The formation of blastomeres is mitosis or meiosis. A brief description of the stages and scheme of cell division through meiosis. Differences in the course of sexual and asexual division

Cell reproduction is one of the most important biological processes, it is a necessary condition for the existence of all living things. Reproduction is carried out by dividing the original cell.

Cell- this is the smallest morphological unit of the structure of any living organism, capable of self-production and self-regulation. The time of its existence from division to death or subsequent reproduction is called the cell cycle.

Tissues and organs are made up of various cells that have their own period of existence. Each of them grows and develops to ensure the vital activity of the organism. The duration of the mitotic period is different: blood and skin cells enter the process of division every 24 hours, and neurons are capable of reproduction only in newborns, and then completely lose their ability to reproduce.

There are 2 types of division - direct and indirect. Somatic cells reproduce indirectly; gametes or germ cells are characterized by meiosis (direct division).

Mitosis - indirect division

Mitotic cycle

The mitotic cycle includes 2 consecutive stages: interphase and mitotic division.

Interphase(rest stage) - preparation of the cell for further division, where duplication of the source material is performed, followed by its uniform distribution among the newly formed cells. It includes 3 periods:

• • Presynthetic(G-1) G - from the English gar, that is, a gap, preparations are underway for the subsequent synthesis of DNA, the production of enzymes. The inhibition of the first period was experimentally carried out, as a result of which the cell did not enter the next phase.
  • Synthetic(S) - the basis of the cell cycle. Replication of chromosomes and centrioles of the cell center occurs. Only after that the cell can proceed to mitosis.
  • Postsynthetic(G-2) or pre-mitotic period - there is an accumulation of mRNA, which is needed for the onset of the actual mitotic stage. In the G-2 period, proteins (tubulins) are synthesized - the main component of the mitotic spindle.

After the end of the premitotic period, mitotic division. The process includes 4 phases:

1. Prophase- during this period, the nucleolus is destroyed, the nuclear membrane (nucleolema) dissolves, centrioles are located at opposite poles, forming an apparatus for division. It has two subphases:
   • early- thread-like bodies (chromosomes) are visible, they are not yet clearly separated from each other;
   • late- separate parts of chromosomes are traced.
2. metaphase- begins from the moment of destruction of the nucleolema, when the chromosomes lie randomly in the cytoplasm and only begin to move towards the equatorial plane. All pairs of chromatids are connected to each other at the centromere.
3. Anaphase- at one moment all the chromosomes are separated and move to opposite points of the cell. This is a short and very important phase, since it is in it that the exact division of the genetic material takes place.
4. Telophase- chromosomes stop, the nuclear membrane, the nucleolus, is formed again. A constriction is formed in the middle, it divides the body of the mother cell into two daughter cells, completing the mitotic process. In the newly formed cells, the G-2 period begins again.

Meiosis - direct division

There is a special process of reproduction that occurs only in germ cells (gametes) - this meiosis (direct division). A distinctive feature for him is the absence of interphase. Meiosis from one original cell produces four, with a haploid set of chromosomes. The whole process of direct division includes two successive stages, which consist of prophase, metaphase, anaphase and telophase.

Before the start of prophase, the germ cells double the initial material, thus, it becomes tetraploid.

Prophase 1:

1. Leptotena- chromosomes are visible in the form of thin threads, they are shortened.
2. Zygoten- the stage of conjugation of homologous chromosomes, as a result, bivalents are formed. Conjugation is an important moment of meiosis, the chromosomes are as close as possible to each other in order to carry out crossing over.
3. Pachytene- there is a thickening of chromosomes, their increasing shortening, there is a crossing over (the exchange of genetic information between homologous chromosomes, this is the basis of evolution and hereditary variability).
4. Diploten- the stage of doubled strands, the chromosomes of each bivalent diverge, keeping the connection only in the area of ​​​​the decussation (chiasm).
5. diakinesis- DNA begins to condense, chromosomes become very short and diverge.

Prophase ends with the destruction of the nucleolema and the formation of the spindle.

Metaphase 1: bivalents are located in the middle of the cell.

Anaphase 1: Doubled chromosomes move to opposite poles.

Telophase 1: the division process is completed, the cells receive 23 bivalents.

Without subsequent doubling of the material, the cell enters into second phase division.

Prophase 2: all the processes that were in prophase 1 are repeated again, namely the condensation of chromosomes, which are randomly located between the organelles.

Metaphase 2: two chromatids connected at the intersection (univalents) are located in the equatorial plane, creating a plate called metaphase.

Anaphase 2:- the univalent is divided into separate chromatids or monads, and they go to different poles of the cell.

Telophase 2: the division process is completed, the nuclear envelope is formed, and each cell receives 23 chromatids.

Meiosis is an important mechanism in the life of all organisms. As a result of this division, we get 4 haploid cells that have half of the desired set of chromatids. During fertilization, two gametes form a complete diploid cell, retaining its inherent karyotype.

It is difficult to imagine our existence without meiotic division, otherwise all organisms with each subsequent generation would receive double sets of chromosomes.

All cellular structures of living organisms normally go through several main stages of development. In the course of its existence, each cell normally goes through the stage of reproduction or division. It can be direct, indirect or reduction. Division is a normal stage in the life of the structural units of various organisms, which ensures the normal existence, growth and reproduction of all living beings on the planet. It is thanks to cell reproduction in the human body that it is possible to renew tissues, restore the integrity of the damaged epithelium or dermis, inherit genetic data, conception, embryogenesis and many other important processes.

There are two main types of reproduction of structural units in the body of multicellular creatures: mitosis and meiosis. Each of these methods of reproduction has characteristic features.

Attention! Cell division is also distinguished by simple division in two - amitosis. In the human body, this process occurs in abnormally altered structures, such as tumors.

Mitosis is the vegetative division of cells with a nucleus, the most common reproduction process. This method is also called indirect reproduction or cloning, since the pair of child structures formed during it turns out to be completely identical to the parent. With the help of cloning, the somatic structural units of the human body multiply.

Attention! Vegetative division is aimed at the formation of exactly the same cells from generation to generation. All cells of the human body, except reproductive ones, reproduce in a similar way.

Cloning is the basis of ontogenesis, that is, the development of an organism from conception to the moment of death. Mitotic division is necessary for the normal functioning of various organs and systems and the formation and preservation of certain characteristics of a person from birth to death at the morphological and biochemical level. The duration of this method of cell reproduction is on average about 1-2 hours.

The course of mitosis is divided into four main phases:

As a result of cloning, two daughter cells are formed from the mother cell, which have an absolutely similar set of chromosomes and retain all the qualitative and quantitative characteristics of the original cell. In the human body due to mitosis there is a constant renewal of tissues.

Attention! The normal course of mitotic processes is provided by neurohumoral regulation, that is, the joint action of the nervous and endocrine systems.

Features of the course of reduction division

Meiotic division is a process that results in the formation of reproductive structural units - gametes. With this method of reproduction, four daughter cells are formed, each of which has 23 chromosomes. Since the gametes formed as a result of this method have an incomplete chromosome set, it is called reduction. In humans, during gametogenesis, the formation of two types of structural units is possible:

• spermatozoa from spermatogonia;
• eggs in follicles.

Characteristics

Since each resulting gamete has a single set of chromosomes, when it fuses with another reproductive cell, the exchange of genetic material occurs and the formation of an embryo that receives a complete chromosome set. It is due to meiosis that combinatorial variability is ensured - this is a process as a result of which a huge list of different genotypes is formed, and the fetus inherits various features of the mother and father.

In the process of formation of haploid structures, the four phases listed above, which are characteristic of mitosis, should also be distinguished. The main difference of the reduction division is that these steps are repeated twice.

Attention! The first telophase ends with the formation of two cells with a complete genetic set of 46 chromosomes. Then the second division begins, due to which four reproductive cells are formed, each of which has 23 chromosomes.

In meiotic division, the first stage takes longer. During that stage, the fusion of chromosomes and the process of exchanging genetic data takes place. Metaphase proceeds in the same way as during mitosis, but with a single set of hereditary data. During anaphase, centromere division does not occur, and haploid chromosomes diverge towards the poles.

The period between two divisions, that is, the interphase, is very short; deoxyribonucleic acid is not produced during this time. Therefore, the cells obtained after the second telophase contain a haploid, that is, a single set of chromosomes. The diploid set is restored when two reproductive cells merge during syngamy. This is the process of joining the male and female gametes formed as a result of meiosis. As a result of the reduction division, a zygote is formed with 46 chromosomes and a complete set of hereditary information received from both parents.

During the fusion of gametes, the formation of various variants of any signs is possible. It is through meiosis that children inherit, for example, the color of the eyes of one of the parents. Due to the recessive carriage of any genes, the transmission of traits through one or more generations is possible.

Attention! Dominant traits are predominant, usually manifested in the first generation of offspring. Recessive - hidden or gradually disappearing in individuals of subsequent generations.

The role of mitotic division:

1. Maintaining a constant number of chromosomes. If the resulting cells had a complete set of chromosomes, then in the fetus after conception their number would double.
2. Due to meiotic division, reproductive cells are formed with different sets of hereditary information.
3. Recombination of hereditary information.
4. Ensuring the variability of organisms.

Comparative characteristics

Differences between cloning and reduction division

Cloning and reduction cell multiplication are quite similar processes. Meiotic division includes the same stages as mitotic division, however, their duration and the processes occurring at its various stages have significant differences.

Video - Mitosis and meiosis

Differences in the course of sexual and asexual division

Cells resulting from mitotic division and gametogenesis carry a different functional load. That is why during meiosis some features of the course are noted:

1. At the first stage of the reduction division, conjugation and crossing over are noted. These processes are necessary for the mutual exchange of genetic information.
2. During anaphase, segregation of similar chromosomes is noted.
3. In the period between two cycles of divisions, there is no reduplication of deoxyribonucleic acid molecules.

Attention! Conjugation is a state of gradual convergence of homologous, that is, similar, chromosomes with each other and the formation of pairs following this. Crossing over - the transition of certain sections from one chromosome to another.

The second stage of gametogenesis proceeds in exactly the same way as mitosis.

Characteristic differences according to the results of the division process:

1. The result of cloning is the formation of two structural units, and the result of reduction division is four.
2. With the help of cloning, the somatic structural units that make up the various tissues of the body are divided. As a result of meiosis, only reproductive cells are formed: eggs and sperm.
3. Cloning leads to the formation of absolutely identical structural units, and during meiotic division, a redistribution of genetic data occurs.
4. As a result of reduction division, the amount of hereditary information in reproductive cells is reduced by 50%. This provides the possibility of subsequent fusion of the genetic data of the mother's and father's cells during fertilization.

Cloning and reduction division are the most important processes that ensure the normal functioning of the body. The daughter cells formed as a result of cloning are identical in everything, including at the level of deoxyribonucleic acid, to the original. This allows you to transfer the chromosome set unchanged from one generation of cells to another. Mitosis underlies normal tissue growth. The biological significance of reduction division is the preservation of a certain number of chromosomes in organisms whose reproduction occurs sexually. At the same time, meiotic division makes it possible to manifest the most important quality of various multicellular organisms - combinative variability. Thanks to her, it is possible to transfer various signs of both father and mother to offspring.

Preparation for ZNO. Biology.
Synopsis 34. Cell cycle. Mitosis. Meiosis

cell cycle

cell cycle- the life of a cell from the moment of its appearance to division or death. An obligatory component of the cell cycle is the mitotic cycle, which includes a period of preparation for division and mitosis itself. There are two major phases: interphase and cell division mitosis or meiosis).
Interphase consists of three periods: presynthetic, or postmitotic, - G 1, synthetic - S, postsynthetic, or premitotic, - G 2.

Mitosis

Mitosis- the main method of division of eukaryotic cells, in which the hereditary material is first doubled, and then its uniform distribution between daughter cells.

There are four phases of mitosis: prophase , metaphase , anaphase and telophase . Before mitosis, the cell prepares for division, or interphase.
Presynthetic period (2n 2c, where n- the number of chromosomes, With- the number of DNA molecules) - cell growth, activation of biological synthesis processes, preparation for the next period.
Synthetic period (2n 4c) is DNA replication.
Postsynthetic period (2n 4c) - preparation of the cell for mitosis, synthesis and accumulation of proteins and energy for the upcoming division, an increase in the number of organelles, doubling of centrioles.
Prophase (2n 4c) - dismantling of nuclear membranes, divergence of centrioles to different poles of the cell, formation of fission spindle threads, "disappearance" of nucleoli, condensation of two-chromatid chromosomes.
metaphase (2n 4c) - alignment of the most condensed two-chromatid chromosomes in the equatorial plane of the cell (metaphase plate), attachment of the spindle fibers with one end to the centrioles, the other - to the centromeres of the chromosomes.
Anaphase (4n 4c) - the division of two-chromatid chromosomes into chromatids and the divergence of these sister chromatids to opposite poles of the cell (in this case, the chromatids become independent single-chromatid chromosomes).
Telophase (2n 2c in each daughter cell) - decondensation of chromosomes, the formation of nuclear membranes around each group of chromosomes, the disintegration of the fission spindle threads, the appearance of the nucleolus, the division of the cytoplasm (cytotomy). Cytotomy in animal cells occurs due to the fission furrow, in plant cells - due to the cell plate.
The biological significance of mitosis. The daughter cells formed as a result of this method of division are genetically identical to the mother. Mitosis ensures the constancy of the chromosome set in a number of cell generations. Underlies such processes as growth, regeneration, asexual reproduction, etc.

Meiosis

Meiosis- This is a special way of dividing eukaryotic cells, as a result of which the transition of cells from a diploid state to a haploid one occurs. Consists of two successive mitotic divisions preceded by a single DNA replication.
first meiotic division(meiosis 1) is called reduction, because it is during this division that the number of chromosomes is halved: from one diploid cell (2 n 4c) form two haploid (1 n 2c).
Interphase 1(at the beginning - 2 n 2c, at the end - 2 n 4c) - the synthesis and accumulation of substances and energy necessary for the implementation of both divisions, an increase in cell size and the number of organelles, doubling of centrioles, DNA replication, which ends in prophase 1.
Prophase 1 (2n 4c) - dismantling of nuclear membranes, divergence of centrioles to different poles of the cell, formation of fission spindle threads, "disappearance" of nucleoli, condensation of two-chromatid chromosomes, conjugation of homologous chromosomes and crossing over. Conjugation- the process of convergence and interlacing of homologous chromosomes. A pair of conjugating homologous chromosomes is called bivalent. Crossing over- the process of exchange of homologous regions between homologous chromosomes.
Metaphase 1 (2n 4c) - alignment of bivalents in the equatorial plane of the cell, attachment of the spindle fibers with one end to the centrioles, the other - to the centromeres of the chromosomes.
Anaphase 1 (2n 4c) - random independent divergence of two-chromatid chromosomes to opposite poles of the cell (from each pair of homologous chromosomes, one chromosome moves to one pole, the other to the other), recombination of chromosomes.
Telophase 1 (1n 2c in each cell) - the formation of nuclear membranes around groups of two-chromatid chromosomes, the division of the cytoplasm. In many plants, a cell from anaphase 1 immediately transitions to prophase 2.
Second meiotic division (meiosis 2) is called equational.
Interphase 2 or interkinesis(1n 2c), is a short break between the first and second meiotic divisions during which DNA replication does not occur. characteristic of animal cells.
Prophase 2 (1n 2c) - dismantling of nuclear membranes, divergence of centrioles to different poles of the cell, formation of fission spindle filaments.
Metaphase 2 (1n 2c) - alignment of two-chromatid chromosomes in the equatorial plane of the cell (metaphase plate), attachment of the spindle fibers with one end to the centrioles, the other - to the centromeres of the chromosomes; 2 block of oogenesis in humans.
Anaphase 2 (2n 2c) - the division of two-chromatid chromosomes into chromatids and the divergence of these sister chromatids to opposite poles of the cell (in this case, the chromatids become independent single-chromatid chromosomes), recombination of chromosomes.
Telophase 2 (1n 1c in each cell) - decondensation of chromosomes, the formation of nuclear membranes around each group of chromosomes, the disintegration of the fission spindle threads, the appearance of the nucleolus, the division of the cytoplasm (cytotomy) with the formation of four haploid cells as a result.
The biological significance of meiosis. Meiosis is the central event of gametogenesis in animals and sporogenesis in plants. Being the basis of combinative variability, meiosis ensures the genetic diversity of gametes.

Amitosis

Amitosis- direct division of the interphase nucleus by constriction without the formation of chromosomes, outside the mitotic cycle. Described for aging, pathologically altered and doomed to death cells. After amitosis, the cell is unable to return to the normal mitotic cycle.

Meiosis is carried out in the cells of organisms that reproduce sexually.

The biological meaning of the phenomenon is determined by a new set of traits in the descendants.

In this paper, we will consider the essence of this process and, for clarity, present it in the figure, see the sequence and duration of germ cell division, and also find out what are the similarities and differences between mitosis and meiosis.

What is meiosis

A process accompanied by the formation of four cells with a single chromosome set from one source.

The genetic information of each newly formed corresponds to half of the set of somatic cells.

Phases of meiosis

Meiotic division includes two stages, each consisting of four phases.

First division

Includes prophase I, metaphase I, anaphase I, and telophase I.

Prophase I

At this stage, two cells with a half set of genetic information are formed. The prophase of the first division includes several stages. It is preceded by premeiotic interphase, during which DNA replication takes place.

Then condensation occurs, forming long thin filaments with a protein axis during leptotene. This thread is attached to the nuclear membrane with the help of terminal extensions - attachment discs. The halves of the doubled chromosomes (chromatids) are not yet distinguishable. When examined, they look like monolithic structures.

Next comes the zygoten stage. Homologues merge to form bivalents, the number of which corresponds to a single number of chromosomes. The process of conjugation (connection) is carried out between paired, similar in genetic and morphological aspects. Moreover, the interaction begins from the ends, spreading along the bodies of the chromosomes. A complex of homologues linked by a protein component is a bivalent or tetrad.

Spiralization occurs during the stage of thick filaments - pachytene. Here, DNA duplication has already been completed, crossing over begins. This is an exchange of homologue sites. As a result, linked genes with new genetic information are formed. Transcription proceeds in parallel. Dense sections of DNA - chromomeres - are activated, which leads to a change in the structure of chromosomes like "lamp brushes".

Homologous chromosomes condense, shorten, diverge (except for the connection points - chiasma). This is a stage in the biology of diplotene or dictyoten. Chromosomes at this stage are rich in RNA, which is synthesized in the same areas. By properties, the latter is close to informational.

Finally, the bivalents diverge towards the periphery of the nucleus. The latter shorten, lose their nucleoli, become compact, not associated with the nuclear envelope. This process is called diakinesis (transition to cell division).

Metaphase I

Next, the bivalents move to the central axis of the cell. Spindles of division depart from each centromere, each centromere is equidistant from both poles. Small amplitude movements of the threads hold them in this position.

Anaphase I

Chromosomes built from two chromatids diverge. Recombination occurs with a decrease in genetic diversity (due to the absence in the set of genes located in loci (areas) of homologues).

Telophase I

The essence of the phase is the divergence of chromatids with their centromeres to opposite parts of the cell. In an animal cell, cytoplasmic division occurs, in a plant cell, the formation of a cell wall.

Second division

After the interphase of the first division, the cell is ready for the second stage.

Prophase II

The longer the telophase, the shorter the duration of the prophase. Chromatids line up along the cell, forming a right angle with their axes relative to the filaments of the first meiotic division. In this stage, they shorten and thicken, the nucleoli undergo disintegration.

Metaphase II

The centromeres are again located in the equatorial plane.

Anaphase II

Chromatids separate from each other, moving towards the poles. Now they are called chromosomes.

Telophase II

Despiralization, stretching of formed chromosomes, disappearance of the division spindle, doubling of centrioles. The haploid nucleus is surrounded by a nuclear membrane. Four new cells are formed.

Comparison table of mitosis and meiosis

Briefly and clearly, the features and differences are presented in the table.

The presented data is a diagram of the differences, and the similarities are reduced to the same phases, DNA replication and coiling before the start of the cell cycle.

The biological significance of meiosis

What is the role of meiosis:

1. Gives new combinations of genes due to crossing over.
2. Supports combinative variability. Meiosis is the source of new traits in a population.
3. Maintains a constant number of chromosomes.

Conclusion

Meiosis is a complex biological process in which four cells are formed, with new traits obtained as a result of crossing over.

Type of lesson: lesson-generalization.

Lesson form: practical lesson.

• to continue the formation of the worldview of students about the continuity of life;
• to acquaint with the chemical and biological difference between the processes occurring in the cell during mitosis and meiosis;
• to form the ability to consistently build the processes of mitosis and meiosis;
• to form the skills of comparative analysis of cell division processes;

1. educational:

a) update students' knowledge about different types of cell division (mitosis, amitosis, meiosis);

b) to form an idea of ​​the main similarities and differences between the processes of mitosis and meiosis, their biological essence;

2. educational: to develop cognitive interest in information from different fields of science;

3. developing:

a) develop skills in working with different types of information and ways of presenting it;

b) continue work on the development of skills to analyze and compare the processes of cell division;

Educational equipment: a computer with a multimedia projector, a model-application “Cell division. Mitosis and meiosis” (demonstration and distribution kits); table “Mitosis. Meiosis".

The structure of the lesson (the lesson is designed for one academic hour, held in the biology room with a multimedia projector, designed for grade 10 of the chemical and biological profile). Brief lesson plan:

1. organizational moment (2 min);

2. actualization of knowledge, basic terms and concepts related to the processes of cell division (8 min);

3. generalization of knowledge about the processes of mitosis and meiosis (13 min);

4. practical work “Similarities and differences between mitosis and meiosis (15 min);

Consolidation of knowledge on the studied topic (5 min);

Homework (2 min).

Detailed outline of the lesson:

1. organizational moment. Explanation of the purpose of the lesson, its place in the topic under study, features of the conduct.

2. updating knowledge, basic terms and concepts related to the processes of cell division: - cell division;

3. generalization of knowledge about the processes of cell division:

3.1. Mitosis:

Demonstration of the interactive model "Mitosis";

Practical work with the model-application "Mitosis" (handout for each student, practicing the students' skills to show the sequence of mitosis processes);

Work with the model-application "Mitosis" (demonstration kit, verification of the results of practical work)

Conversation about the phases of mitosis:

mitosis phase,set of chromosomes(n-chromosomes, c - DNA)	Picture	Phase characteristics, arrangement of chromosomes
Prophase		Dismantling of nuclear membranes, divergence of centrioles to different poles of the cell, formation of fission spindle threads, “disappearance” of nucleoli, condensation of two-chromatid chromosomes.
metaphase		Alignment of the most condensed two-chromatid chromosomes in the equatorial plane of the cell (metaphase plate), attachment of the spindle fibers with one end to the centrioles, the other - to the centromeres of the chromosomes.
Anaphase		The division of two-chromatid chromosomes into chromatids and the divergence of these sister chromatids to opposite poles of the cell (in this case, the chromatids become independent single-chromatid chromosomes).
Telophase		Decondensation of chromosomes, formation of nuclear membranes around each group of chromosomes, disintegration of the fission spindle threads, appearance of the nucleolus, division of the cytoplasm (cytotomy). Cytotomy in animal cells occurs due to the fission furrow, in plant cells - due to the cell plate.

3.2. Meiosis.

Demonstration of the interactive model “Meiosis”

Practical work with the model-application "Meiosis" (handout for each student, developing the students' skills to show the sequence of meiosis processes);

Work with the model-application "Meiosis" (demonstration kit, verification of the results of practical work)

A conversation about the phases of meiosis:

meiosis phase,set of chromosomes(n - chromosomes, c - DNA)	Picture	Phase characteristics, arrangement of chromosomes
Prophase 1 2n4c		Dismantling of nuclear membranes, divergence of centrioles to different poles of the cell, formation of fission spindle filaments, “disappearance” of nucleoli, condensation of two chromatid chromosomes, conjugation of homologous chromosomes, and crossing over.
Metaphase 1 2n4c		Alignment of bivalents in the equatorial plane of the cell, attachment of the spindle fibers with one end to the centrioles, the other - to the centromeres of the chromosomes.
Anaphase 1 2n4c		Random independent divergence of two-chromatid chromosomes to opposite poles of the cell (from each pair of homologous chromosomes, one chromosome moves to one pole, the other to the other), recombination of chromosomes.
Telophase 1 in both cells 1n2c		Formation of nuclear membranes around groups of two-chromatid chromosomes, division of the cytoplasm.
Prophase 2 1n2c		Dismantling of nuclear membranes, divergence of centrioles to different poles of the cell, formation of fission spindle filaments.
Metaphase 2 1n2c		Alignment of two-chromatid chromosomes in the equatorial plane of the cell (metaphase plate), attachment of the spindle fibers with one end to the centrioles, the other - to the centromeres of the chromosomes.
Anaphase 2 2n2c		The division of two-chromatid chromosomes into chromatids and the divergence of these sister chromatids to opposite poles of the cell (in this case, the chromatids become independent single-chromatid chromosomes), recombination of chromosomes.
Telophase 2 in both cells 1n1c Total 4 to 1n1c		Decondensation of chromosomes, formation of nuclear membranes around each group of chromosomes, disintegration of the fission spindle threads, appearance of the nucleolus, division of the cytoplasm (cytotomy) with the formation of two, and as a result of both meiotic divisions, four haploid cells.

Conversation about changing the formula of the cell nucleus

Conversation about the results of meiosis:

one haploid mother cell produces four haploid daughter cells

A discourse on the meaning of meiosis: a)maintains a constant number of chromosomes of a species from generation to generation (the diploid set of chromosomes is restored each time during fertilization as a result of the fusion of two haploid gametes;

b) meiosis - one of the mechanisms for the occurrence of hereditary variability (combinative variability);

4. Practical work “Comparison of mitosis and meiosis” using the presentation “Mitosis and meiosis. Comparative analysis” (see Appendix 1)

Students have homemade table blanks:

Working out the similarities between mitosis and meiosis:

Working out the general differences between mitosis and meiosis (with slight clarifications on division phases):

5. Fixing the material.

Fulfillment of the task of part B of the USE test and measuring materials.

Match the distinguishing features and types of cell division:

Distinguishing Features Types of Cell Division

6. Homework:

Table "Comparison of mitosis and meiosis" in a notebook

Review the material about mitosis and meiosis (details about the stages)

29.30 (V.V. Pasechnik); 19.22 p.130-134 (G.M. Dymshits)

Prepare a table “Comparative characteristics of the course of mitosis and meiosis”

Comparative characteristics of mitosis and meiosis

Bibliography:

1. I.N. Pimenova, A.V. Pimenov - Lectures on General Biology - Saratov, OAO Publishing House Lyceum, 2003

2. General biology: a textbook for grades 10-11 with in-depth study of biology at school / Ed. V.K.Shumny, G.M.Dymshits, A.O.Ruvinsky. - M., "Enlightenment", 2004.

3. N. Green, W. Stout, D. Taylor - Biology: in 3 volumes. T.3 .: per. from English / Ed. R. Sopera. - M., "Mir", 1993

4. T.L. Bogdanova, E.A. Solodova - Biology: a reference book for high school students and applicants to universities - M., “AST-PRESS SCHOOL”, 2004

5. D.I. Mamontov - Open biology: a complete interactive biology course (on CD) - "Physicon", 2005