Mutations associated with changes in chromosome structure. Gene mutations are associated with changes in the number and structure of chromosomes

Changes in the karyotype can be quantitative, structural, or both. Let's consider individual forms of chromosome changes (see diagram).

Numerical mutations of the karyotype. This group of mutations is associated with a change in the number of chromosomes in the karyotype. Quantitative changes in the chromosomal composition of cells are called genomic mutations. They are divided into heterogayuidy, aneuploidy, and polyploidy.

Heteroploidy refers to the overall change in the number of chromosomes relative to the diploid complete set.

Aneuploidy is said to occur when the number of chromosomes in a cell is increased by one (trisomy) or more (polysemy) or decreased by one (monosomy). The terms “hyperploidy” and “hypoploidy” are also used. The first of them means an increased number of chromosomes in the cell, and the second means a decreased number.

Polyploidy is an increase in the number of complete chromosome sets by an even or odd number of times. Polyploid cells can be trigogoid, tetraploid, pentaploid, hexaploid, etc.

Structural mutations of chromosomes. This group of mutations is associated with changes in the shape, size of chromosomes, the order of genes (changes in linkage groups), loss or addition of individual fragments, etc. Changes in the structure of one or more chromosomes are called chromosomal mutations. Several types of structural chromosome mutations have been identified.

Translocations are movements of individual chromosome fragments from one region to another, exchanges of fragments between different chromosomes, chromosome fusions. When mutual exchanges of fragments occur between homologous or non-homologous chromosomes, translocations occur, called reciprocal. If an entire arm of one chromosome is attached to the ends of another chromosome, this type of translocation is called tandem. The fusion of two acrocentric chromosomes in the centromere region forms a Robertsonian-type translocation and the formation of meta- and submetacentric chromosomes. In this case, elimination of blocks of pericentromeric heterochromatin is detected.

Inversions are intrachromosomal aberrations in which chromosome fragments turn 180°. There are peri- and paracentric inversions. If the inverted fragment contains a centromere, the inversion is called pericentric.

Deletions are the loss of the middle fragment of a chromosome, as a result of which it is shortened.

Deficiencies are the loss of the end fragment of a chromosome.

Duplication is the doubling of a fragment of one chromosome (intra-chromosomal duplications) or different chromosomes (interchromosomal duplications).

Ring chromosomes are formed when there are two terminal breaks (shortages).

Isochromosomes arise if, in contrast to normal-. Due to the division of chromatids in length, a horizontal (transverse) division of the chromosome occurs at the centromere, followed by the fusion of homolergic arms into a new chromosome - an isochromosome. Its proximal and distal sections are identical in structure and gene composition. Depending on how many chromatids are changed (one or two), structural abnormalities are divided into chromosomal and chromatid. Figure 34 shows diagrams of the formation of various types of structural changes in chromosomes or aberrations.

All mutations associated with changes in the number and structure of chromosomes can be divided into three groups:

· chromosomal aberrations caused by changes in the structure of chromosomes,

· genomic mutations caused by changes in the number of chromosomes,

Mixoploidy - mutations caused by the presence of cell clones with different chromosome sets.

Chromosomal aberrations. Chromosomal aberrations (chromosomal mutations) are changes in the structure of chromosomes. They are, as a rule, a consequence of unequal crossing over during meiosis. Chromosome aberrations also result from chromosome breaks caused by ionizing radiation, certain chemical mutagens, viruses, and other mutagenic factors. Chromosomal aberrations can be unbalanced or balanced.

Unbalanced mutations result in loss or gain of genetic material and changes in the number of genes or their activity. This leads to a change in phenotype.

Chromosomal rearrangements that do not lead to changes in genes or their activity and do not change the phenotype are called balanced. However, chromosomal aberration disrupts chromosome conjugation and crossing over during meiosis, resulting in gametes with unbalanced chromosomal mutations. Carriers of balanced chromosomal aberrations may experience infertility, a high frequency of spontaneous abortions, and a high risk of having children with chromosomal diseases.

The following types of chromosomal mutations are distinguished:

1. Deletion, or deficiency, is the loss of a section of a chromosome.

2. Duplication – doubling of a chromosome section.

3. Inversion - rotation of a chromosome section by 180 0 (in one of the chromosome sections, genes are located in the reverse sequence compared to normal). If, as a result of the inversion, the amount of chromosomal material does not change and there is no position effect, then the individuals are phenotypically healthy. Pericentric inversion of chromosome 9 is common and does not lead to a change in phenotype. With other inversions, conjugation and crossing over may be disrupted, which leads to chromosome breaks and the formation of unbalanced gametes.

4. Ring chromosome - occurs when two telomeric fragments are lost. The sticky ends of the chromosome join together to form a ring.

This mutation can be either balanced or unbalanced (depending on the amount of chromosomal material that is lost).

5. Isochromosomes – loss of one chromosome arm and duplication of the other. As a result, a metacentric chromosome is formed, having two identical arms. The most common isochromosome on the long arm of the X chromosome. The karyotype is recorded: 46,Х,i(Xq). Isochromosome X is observed in 15% of all cases of Shereshevsky-Turner syndrome.

6. Translocation - transfer of a chromosome section to a non-homologous chromosome, to another linkage group. There are several types of translocations:

a) Reciprocal translocations - mutual exchange of sections between two non-homologous chromosomes.

In populations, the frequency of reciprocal translocations is 1:500. For unknown reasons, reciprocal translocation involving the long arms of chromosomes 11 and 22 is more common. Carriers of balanced reciprocal translocations often experience spontaneous abortions or the birth of children with multiple congenital malformations. The genetic risk in carriers of such translocations ranges from 1 to 10%.

b) Non-reciprocal translocations (transpositions) - movement of a section of a chromosome either within the same chromosome or to another chromosome without mutual exchange.

c) A special type of translocation is Robertsonian translocation (or centric fusion).

It is observed between any two acrocentric chromosomes from group D (13, 14 and 15 pairs) and G (21 and 22 pairs). In centric fusion, two homologous or non-homologous chromosomes lose their short arms and one centromere, and the long arms join. Instead of two chromosomes, one is formed, containing the genetic material of the long arms of two chromosomes. Thus, carriers of Robertsonian translocations are healthy, but they have an increased frequency of spontaneous abortions and a high risk of having children with chromosomal diseases. The frequency of Robertsonian translocations in the population is 1:1000.

Sometimes one of the parents is a carrier of a balanced translocation, in which there is a centric fusion of two homologous chromosomes of group D or G. In such people, two types of gametes are formed. For example, during translocation 21q21q gametes are formed:

2) 0 - i.e. gamete without chromosome 21

After fertilization with a normal gamete, two types of zygotes are formed: 1)21, 21q21q - translocation form of Down syndrome, 2)21.0 - monosomy 21 chromosome, lethal mutation. The probability of having a sick child is 100%.

Р 21q21q x 21.21

healthy carrier is normal

balanced

Gametes 21/21; 0 21

F 1 21.21q21q 21.0

Down syndrome lethal

7. Centric separation is the opposite phenomenon of centric merger. One chromosome is divided into two.

Deletions and duplications change the number of genes in an organism. Inversions, translocations, and transpositions change the location of genes on chromosomes.

9. A marker chromosome is an additional chromosome (or rather, a fragment of a chromosome with a centromere). Usually it looks like a very short acrocentric chromosome, less often - ring-shaped. If the marker chromosome contains only heterochromatin, then the phenotype does not change. If it contains euchromatin (expressed genes), then this is associated with the development of a chromosomal disease (similar to the duplication of any part of a chromosome).

The significance of chromosomal mutations in evolution. Chromosomal mutations play a large role in evolution. In the process of evolution, active rearrangement of the chromosome set occurs through inversions, Robertsonian translocations and others. The farther organisms are from each other, the more different their chromosome set is.

Genomic mutations. Genomic mutations are changes in the number of chromosomes. There are two types of genomic mutations:

1) polyploidy,

2) heteroploidy (aneuploidy).

Polyploidy– an increase in the number of chromosomes by an amount that is a multiple of the haploid set (3n, 4n...). Triploidy (3n=69 chromosomes) and tetraploidy (4n=92 chromosomes) have been described in humans.

Possible reasons for the formation of polyploidy.

1) Polyploidy can be a consequence of non-disjunction of all chromosomes during meiosis in one of the parents. As a result, a diploid germ cell (2n) is formed. After fertilization by a normal gamete, a triploid (3n) will be formed.

2) Fertilization of an egg by two sperm (dispermia).

3) It is also possible for a diploid zygote to merge with a guide body, which leads to the formation of a triploid zygote

4) A somatic mutation may be observed - non-disjunction of all chromosomes during embryonic cell division (mitotic disorder). This leads to the appearance of a tetraploid (4 n) - complete or mosaic form.

Triploidy (Fig.___) is a common cause of spontaneous abortions. This is an extremely rare occurrence in newborns. Most triploids die soon after birth.

Triploids, having two chromosome sets of the father and one chromosome set of the mother, as a rule, form a hydatidiform mole. This is an embryo in which extraembryonic organs (chorion, placenta, amnion) are formed, and the embryoblast practically does not develop. Hydatidiform moles are aborted, and the formation of a malignant tumor of the chorion - choriocarcinoma - is possible. In rare cases, an embryoblast is formed and the pregnancy ends with the birth of a non-viable triploid with multiple congenital malformations. Characteristic in such cases is an increase in the mass of the placenta and cystic degeneration of the chorionic villi.

In triploids, having two chromosome sets of the mother and one chromosome set of the father, the embryoblast develops predominantly. The development of extraembryonic organs is impaired. Therefore, such triploids are aborted early.

Using triploids as an example, different functional activities of the paternal and maternal genomes are observed in the embryonic period of development. This phenomenon is called genomic imprinting. In general, it should be noted that for normal human embryonic development, the mother's genome and the father's genome are absolutely necessary. Parthenogenetic development of humans (and other mammals) is impossible.

Tetraploidy (4n) is an extremely rare phenomenon in humans. Mainly found in materials from spontaneous abortions.

Heteroploidy (or aneuploidy) - an increase or decrease in the number of chromosomes by 1.2 or more. Types of heteroploidy: monosomy, nulisomy, polysomy (tri-, tetra-, pentasomy).

a) Monosomy - absence of one chromosome (2n-1)

b) Nulisomy - absence of one pair of chromosomes (2n-2)

c) Trisomy - one extra chromosome (2n+1)

d) Tetrasomy - two extra chromosomes (2n+2)

e) Pentasomy – three extra chromosomes (2n+3)

Changes in chromosome structure include deletions, translocations, inversions, duplications, and insertions.

Deletions These are changes in the structure of chromosomes in the form of the absence of a section of it. In this case, it is possible to develop a simple deletion or a deletion with duplication of a section of another chromosome.

In the latter case, the cause of changes in chromosome structure, as a rule, is crossing over in meiosis in the carrier of the translocation, which leads to the appearance of an unbalanced reciprocal chromosomal translocation. Deletions can be located at the end or in the internal regions of the chromosome and are usually associated with mental retardation and developmental defects. Small deletions in the telomere region are relatively often found in nonspecific mental retardation in combination with microdevelopmental anomalies. Deletions can be detected by routine chromosome retrieval, but microdeletions can only be identified by microscopic examination in prophase. In cases of submicroscopic deletions, the missing region can only be detected using molecular probes or DNA analysis.

Microdeletions are defined as small chromosomal deletions, visible only in high-quality metaphase preparations. These deletions occur more frequently in multiple genes, and the patient's diagnosis is suggested based on unusual phenotypic manifestations that appear to be associated with a single mutation. Williams, Langer-Gidion, Prader-Willi, Rubinstein-Taybi, Smith-Magenis, Miller-Dieker, Alagille, DiGeorge syndromes are caused by microdeletions. Submicroscopic deletions are invisible under microscopic examination and are only detected when specific DNA testing techniques are used. Deletions are recognized by the absence of staining or fluorescence.

Translocations represent a change in the structure of chromosomes in the form of transfer of chromosomal material from one to another. There are Robertsonian and reciprocal translocations. Frequency 1:500 newborns. Translocations can be inherited from parents or occur de novo in the absence of pathology in other family members.

Robertsonian translocations involve two acrocentric chromosomes that are fused close to the centromere region with subsequent loss of nonfunctional and highly truncated short arms. After translocation, the chromosome consists of long arms that are made up of two spliced ​​chromosomes. Thus, the karyotype has only 45 chromosomes. The negative consequences of losing short arms are unknown. Although carriers of the Robertsonian translocation generally have a normal phenotype, they are at increased risk of miscarriages and having abnormal offspring.

Reciprocal translocations occur as a result of breakages of non-homologous chromosomes in combination with reciprocal exchange of lost segments. Carriers of a reciprocal translocation usually have a normal phenotype, but they also have an increased risk of having offspring with chromosomal abnormalities and miscarriages due to abnormal chromosome segregation in germ cells.

Inversions– changes in the structure of chromosomes that occur when it breaks at two points. The broken section is turned over and attached to the break site. Inversions occur in 1:100 newborns and can be peri- or paracentric. With pericentric inversions, breaks occur on two opposite arms, and the part of the chromosome containing the centromere rotates. Such inversions are usually detected in connection with a change in the position of the centromere. In contrast, with paracentric inversions, only the area located on one shoulder is involved. Carriers of inversions usually have a normal phenotype, but they may have an increased risk of spontaneous miscarriages and the birth of offspring with chromosomal abnormalities.

Ring chromosomes are rare, but their formation is possible from any human chromosome. Formation of the ring is preceded by deletions at each end. The ends are then “glued” together to form a ring. Phenotypic manifestations of ring chromosomes range from mental retardation and multiple developmental anomalies to normal or minimal changes, depending on the amount of “lost” chromosomal material. If a ring replaces a normal chromosome, this leads to the development of partial monosomy. The phenotypic manifestations in these cases are often similar to those observed with deletions. If a ring is added to normal chromosomes, the phenotypic manifestations of partial trisomy occur.

Duplication is an excess amount of genetic material belonging to one chromosome. Duplications can occur as a result of pathological segregation in carriers of translocations or inversions.

Insertions(inserts) are changes in the structure of chromosomes that occur when they break at two points, with the broken section being integrated into the break zone on another part of the chromosome. To form an insertion, three breakpoints are required. One or two chromosomes may be involved in this process.

Telomeric, subtelomeric deletions. Because chromosomes are closely intertwined during meiosis, small deletions and duplications in the region near the ends are relatively common. Subtelomeric chromosomal rearrangements are more often (5-10%) found in children with moderate or severe mental retardation of unknown etiology without pronounced dysmorphic features.

Submicroscopic subtelomeric deletions (less than 2-3 Mb) are the second most common cause of mental retardation after trisomy 21. Clinical manifestations of this change in chromosome structure in some of these children include prenatal growth restriction (about 40% of cases) and a family history of mental retardation ( 50% of cases). Other symptoms occur in approximately 30% of patients and include microcephaly, hypertelorism, nasal, ear, or hand defects, cryptorchidism, and short stature. After excluding other causes of developmental delay, FISH using multiple telomeric probes at metaphase is recommended.

9.Classification of mutations

Mutational variability occurs when mutations occur - permanent changes in the genotype (i.e., DNA molecules), which can affect entire chromosomes, their parts or individual genes.
Mutations can be beneficial, harmful or neutral. According to the modern classification, mutations are usually divided into the following groups.
1. Genomic mutations– associated with changes in the number of chromosomes. Of particular interest is POLYPLOIDY - a multiple increase in the number of chromosomes. The occurrence of polyploidy is associated with a violation of the cell division mechanism. In particular, nondisjunction of homologous chromosomes during the first division of meiosis leads to the appearance of gametes with a 2n set of chromosomes.
Polyploidy is widespread in plants and much less common in animals (roundworms, silkworms, some amphibians). Polyploid organisms, as a rule, are characterized by larger sizes and enhanced synthesis of organic substances, which makes them especially valuable for breeding work.
2. Chromosomal mutations- These are rearrangements of chromosomes, changes in their structure. Individual sections of chromosomes can be lost, doubled, or change their position.
Like genomic mutations, chromosomal mutations play a huge role in evolutionary processes.
3. Gene mutations associated with changes in the composition or sequence of DNA nucleotides within a gene. Gene mutations are the most important among all categories of mutations.
Protein synthesis is based on the correspondence of the arrangement of nucleotides in the gene and the order of amino acids in the protein molecule. The occurrence of gene mutations (changes in the composition and sequence of nucleotides) changes the composition of the corresponding enzyme proteins and, ultimately, leads to phenotypic changes. Mutations can affect all features of the morphology, physiology and biochemistry of organisms. Many hereditary human diseases are also caused by gene mutations.
Mutations in natural conditions are rare - one mutation of a certain gene per 1000-100000 cells. But the mutation process is ongoing, there is a constant accumulation of mutations in genotypes. And if we take into account that the number of genes in an organism is large, then we can say that in the genotypes of all living organisms there is a significant number of gene mutations.
Mutations are the largest biological factor that determines the enormous hereditary variability of organisms, which provides material for evolution.

1. According to the nature of the change in phenotype, mutations can be biochemical, physiological, anatomical and morphological.

2. According to the degree of adaptability, mutations are divided into beneficial and harmful. Harmful - can be lethal and cause the death of the body even in embryonic development.

3. Mutations can be direct or reverse. The latter are much less common. Typically, a direct mutation is associated with a defect in gene function. The probability of a secondary mutation in the opposite direction at the same point is very small; other genes mutate more often.

Mutations are often recessive, since dominant ones appear immediately and are easily “rejected” by selection.

4. According to the nature of the change in the genotype, mutations are divided into gene, chromosomal and genomic.

Gene, or point, mutations are a change in a nucleotide in one gene in a DNA molecule, leading to the formation of an abnormal gene, and, consequently, an abnormal protein structure and the development of an abnormal trait. A gene mutation is the result of an "error" during DNA replication.

Chromosomal mutations - changes in chromosome structure, chromosomal rearrangements. The main types of chromosomal mutations can be distinguished:

a) deletion - loss of a section of a chromosome;

b) translocation - transfer of part of the chromosomes to another non-homologous chromosome, as a result - a change in the linkage group of genes;

c) inversion - rotation of a chromosome section by 180°;

d) duplication - doubling of genes in a certain region of the chromosome.

Chromosomal mutations lead to changes in the functioning of genes and are important in the evolution of the species.

Genomic mutations are changes in the number of chromosomes in a cell, the appearance of an extra chromosome or the loss of a chromosome as a result of a disorder in meiosis. A multiple increase in the number of chromosomes is called polyploidy. This type of mutation is common in plants. Many cultivated plants are polyploid in relation to their wild ancestors. An increase in chromosomes by one or two in animals leads to developmental abnormalities or death of the organism.

Knowing the variability and mutations in one species, one can foresee the possibility of their occurrence in related species, which is important in selection.

10. Phenotype and genotype - their differences

The genotype is the totality of all the genes of an organism, which are its hereditary basis.
Phenotype is a set of all signs and properties of an organism that are revealed during the process of individual development under given conditions and are the result of the interaction of the genotype with a complex of factors of the internal and external environment.
Phenotype in general is what can be seen (a cat's color), heard, felt (smelled), and the behavior of the animal.
In a homozygous animal, the genotype coincides with the phenotype, but in a heterozygous animal, it does not.
Each biological species has a phenotype unique to it. It is formed in accordance with the hereditary information contained in the genes. However, depending on changes in the external environment, the state of traits varies from organism to organism, resulting in individual differences - variability.
45. Cytogenetic monitoring in animal husbandry.

The organization of cytogenetic control should be built taking into account a number of basic principles. 1. it is necessary to organize the rapid exchange of information between institutions involved in cytogenetic control; for this purpose, it is necessary to create a single data bank that would include information about carriers of chromosomal pathology. 2. inclusion of information about the cytogenetic characteristics of the animal in breeding documents. 3. The purchase of seed and breeding material from abroad should be carried out only with a cytogenetic certificate.

Cytogenetic examination in the regions is carried out using information on the prevalence of chromosomal abnormalities in breeds and lines:

1) breeds and lines in which cases of chromosomal pathology transmitted by inheritance have been registered, as well as descendants of carriers of chromosomal abnormalities in the absence of a cytogenetic passport;

2) breeds and lines not previously studied cytogenetically;

3) all cases of massive reproductive disorders or genetic pathology of unknown nature.

First of all, producers and males intended for herd repair, as well as breeding young animals of the first two categories, are subject to examination. Chromosomal aberrations can be divided into two large classes: 1. constitutional - inherent in all cells, inherited from parents or arising during the maturation of gametes and 2. somatic - arising in individual cells during ontogenesis. Taking into account the genetic nature and phenotypic manifestation of chromosomal abnormalities, animals carrying them can be divided into four groups: 1) carriers of heritable abnormalities with a predisposition to a decrease in reproductive qualities by an average of 10%. Theoretically, 50% of descendants inherit the pathology. 2) carriers of hereditary anomalies, leading to a clearly expressed decrease in reproduction (30-50%) and congenital pathology. About 50% of descendants inherit the pathology.

3) Animals with anomalies that arise de novo, leading to congenital pathology (monosomy, trisomy and polysomy in the system of autosomes and sex chromosomes, mosaicism and chimerism). In the vast majority of cases, such animals are infertile. 4) Animals with increased karyotype instability. Reproductive function is reduced, a hereditary predisposition is possible.

46. ​​pleitropy (multiple gene action)
The pleiotropic effect of genes is the dependence of several traits on one gene, that is, the multiple effects of one gene.
The pleiotropic effect of a gene can be primary or secondary. With primary pleiotropy, a gene exhibits its multiple effects.
With secondary pleiotropy, there is one primary phenotypic manifestation of a gene, followed by a stepwise process of secondary changes leading to multiple effects. With pleiotropy, a gene, acting on one main trait, can also change and modify the expression of other genes, and therefore the concept of modifier genes has been introduced. The latter enhance or weaken the development of traits encoded by the “main” gene.
Indicators of the dependence of the functioning of hereditary inclinations on the characteristics of the genotype are penetrance and expressivity.
When considering the effect of genes and their alleles, it is necessary to take into account the modifying influence of the environment in which the organism develops. This fluctuation of classes during splitting depending on environmental conditions is called penetrance - the strength of phenotypic manifestation. So, penetrance is the frequency of expression of a gene, the phenomenon of the appearance or absence of a trait in organisms of the same genotype.
Penetrance varies significantly among both dominant and recessive genes. It can be complete, when the gene manifests itself in 100% of cases, or incomplete, when the gene does not manifest itself in all individuals containing it.
Penetrance is measured by the percentage of organisms with a phenotypic trait from the total number of examined carriers of the corresponding alleles.
If a gene completely determines phenotypic expression, regardless of the environment, then it has 100 percent penetrance. However, some dominant genes are expressed less regularly.

The multiple or pleiotropic effect of genes is associated with the stage of ontogenesis at which the corresponding alleles appear. The earlier the allele appears, the greater the pleiotropy effect.

Considering the pleiotropic effect of many genes, it can be assumed that some genes often act as modifiers of the action of other genes.

47. modern biotechnologies in animal husbandry. Application of breeding - gene value (research axes; transpl. Fruit).

Embryo transplantation

The development of the method of artificial insemination of farm animals and its practical application have provided great success in the field of improving animal genetics. The use of this method in combination with long-term frozen storage of semen has opened up the possibility of obtaining tens of thousands of offspring from a single sire per year. This technique essentially solves the problem of rational use of producers in livestock farming practice.

As for females, traditional methods of breeding animals allow them to produce only a few offspring in their entire life. The low reproductive rate of females and the long time interval between generations (6-7 years in cattle) limit the genetic process in livestock production. Scientists see a solution to this problem in the use of embryo transplantation. The essence of the method is that genetically outstanding females are freed from the need to bear a fetus and feed their offspring. In addition, they are stimulated to increase the yield of eggs, which are then removed at the early embryonic stage and transplanted into less genetically valuable recipients.

Embryo transplantation technology includes such basic steps as inducing superovulation, artificial insemination of the donor, embryo retrieval (surgical or non-surgical), assessment of their quality, short-term or long-term storage and transplantation.

Stimulation of superovulation. Female mammals are born with a large (several tens or even hundreds of thousands) number of germ cells. Most of them gradually die as a result of follicular atresia. Only a small number of primordial follicles become antral during growth. However, almost all growing follicles respond to gonadotropic stimulation, which leads them to final maturation. Treatment of females with gonadotropins in the follicular phase of the reproductive cycle or in the luteal phase of the cycle in combination with inducing regression of the corpus luteum with prostaglandin F 2 (PGF 2) or its analogues leads to multiple ovulation or so-called superovulation.

Cattle. Induction of superovulation in female cattle is carried out by treatment with gonadotropins, follicle-stimulating hormone (FSH) or pregnant mare blood serum (MAB), starting from the 9-14th day of the sexual cycle. 2-3 days after the start of treatment, the animals are injected with prostaglandin F 2a or its analogues to cause regression of the corpus luteum.

Due to the fact that the timing of ovulation in hormonally treated animals increases, the technology of their insemination also changes. Initially, multiple insemination of cows using multiple doses of semen was recommended. Typically, 50 million live sperm are introduced at the beginning of the heat and insemination is repeated after 12-20 hours.

Embryo extraction. Cattle embryos pass from the oviduct into the uterus between the 4th and 5th day after the start of estrus (between the 3rd and 4th day after ovulation),

Due to the fact that non-surgical extraction is possible only from the horns of the uterus, embryos are removed no earlier than the 5th day after the start of the hunt.

Despite the fact that excellent results have been achieved with the surgical extraction of embryos from cattle, this method is ineffective - relatively expensive, inconvenient for use in production conditions.

Non-surgical embryo retrieval involves the use of a catheter.

The most optimal time for embryo retrieval is 6-8 days after the start of estrus, since early blastocysts of this age are most suitable for deep freezing and can be transplanted non-surgically with high efficiency. A donor cow is used 6-8 times a year, removing 3-6 embryos.

In sheep and pigs, non-surgical embryo retrieval is not possible
due to the difficulty of passing the catheter through the cervix into the horns of the uterus. One
However, surgery in these species is relatively simple
and short-lived.

Embryo transfer. In parallel with the development of surgical embryo retrieval from cattle, significant progress has also been made in non-surgical embryo transfer. Fresh nutrient medium (a column 1.0-1.3 cm long) is collected into the tray, then a small air bubble (0.5 cm) and then the main volume of the medium with the embryo (2-3 cm). After this, a little air (0.5 cm) and a nutrient medium (1.0-1.5 cm) are sucked in. The pie with the embryo is placed in a Cass catheter and stored in a thermostat at 37°C until transplantation. By pressing the catheter rod, the contents of the paillette along with the embryo are squeezed into the uterine horn.

Embryo storage. The use of embryo transplantation required the development of effective methods for storing them in the period between extraction and transplantation. In production settings, embryos are usually removed in the morning and transferred at the end of the day. To store embryos during this time, use phosphate buffer with some modifications by adding fetal bovine serum and at room temperature or 37°C.

Observations show that bovine embryos can be cultured in vitro for up to 24 hours without a noticeable decrease in their subsequent engraftment.

Transplantation of pig embryos cultured for 24 hours is accompanied by normal engraftment.

The survival rate of embryos can be increased to a certain extent by cooling them below body temperature. The sensitivity of embryos to cooling depends on the animal species.

Pig embryos are particularly sensitive to cooling. It has not yet been possible to maintain the viability of pig embryos in the early stages of development after cooling them below 10-15°C.

Cattle embryos in the early stages of development are also very sensitive to cooling to 0°C.

Experiments in recent years have made it possible to determine the optimal relationship between the rate of cooling and thawing of cattle embryos. It has been established that if embryos are cooled slowly (1°C/min) to a very low temperature (below 50°C) and then transferred to liquid nitrogen, they also require slow thawing (25°C/min or slower). Rapid thawing of such embryos can cause osmotic rehydration and destruction. If embryos are frozen slowly (1°C/min) only to -25 and 40°C and then transferred to liquid nitrogen, they can be thawed very quickly (300°C/min). In this case, the residual water, when transferred to liquid nitrogen, is transformed into a glassy state.

The identification of these factors led to a simplification of the procedure for freezing and thawing cattle embryos. In particular, embryos, like sperm, are thawed in warm water at 35°C for 20 s immediately before transplantation without the use of special equipment at a given rate of temperature increase.

Fertilization of eggs outside the animal's body

The development of a system for fertilization and ensuring the early stages of development of mammalian embryos outside the animal body (in vitro) is of great importance in solving a number of scientific problems and practical issues aimed at increasing the efficiency of animal breeding.

For these purposes, embryos are needed in the early stages of development, which can only be removed surgically from the oviducts, which is labor-intensive and does not provide a sufficient number of embryos to carry out this work.

Fertilization of mammalian eggs in vitro includes the following main stages: maturation of oocytes, capacitation of sperm, fertilization and provision of early stages of development.

Maturation of oocytes in vitro. The large number of germ cells in the ovaries of mammals, particularly those of cattle, sheep and pigs with high genetic potential, represents a source of enormous potential for the reproductive capacity of these animals to accelerate genetic progress compared to using the capabilities of normal ovulation. In these animal species, as in other mammals, the number of oocytes that ovulate spontaneously during estrus is only a small fraction of the thousands of oocytes present in the ovary at birth. The remaining oocytes regenerate inside the ovary or, as they usually say, undergo atresia. Naturally, the question arose whether it was possible to isolate oocytes from the ovaries through appropriate processing and carry out their further fertilization outside the animal’s body. At present, methods for using the entire supply of oocytes in the ovaries of animals have not been developed, but a significant number of oocytes can be obtained from cavity follicles for their further maturation and fertilization outside the body.

Currently, in vitro maturation of only bovine oocytes has found practical application. Oocytes are obtained from the ovaries of cows after the slaughter of animals and by intravital extraction, 1-2 times a week. In the first case, the ovaries are taken from the animals after slaughter and delivered to the laboratory in a thermostated container for 1.5-2.0 hours. In the laboratory, the ovaries are washed twice with fresh phosphate buffer. Oocytes are removed from follicles, which are 2-6 mm in diameter, by suction or cutting the ovary into plates. Oocytes are collected in TCM 199 medium with the addition of 10% blood serum from a cow in heat, then washed twice and only oocytes with compact cumulus and homogeneous cytoplasm are selected for further maturation in vitro.

Recently, a method has been developed for the intravital extraction of oocytes from the ovaries of cows using an ultrasound device or laparoscope. In this case, oocytes are sucked from follicles with a diameter of at least 2 mm, 1-2 times a week from the same animal. On average, 5-6 oocytes per animal are obtained once. Less than 50% of oocytes are suitable for in vitro maturation.

Positive value - despite the low yield of oocytes, with each retrieval the animal can be reused.

Sperm capacitation. An important stage in the development of the method of fertilization in mammals was the discovery of the phenomenon of sperm capacitation. In 1951 M.K. Chang and at the same time G.R. Austin found that fertilization in mammals occurs only if sperm are present in the animal’s oviduct for several hours before ovulation. Based on observations of sperm penetration into rat eggs at various times after mating, Austin coined the term capacitations. It means that some physiological changes must occur in the sperm before the sperm acquires the ability to fertilize.

Several methods have been developed for capacitation of ejaculated sperm from domestic animals. High ionic strength media was used to remove proteins from the sperm surface that appear to inhibit sperm capacitation.

However, the method of sperm capacitation using heparin has received the most recognition (J. Parrish et al., 1985). Pietes with frozen bull semen are thawed in a water bath at 39°C for 30-40 s. Approximately 250 µl of thawed seed is layered under 1 ml of capacitation medium. The capacitation medium consists of modified Thyroid medium, without calcium ions. After incubation for one hour, the top layer of medium with a volume of 0.5-0.8 ml, containing the majority of motile sperm, is removed from the tube and washed twice by centrifugation at 500 g for 7-10 minutes. After 15 min of incubation with heparin (200 µg/ml), the suspension is diluted to a concentration of 50 million sperm per ml.

In vitro fertilization and ensuring the early stages of embryo development. Fertilization of eggs in mammals occurs in the oviducts. This makes it difficult for a researcher to access the study of environmental conditions in which the fertilization process occurs. Therefore, an in vitro fertilization system would be a valuable analytical tool for studying the biochemical and physiological factors involved in the process of successful gamete union.

The following scheme is used for in vitro fertilization and cultivation of early cattle embryos. In vitro fertilization is carried out in a drop of modified Thyroid medium. After in vitro maturation, the oocytes are partially cleared of surrounding expanded cumulus cells and transferred into microdroplets of five oocytes each. A sperm suspension of 2-5 µl is added to the oocyte medium to achieve a sperm droplet concentration of 1-1.5 million/ml. 44-48 hours after insemination, the presence of oocyte fragmentation is determined. The embryos are then placed on a monolayer of epithelial cells to further develop for 5 days.

Interspecies embryo transfers and production of chimeric animals

It is generally accepted that successful embryo transfer can only be carried out between females of the same species. The transplantation of embryos, for example, from sheep to goats and vice versa, is accompanied by their engraftment, but does not result in the birth of offspring. In all cases of interspecies pregnancies, the immediate cause of abortion is a dysfunction of the placenta, apparently due to the immunological reaction of the maternal body to foreign antigens of the fetus. This incompatibility can be overcome by producing chimeric embryos using microsurgery.

First, chimeric animals were obtained by combining blastomeres from embryos of the same species. For this purpose, complex chimeric sheep embryos were obtained by combining 2-, 4-, 8-cell embryos from 2-8 parents.

Embryos were inoculated into agar and transferred into ligated sheep oviducts to develop to the early blastocyst stage. Normally developing blastocysts were transplanted into recipients to produce live lambs, most of which were found to be chimeric based on blood tests and external signs.

Chimeras have also been obtained in cattle (G. Brem et al., 1985) by combining halves of 5-6.5-day embryos. Five of seven calves obtained after non-surgical transfer of aggregated embryos had no evidence of chimerism.

Animal Cloning

The number of descendants from one individual, as a rule, is small in higher animals, and the specific complex of genes that determines high productivity arises rarely and undergoes significant changes in subsequent generations.

Producing identical twins is of great importance for animal husbandry. On the one hand, the yield of calves from one donor increases, and on the other hand, genetically identical twins appear.

The possibility of microsurgically dividing mammalian embryos in the early stages of development into two or more parts, so that each subsequently develops into a separate organism, was proposed several decades ago.

Based on these studies, it can be assumed that a sharp decrease in the number of embryonic cells is a major factor reducing the ability of these embryos to develop into viable blastocysts, although the developmental stage at which division occurs is of little importance.

Currently, a simple technique is used to separate embryos at different stages of development (from late morula to hatched blastocyst) into two equal parts.

A simple separation technique has also been developed for 6-day-old pig embryos. In this case, the inner cell mass of the embryo is cut with a glass needle.

Mutations are changes in a cell's DNA. Occur under the influence of ultraviolet radiation, radiation (X-rays), etc. They are inherited and serve as material for natural selection.

Gene mutations- change in the structure of one gene. This is a change in the nucleotide sequence: deletion, insertion, substitution, etc. For example, replacing A with T. The reasons are violations during DNA doubling (replication). Examples: sickle cell anemia, phenylketonuria.

Chromosomal mutations- change in the structure of chromosomes: loss of a section, doubling of a section, rotation of a section by 180 degrees, transfer of a section to another (non-homologous) chromosome, etc. The reasons are violations during crossing over. Example: Cry Cat Syndrome.

Genomic mutations- change in the number of chromosomes. The causes are disturbances in the divergence of chromosomes.

• Polyploidy- multiple changes (several times, for example, 12 → 24). It does not occur in animals; in plants it leads to an increase in size.
• Aneuploidy- changes on one or two chromosomes. For example, one extra twenty-first chromosome leads to Down syndrome (with a total number of chromosomes of 47).

Cytoplasmic mutations- changes in the DNA of mitochondria and plastids. They are transmitted only through the female line, because mitochondria and plastids from sperm do not enter the zygote. An example in plants is variegation.

Somatic- mutations in somatic cells (cells of the body; there can be four of the above types). During sexual reproduction they are not inherited. Transmitted during vegetative propagation in plants, budding and fragmentation in coelenterates (hydra).

The concepts below, except two, are used to describe the consequences of a violation of the arrangement of nucleotides in the DNA region that controls protein synthesis. Identify these two concepts that “fall out” from the general list, and write down the numbers under which they are indicated.
1) violation of the primary structure of the polypeptide
2) chromosome divergence
3) change in protein functions
4) gene mutation
5) crossing over

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Choose one, the most correct option. Polyploid organisms arise from
1) genomic mutations

3) gene mutations
4) combinative variability

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Establish a correspondence between the characteristic of variability and its type: 1) cytoplasmic, 2) combinative
A) occurs during independent chromosome segregation in meiosis
B) occurs as a result of mutations in mitochondrial DNA
B) occurs as a result of chromosome crossing
D) manifests itself as a result of mutations in plastid DNA
D) occurs when gametes meet by chance

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Choose one, the most correct option. Down syndrome is the result of a mutation
1) genomic
2) cytoplasmic
3) chromosomal
4) recessive

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1. Establish a correspondence between the characteristics of the mutation and its type: 1) genetic, 2) chromosomal, 3) genomic
A) change in the sequence of nucleotides in a DNA molecule
B) change in chromosome structure
B) change in the number of chromosomes in the nucleus
D) polyploidy
D) change in the sequence of gene location

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2. Establish a correspondence between the characteristics and types of mutations: 1) gene, 2) genomic, 3) chromosomal. Write numbers 1-3 in the order corresponding to the letters.
A) deletion of a section of a chromosome
B) change in the sequence of nucleotides in a DNA molecule
C) a multiple increase in the haploid set of chromosomes
D) aneuploidy
D) change in the sequence of genes in a chromosome
E) loss of one nucleotide

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Choose three options. What is a genomic mutation characterized by?
1) change in the nucleotide sequence of DNA
2) loss of one chromosome in the diploid set
3) a multiple increase in the number of chromosomes
4) changes in the structure of synthesized proteins
5) doubling a chromosome section
6) change in the number of chromosomes in the karyotype

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1. Below is a list of characteristics of variability. All but two of them are used to describe the characteristics of genomic variation. Find two characteristics that “fall out” from the general series and write down the numbers under which they are indicated.
1) limited by the reaction norm of the trait
2) the number of chromosomes is increased and is a multiple of the haploid
3) an additional X chromosome appears
4) has a group character
5) loss of the Y chromosome is observed

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2. All of the characteristics below, except two, are used to describe genomic mutations. Identify two characteristics that “fall out” from the general list and write down the numbers under which they are indicated.
1) violation of the divergence of homologous chromosomes during cell division
2) destruction of the fission spindle
3) conjugation of homologous chromosomes
4) change in the number of chromosomes
5) increase in the number of nucleotides in genes

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3. All of the characteristics below, except two, are used to describe genomic mutations. Identify two characteristics that “fall out” from the general list and write down the numbers under which they are indicated.
1) change in the nucleotide sequence in a DNA molecule
2) multiple increase in chromosome set
3) reduction in the number of chromosomes
4) doubling of a chromosome section
5) nondisjunction of homologous chromosomes

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Choose one, the most correct option. Recessive gene mutations change
1) sequence of stages of individual development
2) composition of triplets in a DNA section
3) set of chromosomes in somatic cells
4) structure of autosomes

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Choose one, the most correct option. Cytoplasmic variability is due to the fact that
1) meiotic division is disrupted
2) Mitochondrial DNA can mutate
3) new alleles appear in autosomes
4) gametes are formed that are incapable of fertilization

Answer

1. Below is a list of characteristics of variability. All but two of them are used to describe the characteristics of chromosomal variation. Find two characteristics that “fall out” from the general series and write down the numbers under which they are indicated.
1) loss of a chromosome section
2) rotation of a chromosome section by 180 degrees
3) reduction in the number of chromosomes in the karyotype
4) the appearance of an additional X chromosome
5) transfer of a chromosome section to a non-homologous chromosome

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2. All the signs below, except two, are used to describe a chromosomal mutation. Identify two terms that “drop out” from the general list and write down the numbers under which they are indicated.
1) the number of chromosomes increased by 1-2
2) one nucleotide in DNA is replaced by another
3) a section of one chromosome is transferred to another
4) there was a loss of a chromosome section
5) a section of the chromosome is turned 180°

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3. All but two of the characteristics below are used to describe chromosomal variation. Find two characteristics that “fall out” from the general series and write down the numbers under which they are indicated.
1) multiplication of a chromosome section several times
2) the appearance of an additional autosome
3) change in nucleotide sequence
4) loss of the terminal portion of the chromosome
5) rotation of the gene in the chromosome by 180 degrees

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Choose one, the most correct option. What type of mutations are changes in the DNA structure in mitochondria?
1) genomic
2) chromosomal
3) cytoplasmic
4) combinative

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Choose one, the most correct option. The variegation of night beauty and snapdragon is determined by variability
1) combinative
2) chromosomal
3) cytoplasmic
4) genetic

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1. Below is a list of characteristics of variability. All but two of them are used to describe the characteristics of gene variation. Find two characteristics that “fall out” from the general series and write down the numbers under which they are indicated.
1) due to the combination of gametes during fertilization
2) caused by a change in the nucleotide sequence in the triplet
3) is formed during the recombination of genes during crossing over
4) characterized by changes within the gene
5) formed when the nucleotide sequence changes

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2. All of the following characteristics, except two, are causes of gene mutation. Identify these two concepts that “fall out” from the general list, and write down the numbers under which they are indicated.
1) conjugation of homologous chromosomes and gene exchange between them
2) replacing one nucleotide in DNA with another
3) change in the sequence of nucleotide connections
4) the appearance of an extra chromosome in the genotype
5) loss of one triplet in the DNA region encoding the primary structure of the protein

Answer

3. All of the characteristics below, except two, are used to describe gene mutations. Identify two characteristics that “fall out” from the general list and write down the numbers under which they are indicated.
1) replacement of a pair of nucleotides
2) the occurrence of a stop codon within the gene
3) doubling the number of individual nucleotides in DNA
4) increase in the number of chromosomes
5) loss of a chromosome section

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4. All of the characteristics below, except two, are used to describe gene mutations. Identify two characteristics that “fall out” from the general list and write down the numbers under which they are indicated.
1) adding one triplet to DNA
2) increase in the number of autosomes
3) change in the sequence of nucleotides in DNA
4) loss of individual nucleotides in DNA
5) multiple increase in the number of chromosomes

Answer

5. All but two of the characteristics below are typical of gene mutations. Identify two characteristics that “fall out” from the general list and write down the numbers under which they are indicated.
1) the emergence of polyploid forms
2) random doubling of nucleotides in a gene
3) loss of one triplet during replication
4) formation of new alleles of one gene
5) violation of the divergence of homologous chromosomes in meiosis

Answer

Choose one, the most correct option. Polyploid wheat varieties are the result of variability
1) chromosomal
2) modification
3) genetic
4) genomic

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Choose one, the most correct option. It is possible for breeders to obtain polyploid wheat varieties due to mutation
1) cytoplasmic
2) genetic
3) chromosomal
4) genomic

Answer

Establish a correspondence between characteristics and mutations: 1) genomic, 2) chromosomal. Write numbers 1 and 2 in the correct order.
A) multiple increase in the number of chromosomes
B) rotate a section of a chromosome by 180 degrees
B) exchange of sections of non-homologous chromosomes
D) loss of the central part of the chromosome
D) doubling of a chromosome section
E) multiple change in the number of chromosomes

Answer

Choose one, the most correct option. The appearance of different alleles of the same gene occurs as a result
1) indirect cell division
2) modification variability
3) mutation process
4) combinative variability

Answer

All but two of the terms listed below are used to classify mutations by changes in genetic material. Identify two terms that “drop out” from the general list and write down the numbers under which they are indicated.
1) genomic
2) generative
3) chromosomal
4) spontaneous
5) genetic

Answer

Establish a correspondence between the types of mutations and their characteristics and examples: 1) genomic, 2) chromosomal. Write numbers 1 and 2 in the order corresponding to the letters.
A) loss or appearance of extra chromosomes as a result of meiotic disorder
B) lead to disruption of gene functioning
C) an example is polyploidy in protozoa and plants
D) duplication or loss of a chromosome section
D) a striking example is Down syndrome

Answer

Establish a correspondence between the categories of hereditary diseases and their examples: 1) genetic, 2) chromosomal. Write numbers 1 and 2 in the order corresponding to the letters.
A) hemophilia
B) albinism
B) color blindness
D) “cry of the cat” syndrome
D) phenylketonuria

Answer

Find three errors in the given text and indicate the numbers of sentences with errors.(1) Mutations are randomly occurring permanent changes in the genotype. (2) Gene mutations are the result of “errors” that occur during the duplication of DNA molecules. (3) Genomic mutations are those that lead to changes in the structure of chromosomes. (4) Many cultivated plants are polyploids. (5) Polyploid cells contain one to three extra chromosomes. (6) Polyploid plants are characterized by more vigorous growth and larger sizes. (7) Polyploidy is widely used in both plant and animal breeding.

Answer

Analyze the table “Types of variability”. For each cell indicated by a letter, select the corresponding concept or corresponding example from the list provided.
1) somatic
2) genetic
3) replacement of one nucleotide with another
4) gene duplication in a section of a chromosome
5) addition or loss of nucleotides
6) hemophilia
7) color blindness
8) trisomy in the chromosome set

Answer

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