Introduction

Chromosomal abnormalities usually cause a whole range of disorders in the structure and functions of various organs, as well as behavioral and mental disorders. Among the latter, a number of typical features are often found, such as mental retardation of varying degrees, autistic traits, underdeveloped social interaction skills, leading asociality and antisociality.

Reasons for changes in the number of chromosomes

Changes in the number of chromosomes occur as a result of a violation of cell division, which can affect both the sperm and the egg. Sometimes this leads to chromosomal abnormalities

Chromosomes contain genetic information in the form of genes. The nucleus of every human cell, with the exception of the egg and sperm, contains 46 chromosomes, forming 23 pairs. One chromosome in each pair comes from the mother and the other from the father. In both sexes, 22 of the 23 pairs of chromosomes are the same, only the remaining pair of sex chromosomes is different. Women have two X chromosomes (XX), and men have one X and one Y chromosome (XY). Therefore, the normal set of chromosomes (karyotype) for a man is 46, XY, and for women - 46, XX.

If an error occurs during a special type of cell division that produces eggs and sperm, abnormal germ cells arise, which leads to the birth of offspring with a chromosomal abnormality. Chromosomal imbalance can be both quantitative and structural.

There are four main quantitative chromosomal abnormalities, each of which is associated with a specific syndrome:

47, XYY - XYY syndrome;

47, XXY - Klinefelter syndrome;

45, X - Turner syndrome;

47, XXX - trisomy.

chromosomal abnormality antisocial characterological

Extra Y chromosome as a cause of antisociality

Karyotype 47, XYY appears only in men. Characteristic signs of people with an additional Y chromosome are tall height. At the same time, growth acceleration begins at a fairly early age and continues for a very long time.

The frequency of this disease is 0.75 - 1 per 1000 people. A cytogenetic examination conducted in 1965 in America revealed that out of 197 mental patients kept as especially dangerous under conditions of strict supervision, 7 of them had the XYY chromosome set. According to English data, among criminals taller than 184 cm, approximately every fourth person has this particular set of chromosomes.

Most sufferers of XYS syndrome do not come into conflict with the law; however, some of them easily succumb to impulses leading to aggression, homosexuality, pedophilia, theft, arson; any compulsion causes them to have outbursts of angry rage, very poorly controlled by inhibitory nerves. Due to the double Y chromosome, the X chromosome becomes “fragile” and the carrier of this set becomes, so to speak, a kind of “super-man”.

Let's consider one of the more sensational examples of this phenomenon in the world of crime.

In 1966, the public was outraged by an incident in Chicago when a man named Richard Speck brutally murdered eight female medical students. On July 14, 1966, he was brought to the outskirts of Chicago, where he knocked on a house where nine female medical students lived. He promised the student who opened the door not to harm anyone, saying that he just needed money to buy a ticket to New Orleans. Having entered the house, he gathered all the students in one room, tying them up. Having found out where the money was, he did not calm down and, choosing one of the students, took her out of the room. Later he came for another one. At this time, one of the girls, even being tied up, managed to hide under the bed. All the others were killed. He raped one of the girls. After that, he went to the nearest pub to go on a spree with the proceeds of 50 dollars. A few days later he was caught. During the investigation he tried to commit suicide. Richard Speck, the killer of eight female students, was found to have an extra Y chromosome - the "crime chromosome" - in a blood test.

The question of the need for early identification of chromosomal aberrants with the XYY karyotype, the need for special measures to protect both the general population and criminals with a lower potential for aggressiveness from them is already widely discussed in foreign genetic and legal literature.

An adult man who has been diagnosed with karyotype 47, XYY for the first time needs psychological support; Medical genetic consultations may be required.

Since the karyological isolation of individuals with XYY syndrome among tall criminals is a technically labor-intensive task, rapid methods for identifying the extra Y chromosome have appeared, namely staining smears of the oral mucosa with acryquiniprite and fluorescent microscopy (YY is highlighted in the form of two luminous dots).

A change in the number of chromosomes in a cell means a change in the genome. (Therefore, such changes are often called genomic mutations.) Various cytogenetic phenomena associated with changes in the number of chromosomes are known.

Autopolyploidy

Autopolyploidy is the repeated repetition of the same genome, or the basic number of chromosomes (x).

This type of polyploidy is characteristic of lower eukaryotes and angiosperms. In multicellular animals, autopolyploidy is extremely rare: in earthworms, some insects, some fish and amphibians. Autopolyploids in humans and other higher vertebrates die in the early stages of intrauterine development.

In most eukaryotic organisms, the basic number of chromosomes (x) coincides with the haploid set of chromosomes (n); in this case, the haploid number of chromosomes is the number of chromosomes in cells formed in the chord of meiosis. Then diploid (2n) contains two genomes x, and 2n=2x. However, in many lower eukaryotes, many spore plants and angiosperms, diploid cells contain not 2 genomes, but some other number. The number of genomes in diploid cells is called the genome number (Ω). The sequence of genomic numbers is called a polyploid series.

There are balanced and unbalanced autopolyploids. Balanced polyploids are polyploids with an even number of chromosome sets, and unbalanced polyploids are polyploids with an odd number of chromosome sets, for example:

unbalanced polyploids

haploids

triploids

pentaploids

hectaploids

enneaploids

balanced polyploids

diploids

tetraploids

hexaploids

octoploids

decaploids

Autopolyploidy is often accompanied by an increase in the size of cells, pollen grains and overall size of organisms, and an increased content of sugars and vitamins. For example, triploid aspen (3x = 57) reaches gigantic sizes, is durable, and its wood is resistant to rotting. Among cultivated plants, both triploids (a number of varieties of strawberries, apple trees, watermelons, bananas, tea, sugar beets) and tetraploids (a number of varieties of rye, clover, grapes) are widespread. Under natural conditions, autopolyploid plants are usually found in extreme conditions (at high latitudes, in high mountains); Moreover, here they can displace normal diploid forms.

The positive effects of polyploidy are associated with an increase in the number of copies of the same gene in cells, and, accordingly, an increase in the dose (concentration) of enzymes. However, in some cases, polyploidy leads to inhibition of physiological processes, especially at very high ploidy levels. For example, wheat with 84 chromosomes is less productive than wheat with 42 chromosomes.

However, autopolyploids (especially unbalanced ones) are characterized by reduced fertility or complete infertility, which is associated with disorders of meiosis. Therefore, many of them are only capable of vegetative reproduction.

Allopolyploidy

Allopolyploidy is the repeated repetition of two or more different haploid chromosome sets, which are designated by different symbols. Polyploids obtained as a result of distant hybridization, that is, from the crossing of organisms belonging to different species and containing two or more sets of different chromosomes, are called allopolyploids.

Allopolyploids are widespread among cultivated plants. However, if somatic cells contain one genome from different species (for example, one genome A and one genome B), then such an allopolyploid is sterile. The infertility of simple interspecific hybrids is due to the fact that each chromosome is represented by one homologue, and the formation of bivalents in meiosis is impossible. Thus, during distant hybridization, a meiotic filter arises, preventing the transmission of hereditary inclinations to subsequent generations through sexual contact.

Therefore, in fertile polyploids, each genome must be doubled. For example, in different types of wheat, the haploid number of chromosomes (n) is 7. Wild wheat (einkorn) contains 14 chromosomes in somatic cells of only one doubled genome A and has a genomic formula 2n = 14 (14A). Many allotetraploid durum wheats contain 28 chromosomes of duplicated genomes A and B in somatic cells; their genomic formula is 2n = 28 (14A + 14B). Soft allohexaploid wheat contains 42 chromosomes of duplicated genomes A, B, and D in somatic cells; their genomic formula is 2n = 42 (14A + 14B + 14D).

Fertile allopolyploids can be obtained artificially. For example, the radish-cabbage hybrid, synthesized by Georgy Dmitrievich Karpechenko, was obtained by crossing radish and cabbage. The radish genome is designated by the symbol R (2n = 18 R, n = 9 R), and the cabbage genome is designated by the symbol B (2n = 18 B, n = 9 B). The initially obtained hybrid had a genomic formula of 9 R + 9 B. This organism (amphihaploid) was sterile, since meiosis produced 18 single chromosomes (univalents) and not a single bivalent. However, in this hybrid some gametes turned out to be unreduced. The fusion of such gametes resulted in a fertile amphidiploid: (9 R + 9 B) + (9 R + 9 B) → 18 R + 18 B. In this organism, each chromosome was represented by a pair of homologues, which ensured the normal formation of bivalents and normal chromosome segregation in meiosis: 18 R + 18 B → (9 R + 9 B) and (9 R + 9 B).

Currently, work is underway to create artificial amphidiploids in plants (for example, wheat-rye hybrids (triticale), wheat-wheatgrass hybrids) and animals (for example, hybrid silkworms).

The silkworm is the subject of intensive breeding work. It should be taken into account that in this species (like in most butterflies) females are heterogametic sex (XY), and males are homogametic (XX). To quickly reproduce new breeds of silkworms, induced parthenogenesis is used - unfertilized eggs are removed from females even before meiosis and heated to 46 °C. From such diploid eggs only females develop. In addition, androgenesis is known in the silkworm - if the egg is heated to 46 ° C, the nucleus is killed with X-rays, and then inseminated, then two male nuclei can penetrate into the egg. These nuclei fuse with each other, and a diploid zygote (XX) is formed, from which a male develops.

Autopolyploidy is known for the silkworm. In addition, Boris Lvovich Astaurov crossed the mulberry silkworm with a wild variety of the tangerine silkworm, and as a result, fertile allopolyploids (more precisely, allotetraploids) were obtained.

In the silkworm, the yield of silk from male cocoons is 20-30% higher than from female cocoons. V.A. Strunnikov, using induced mutagenesis, developed a breed in which males in the X chromosomes carry different lethal mutations (balanced lethal system) - their genotype is l1+/+l2. When such males are crossed with normal females (++/Y), only future males emerge from the eggs (their genotype is l1+/++ or l2/++), and the females die at the embryonic stage of development, since their genotype is either l1+/Y or +l2/Y. To breed males with lethal mutations, special females are used (their genotype is +l2/++·Y). Then, when crossing such females and males with two lethal alleles in their offspring, half of the males die, and half carry two lethal alleles.

There are breeds of silkworms that have an allele for dark egg coloring on the Y chromosome. Then the dark eggs (XY, from which the females should hatch) are discarded, and only the light ones (XX) are left, which later produce cocoons of males.

Aneuploidy

Aneuploidy (heteropolyploidy) is a change in the number of chromosomes in cells that is not a multiple of the main chromosome number. There are several types of aneuploidy. With monosomy, one of the chromosomes of the diploid set (2n – 1) is lost. With polysomy, one or more chromosomes are added to the karyotype. A special case of polysomy is trisomy (2n + 1), when instead of two homologues there are three. With nullisomy, both homologues of any pair of chromosomes are absent (2n – 2).

In humans, aneuploidy leads to the development of severe hereditary diseases. Some of them are associated with changes in the number of sex chromosomes (see Chapter 17). However, there are other diseases:

– Trisomy on chromosome 21 (genotype 47, +21); Down syndrome; frequency among newborns is 1:700. Slow physical and mental development, wide distance between the nostrils, wide bridge of the nose, development of the eyelid fold (epicanthus), half-open mouth. In half of the cases, there are disturbances in the structure of the heart and blood vessels. Usually the immune system is reduced. Average life expectancy is 9-15 years.

– Trisomy on chromosome 13 (genotype 47, +13); Patau syndrome. The frequency among newborns is 1:5,000.

– Trisomy on chromosome 18 (genotype 47, +18); Edwards syndrome. The frequency among newborns is 1:10,000.

Haploidy

The reduction in the number of chromosomes in somatic cells to the basic number is called haploidy. There are haplobiont organisms for which haploidy is a normal state (many lower eukaryotes, gametophytes of higher plants, male hymenopteran insects). Haploidy as an anomalous phenomenon occurs among sporophytes of higher plants: tomato, tobacco, flax, datura, and some cereals. Haploid plants have reduced viability; they are practically sterile.

Pseudopolyploidy (false polyploidy)

In some cases, a change in the number of chromosomes can occur without a change in the amount of genetic material. Figuratively speaking, the number of volumes changes, but the number of phrases does not change. This phenomenon is called pseudopolyploidy. There are two main forms of pseudopolyploidy:

1. Agmatopolyploidy. It is observed when large chromosomes break up into many small ones. Found in some plants and insects. In some organisms (for example, roundworms), fragmentation of chromosomes occurs in somatic cells, but the original large chromosomes are retained in the germ cells.

2. Chromosome fusion. It is observed when small chromosomes combine into large ones. Found in rodents.

5.2. Chromosomal mutations

Chromosomal mutations are divided into two categories: 1) mutations associated with changes in the number of chromosomes in the karyotype (sometimes they are also called numerical aberrations or genomic mutations); 2) mutations, consisting of changes in the structure of individual chromosomes (structural aberrations).

Changes in the number of chromosomes. They can be expressed in the addition of one or more haploid sets (n) to the original diploid set of chromosomes (2n), which leads to the occurrence of polyploidy (triploidy, 3n, tetraploidy, 4n, etc.). Additions or losses of one or more chromosomes are also possible, resulting in aneuploidy (heteroploidy). If aneuploidy is associated with the loss of one chromosome (formula 2n-1), then it is customary to speak of monosomy; loss of a pair of homologous chromosomes (2n-2) leads to nullisomy; when one chromosome (2n + 1) is added to the diploid set, trisomy occurs. In cases where there is an increase in the set by two or more chromosomes (but less than the haploid number), the term “polysemy” is used.

Polyploidy is very common in some plant groups. Obtaining polyploid varieties of cultivated plants is an important task of breeding practice, since with increasing ploidy the economic value of such plants increases (leaves, stems, seeds, and fruits become larger). On the other hand, polyploidy is quite rare in dioecious animals, since in this case the balance between sex chromosomes and autosomes is often disturbed, which leads to infertility of individuals or to mortality (death of the organism). In mammals and humans, the resulting polyploids, as a rule, die in the early stages of ontogenesis.

Aneuploidy is observed in many species of organisms, especially plants. Trisomy of some agricultural plants also has a certain practical value, while monosomy and nullisomy often lead to the non-viability of the individual. Human aneuploidies are the cause of severe chromosomal pathology, which manifests itself in serious developmental disorders of the individual, his disability, often ending in the early death of the organism at one or another stage of ontogenesis (death). Human chromosomal diseases will be discussed in more detail in subsection. 7.2.

The causes of polyploidy and aneuploidy are associated with disturbances in the divergence of the diploid complex of chromosomes (or chromosomes of individual pairs) of parent cells into daughter cells during the process of meiosis or mitosis. So, for example, if during oogenesis in a person there is a nondisjunction of one pair of autosomes of the mother cell with a normal karyotype (46, XX), then the formation of eggs with mutant karyotypes 24 will occur ,X And 22.X. Consequently, when such eggs are fertilized by normal sperm (23.X or 23.X), zygotes (individuals) with trisomy may appear (47.XX or 47 ,XY) and with monosomy (45.XX or 45.XY) for the corresponding autosome. In Fig. Figure 5.1 shows a general diagram of possible oogenesis disorders at the stage of reproduction of primary diploid cells (during mitotic division of oogonia) or during the maturation of gametes (during meiotic division), leading to the appearance of triploid zygotes (see Fig. 3.4). Similar effects will be observed with corresponding disorders of spermatogenesis.

If the above disorders affect mitotically dividing cells in the early stages of embryonic development (embryogenesis), then individuals appear with signs of mosaicism (mosaic), i.e. having both normal (diploid) cells and aneuploid (or polyploid) cells.

Currently, various agents are known, for example, high or low temperatures, some chemicals called “mitotic poisons” (colchicine, heteroauxin, acenaphthol, etc.), which disrupt the normal functioning of the cell division apparatus in plants and animals, preventing

normal completion of the process of chromosome segregation in anaphase and telophase. With the help of such agents, polyploid and aneuploid cells of various eukaryotes are obtained under experimental conditions.

Changes in chromosome structure (structural aberrations). Structural aberrations are intrachromosomal or interchromosomal rearrangements that occur when chromosomes are broken under the influence of environmental mutagens or as a result of disturbances in the crossing-over mechanism, leading to incorrect (unequal) genetic exchange between homologous chromosomes after enzymatic “cutting” of their conjugating sites.

Intrachromosomal rearrangements include deletions (deficiencies), i.e. losses of individual sections of chromosomes, duplications (duplications) associated with the doubling of certain sections, as well as inversions and non-reciprocal translocations (transpositions), changing the order of genes in the chromosome (in the linkage group). An example of interchromosomal rearrangements are reciprocal translocations (Fig. 5.2).

Deletions and duplications can change the number of individual genes in an individual's genotype, which leads to an imbalance in their regulatory relationships and corresponding phenotypic manifestations. Large deletions are usually lethal in the homozygous state, while very small deletions are most often not the direct cause of death in homozygotes.

Inversion occurs as a result of a complete break in the two edges of a chromosomal region, followed by a rotation of this region by 180° and reunification of the broken ends. Depending on whether the centromere is included or not included in the inverted region of the chromosome, inversions are divided into pericentric and paracentric (see Fig. 5.2). The resulting rearrangements in the arrangement of genes on a separate chromosome (rearrangements of the linkage group) can also be accompanied by disturbances in the expression of the corresponding genes.

Rearrangements that change the order and (or) content of gene loci in linkage groups also occur in the case of translocations. The most common are reciprocal translocations, in which there is a mutual exchange of previously broken sections between two non-homologous chromosomes. In the case of non-reciprocal translocation, the damaged area moves (transposition) within the same chromosome or to the chromosome of another pair, but without mutual (reciprocal) exchange (see Fig. 5.2).

explanations of the mechanism of such mutations. These rearrangements consist of the centric fusion of two non-homologous chromosomes into one or the division of one chromosome into two as a result of its break in the centromere region. Consequently, such rearrangements can lead to changes in the number of chromosomes in the karyotype without affecting the total amount of genetic material in the cell. It is believed that Robertsonian translocations are one of the factors in the evolution of karyotypes in different species of eukaryotic organisms.

As noted earlier, in addition to errors in the recombination system, structural aberrations are usually caused by chromosome breaks that occur under the influence of ionizing radiation, certain chemicals, viruses and other agents.

The results of experimental studies of chemical mutagens indicate that the heterochromatic regions of chromosomes are the most sensitive to their effects (most often breaks occur in the centromere region). In the case of ionizing radiation, such a pattern is not observed.

Basic terms and concepts: aberration; aneuploidy (heteroploidy); deletion (lack); duplication (duplication); mortality; "mitotic poisons"; monosomy; non-reciprocal translocation; nullisomia; paracentric inversion; pericentric inversion; polyploidy; polysemy; reciprocal translocation; Robertsonian translocation; transposition; trisomy; chromosomal mutation.

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

Answer

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

3) gene mutations
4) combinative variability

Answer

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

Answer

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

Answer

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

Answer

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 chromosome section
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

Answer

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

Answer

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

Answer

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

Answer

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

Answer

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

Answer

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

Answer

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°

Answer

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

Answer

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

Answer

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

Answer

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

Answer

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 section 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

Answer

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 of the characteristics below, except two, are typical for 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

Answer

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 meiosis 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

© D.V. Pozdnyakov, 2009-2019

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 unified 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 the hunt, 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’s 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 capacitation of sperm 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.