In the last two years, in variants test tasks The Unified State Exam in biology began to appear more and more questions on the methods of reproduction of organisms, methods of cell division, differences between the different stages of mitosis and meiosis, sets of chromosomes (n) and DNA content (c) in various stages cell life.
I agree with the authors of the assignments. To thoroughly understand the essence of the processes of mitosis and meiosis, you need to not only understand how they differ from each other, but also know how the set of chromosomes changes ( n), and, most importantly, their quality ( With), at various stages of these processes.
We remember, of course, that mitosis and meiosis are various ways divisions kernels cells rather than the division of the cells themselves (cytokinesis).
We also remember that thanks to mitosis, diploid (2n) somatic cells reproduce and ensure asexual reproduction, and meiosis ensures the formation of haploid (n) germ cells (gametes) in animals or haploid (n) spores in plants.
For ease of perception of information
In the figure below, mitosis and meiosis are depicted together. As we see, this diagram does not include , it does not contain full description what happens in cells during mitosis or meiosis. The purpose of this article and this figure is to draw your attention only to those changes that occur with the chromosomes themselves on different stages mitosis and meiosis. This is precisely what the emphasis is placed on in the new USE test tasks.
In order not to overload the figures, the diploid karyotype in cell nuclei is represented by only two pairs homologous chromosomes (i.e. n = 2). The first pair are larger chromosomes ( red And orange). The second pair are smaller ones ( blue And green). If we were to specifically depict, for example, a human karyotype (n = 23), we would have to draw 46 chromosomes.
So what was the set of chromosomes and their quality before the start of division in the interphase cell during the period G1? Of course he was 2n2c. We do not see cells with such a set of chromosomes in this figure. Since after S During the interphase period (after DNA replication), the number of chromosomes, although remains the same (2n), but since each chromosome now consists of two sister chromatids, the cell karyotype formula will be written like this : 2n4c. And these are the cells with such double chromosomes, ready to begin mitosis or meiosis, that are shown in the figure.
This drawing allows us to answer the following test questions:
— How does prophase of mitosis differ from prophase I of meiosis? In prophase I of meiosis, chromosomes are not freely distributed throughout the entire volume of the former cell nucleus(the nuclear membrane dissolves in prophase), as in prophase of mitosis, and homologues combine and conjugate (intertwine) with each other. This can lead to crossover : exchange of some identical regions of sister chromatids among homologues.
— How does metaphase of mitosis differ from metaphase I of meiosis? In metaphase I of meiosis, cells are not lined up along the equator bichromatid chromosomes as in metaphase of mitosis, in bivalents(two homologues together) or tetrads(tetra - four, according to the number of sister chromatids involved in conjugation).
— How does anaphase of mitosis differ from anaphase I of meiosis? During anaphase of mitosis, the spindle filaments move the cells towards the poles sister chromatids(which at this time should already be called single chromatid chromosomes). Please note that at this time, since two single-chromatid chromosomes were formed from each bichromatid chromosome, and two new nuclei have not yet been formed, the chromosomal formula of such cells will be 4n4c. In anaphase I of meiosis, dichromatid homologues are pulled apart by spindle filaments towards the cell poles. By the way, in the figure at anaphase I we see that one of the sister chromatids of the orange chromosome has sections from the red chromatid (and, accordingly, vice versa), and one of the sister chromatids of the green chromosome has sections from the blue chromatid (and, accordingly, vice versa). Therefore, we can assert that during prophase I of meiosis, not only conjugation, but also crossing over occurred between homologous chromosomes.
— How does telophase of mitosis differ from telophase I of meiosis? During the telophase of mitosis, the two newly formed nuclei (there are not two cells yet, they are formed as a result of cytokinesis) will contain diploid set of single chromatid chromosomes - 2n2c. In telophase I of meiosis, the two resulting nuclei will contain haploid set of bichromatid chromosomes - 1n2c. Thus, we see that meiosis I has already provided reduction division (the number of chromosomes has halved).
— What ensures meiosis II? Meiosis II is called equational(equalizing) division, as a result of which the four resulting cells will contain a haploid set of normal single-chromatid chromosomes - 1n1c.
— How does prophase I differ from prophase II? In prophase II, cell nuclei do not contain homologous chromosomes, as in prophase I, so homologues do not combine.
— How does metaphase of mitosis differ from metaphase II of meiosis? A very “insidious” question, since from any textbook you will remember that meiosis II generally proceeds as mitosis. But, pay attention, during the metaphase of mitosis, the cells line up along the equator dichromatid chromosomes and each chromosome has its homologue. In metaphase II of meiosis, they also line up along the equator dichromatid chromosomes, but no homologous ones . In a color drawing, as in this article above, this is clearly visible, but in the exam the drawings are black and white. This black and white drawing of one of the test tasks depicts metaphase of mitosis, since there are homologous chromosomes (large black and large white are one pair; small black and small white are the other pair).
— There may be a similar question regarding anaphase of mitosis and anaphase II of meiosis .
— How does telophase I of meiosis differ from telophase II? Although the set of chromosomes in both cases is haploid, during telophase I the chromosomes are bichromatid, and during telophase II they are single-chromatid.
When I wrote such an article on this blog, I never thought that the content of tests would change so much in three years. Obviously, due to the difficulties of creating more and more new tests, relying on school curriculum in biology, the author-compilers no longer have the opportunity to “dig in breadth” (everything has long been “dug up”) and they are forced to “dig deep”.
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Who has questions about the article to Biology tutor via Skype, please contact me in the comments.
Meiosis is a division in the zone of sexual maturation cells, accompanied by a halving of the number of chromosomes. It consists of two sequential divisions that have the same phases as mitosis. However, as shown in the table "Comparison of Mitosis and Meiosis", the duration of the individual phases and the processes occurring in them differ significantly from the processes occurring during mitosis.
These differences are mainly as follows.
In meiosis, prophase I is longer. Conjugation (joining of homologous chromosomes) and exchange of genetic information occurs in it. In anaphase I, the centromeres holding the chromatids together do not divide, and one of the homologmeiosis Mitosis and its phases of mitosis and egg chromosomes moves to the poles. The interphase before the second division is very short, during which DNA is not synthesized. Cells (halites) formed as a result of two meiotic divisions contain a haploid (single) set of chromosomes. Diploidy is restored by the fusion of two cells - maternal and paternal. The fertilized egg is called a zygote.
Mitosis, or indirect division, is most widespread in nature. Mitosis underlies the division of all non-sexual cells(epithelial, muscle, nervous, bone, etc.). Mitosis consists of four successive phases (see table below). Mitosis ensures that the genetic information of the parent cell is evenly distributed among the daughter cells. The period of cell life between two mitoses is called interphase. It is ten times longer than mitosis. A number of very important processes take place in it prior to cell division: ATP molecules are synthesized and proteins, each chromosome doubles, forming two sister chromatids held together by a common centromere, and the number of main organelles of the cytoplasm increases.
In prophase, the chromosomes, consisting of two sister chromatids held together by the centromere, spiral and as a result thicken. By the end of prophase, the nuclear membrane and nucleoli disappear and the chromosomes are dispersed throughout the cell, the centrioles move to the poles and form a spindle. In metaphase, further spiralization of chromosomes occurs. During this phase they are most clearly visible. Their centromeres are located along the equator. The spindle threads are attached to them.
In anaphase, centromeres divide, sister chromatids separate from each other and, due to the contraction of spindle filaments, move to opposite poles of the cell.
In telophase, the cytoplasm divides, chromosomes unwind, and nucleoli and nuclear membranes are formed again. In animal cells, the cytoplasm is laced together; in plant cells, a septum is formed in the center of the mother cell. So from one original cell (mother) two new daughter cells are formed.
Meiosis and mitosis
Table - Comparison of mitosis and meiosis
|
1 division |
2 division |
||
|
Interphase |
Chromosome set 2n There is an intensive synthesis of proteins, ATP and other organic matter The chromosomes double, each consisting of two sister chromatids held together by a common centromere. |
Set of chromosomes 2n The same processes are observed as in mitosis, but longer, especially during the formation of eggs. |
The set of chromosomes is haploid (n). There is no synthesis of organic substances. |
|
Short-lived, chromosome spiralization occurs, the nuclear membrane and nucleolus disappear, a spindle is formed |
Longer lasting. At the beginning of the phase, the same processes occur as in mitosis. In addition, chromosome conjugation occurs, in which homologous chromosomes come together along their entire length and become twisted. In this case, an exchange of genetic information can occur (crossing of chromosomes) - crossing over. The chromosomes then separate. |
Short; the same processes as in mitosis, but with n chromosomes. |
|
|
Metaphase |
Further spiralization of chromosomes occurs, their centromeres are located along the equator. |
Processes similar to those in mitosis occur. | |
|
The centromeres holding sister chromatids together divide, each of them becomes a new chromosome and moves to opposite poles. |
Centromeres do not divide. One of the homologous chromosomes, consisting of two chromatids held together by a common centromere, departs to opposite poles. |
The same thing happens as in mitosis, but with n chromosomes. |
|
|
Telophase |
The cytoplasm divides, two daughter cells are formed, each with a diploid set of chromosomes. The spindle disappears and nucleoli form. |
Does not last long Homologous chromosomes fall into different cells with a haploid set of chromosomes. Cytoplasm does not always divide. |
The cytoplasm divides. After two meiotic divisions, 4 cells with a haploid set of chromosomes are formed. |
Cell cycle- this is the period of existence of a cell from the moment of its formation by dividing the mother cell until its own division.
Cell cycle duration eukaryotes
The length of the cell cycle varies among different cells. Rapidly reproducing cells of adult organisms, such as hematopoietic or basal cells of the epidermis and small intestine, may be included in cell cycle every 12-36 hours. Short cell cycles (about 30 minutes) are observed when eggs are rapidly crushed echinoderms, amphibians and other animals. Under experimental conditions, many cell culture lines have a short cell cycle (about 20 hours). For most actively dividing cells, the duration of the period between mitoses is approximately 10-24 hours.
Cell cycle phases eukaryotes
Cell cycleeukaryotes consists of two periods:
A period of cell growth called " interphase", during which synthesis occurs DNA And proteins and preparation for cell division is carried out.
The period of cell division, called “phase M” (from the word mitosis - mitosis).
Interphase consists of several periods:
G 1 - phases(from English gap- interval), or phase initial growth, during which synthesis occurs mRNA, proteins, other cellular components;
S- phases(from English synthesis- synthesis), during which it goesDNA replication cell nucleus , doubling also occurs centrioles(if they exist, of course).
G 2 - phase during which preparations formitosis .
In differentiated cells that no longer divide, there may be no G 1 phase in the cell cycle. Such cells are found in resting phase G 0 .
Periodcell division (phase M) includes two stages:
-mitosis(division of the cell nucleus);
-cytokinesis(cytoplasmic division).
In its turn, mitosis is divided into five stages.
The description of cell division is based on light microscopy data in combination with microcine photography and the results light And electronic microscopy fixed and stained cells.
Cell cycle regulation
The natural sequence of changes in periods of the cell cycle occurs through the interaction of such proteins, How cyclin-dependent kinases And cyclins. Cells, which are in the G 0 phase, can enter the cell cycle when exposed to growth factors. Various growth factors such as platelet, epidermal, nerve growth factor, binding to its receptors, trigger an intracellular signaling cascade, ultimately leading to transcriptions genes cyclins And cyclin-dependent kinases. Cyclin-dependent kinases become active only when interacting with the corresponding cyclins. Contents of various cyclins V cage changes throughout the cell cycle. Cyclin is a regulatory component of the cyclin-cyclin-dependent kinase complex. Kinase is also the catalytic component of this complex. Kinases not active without cyclins. At different stages of the cell cycle are synthesized different cyclins. Yes, content cyclin B in oocytes frogs reaches its maximum at the moment mitosis when the entire cascade of reactions starts phosphorylation, catalyzed by the cyclin B/cyclin-dependent kinase complex. By the end of mitosis, cyclin is rapidly destroyed by proteinases.
Cell cycle checkpoints
To determine the completion of each phase of the cell cycle, it requires the presence of checkpoints. If the cell “passes” the checkpoint, then it continues to “move” through the cell cycle. If some circumstances, such as DNA damage, prevent the cell from passing through a checkpoint, which can be compared to a kind of checkpoint, then the cell stops and another phase of the cell cycle does not occur. at least until the obstacles that prevented the cell from passing through the checkpoint are removed. There are at least four checkpoints in the cell cycle: a checkpoint in G1, which checks for intact DNA before entering S phase, a checkpoint in S phase, which checks for correct DNA replication, a checkpoint in G2, which checks for lesions missed when passing previous verification points, or obtained at subsequent stages of the cell cycle. In the G2 phase, the completeness of DNA replication is detected, and cells in which DNA is under-replicated do not enter mitosis. At the spindle assembly checkpoint, it is checked that all kinetochores are attached to microtubules.
Cell cycle disorders and tumor formation
An increase in the synthesis of the p53 protein leads to the induction of the synthesis of the p21 protein, a cell cycle inhibitor.
Disruption of normal cell cycle regulation is the cause of most solid tumors. In the cell cycle, as already mentioned, passing checkpoints is possible only if the previous stages are completed normally and there are no breakdowns. Tumor cells are characterized by changes in the components of cell cycle checkpoints. When cell cycle checkpoints are inactivated, dysfunction of some tumor suppressors and proto-oncogenes is observed, in particular p53, pRb, Myc And Ras. The p53 protein is one of the transcription factors that initiates protein synthesis p21, which is an inhibitor of the CDK-cyclin complex, which leads to cell cycle arrest in the G1 and G2 periods. Thus, a cell whose DNA is damaged does not enter S phase. With mutations leading to the loss of p53 protein genes, or with their changes, there is no blockade of the cell cycle, the cells enter mitosis, which leads to the appearance of mutant cells, most of of which is non-viable, the other gives rise to malignant cells.
Cell division
All cells appear by division of parent cells. Most cells have a cell cycle consisting of two main stages: interphase and mitosis.
Interphase consists of three stages. Within 4–8 hours after birth, the cell increases its mass. Some cells (for example, nerve cells in the brain) remain in this stage forever, while others double their chromosomal DNA within 6–9 hours. When the cell mass doubles, it begins mitosis.
In progress anaphase chromosomes move to the poles of the cell. When the chromosomes reach the poles, it begins telophase. The cell divides in two in the equatorial plane, the spindle filaments are destroyed, and nuclear membranes form around the chromosomes. Each daughter cell receives its own set of chromosomes and returns to the interphase stage. The whole process takes about an hour.
The process of mitosis can vary depending on the type of cell. There are no centrioles in a plant cell, although a spindle is formed. In fungal cells, mitosis occurs inside the nucleus; the nuclear membrane does not disintegrate.
The presence of chromosomes is not a necessary condition for cell division. On the other hand, one or more mitoses may stop at the telophase stage, resulting in multinucleated cells (for example, in some algae).
Reproduction by mitosis is called asexual or vegetative, as well as cloning. In mitosis, the genetic material of the parent and daughter cells is identical.
Meiosis, unlike mitosis, is an important element sexual reproduction. Meiosis produces cells containing only one set of chromosomes, which makes possible the subsequent fusion of sex cells (gametes) of two parents. Essentially, meiosis is a type of mitosis. It involves two successive cell divisions, but the chromosomes are duplicated only in the first of these divisions. The biological essence of meiosis is to reduce the number of chromosomes by half and form haploid gametes (that is, gametes with one set of chromosomes).
As a result of meiotic division in animals, four are formed gametes. If male reproductive cells have approximately the same size, then when eggs are formed, the distribution of cytoplasm occurs very unevenly: one cell remains large, and the other three are so small that they are almost entirely occupied by the nucleus. These small cells serve only to house excess genetic material.
Male and female gametes fuse to form zygote. In this case, the chromosome sets are combined (this process is called syngamy), as a result of which a double set of chromosomes is restored in the zygote - one from each parent. Random segregation of chromosomes and the exchange of genetic material between homologous chromosomes lead to the emergence of new combinations of genes, increasing genetic diversity. The resulting zygote develops into an independent organism.
Recently, experiments have been carried out on the artificial fusion of cells of the same or different types. The outer surfaces of the cells were glued together, and the membrane between them was destroyed. In this way, it was possible to obtain hybrid cells of a mouse and a chicken, a human and a mouse. However, during subsequent divisions, the cells lost most of the chromosomes of one of the species.
In other experiments, the cell was divided into components, such as the nucleus, cytoplasm, and membrane. The components of the different cells were then put back together, resulting in a living cell made up of components from different types of cells. In principle, experiments in assembling artificial cells could be the first step towards creating new forms of life.
Meiosis is the division that produces sex cells (in plants, spores). Biological significance of meiosis:
- recombination(mixing of hereditary information)
- reduction(reduction in the number of chromosomes by 2 times).
Differences between meiosis and mitosis based on the results
Tests and assignments
All of the terms below are used to describe meiosis. Define two terms that “fall out” from general list, and write down in the numbers under which they are indicated.
1) bivalents
2) reduction division
3) cloning
4) fertilization
5) crossing over
Answer
1. Establish a correspondence between the methods of cell division and their characteristics: 1) mitosis, 2) meiosis. Write numbers 1 and 2 in the correct order.
A) reduction division
B) ensures growth, regeneration
B) daughter cells are identical to the parent
D) four haploid cells are formed
D) increases genetic diversity
E) indirect division
Answer
2. Establish a correspondence between the processes occurring during cell division and the methods of division: 1) mitosis, 2) meiosis. Write numbers 1 and 2 in the correct order.
A) ensures the growth and development of the body
B) as a result of division they are formed somatic cells
C) maintains the constancy of the number of chromosomes in the cells of individuals of the same species during sexual reproduction
D) underlies combinative variability
D) is the basis of vegetative reproduction
E) bivalents are formed during fission
Answer
3. Establish a correspondence between the characteristics of the processes and the method of cell division: 1) mitosis, 2) meiosis. Write numbers 1 and 2 in the correct order.
A) formation of germ cells in mammals
B) body growth
B) division of the zygote
D) conjugation and crossing over
D) reducing the number of chromosomes by half
Answer
4. Establish a correspondence between the processes and the method of cell division: 1) mitosis, 2) meiosis. Write numbers 1 and 2 in the correct order.
A) somatic cell division occurs
B) the chromosome set is halved
C) a new combination of genes is formed
D) conjugation and crossing over occur
D) bivalents are located along the equator of the cell
Answer
5. Establish a correspondence between the processes and methods of division: 1) meiosis, 2) mitosis. Write numbers 1 and 2 in the correct order.
A) bivalents are formed
B) formation of diploid cells occurs
B) the number of chromosomes changes
D) crossing over occurs
D) the content of genetic material does not change
E) there is a divergence of bichromatid chromosomes to the poles of the cell
Answer
6. Establish a correspondence between the characteristics of cell division and its type: 1) Mitosis, 2) Meiosis. Write numbers 1 and 2 in the correct order.
A) occurs in two stages
B) after division, diploid cells are formed
C) the resulting cells have a set of chromosomes and DNA 2n2c
D) accompanied by chromosome conjugation
D) the resulting cells have a set of chromosomes and DNA nс
E) crossing over occurs
Answer
7. Establish a correspondence between the type of cell division and biological significance: 1) mitosis, 2) meiosis. Write numbers 1 and 2 in the order corresponding to the letters.
A) genetic stability
B) combinative variability
B) regeneration
D) body growth
D) asexual reproduction
E) sexual reproduction
Answer
8. Establish a correspondence between the characteristics of the process and the methods of cell division: 1) mitosis, 2) meiosis. Write numbers 1 and 2 in the order corresponding to the letters.
1) pairs of homologous chromosomes are formed
2) homologous chromosomes diverge to the poles
3) conjugation and crossing over occur
4) there is a reduction in the number of chromosomes
5) at the end of the process, two daughter cells are formed
6) the identity of the hereditary information of new cells to the mother cell is maintained
Answer
9. Establish a correspondence between the characteristics of the process and the methods of cell division: 1) mitosis, 2) meiosis. Write numbers 1 and 2 in the order corresponding to the letters.
A) cells with the chromosome set nc are formed
B) bichromatid chromosomes diverge to the poles
B) conjugation and crossing over occur
D) the number of chromosomes remains unchanged
D) at the end of the process, four daughter cells are formed
E) reduction in the number of chromosomes
Answer
10. Establish a correspondence between the characteristics and methods of cell division: 1) mitosis, 2) meiosis. Write numbers 1 and 2 in the order corresponding to the letters.
A) reduction in the number of chromosomes in a cell
B) the formation of cells identical to the mother
B) formation of somatic cells
D) formation of gametes in animals
D) ensuring the growth of organisms
E) formation of spores in plants
Answer
COLLECTING 11:
A) retains the karyotype of the original cell
Choose the one that suits you best correct option. During meiosis, bichromatid chromosomes move to the poles of the cell in
1) anaphase I division
2) anaphase II division
3) prophase of division I
4) prophase of division II
Answer
Choose one, the most correct option. The first meiotic division is different from the second meiotic division
1) divergence of daughter chromatids into resulting cells
2) divergence of homologous chromosomes and the formation of two haploid cells
3) division into two parts of the primary constriction of chromosomes
4) the formation of two diploid cells
Answer
All of the following characteristics, except two, can be used to characterize the processes and biological significance of meiosis. Identify two characteristics that “drop out” from the general list and write down the numbers under which they are indicated.
1) formation of cells with double the number of chromosomes
2) formation of haploid cells
3) formation of bivalents
4) the emergence of new gene combinations
5) appearance more somatic cells
Answer
Look at the picture of cell division and determine (A) its type, (B) the number of chromosomes in the cell shown on the left, and (C) what specific cells are formed in animals as a result of such division. For each letter, select the corresponding term from the list provided.
1) mitosis
2) transcription
3) diploid
4) meiosis
5) direct
6) haploid
7) gamete
8) somatic
Answer
Choose three options. What signs characterize meiosis?
1) the presence of two divisions following one after another
2) the formation of two cells with the same hereditary information
3) divergence of homologous chromosomes into different cells
4) formation of diploid daughter cells
5) absence of interphase before the first division
6) conjugation and crossing over of chromosomes
Answer
1. Establish the sequence of processes occurring during meiosis
1) arrangement of pairs of homologous chromosomes in the equatorial plane
2) conjugation, crossing over of homologous chromosomes
3) location in the equatorial plane and divergence of sister chromosomes
4) formation of four haploid nuclei
5) divergence of homologous chromosomes
Answer
2. Establish the sequence of processes of the first meiotic division. Write down the corresponding sequence of numbers.
1) chromosome conjugation
2) crossing over
3) arrangement of pairs (bivalents) of homologous chromosomes at the equator of the cell
4) divergence of homologous chromosomes, consisting of two chromatids, to opposite poles of the cell
5) spiralization of chromosomes with the formation of bivalents
6) formation of nuclei, division of the cytoplasm - the formation of two daughter cells
Answer
3. Establish the sequence of processes occurring in meiosis.
1) divergence of homologous chromosomes to the poles of the cell
2) divergence of sister chromosomes (chromatids) to the cell poles
3) gene exchange between homologous chromosomes
4) the formation of four cells with haploid set chromosomes
5) conjugation of homologous chromosomes
Answer
4. Establish the sequence of meiotic processes. Write down the corresponding sequence of numbers.
1) arrangement of pairs of chromosomes along the equator of the cell
2) divergence of sister chromatids to opposite poles of the cell
3) conjugation and crossing over
4) formation of nuclei with a set of chromosomes and DNA nc
5) divergence of bichromatid chromosomes to opposite poles of the cell
Answer
5. Establish the sequence of processes occurring during meiotic division of an animal cell. Write down the corresponding sequence of numbers.
1) the formation of two cells with a haploid set of chromosomes
2) divergence of homologous chromosomes
3) conjugation with possible crossing over of homologous chromosomes
4) location in the equatorial plane and divergence of sister chromosomes
5) arrangement of pairs of homologous chromosomes in the equatorial plane of the cell
6) formation of four haploid nuclei
Answer
Look at the picture depicting cell division and determine A) the type of division, B) the set of chromosomes in the original cell, C) what specific cells are formed. Write down three numbers (numbers of terms from the proposed list) in the correct order.
1) mitosis
2) transcription
3) diploid
4) meiosis
5) direct
6) haploid
7) gamete
8) somatic
Answer
Choose one, the most correct option. Spores in flowering plants, unlike bacterial spores, are formed in the process
1) adaptation to life in unfavorable conditions
2) mitosis of haploid cells
3) meiosis of diploid cells
4) sexual reproduction
Answer
Choose one, the most correct option. DNA duplication and the formation of two chromatids during meiosis occurs in
1) prophase of the first meiotic division
2) prophase of the second division of meiosis
3) interphase before the first division
4) interphase before the second division
Answer
Look at the picture of cell division and determine (A) its phases, (B) the set of chromosomes in the daughter cells, and (C) what specific cells are formed as a result of such division in plants.
2) somatic
3) diploid
4) prophase 2, metaphase 2, anaphase 2, telophase 2
5) prophase 1, metaphase 1, anaphase 1, telophase 1
6) haploid
7) dispute
8) first meiotic division
Answer
Look at the picture depicting cell division and determine: A) what phases of division are depicted, B) the set of chromosomes of cells in each phase, C) what specific cells are formed in plants as a result of such division. Write down three numbers (numbers of terms from the proposed list) in the correct order.
1) prophase, metaphase, telophase
2) interphase
3) diploid
4) prophase 2, metaphase 2, anaphase 2
5) prophase 1, metaphase 1, anaphase 1
6) haploid
7) dispute
8) somatic
Answer
All of the characteristics listed below, except two, are used to describe the cell shown in the figure. Identify two characteristics that “fall out” from the general list and write down the numbers under which they are indicated.
1) homologous chromosomes are present
2) each chromosome contains one DNA molecule
3) the cell lacks a cell center
4) the formation of a mitotic spindle occurs
5) a metaphase plate has formed
Answer
All of the following characteristics, except two, can be used to describe the processes of the first meiotic division. Identify two characteristics that “drop out” from the general list and write down the numbers under which they are indicated.
1) formation of two haploid nuclei
2) divergence of single-chromatid chromosomes to opposite poles of the cell
3) formation of four cells with a set of nc
4) exchange of sections of homologous chromosomes
5) chromosome spiralization
Answer
Choose one, the most correct option. In the first division of meiosis,
1) polyploid cells
2) diploid cells
3) gametes
4) haploid cells
Answer
Choose one, the most correct option. During sexual reproduction, the maintenance of the constancy of the chromosome set in a series of generations of the species is ensured
1) recombination of genes in chromosomes
2) the formation of identical daughter cells
3) divergence of sister chromosomes
4) a decrease in the number of chromosomes in gametes
Answer
How does prophase of the first division of meiosis differ from prophase of mitosis? In response, write down the numbers of two correct options out of the five proposed.
1) the nuclear membrane disappears
2) chromosome spiralization occurs
3) chromosome conjugation occurs
4) chromosomes are arranged randomly
5) crossing over occurs
Answer
All but two of the characteristics listed below are used to describe the phase of meiosis shown in the figure. Identify two characteristics that “drop out” from the general list and write down the numbers under which they are indicated.
1) chromosome bivalents are located at the equator of the cell
2) homologous chromosomes, consisting of two chromatids, diverge to opposite poles
3) daughter chromatids diverge to opposite poles of the cell
4) there is a reduction in the number of chromosomes
5) chromosome set in the n2c cell at each cell pole
Answer
Look at the picture and determine (A) the type of division, (B) the phase of division, (C) the amount of genetic material in the cell. For each lettered cell, select the appropriate term from the list provided. Write down the selected numbers in the order corresponding to the letters.
1) anaphase II
2) n2c (at each cell pole)
3) metaphase
4) meiosis
5) 2n2c
6) mitosis
7) anaphase I
Answer
How many spermatozoa are formed as a result of spermatogenesis from one diploid primary germ cell? Write down only the corresponding number in your answer.
Answer
All but two of the following characteristics can be used to describe meiosis. Identify two characteristics that “drop out” from the general list and write down the numbers under which they are indicated.
1) two diploid cells are formed
2) four haploid cells are formed
3) one division occurs, consisting of four phases
4) two divisions occur, each of which consists of four phases
5) homologous chromosomes containing two chromatids diverge to the poles of the cell
Answer
All of the following characteristics, except two, can be used to describe the processes that occur in the prophase of the first meiotic division. Identify two characteristics that “drop out” from the general list, and write down the numbers under which they are indicated in your answer.
1) formation of two nuclei
2) divergence of homologous chromosomes
3) bringing together homologous chromosomes
4) exchange of sections of homologous chromosomes
5) chromosome spiralization
Answer
Select three features of mitotic cell division.
1) bichromatid chromosomes diverge to the poles
2) sister chromatids move towards the poles
3) double chromosomes appear in daughter cells
4) as a result, two diploid cells are formed
5) the process takes place in one division
6) as a result, haploid cells are formed
Answer
Select three differences between the first meiotic division and the second
1) pairs of homologous chromosomes are located at the equator of the cell
2) there is no telophase
3) conjugation and crossing over of chromosomes occurs
4) there is no conjugation and crossing over of chromosomes
5) sister chromatids diverge to the cell poles
6) homologous chromosomes diverge to the cell poles
Answer
What processes occur during meiosis?
1) transcription
2) reduction
3) denaturation
4) crossing over
5) conjugation
6) broadcast
Answer
The biological essence of meiosis is:
1) the emergence of a new nucleotide sequence;
2) the formation of cells with double the number of chromosomes;
3) formation of haploid cells;
4) recombination of sections of non-homologous chromosomes;
5) new combinations of genes;
6) the appearance of a larger number of somatic cells.
Answer
Choose three correct answers out of six and write down the numbers under which they are indicated. During the process of meiosis occurs
1) formation of germ cells
2) formation of prokaryotic cells
3) reducing the number of chromosomes by half
4) preservation of the diploid set of chromosomes
5) formation of two daughter cells
6) development of four haploid cells
Answer
Establish a correspondence between the characteristics and phases of cell division: 1) metaphase of mitosis, 2) anaphase of mitosis, 3) prophase I of meiosis. Write numbers 1-3 in the order corresponding to the letters.
A) exchange of chromosome sections
B) alignment of chromosomes along the equator of the cell
B) formation of the spindle
D) set of chromosomes and number of DNA molecules in a cell – 4n4c
D) division of chromosome centromeres
Answer
Establish a correspondence between the feature of the process and the phase of meiosis for which it is characteristic: 1) anaphase I, 2) anaphase II, 3) telophase II. Write numbers 1-3 in the order corresponding to the letters.
A) divergence of sister chromosomes to different poles of the cell
B) formation of four haploid nuclei
B) divergence of bichromatid chromosomes to opposite poles
D) doubling the number of chromosomes in a cell when sister chromatids diverge
D) independent divergence of chromosomes from each homologous pair
Answer
Establish a correspondence between the characteristics and phases of meiosis: 1) prophase of the first division, 2) anaphase of the second division. Write numbers 1 and 2 in the order corresponding to the letters.
A) conjugation of homologous chromosomes
B) formation of bivalents
B) chromatid separation
D) reduction of spindle microtubules
D) dissolution of the karyolemma
Answer
1) anaphase
2) metaphase
3) prophase
4) telophase
5) mitosis
6) meiosis I
7) meiosis II
Answer
Determine the phase and type of division shown in the figure. Write two numbers in the order specified in the task, without separators (spaces, commas, etc.).
1) anaphase
2) metaphase
3) prophase
4) telophase
5) mitosis
6) meiosis I
7) meiosis II
Answer
Determine the phase and type of division shown in the figure. Write two numbers in the order specified in the task, without separators (spaces, commas, etc.).
1) anaphase
2) metaphase
3) prophase
4) telophase
5) mitosis
6) meiosis I
7) meiosis II
Answer
Determine the phase and type of division shown in the figure. Write two numbers in the order specified in the task, without separators (spaces, commas, etc.).
1) anaphase
2) metaphase
3) prophase
4) telophase
5) mitosis
6) meiosis I
7) meiosis II
Answer
© D.V. Pozdnyakov, 2009-2019
The purpose of the lesson: repetition of material about methods of cell reproduction.
Tasks
Educational: to form and consolidate knowledge about two types of cell division, about the importance of cell division for unicellular and multicellular organisms, about the processes occurring in the various phases of mitosis and meiosis, about the differences between meiosis and mitosis.
Developmental: developing the skills to work in a group, characterize objects and phenomena, compare them, justify conclusions, apply knowledge, evaluate yourself and your knowledge; development of interest in the subject.
Educational: fostering respectful attitudes towards each other.
Equipment: sheets of Whatman paper and paper, felt-tip pens, glue, tape, scissors, files with tasks, instruction card for each team.
Preparing for the lesson
1. At the previous lesson, students should be familiarized with the principles and rules of conducting a workshop lesson.
2. Since the topic “Cell Division” was studied in the 9th grade and the students forgot a lot, as homework They had to repeat material on the topic: “Cell division.”
Dividing the class into teams
Students are asked to choose one of the following questions and write it down on a piece of paper. (Most likely, the student will choose a question for which he knows or assumes he knows the answer.)
In what biological meaning meiosis?
How is mitosis different from meiosis?
What is the biological meaning of mitosis?
From a piece of paper with a written question you need to fold a paper airplane. Standing in a circle, students launch their airplanes (all at the same time at the teacher’s command) and, picking up the airplane that fell nearby, repeat this operation 2 times. Having opened the airplanes, students are divided into three teams - on the same questions.
Each team receives a file containing material for work: a list of terms, definitions, diagrams, historical information.
Instruction card
Select from the list of terms (Appendix 2) those that are relevant to the topic “Cell division. Mitosis. Meiosis". The selected command words are read aloud.
Select definitions (Appendix 3) that correspond to the selected terms from the previous assignment. Be careful, some definitions have been replaced! To complete this task correctly, you need to find and ask the other team for your definition. Terms cannot be changed!
Select the appropriate pictures for the processes occurring in a cell during mitosis or meiosis (Appendix 4).
Paste words, definitions and pictures in a logical sequence onto a piece of Whatman paper. Prepare short story about this biological process.
(Teams display their work on a stand. Team members talk about the processes depicted on whatman paper.)
Answer the question written on your “airplane” sheet. Write the answer in your notebook. (When completing this task, you can use the original source. Each team reads its answer to the question out loud.)
Reflection
Option 1(if there is a lot of time left until the end of the lesson).
Give two or three arguments in support of the fact that the topic “Cell division. Mitosis and meiosis" must be studied in the course general biology high school.
Option 2(if there is not enough time).
Are you satisfied with the lesson, your work in the lesson? Think, evaluate your emotional condition. Write down the answer on a piece of paper and stick it on the stand when you leave.
Homework
Answer the following questions.
What factors cause disruption of mitosis and meiosis?
What consequences can this lead to?
Appendix 1. Historical background
Flemming Walter (1843–1905), German histologist. Professor at universities in Prague (from 1873) and Kiel (1876–1901). Major works on the histology of mollusks, tissue regeneration, the study of connective and adipose tissue, the structure of follicles, spinal ganglion cells, etc. His research became especially famous thin structure cells. Using the methods of fixation (Flemming's liquid) and staining he developed, he studied the structure of protoplasm, nucleus, centrosomes and, in particular detail, the process of cell division (direct and indirect). These studies had great importance for the development of cytology; his methods of fixation and staining became widespread in laboratory practice.
Strasburger Edward (1844–1912), German botanist, Pole by origin, member of the Polish Academy of Sciences in Krakow (1888). Studied in Warsaw, Bonn and Jena. He was an associate professor at the Warsaw (1867–1869), a professor at the Jena (1869–1880) and Bonn (1880–1911) universities. Main works in the field of cytology, anatomy and embryology of plants. Studied mitosis. Described meiosis in higher plants, explained biological significance reduction in the number of chromosomes. He studied the process of fertilization, the phenomena of parthenogenesis and apogamy. The scientist’s work was of great importance for the preparation of the chromosomal theory of heredity and the development of ideas about the genetic unity of higher plants. Improved the technique cytological studies. Co-author of the republished course of botany (Textbook of Botany, 1894; 30th edition - 1971), translated into a number of languages, including Russian.
Chistyakov Ivan Dorofeevich (1843–1877), Russian botanist. He graduated from Moscow University (1868) and was retained there, from 1871 he became a professor and head of the Botanical Garden. Founder of the Moscow school of embryologists and plant cytologists. One of the first to observe and describe mitosis in plants (1874).
Appendix 2. Terms
(The underlined words are the students' correct choices.)
File No. 1 (blue)
Mitosis, prophase, metaphase, anaphase, telophase, amitosis, cell cycle, photosynthesis.
File No. 2 (green)
Meiosis, 1st division, prophase 1, metaphase 1, anaphase 1, telophase 1, crossing over, assimilation, dissimilation.
File No. 3 (red)
Meiosis, 2nd division, prophase 2, metaphase 2, anaphase 2, telophase 2, interphase, polymers.
Appendix 3. Definitions
File No. 1 (blue)
Mitosis is a method of dividing eukaryotic cells in which each of the two newly emerging cells receives the same genetic material as in the original cell.
Prophase– chromosomes spiral and become clearly visible in a light microscope, the nucleolus disappears, two centrioles diverge to the poles of the cell, microtubules extending from them form a spindle, the nuclear envelope disintegrates.
Anaphase
Telophase– a nuclear membrane is formed around the chromosomes collected at the poles, the chromosomes despiral (from compact they turn into thin and long, indistinguishable in a light microscope). Nucleoli are formed. This stage ends with cytokinesis (division of the cytoplasm) and the formation of two diploid cells.
Amitosis– direct division of nuclei by constriction does not always end with cytokinesis; as a result, multinucleated cells usually appear. After amitosis, cells are not able to begin mitotic division. This process is characteristic of dying cells.
Cell cycle– the period of cell life from division to division, the main part of the cell’s life.
Interphase– period between divisions (lat. inter- between). The cell grows rapidly, the number of structures and substances in the cell increases, the number of chromosomes doubles.
(Definition interphase in this file onlyno, but the definition metaphases absent.)
File No. 2 (green)
Meiosis(Greek meiosis
1st division- first division of meiosis.
Prophase 1– chromosomes begin to condense and become visible under a light microscope. Then homologous chromosomes begin to move closer to each other - to conjugate. A pair of conjugating chromosomes is called a bivalent (each bivalent is formed by 4 chromatids). DNA replication ends. The phase ends with the disappearance of the nuclear membrane and nucleolus.
Metaphase 1– bivalents line up in the equatorial plane of the cell. The spindle filaments are attached to the centromeres.
Anaphase 1– the bivalent breaks up into two chromosomes, which go to different poles of the cell.
Telophase 1– chromosomes decondense (from compact they turn into thin and long ones, indistinguishable in a light microscope). A nuclear envelope is formed around the chromosomes collected at the poles. Nucleoli are formed. This stage ends with cytokinesis (division of the cytoplasm) and the formation of two diploid cells.
Metaphase
(Definition metaphases in this file onlyno, but the definition crossing over absent.)
File No. 3 (red)
Meiosis(Greek meiosis– reduction) is a method of dividing eukaryotic cells, in which a reduction (decrease) in the number of chromosomes occurs, i.e. From a diploid (containing a double set of chromosomes) cells, haploid (containing a single set of chromosomes) cells are formed.
2nd division- second division of meiosis.
Prophase 2– chromosomes spiral and become clearly visible in a light microscope, the nucleolus disappears, two centrioles diverge to the poles of the cell, microtubules extending from them form a spindle.
Metaphase 2– all chromosomes line up in the equatorial plane of the cell; at this stage they can be clearly distinguished and counted in the cell.
Anaphase 2- the stage during which sister chromatids, which have become independent chromosomes, diverge to opposite poles of the cell.
Telophase 2– a nuclear membrane is formed around the chromosomes collected at the poles. Chromosomes despiral (from compact they turn into thin and long ones, indistinguishable under a light microscope). Nucleoli are formed. This stage ends with cytokinesis (division of the cytoplasm) and the formation of four haploid cells.
Crossing over(English) сrossing-over– precross) – exchange of identical sections of homologous chromosomes.
(Definition crossing over in this file onlyno, but the definition interphase absent.)
So meticulously described in any textbook. Is there really anything else that needs to be added here?
But don’t rush to conclusions, but please rely on my experience as a biology tutor. What we will talk about today may be useful to many. And we will talk about the misunderstandings that arise during exams when answering these questions.
And in general about possible errors youth, when we sometimes let the most important information in life go unnoticed...
Again, perhaps I’ll start with some criticism of textbooks. The topic of division is so important that it is given a lot of space. It would seem that nothing else could be better : To explain the processes, a pile of color illustrations and various diagrams are provided.
Mitosis is the four stages of division. Meiosis - as many as eight stages of division, indicating not only the names of the processes themselves, but also detailed description of what happens to which cellular “thing” at each stage.
I agree that in order to pass the exam, all these “meticulous details” have to be learned, or rather memorized. That is, all this is remembered for a short time. But because of the pile of private little things, the most important thing slips away, and then the very essence and meaning of the phenomena is not remembered.
And what should really stay in your head for a long time, so that in the end you don’t do the most simple mistakes neither in exams nor, more importantly, in your life.
1. At least do not confuse the names of the processes themselves with each other
Otherwise, it turns out like with concepts - the names of the processes themselves are remembered, but in 50% of cases it’s exactly the opposite.
After “pulling away” to the poles of the mother cell in anaphase of mitosis one chromatid chromosomes, in the newly formed two daughter cells the DNA content becomes identical to the original mother cell - 2n2с.
Since as a result of mitosis, two full-fledged cells are formed from one original cell (they say “mother cell”), with genetic information completely identical to the original cell, mitosis can be called the term “reproduction” - this is asexual reproduction.
What is the essence of meiosis?
The word “meiosis” itself can be pronounced softly, in a sing-song voice (m-ee-e-y-oz) - this is a type of reduction cell division, leading to the formation of four from one cell, but with a half, haploid set of chromosomes ( 1n1с).
And now, remember my seditious thought. Meiosis, unlike mitosis, is not reproduction. This is a way of forming haploid cells (spores in plants and gametes in animals). Gametes only after the process of fertilization, which in in this case and is sexual reproduction, will serve to form a new organism.
Once again, I draw your attention to the fact that in animal organisms, cells of specialized tissues of the gonads are divided by meiosis, from which gametes or germ cells are formed. In plants, spores are formed by meiosis, and then gametes are formed by mitosis.
Meiosis, like mitosis, is preceded by the doubling of the cell’s genetic material, but meiosis occurs in two stages: meiosis I and meiosis II .
The reduction in the number of chromosomes itself, that is, a decrease in their number by half, occurs after the first stage of meiosis, since during the prophase of meiosis I conjugation of homologous chromosomes occurred, but the chromosomes in the two formed haploid cells still remain bichromatid ( 1n2c).
There is very little time between meiosis I and meiosis II, additional DNA doubling Not is happening and again each cell forms two haploid cells ( 1n), but they are already “normal” - monochromatid ( 1s).
2. What else is very important for anyone to remember, especially young people - potential parents
It is during meiosis, during the maturation of germ cells, that as a result of the conjugation of homologous chromosomes, any “shuffling” of genetic material between homologous chromosomes can occur in prophase I of meiosis - crossing over.
And at this moment of formation of both eggs and sperm, it is especially important that there are no adverse factors affecting the human body ( nervous shocks, large doses medicines, alcohol, nicotine and other drugs) that can lead to crossing-over errors during meiosis (and, therefore, to the appearance of genetic inferior offspring).
3. What else should you pay attention to?
Even if you remember well that all somatic cells of the body reproduce by mitosis, and meiosis is the method of formation of sex cells, the following mistake is made.
Yes, meiosis is a way to form germ cells, but... But only at organisms !!! Again, I want to emphasize that all higher plants (mosses, ferns, gymnosperms and angiosperms) undergo meiotic division controversy! Subsequently, from haploid spores by mitoses plants - gametes.
The authors of school textbooks should pay attention to this, since the writers of test items like (and they are right) to include questions on the fundamental processes of the functioning of living systems. And the methods of reproduction of cells of living organisms and methods of sexual reproduction of organisms of different taxa are precisely such processes.
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Now I’m writing and thinking what a pity it is that this blog is still invisible on the Internet (I hope “for now”). After all, the information in this post is useful to everyone, especially the younger generation, so that they don’t end up paying for their children’s health for the rest of their lives due to ignorance.
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