding another amino acid - tyrosine. Phenotypically this will manifest itself in a serious illness. A similar substitution in position 63 -chain histidine polypeptide to tyrosine will lead to hemoglobin destabilization. Methemoglobinemia disease develops. Replacement, as a result of mutation, of glutamic acid with valine in the 6th position -chain is the cause of a serious disease - sickle cell anemia. We will not continue the sad list. We only note that when replacing the first two nucleotides, an amino acid may appear similar in physical and chemical properties to the previous one. So, replacing the 2nd nucleotide in one of the triplets encoding glutamic acid (GAA) in -chain on “U” leads to the appearance of a new triplet (GUA) encoding valine, and replacing the first nucleotide with “A” forms an AAA triplet encoding the amino acid lysine. Glutamic acid and lysine are similar in physicochemical properties - they are both hydrophilic. Valine is a hydrophobic amino acid. Therefore, the replacement of hydrophilic glutamic acid with hydrophobic valine significantly changes the properties of hemoglobin, which ultimately leads to the development of sickle cell anemia, while the replacement of hydrophilic glutamic acid with hydrophilic lysine changes the hemoglobin function to a lesser extent - mild anemia occurs in patients. As a result of replacing the third base, a new triplet can encode the same amino acids as the previous one. For example, if uracil was replaced by cytosine in the CAU triplet and the CAA triplet appeared, then practically no phenotypic changes in humans would be detected. This is understandable since both triplets encode the same amino acid - histidine.

In conclusion, it is appropriate to emphasize that the degeneracy of the genetic code and the degeneracy of the third base from a general biological standpoint are protective mechanisms that are embedded in evolution in the unique structure of DNA and RNA.

in. Unambiguity.

Each triplet (except for senseless ones) encodes only one amino acid. Thus, in the codon - amino acid direction, the genetic code is unique, in the amino acid - codon direction - ambiguous (degenerate).

Unequivocal

Codon amino acid

Degenerate

And in this case, the need for unambiguity in the genetic code is obvious. In another embodiment, when translating the same codon, different amino acids would be inserted into the protein chain and, as a result, proteins with different primary structures and different functions would be formed. Cell metabolism would go into the mode of "one gene - several polypeptides." It is clear that in such a situation the regulatory function of genes would be completely lost.

polarity

Reading information from DNA and mRNA occurs in only one direction. Polarity is important for determining higher-order structures (secondary, tertiary, etc.). We said earlier that lower-order structures define higher-order structures. The tertiary structure and higher-order structures in proteins are formed immediately as soon as the synthesized RNA chain departs from the DNA molecule or the polypeptide chain departs from the ribosome. While the free end of the RNA or polypeptide acquires a tertiary structure, the other end of the chain continues to be synthesized on DNA (if RNA is transcribed) or on the ribosome (if the polypeptide is transcribed).

Therefore, the unidirectional process of reading information (in the synthesis of RNA and protein) is essential not only for determining the sequence of nucleotides or amino acids in the synthesized substance, but for the rigid determination of secondary, tertiary, etc. structures.

e. Non-overlap.

The code can be overlapping and not overlapping. For most organisms, the code is not overlapping. Overlapping code found in some phages.

The essence of the non-overlapping code is that the nucleotide of one codon cannot simultaneously be the nucleotide of another codon. If the code were overlapping, then a sequence of seven nucleotides (GTsUCH) could encode not two amino acids (alanine-alanine) (Fig. 33, A) as in the case of a non-overlapping code, but three (if one nucleotide is common) (Fig. . 33, B) or five (if two nucleotides are common) (see Fig. 33, C). In the last two cases, a mutation of any nucleotide would lead to a violation in the sequence of two, three, etc. amino acids.

However, it was found that a mutation of one nucleotide always violates the inclusion of one amino acid in the polypeptide. This is a significant argument that the code is not overlapping.

Let us explain this in Figure 34. The bold lines show the triplets encoding amino acids in the case of a non-overlapping and overlapping code. The experiments clearly showed that the genetic code is not overlapping. Without going into the details of the experiment, we note that if the third nucleotide is replaced in the nucleotide sequence (see Fig. 34)At   (marked with an asterisk) on any other then:

1. With a non-overlapping code, a protein controlled by this sequence would have a replacement for one (first) amino acid (marked with asterisks).

2. With the overlapping code in option A, there would be a substitution in two (first and second) amino acids (marked with asterisks). In option B, the replacement would affect three amino acids (marked with asterisks).

However, numerous experiments have shown that when a single nucleotide in a DNA is violated, the violations in the protein always relate to only one amino acid, which is characteristic of a non-overlapping code.

ГЦУГЦУГ ГЦУЦУГ ГЦУГЦУГ

ГЦУ ГЦУ ГЦУ УГЦ ЦУГ ГЦУ ЦУГ УГЦ ГЦУ ЦУГ

*** *** *** *** *** ***

Alanin - Alanin Ala - Cis - Lei Ala - Lei - Lei - Ala - Lei

A B C

Non-overlapping code. Overlapping code.

Fig. 34. Scheme explaining the presence of a non-overlapping code in the genome (explanation in the text).

The non-overlap of the genetic code is associated with another property - the reading of information starts from a certain point - the initiation signal. Such an initiation signal in mRNA is a codon encoding AUG methionine.

It should be noted that a person still has a small number of genes that depart from the general rule and overlap.

e. Compactness.

There are no punctuation marks between the codons. In other words, triplets are not separated from each other, for example, by one meaningless nucleotide. The absence of “punctuation marks” in the genetic code has been proven in experiments.

g. Universality.

The code is the same for all organisms living on Earth. Direct evidence of the universality of the genetic code was obtained by comparing DNA sequences with corresponding protein sequences. It turned out that all bacterial and eukaryotic genomes use the same sets of code values. There are exceptions, but not many.

The first exceptions to the universality of the genetic code were found in the mitochondria of certain animal species. This concerned the codon of the CAA terminator, which was read in the same way as the UGG codon encoding the amino acid tryptophan. Other rarer deviations from universality have been found.

MH. The genetic code is a system for recording hereditary information in nucleic acid molecules, based on a certain alternation of nucleotide sequences in DNA or RNA that form codons,

corresponding to amino acids in a protein.Genetic code has several properties.

The opening of the inheritance case shall be carried out by a notary when the relatives of the deceased testator, the testator contact him, provided they provide evidence of his death. In fact, to open a hereditary business is a duty and one of the main functions of a notary. Before the start of the formation of the inheritance case, the notary determines the time and place of opening the inheritance, attaching the documents on these procedures to the totality of the documents composing it.

How to determine the moment of discovery, where and how should the inheritance case be opened after death?

Procedures related to the opening of an inheritance by law or by will are regulated by articles 1110, 1113, 1153, 1162, 1115, 1154-55 of civil law. Heirs should understand that these notarial acts will be performed by a notary only after he receives a statement, as well as evidence of the death of the testator.

The first question that potential heirs are faced with is how to find out which notary conducts the inheritance business or which notary should be contacted to carry out all the inheritance procedures.

In this case, the presence or absence of a will matters. So, in the presence of the will, its opening is carried out by that notary who assured him. Otherwise, :

• in a notary's office at the place of permanent residence;
• the presence of the testator or the bulk of the property of the deceased, which is determined by its value.

Search for the place of opening of the inheritance and the notary serving the heirs

Before contacting the notary office, the recipients must prepare a number of documents:

• Document on the death of the testator;
• Evidence of kinship;
• A copy of the will, if any;
• A certificate from the last place of residence of the deceased;
• Documents for inheritance property;
• Passports of the beneficiaries.

Returning to the question of how to find a notary serving the place of opening the inheritance, it is worth explaining that information about all notaries working in the country is presented on the website of the Federal Notary Chamber - notariat.ru. Here on the main page there is a tab “find a notary”. Without information about a notary public, you can search for notaries in a specific region or area in the "find a notary's office" tab. As a rule, a notary public opens a case at the place of opening of the inheritance, that is, at the place of the last registration of the deceased testator.

The notary opens the case after after filing a statement from the heir.

What documents and certificates will be needed?

The basis for notarial procedures, when the inheritance is opened after death, and for opening, and for the formation of the case, are the documents provided by the heirs. So, in a notary's office at the place where the hereditary business is opened, potential heirs represent:

• Application for opening hereditary procedures;
• Certificates from the last place of residence of the deceased relative;
• Extracts from real estate registers confirming the deceased's rights to the real estate object at his disposal, if there are several of them, then individually;
• Owner's certificates for vehicles;
• Information on bank accounts, securities and from pension funds.

Supporting documents must be attached throughout the property mass indicated in the application. You can send them by mail or transfer at a personal reception.

The procedure for the notary to conduct business: how to open and finish?

  Opening an inheritance is the most important function of notaries to ensure the rights of citizens to inherit. Article 1154 defines the terms within which the heirs must enter into their rights. How much you can enter into the inheritance. During this period, a hereditary business is opened.

The final decision can be made after six months, that is, the inheritance case is open, but not completed. This is due to the peculiarities of the inheritance case itself, for example, if it was initiated in favor of each other or controversial issues arose. Notary services are not free. How much does it cost to have a notarial case.

The notary public procedure for completing all documentation is regulated by the Notarial Records Office Rules:

• Acceptance of applications from heirs with accompanying documents;
• Their registration and the issuance by a notary of a certificate of opening a hereditary case;
• Formation of inventory of property;
• Taking measures to ensure the preservation of the inheritance and its integrity;
• Other relatives and legal heirs are duly notified that an inheritance case has been opened;
• Authentication of the submitted documents is carried out.

Documents, on the basis of which the case is opened, are registered in the notary's office in the case book by the date of their receipt. Then they are placed in a folder with the case, which is assigned a number in order, indicating the year of opening. After that, the case must also be registered in the Alphabet Book and entered in.

After closing all notarial procedures, the original document, which became the basis for the formation of the case, is returned to the recipients on receipt, the latter is filed into the case. Also, all documents included in the inheritance file and attached to it are entered in the book of accounting.

The heirs have the right to entrust the notary with the provision of measures to preserve the property included in the estate. This statement is also subject to registration in a special journal for registering statements, instructions, after which it is also invested in the case.

Should a notary public find heirs by law?

Notification of other relatives who may claim the inheritance or who have legal inheritance rights is the responsibility of the notary's office.

The notary public identifies such relatives:

• requesting information either from relatives applying for the opening of an inheritance;
• by sending official inquiries at the place of residence of the testator.

The written notice shall indicate the data of the notary and the notary's office for circulation, so that the heirs do not decide how to determine the notary by inheritance, and do not take measures to reopen the inheritance case.

Additional information about the location and time of opening the inheritance in this video:

As a rule, if disputes between the heirs do not arise, within six months they receive the appropriate certificate, and take over the possession and use of the hereditary property. The notary has the right to consider the case completed and transfer it to temporary storage.

Elements of the correct answer

1. Each organism is individual in its hereditary characteristics, this applies to the structure of proteins.

2. When organs and tissues are transplanted, there is a risk of their rejection due to incompatibility of the donor and recipient proteins.

Answer yourself

What is the relationship between genes and body proteins?

What encodes a gene and how?

Elements of the correct answer

1. It is necessary that the gene responsible for the phenotypic trait be inherited by the body.

2. It is necessary that the gene be either dominant or recessive, but in this case be in a homozygous state.

Answer yourself

What conditions contribute to the variability of the body?

How are variability and heredity related?

Elements of the correct answer

1. Inherited signs do not always appear, for example, a sign may be recessive and be in a heterozygous state.

2. The manifestation of phenotypic characters depends on many factors (for example, penetrance and expressiveness of genes), therefore, despite the presence of the corresponding genes, the inherited trait may not appear.

Answer yourself

What is the relationship between the genotype and phenotype of the body?

Is it possible to determine its genotype by the phenotype of an organism? Justify the answer.

Elements of the correct answer

1. These plants differ from each other in one sign - the shape of the seeds.

2. This trait is controlled by one pair of allelic genes.

Answer yourself

Why is the crossing of pea plants with yellow and smooth seeds with plants that produce green and wrinkled seeds called dihybrid?

Why is the first generation of monohybrid crosses showing no sign of wrinkling of seeds?

Elements of the correct answer

1. In hybrids of the first generation, only a dominant trait is manifested.

2. The recessive trait in these hybrids is suppressed.

Answer yourself

How is Mendel’s first law formulated?

Why, according to the first law of Mendel in F2 (offspring from crossing F1 hybrids), the splitting is approximately equal to 3: 1?

Elements of the correct answer

1. Mendel’s laws are statistical in nature; confirmed on a large number of individuals (large statistical sample).

2. In real life, organisms that produce a small number of offspring, there are deviations from the laws of Mendel, due to statistics.

3. Perhaps incomplete dominance, non-allelic interactions of genes.

Answer yourself

Are Mendel’s laws confirmed in families with two or three children? Explain the answer.

How can we explain that in the same family, children inherit different characters from their parents?

Elements of the correct answer

1. Pea - a plant with pronounced contrasting allelic traits.

2. Pea - a self-pollinating plant, which allows you to experiment with clean lines and conduct artificial cross-pollination.

Answer yourself

What patterns underlie genotype and phenotype cleavage for monohybrid crosses?

What patterns underlie genotypic and phenotypic digestion during dihybrid crosses?

What is the essence of the gamete purity hypothesis?

Elements of the correct answer

1. The donkey and the horse have different karyotypes (the donkey has 62 chromosomes and the horse has 64 chromosomes). Horse chromosomes are not homologous to donkey chromosomes.

2. Different chromosomes in meiosis do not conjugate to each other. Therefore, hybrids - mules - are barren.

Answer yourself

Why is the number and nucleotide composition of chromosomes considered a species trait of organisms?

What is the biological meaning of conjugation of chromosomes and crossing over?

Elements of the correct answer

1. With complete dominance, heterozygous individuals in the phenotype exhibit a dominant trait (plant with red flowers? Plant with white flowers \u003d plant with red flowers: AA   x aa = Aa;   Aa- red flowers).

2. With incomplete dominance in the heterozygous state, an intermediate phenotype appears (plant with red flowers? Plant with white flowers \u003d plant with pink flowers: AA   x aa = Aa;   Aa- pink flowers).

Answer yourself

In what cases is the intermediate nature of inheritance manifested?

Is it possible to say that the phenomenon of incomplete domination refutes the hypothesis of gamete purity?

Elements of the correct answer

Gametes of one organism - AB, Ab; another - AB, aB.

Answer yourself

What types of gametes gives an individual with a genotype SSBbKK?

Record the results of the crossing of heterozygous individuals on two signs in the Pennet lattice.

Elements of the correct answer

1. An analysis of crosses is carried out to establish the genotype of a specific individual - to identify its recessive gene.

2. For this, an individual homozygous for a recessive gene is crossed with an individual whose genotype is unknown.

Answer yourself

Is it possible to determine the genotype of an individual by phenotype? Explain the answer.

How can you accurately determine the genotype of an individual?

Elements of the correct answer

1. The law is valid for genes located on the same chromosome.

2. The law is violated by crossing over homologous chromosomes.

Answer yourself

Under what conditions does crossing over occur?

Between what chromosomes crossing over does not happen?

What are the causes of combinational variability?

Elements of the correct answer

1. These structures include mitochondria, chloroplasts, and the cell center.

2. These organoids contain DNA.

Answer yourself

Is there inheritance transmitted not through the chromosome apparatus of the cell?

What is common between the nucleus, mitochondria and chloroplasts?

Elements of the correct answer

1. Sex is determined by a pair of sex chromosomes located in human nuclear cells.

2. In men, this pair consists of a set designated Hu, among women - XX.

Answer yourself

What is homo-and hetero-visibility?

How does gender-related inheritance manifest itself?

Why are there no tortoiseshell cats?

Elements of the correct answer

1. Related marriages.

2. The age of the woman giving birth to a child (38–42 years).

3. The work of parents in harmful enterprises (nuclear, chemical, etc.).

Answer yourself

What risks of increasing the incidence of hereditary diseases can you name? Explain your choice.

How is Down's syndrome manifested and what are the causes of this disease?

Elements of the correct answer

1. Gene mutations affect one of the gene regions. For example, one nucleotide in a triplet may drop out or be replaced. A mutation may be neutral, or it may be harmful or beneficial.

2. Chromosomal mutations can lead to serious health consequences. They are associated with chromosome rearrangement.

3. Genomic mutation affects the genome. As a result of such a mutation, the number of chromosomes in the karyotype changes. If one or more haploid sets are added to a chromosome set, then the phenomenon is called polyploidy. The phenomenon of polyploidy allows you to overcome interspecific sterility.

C2 level questions

Typically, questions on genetics are not found in exam papers at the C2 level. However, we present assignments corresponding to this level, for better understanding by students of genetic concepts.

Elements of the correct answer

Mistakes were made in sentences 2, 5, 6.

Proposition 2 erroneously indicates the number of characters by which the plants differed.

Proposition 5 erroneously indicates the proportion of hybrids with yellow seeds.

Proposition 6 erroneously named a sign of yellow coloration.

Elements of the correct answer

Mistakes were made in sentences 3, 4, 5.

Proposition 3 contains an error in indicating the nature of the genetic proximity of species.

Proposition 4 erroneously indicates the likelihood of crossing between certain species.

In Proposition 5, one of the factors of protection against foreign genes is incorrectly named.

Elements of the correct answer

Mistakes were made in sentences 1, 2, 4, 6.

Sentence 1 erroneous definition of a gene.

Proposition 2 erroneously indicates a set of chromosomes in somatic cells.

Proposition 4 incorrectly defines dominance.

Elements of the correct answer

Errors were made in the recording of gametes formed by the parental individuals and in the recording of one of the genotypes.

Correct your mistakes using the Pennet grid.

Elements of the correct answer

Mistakes were made in sentences 2, 3, 4.

Proposition 2 erroneously indicates the nature of the transfer of genes from parents to offspring.

Proposition 3 incorrectly defined the phenotype.

Proposition 4 incorrectly defines the genotype.

Elements of the correct answer

1. The record in gene expression has letter designations.

2. The record in chromosome expression is shown in alphabetic and graphic form.

Answer yourself

Find the error in the condition of the problem.

In dogs, the sign of black coat dominates the sign of brown. When crossing two black dogs received black and brown puppies. In the second generation, 3 black and two brown puppies were obtained from brown parents. What are the genotypes of the first pair of parents?

Find errors in the text above.

Two sons were born in the family of a retired hussar colonel Ivan Alexandrovich Prilezhaev. The boys grew up energetic guys, participated in all the boyish fun. However, here's the trouble - one of them, Peter, suffered from hemophilia, but Stepan did not have it. The boys' mother, Polina Arkadyevna, accused Petya of her husband of illness. Ivan Alexandrovich did not consider himself guilty. When the boys grew up, then, according to tradition, they had to go to serve in the hussar regiment. However, both were rejected for medical reasons, telling their father that the boys had a heavy heredity and that they should not be served. Any scratch is dangerous for both, and even more so injury. After some time, Peter married a girl who was healthy in terms of hemophilia and who had no hereditary diseases in his family. They had two boys and two girls. All children suffered from hemophilia. Stepan also married - his second daughter from the same family. He had a hemophilicus boy and two healthy girls. Nothing is known about the health of the grandchildren in this family.

What process is shown in the figure? Identify the formed gametes and explain the reason for the appearance of different gametes.

C6 level questions

Mono Hybrid Crossbreeding Tasks

Genetics Problem Solving Algorithm

1. Select the lettering of the alleles.

2. Record all the given conditions of the task.

3. Write the genotypes of the mating individuals.

4. Write down the types of gametes formed by the parents.

5. Record the genotypes and phenotypes of the offspring.

The most important condition for the correct solution of the problem is a complete understanding of what is known and what is being asked. For example, if the condition says that 9 mice were obtained from two gray mice, of which one or two were white, then this means that both parents were heterozygous for the dominant trait of gray color, and white coat color was a recessive trait. This example shows how, based on the conditions of the problem, to derive the data necessary for its solution. Having understood the meaning of the task and received additional data from its conditions, correctly make a record of the solution. In the given task, the entry will look like this:

If the problem is not asked about what the splitting of the characters in the offspring was in relation to, then you do not need to show it. It is enough to present all possible genotypes in F1.

Examples of simple tasks

1. What F1 offspring can be expected from crossing a red-flowered heterozygous pea plant ( A) with a white-flowered plant? Will there be a splitting of signs and in what proportion?

2. From Drosophila flies with normal wings and flies with shortened wings, flies with normal and shortened wings were obtained in a 1: 1 ratio. Identify the genotypes of parents and offspring.

3.   The black plumage of Andalusian chickens does not completely dominate the white plumage. A black-feathered rooster was crossed with a white plumage chicken. Some of the chickens born from this cross were blue plumage. Record the genotypes of all individuals mentioned in the condition. What kind of splitting by genotype and phenotype should be expected in the offspring of these parents, provided that there will be a lot of chickens? Is it possible to draw a clean line of chickens with blue feathers?

4. When crossing two tall ( FROM) plants received 25% of the seeds from which stunted plants grew. What are the genotypes of stunted plants?

Digibrid Crossbreeding Tasks

When solving problems of this type, it is necessary:

a) carefully read the condition of the task;
  b) during the reading of the task, make the necessary entries;
  c) having understood the condition of the problem, it is necessary to designate the alleles with the corresponding letters, draw the Pennet lattice and fill it in accordance with the logic of the solution;
  d) to ensure that the general form of the record of the decision meets the requirements.

An example of a task parsed in textbooks

Yellow pea plants ( A) smooth ( IN) seeds crossed with plants giving green ( a) wrinkled ( b) seeds. Both lines were clean. What will be the hybrid offspring in F1 and F2 by genotypes and phenotypes?

The logic of reasoning is as follows.

1. If the lines are clean, then the parents are homozygous for both traits.

2. Each parent gives one variety of gametes.

Genotype AABB   gives gametes AB.
  Genotype aabb   gives gametes ab.
  Therefore, all hybrids of the first generation will have a genotype Aabb.
  Individuals with this genotype form 4 varieties of gametes: AB, aB, Ab, ab.

3. To determine the genotypes of individuals of the second generation, it is necessary to draw the Pennet lattice and write the gamete types formed by the parents in the upper horizontal row and the left vertical column. Then, in the remaining free fields, record the obtained genotypes of the offspring.

- both dominant genes;
  - the dominant gene of one of the traits;
  - the dominant gene of another trait;
  - only recessive genes.

The result in this case will be as follows: 9 AB : 3Ab : 3aB : 1ab.

5. Answer: hybrid offspring in F1 - Aabb, in the second generation there will be 16 genotypes (shown in the Pennet lattice) and 4 phenotypes:

- plants with yellow smooth seeds;
- plants with yellow wrinkled seeds;
  - plants with green smooth seeds;
  - plants with green wrinkled seeds.

Tasks encountered in the examination papers

Elements of the correct answer

For the correct solution, you need to prove that:

1) genotype flies Hu   (males) can be red-eyed and white-eyed;
  2) heterozygous females are always red-eyed, recessively homozygous females are white-eyed, and females homozygous for the dominant trait are red-eyed.

To prove these two points, it is necessary to cross a red-eyed heterozygous female with a white-eyed male. Some males obtained from this cross will have white eyes. Consequently, the recessive trait is linked to Xchromosome.

Elements of the correct answer

Girls are carriers, boys are color blind.

Girls are carriers, boys are healthy.

Half of the boys and girls are healthy, half of the carrier girls, half of the boys are color blind.

Elements of the correct answer for independent decision

1. Record the letter designations of the alleles of the genotypes of the parents and the crossing pattern.

2. Identify all genotypes indicated in the condition.

3. Draw up a diagram of the new cross and record its results.

Elements of the correct answer

1. Genotypes of parents X f X   and Hu.

2. Genotypes of children X f U, X f X, XX, Hu.

3. The nature of inheritance is dominant, linked to Xchromosome.

Elements of the correct answer

1. By condition, the baldness gene was inherited only by boys.

2. All women in the families in question were with normal hair.

3. Therefore, this gene was transmitted from fathers, ie on the male line.

4. Conclusion: the symptom is linked to At-chromosome and is transmitted from fathers to sons.

P1 Hul x XX
   F1 2 Hul and 4 XX
   P2 Hul x XX
   F2 Grandchildren Hul

Decide for yourself

Draw a diagram illustrating the text below, showing the genotypes and inheritance of hemophilia.

An example of inheritance linked to the floor is the inheritance of a recessive semi-lethal gene that causes blood clotting in the air - hemophilia. This disease appears almost exclusively in boys. With hemophilia, the formation of a factor that accelerates blood coagulation is disrupted. The recessive gene that controls the synthesis of this factor is located in a specific area Xchromosomes and does not have an allele in Atchromosome. After solving the problem, answer the question: “Why are women with hemophilia extremely rare?”
   Record the results of the cross that can be obtained in the following cases:

a) the father is hemophilic, the mother is the carrier of the hemophilia gene;
   b) the father is healthy, the mother is the carrier of the hemophilia gene;
   c) the father is hemophilic; the mother does not carry the hemophilia gene.

A person has large eyes and a Roman nose (with a hump) dominate over small eyes and a Greek (straight) nose. A woman with big eyes and a Greek nose married a man with small eyes and a Roman nose. They had four children, two of whom were with large eyes and a Roman nose. What are the genotypes of parents? How likely is this couple to have a baby with small eyes and a Roman nose? How likely is this couple to have a baby with small eyes and a Greek nose?

102. How is hereditary information encoded in a cell?

In polynucleotide chains of DNA and RNA, every three successive bases form a triplet.

A triplet is not a random grouping of three nucleotides, but one in which each triplet controls the inclusion of a very specific amino acid in the protein molecule. The number of possible combinations of nitrogenous bases forming a triplet is small and amounts to 4 3 \u003d 64. Using the triplets, the sequence of 20 amino acids in a protein molecule is encoded, and 64 triplets are formed to encode all amino acids.

As an example, we can give several triplets: HCC encodes alanine, HCC encodes proline, UUU encodes phenylalanine. Thus, the sequence of triplets of HCC, CCU, UUU corresponds to the sex and peptide region containing alanine, proline, phenylalanine. In other words, the base sequence in DNA carries information about the sequence of amino acids in a protein molecule. A triplet is an information unit - a codon.

The genetic code is triple - three bases encode one amino acid; non-overlapping - the bases that make up one triplet are not part of neighboring triplets; degenerate - one amino acid can be encoded by several triplets, for example:

Alanin - ЦУГ, ЦАГ, ЦЦГ leucine - UAU, УУЦ, УГУ proline - ЦЦЦ, ЦАЦ.

Data on the decoding of the genetic code are presented in table. 6.

Amino acids in a protein are located in the same sequence as codons are located in a gene. This position is called colinearity, i.e., the linear correspondence of amino acids in a protein and the triplets encoding them on a certain DNA segment.

Remember what structure proteins have. What determines the structure, shape and properties of a protein molecule? Why are the proteins of each organism different from each other?

Such signs of the living as self-reproduction, heredity and variability are manifested already at the molecular genetic level. They are associated with certain organic substances and with the hereditary (genetic) program of the body.

DNA and genes.   By the beginning of the 50s. XX century Scientists have suggested that the main function of genes is to determine the structure of proteins, primarily enzyme proteins. Numerous studies have shown that mainly the transformation of substances in living systems occurs under the control of enzymes. Therefore, scientists put forward an assumption that can be formulated as follows: "one gene - one protein-enzyme." Only the discovery of the double helix of the DNA molecule made it possible to find out the general principles of the process of transferring genetic information in the living.

Carriers of hereditary information are DNA molecules. They store information about the structure. properties, functions of proteins of each cell and the organism as a whole. A section of a DNA molecule containing information about the structure of a single protein-enzyme molecule was called a gene (from Greek genos — genus, origin). He is the hereditary factor of any living body of nature.

Genetic code.   There are 20 amino acids in proteins, the sequence of which determines the structure and properties of proteins. Information on the structure of the protein should be recorded as a nucleotide sequence on DNA. The rules for translating a nucleotide sequence in a nucleic acid into an amino acid sequence of a protein are called the genetic code (from the French code - a collection of conventional abbreviations and names).

It was decrypted in the 60s. XX century as a result of a series of experiments and mathematical calculations.

A DNA molecule consists of a set of four nucleotides (A, T, G, C). If one nucleotide would correspond to each amino acid, then only 4 amino acids could be encoded. If we assume that one amino acid is encoded by a combination of two nucleotides, then in this case only 42 \u003d 16 amino acids can be encoded. Scientists have suggested that one amino acid should be encoded by three nucleotides. This number of combinations is more than enough to encode 20 amino acids (Fig. 29). In addition, not one, but several such combinations can correspond to one amino acid.

Fig. 29. The rule of converting the nucleotide sequence in DNA to the amino acid sequence in a protein

The genetic code has a number of properties (Fig. 30). The code is braided - each amino acid corresponds to a combination of 3 nucleotides. There are 64 such triplets (codons) in total. Of these, 61 are semantic triplets, that is, correspond to 20 amino acids, and 3 are meaningless stop codons that do not correspond to amino acids. They fill the gaps between the genes.

Fig. 30. Some properties of the genetic code

The code is unique - each triplet (codon) corresponds to only one amino acid. The code is degenerate (redundant) - there are amino acids that are encoded by more than one triplet (codon). More often, amino acids have 2-3 triplets (codon).

The code is universal - all organisms have the same genetic code, i.e., the same amino acids in different organisms are encoded by the same triplets (codons).

The code is continuous - there are no gaps between the triplets (codons) inside the gene.

The code is not overlapping - the final nucleotide of one triplet (codon) cannot serve as the beginning of another.

The amino acid sequence of a single protein molecule is encrypted in a specific section of a DNA molecule using the genetic code. Since protein synthesis occurs in the cytoplasm, and DNA molecules are located in the nucleus, a structure is needed that would copy the nucleotide sequence onto the DNA and transfer it to the site of protein synthesis. Such an intermediary is informational RNA.

In addition to the information carrier, substances are needed that ensure the delivery of the corresponding amino acids to the place of synthesis and determine their places in the polypeptide chain. Such substances are transport RNA. They not only ensure the delivery of amino acids to the place of synthesis, but also their coding. Protein synthesis proceeds on ribosomes, for the assembly of which another type of nucleic acid is required - ribosomal RNA. Therefore, for the realization of hereditary information in the living at the molecular genetic level, DNA molecules and all types of RNA are necessary.

Material Exercises

1. Why were the hereditary properties of the organism originally associated with proteins?
2. How is the protein structure encoded in the DNA molecule?
3. What is a gene?
4. What is a genetic code? Describe each of its properties.
5. What function do stop codons perform?