1. A permanent preparation was studied at low magnification, but when transferred to high magnification, the object is not visible, even with correction with macro- and micrometer screws and sufficient lighting. It is necessary to determine what this may be due to?
2. The preparation is placed on the microscope stage, which has a mirror at the base of the tripod leg. There is weak artificial light in the auditorium. The object is clearly visible at a low magnification, however, when trying to examine it with a magnification of the x40 lens, the object is not visible in the field of view, a dark spot is visible. It is necessary to determine what this may be due to?
3. The study preparation was damaged: the glass slide and coverslip were broken. Explain how this could happen?
4. The total magnification of the microscope is 280 in one case, and 900 in the other. Explain what lenses and eyepieces were used in the first and second cases and what objects they allow you to study?
5. You have been given a permanent preparation for examination of the object at high magnification of the microscope. How should the preparation be positioned in order to see the object at high magnification? Explain why incorrect manipulations with the specimen can only be detected at high magnification.
6. Explain what prospects can expect a cell of epithelial tissue that does not have centrioles?
7. A 7-fold endoreduplication occurred in the diploid cell.
How much hereditary material does she have?
8. One of the fundamental initial conclusions of classical genetics is the idea of the equality of the male and female sexes in the transmission of hereditary information to offspring. Is this conclusion confirmed by a comparative analysis of the entire amount of hereditary information introduced into the zygote by the spermatozoon and the egg?
9. After the cell exited mitosis, a mutation occurred in the gene carrying the program for the synthesis of the helicase enzyme.
How will this event affect the mitotic cycle of the cell?
10. After fertilization, a 46,XX zygote was formed, from which a female body should be formed. However, during the first mitotic division (fragmentation) of this zygote into two blastomeres, one of the two X chromosomes did not divide into two chromatids and completely moved to the pole in anaphase. The behavior of the second X chromosome passed without deviations from the norm. All subsequent mitotic cell divisions during embryogenesis also proceeded without violations of the mitosis mechanism.
What will be the chromosome set of cells of an individual that develops from this zygote and (presumably) the phenotypic features of this organism?
11. It is well known that identical (monozygous) twins are genetically identical. According to the phenotype, in the normal course of the cytological processes of their formation and development under the same environmental conditions, they are similar to each other "like two drops of water."
Can monozygotic twins be of different sexes - a boy and a girl? If they can't, then why? And if they can, then as a result, what are the disturbances in the mitotic cycle of the dividing zygote?
2. Situational tasks on the topic "Molecular bases of heredity and variability"
Genome - General Questions
1. Explain the reason for the situation in which the gene of a eukaryotic cell, which occupies a DNA region of 2400 base pairs, encodes a polypeptide consisting of 180 amino acid residues.
Answer: To encode 180 amino acid residues, 540 nucleotides (180 triplets) of the DNA template chain are sufficient. Plus the same amount - the coding chain. Total - 1080 nucleotides or 540 pairs of nucleotides.
2. When analyzing the nucleotide composition of bacteriophage DNA M 13, the following quantitative ratio of nitrogenous bases was found: A-23%, G-21%, T-36%, C-20%. How can one explain the reason that in this case the principle of equivalence established by Chargaff is not observed?
Answer: The reason is that the M13 bacteriophage (like most phages) contains single-stranded DNA.
A microscope uses the magnifying power of convex lenses to magnify very small objects. On fig. P.2.3 shows a microscope with details of its structure. A microscope is an expensive instrument, so you must handle it carefully and do not neglect the following rules:
1. Store the microscope in a drawer (or under a hood) to protect it from dust.
2. Take it out of the drawer with both hands and put it back gently to avoid shaking.
3. The lenses must be clean, for this they must be wiped with a piece of cloth.
4. The microscope should always be focused by moving the tube up from the specimen. Otherwise, it is very easy to damage the preparation.
5. Keep both eyes open and look with them in turn.
Setting the Microscope to Operate at Low Magnification
1. Place the microscope on a table and sit in a comfortable position. The object to be examined on the microscope stage must be illuminated. To do this, use a special illuminator, light from a window or from a table lamp. In the last two cases, the concave surface of the mirror under the object stage is used. Using a mirror, light is directed through a hole in the stage. If a suitable condenser is available, a flat mirror surface is used to direct light through it.
2. Use the coarse adjustment screw to lift up the microscope tube and turn the turret until the low magnification objective (× 10 or 16 mm) fits into the slot in the tube (you will hear a click).
3. Place the specimen you are about to examine on the microscope stage so that the material under the coverslip is above the middle of the hole in the microscope stage.
4. Looking at the stage and specimen from the side, lower the tube with the coarse adjustment screw until the low power objective is about 5 mm from the specimen.
5. While looking through the microscope, turn the coarse adjustment screw until the object is in focus.
Setting up the microscope for high magnification
1. When working with a high magnification lens, artificial light is needed to create sufficient illumination. To do this, use a table lamp or a special illuminator for a microscope with a frosted light bulb. When working with an incandescent lamp, it is necessary to place a sheet of paper between it and the microscope. Turn the mirror upside down so that the light is reflected back into the microscope.
2. Focus the condenser without removing the specimen from the stage. Raise the condenser so that the distance between it and the stage is no more than 5 mm. While looking through the microscope, turn the coarse adjustment screw until the object is in focus. Now focus the condenser until the lamp image is superimposed exactly on the preparation. Place the condenser slightly out of focus so that the image of the lamp disappears. Now the lighting should be optimal. A diaphragm is built into the condenser. It regulates the size of the hole through which light passes. This hole should be opened as wide as possible. Thus, the maximum clarity of the image is achieved (see Fig. A.2.3).
3. Rotate the turret until the high magnification objective (×40 or 4mm) fits into the slot. If focus has already been set at low magnification, turning the turret will automatically position the high magnification lens at approximately focus. Always focus by moving the lens up using the fine adjustment screw.
4. If the focus is not established when moving the lens with high magnification lenses, do the following: looking at the stage from the side, lower the microscope tube until the lens almost touches the preparation. Watch the reflection of the objective lens on the preparation and ensure that the lens almost touches its reflection.
5. While looking into the microscope and turning the fine adjustment screw, slowly raise the objective until the image is in focus.
Increase
Magnification of an object under a microscope occurs with the help of an eyepiece and an objective lens (Table A.2.1).
Oil immersion
In order to obtain higher magnification than with a normal high magnification lens, an oil immersion lens must be used. The ability of a lens to collect light is greatly enhanced if liquid is placed between the objective lens and the coverslip. The liquid must have the same refractive index as the lens itself. Therefore, cedar oil is usually used as a liquid.
1. Put the preparation on the stage and focus the image in the same way as when working with a normal high magnification. Replace the high magnification lens with an oil immersion lens.
2. Drop a drop of cedar oil on a cover glass directly above the object under study.
3. Focus the image again, now at low magnification, then rotate the turret to mount the objective with the oil immersion lens so that its tip touches the oil drop.
4. While looking through the microscope, focus the lens very carefully with the fine adjustment screw. Remember that the focal plane of the lens is only 1 mm from the surface of the coverslip.
5. When finished, wipe the oil off the lens with a soft cloth.
| 1. | Wash and dry your hands |
| 2. | Put on gloves |
| 3. Preparing the microscope for work: | |
| 3.1. | Set the microscope on the desktop at a distance of 3-5 cm from the edge, unwind the cord, plug the plug into the socket. |
| 3.2. | Set the low power lens (8x) at a distance of about 1 cm (focal length of the low power lens) |
| 3.3. | Bring the condenser into working position, slightly open the diaphragm. |
| 3.4. | Bring the binocular head into working position |
| 3.5. | Turn on the illuminator |
| 4. Work at low and medium magnification: | |
| 4.1. | Place the specimen on the stage with the coverslip up. |
| 4.2. | By moving the macrometer screw, find the focus of low magnification |
| 4.3. | Consider the preparation, select the area to be studied at higher magnification and place it in the center of the field of view |
| 4.4. | Without changing the focus (without raising the tube), turn the turret and install a stronger objective (40x). |
| 4.5. | Raise the condenser, open the diaphragm |
| 4.6. | Focus the object with the micrometer screw by turning it half a turn forward or backward |
| 5. Completion of work | |
| 5.1. | Turn off the light, set the revolver to a low magnification, remove the preparation from the stage, close the diaphragm, lower the condenser, lower the tube, bring the eyepieces together in the binocular head |
| 5.2. | Unplug the cord from the outlet, wrap it carefully around the base of the microscope. Put a cover on the microscope. |
| 5.3. |
3- the preparation prepared by the laboratory assistant is of poor quality, because contains dark brown clumps. This artifact (pigment grains) was formed as a result of the reaction of acid formalin with hemoglobin.
4- To remove the pigment, sections must be placed:
in 1-5% ammonia solution (for 15-20 minutes),
70% alcohol (for 15-20 minutes),
1% KOH in 80° alcohol (10 min).
The sections are then rinsed with water.
Having stained the deparaffinized section with hematoxylin, the medical laboratory technician was dissatisfied with the result: the background of the preparation was dark, the structure of the nuclei was not visible.
EXERCISE 1
- Indicate which stage of preparation staining was performed unsatisfactorily; prepare the workplace for staining preparations
- Prepare preparation for staining
- Stain the slide with hematoxylin and eosin.
- Tell us about the rules for archiving histological preparations
1. The dark background of the preparation and the fuzzy structure of the nuclei may appear with poor differentiation of the preparation with hydrochloric alcohol.
2-3 deparaffinization and staining of preparations with hematoxylin-eosin
| 1. | Wash and dry your hands |
| 2. | Put on gloves |
| 3. Prepare the workplace: | |
| 3.1. | Prepare tray, napkins, hourglass, parffin slices |
| 3.2. | Place a tripod on the tray |
| 3.3. | Make a battery for dewaxing by arranging the solutions in the following sequence: xylene (1) - xylene (2) - alcohol 100 - alcohol 96 (1) - alcohol 96 (2) - alcohol 70 distilled water |
| 3.4. | Make up a battery for staining by arranging the solutions in the following sequence: distilled water - hematoxylin - distilled water - tap water - eosin distilled water |
| 4. dewaxing | |
| 4.1. | Place sections in xylene solution 1-2 for 3-5 minutes in each |
| 4.2. | Carry out sections on a battery of alcohols of descending concentration |
| 4.3. | Rinse sections in distilled water. |
| 5. staining of sections with hematoxylin-eosin | |
| 5.1. | Transfer deparaffinized sections to distilled water. |
| 5.2. | stain with hematoxylin 2-5 min |
| 5.3. | rinse with distilled water - 1 min |
| 5.4. | rinse with tap water - 3-5 min |
| 5.5. | stain with 1% eosin solution - 0.5-1 min |
| 5.6. | rinse quickly with distilled water |
| 6. Completion of work | |
| 6.1. | Disassemble the battery, put the bottles with solutions in place, dispose of the used wipes |
| 6.2. | Remove gloves and place in disinfectant |
4. archiving
After completing the cutting of pieces from the surgical material, the medical laboratory technician placed all instruments, used gloves, and the remaining material in a disinfectant solution.
EXERCISE 1
- Evaluate the actions of the laboratory assistant and prepare the workplace for taking surgical material
- Mark and fix the material
- Disinfect used utensils and tools
- Tell us about the rules for archiving the material remaining after the study (wet archive)
1. Medical Lab Technician Wrong. The remaining material should be placed in 10% neutral formalin (wet archive).
2-3-taking, marking and fixing the material
| 1. | Wash and dry your hands |
| 2. | Put on gloves |
| 3.1. | spread an oilcloth (place a tray) |
| 3.2. | put on an oilcloth (tray): a container with a wide mouth and a ground-in lid filled with 10% neutral formalin; histological cassettes, tweezers |
| 4. marking and fixing the material | |
| 4.1. | open the cassette (put a gauze pad on the tray) |
| 4.2. | place in the cassette (on a napkin) a piece of material cut out by the doctor |
| 4.3. | Prepare a paper label: write with a simple pencil the serial number under which the material is registered in the journal |
| 4.4. | Place the label in the cassette (on a napkin with material) |
| 4.5. | Close the cassette, you should hear a click (tie a napkin). |
| 4.6. | Place the cassette (napkin) with the material into a wide-mouth container filled with 10% neutral formalin. In this case, the volume of the fixative should exceed the volume of the material to be fixed by 10-20 times. |
| 4.7. | Close the container with a lid and leave under the hood for the time required for fixation (1 day). |
| 5. Completion of work | |
| 5.1. | put the used instruments in a container for disinfection, exposure 1 hour. |
| 5.2. | wipe the oilcloth (tray) with a rag soaked in a disinfectant solution. |
| 5.3. | throw the rags into a container with a disinfectant solution, exposure 1 hour. |
| 5.4. | remove rubber gloves, immerse them in a container with disinfectant, exposure 1 hour. |
4. wet archive
A medical laboratory technician was given the task of pouring surgical material into paraffin. To this end, he used the following algorithm of actions: alcohol 70% - alcohol 96% (1) - alcohol 96% (2) - alcohol 100% - xylene (1) - xylene (2) - a mixture of xylene with paraffin (at 37º C) - paraffin (56º C).
2. Demonstrate material dehydration technique
3. Embed material in paraffin
4. Tell us about the rules for archiving paraffin blocks
Medical laboratory technician used the correct algorithm of actions
1-3 compaction of the material and pouring it into paraffin.
| 1. | Wash and dry your hands |
| 2. | Put on gloves |
| 3. Prepare the workplace: | |
| 3.1. | Prepare a battery for dehydration and compaction of the material |
| 3.2. | Prepare tools. |
| 3.3. | Prepare molds for pouring. |
| 3.4. | Prepare a container with cold water to quickly cool the paraffin. |
| 4. dehydration | |
| 4.1. | Place the washed material in 70% alcohol. |
| 4.2. | Demonstrate how material is transferred from one reagent to another, indicate the holding time in each reagent. |
| 5. Pouring material | |
| 5.1. | Remove paraffin containers (2nd portion) and filling paraffin from the thermostat. |
| 5.2. | Place the paraffin containers in a water bath. |
| 5.3. | With warm tweezers, transfer the material to the center of the paper mold. |
| 5.4. | Fill the mold with paraffin for pouring. |
| 5.5. | Immerse the molds to the brim in cold water until a film appears on the surface. |
| 5.6. | Completely submerge the mold in water. |
| 6. Completion of work | |
| 6.1. | Remove the paraffin containers from the thermostat. |
| 6.2. | Dispose of the cassette (gauze). |
| 6.3. | Remove gloves and place in disinfectant. |
4.archiving
When making paraffin sections from a block of skin with hair, a medical laboratory technician experienced difficulty: the sections were covered with stripes and torn.
1. Name the possible reasons for the difficulty in cutting this block.
2. Is it possible to fix this artifact?
3. Technique for applying an adhesive medium to glass slides. What can be used as an adhesive material when sticking sections on glass slides?
1. The causes of breaks and stripes on paraffin media can be:
Cutting surface defect
Sticking of paraffin on the cutting edge of the blade
Poor quality paraffin
2. To eliminate the artifact, you should:
Move the blade a little and see if the location of the scratches on the cut has changed with it. If the scratches have also shifted, then replace the blade.
· Clean the blade with a brush dipped in xylene. When brushing, the brush should be moved upwards away from the incisal edge, but never downwards onto the incisal edge.
· Sample duplicate should be decalcified or refilled.
3. As an adhesive material for gluing sections on a glass slide, you can use ready-made gelatin adhesive for sections or prepare your own adhesive medium based on whey or egg white with glycerin.
When starting to stain a paraffin section from a piece of thyroid gland, the medical laboratory technician forgot to deparaffinize.
1. Can a non-deparaffinized preparation be stained? What is the purpose of deparaffinization?
2. Is it possible to correct such an error?
3. Types of the most commonly used histological stains.
1. A non-deparaffinized preparation cannot be stained. Dewaxing is used to remove paraffin from the section. The dewaxed preparation can be dried and stored. Paraffin solvent - xylene should be changed after processing 100-200 sections.
2. Correction is not possible.
3. In histological practice, basic (alkaline), acid and neutral dyes are used. Basic dyes stain structures of an acidic nature. First of all, cell nuclei (DNA, chromatin, nucleolar RNA). This staining is called basophilic. Among these dyes, the most common nuclear dye is hematoxylin. Cytoplasmic structures with basic properties are stained with acidic dyes. The most common acid dye is eosin. Among the neutral dyes, the most commonly used dye is Sudan (Sudan III, IV), which dissolves in fats. It is used to detect fatty inclusions in the cytoplasm of cells.
| signs | prokaryotes | eukaryotes |
| 1. Morphologically formed and separated from the cytoplasm by the nuclear membrane of the nucleus. | ||
| 2. Number of chromosomes | ||
| 3. Chromosomes are circular | ||
| 4. Chromosomes are linear | ||
| 5. Ribosome sedimentation constant | ||
| 6. Localization of ribosomes: - scattered in the cytoplasm - attached to the endoplasmic reticulum | ||
| 7. Golgi apparatus | ||
| 8. Lysosomes | ||
| 9. Vacuoles surrounded by a membrane | ||
| 10. Gas vacuoles not surrounded by a membrane | ||
| 11. Peroxisomes | ||
| 12. Mitochondria | ||
| 13. Plastids (in phototrophs) | ||
| 14. Mesosomes | ||
| 15. Microtubule system | ||
| 16. Flagella (if present): - diameter - in diameter they have a characteristic arrangement of microtubules "9 + 2" | ||
| 17. Membrane contains: - branched and cyclopropane fatty acids - polyunsaturated fatty acids and sterols | ||
| 18. Cell walls contain: - peptidoglycan (murein, pseudomurein) - teichoic acids - lipopolysaccharides - polysaccharides (cellulose, chitin) | ||
| 19. Cell reproduction occurs by: - simple division - mitosis | ||
| 20. Characteristic division of the protoplast by internal membranes into functionally different compartments | ||
| 21. Three-dimensional cytoskeleton, includes microtubules, intermediate and actin filaments | ||
| 22. Communication between compartments is carried out due to cyclosis, endo and exocytosis | ||
| 23. Presence of endospores |
5.4. Final control of knowledge:
- Questions on the topic of the lesson:
1. Explain the essence of the science "Biology" and its significance in medicine.
2. Justify why we study Man as an object of medicine, first of all, as a representative of the animal world.
3. System of classification of living organisms.
4. The idea of non-cellular and cellular forms of life.
5. Concepts about pro- and eukaryotes.
6. Diversity of cellular life forms.
7. The idea of magnifying devices, the history of their discovery and improvement.
8. The importance of magnifying instruments in the development of biology and medicine.
- Test tasks:
1. Stage refers to part of the microscope
1) mechanical
2) optical
3) lighting
4) dissecting
2. The components of the illumination part of the microscope are arranged
1) in the sockets of the revolver
2) at the top of the tube
3) at the base of the tripod foot
4) on the subject table
3. Purpose of macrometer screw
1) moving the holder with the eyepiece in the vertical direction
2) moving the holder with the eyepiece in the horizontal direction
3) moving the table with the object in the vertical direction
4) moving the table with the object in the horizontal direction
4. The magnification of the eyepiece of the Biolam microscope can be
5. Magnification of the immersion objective
- Solution of situational problems:
Task #1
A permanent preparation was studied at low magnification, but when transferred to high magnification, the object is not visible, even with correction with macro- and micrometer screws and sufficient lighting. It is necessary to determine what this may be due to?
Task #2
The preparation is placed on the microscope stage, which has a mirror at the base of the tripod leg. There is weak artificial light in the auditorium. The object is clearly visible at a low magnification, however, when trying to examine it with a magnification of the x40 lens, the object is not visible in the field of view, a dark spot is visible. It is necessary to determine what this may be due to?
6. Homework to understand the topic of the lesson(according to the guidelines for extracurricular work on the topic of the lesson)
1. Preparation of micropreparations of representatives of prokaryotic (bacterial cells) and eukaryotic organisms (nerve cells, onion skin cells).
- Mandatory
1. Biology in 2 books. Medical textbook. specialist. universities / ed. V.N. Yarygina. M.: Higher. school, 2005.
2. Guide to practical exercises in biology: textbook / ed. V.V. Markin. M.: Medicine, 2006.
- Additional
1. General and medical genetics: textbook / ed. V.P. Shchipkov. M.: Academy, 2003.
2. Ginter E.K. Medical genetics: textbook. M.: Medicine, 2003.
3. Bochkov N.P. Clinical genetics: textbook. M.: GEOTAR-Media, 2004.
4. Severtsov A.S. evolution theory. M.: Vlados, 2005.
5. Zhimulev I.F. General and molecular genetics: a textbook. Novosibirsk: Sibuniverizd., 2007.
7. Grigoriev A.I. Human ecology: textbook. M.: GEOTAR-Media, 2008.
8. Chernova N.M. General ecology: textbook. M.: Bustard, 2004.
- Electronic resources
1. Electronic library on discipline Biology. Moscow: Russian doctor, 2003.
2. IHD KrasGMU
4. DB Medicine
5. DB Medical Geniuses
Moscow: Agropromizdat, 1988. - 271 p.
ISBN 5-10-000614-5
Download(direct link) :
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A permanent microtome preparation with longitudinal sections of the roots is first viewed at low magnification of the microscope. A cap is clearly visible at the root tip, which protects the growth cone from damage during growth.
in the soil. This is followed by a cone of root growth, or a zone of cell division (about 2 mm). Behind the growth cone there is a zone of extension, where the cells are elongated, and then a zone of absorption with root hairs. Mitosis is studied on the meristematic cells of the root growth cone, where there are many dividing cells. The meristem consists of rows of rectangular cells. Each row of cells originates from a single cell.
After examining the root at low magnification, the preparation should be viewed with a 40X objective.
Interphase. On conventional permanent preparations, the interphase state of the nucleus is characterized by a delicate chromatin structure. Chromosomes at this time are strongly despiralized and are not detected. The nuclei have a rounded shape and a homogeneous granular structure. Of the other components of the nucleus, the nucleoli are clearly visible. When using some nuclear fixatives, such as Brodsky, and staining preparations with hematoxylin, one can see with immersion under a microscope (lens 90X) in the nucleus of a plant cell a chromatin network and large chromatin grains forming chromocenters.
After completion of interphase, cells enter mitosis. Cell division usually begins with transformations in the nucleus.
In prophase (Fig. 47), the nucleus increases, and chromosome threads become clearly visible in it, which in this
Rice. 47. Mitosis in the cells of the onion root Allium sera (microtomy preparation):
1 prophase; "2 - metaphase; I - anaphase; 4 - body phase; 5 - interphase.
time is already spiralized. Each chromosome after doubling in interphase consists of two sister chromatids connected by one centromere. At the end of prophase, the nuclear envelope and nucleoli usually disappear. On preparations, one can always find early and late prophases and compare them with each other. Chromosomal threads are more clearly visible in late prophase, and it is often possible to notice that they are doubled.
Metaphase. After the nuclear envelope disappears, it can be seen that the chromosomes have reached maximum condensation, become shorter and move towards the equator of the cell, located in the same plane. This period in mitosis is called metaphase. The cell already has a mitotic (achromatic) spindle, consisting of supporting and pulling filaments. The first of them stretch from one pole to another, and the second connect the centromeres of chromosomes with the poles.
On preparations stained with hematoxylin, the filaments of the mitotic spindle are not always visible, since this dye is nuclear. However, in the training film and on other preparations, it is clearly seen that each chromosome, being attached to the mitotic spindle, consists of two parallel chromatids.
The doubled chromosome in metaphase is usually located perpendicular to the filaments of the mitotic spindle and at an equal distance from the poles. The centromeres of all chromosomes are in the same equatorial plane, which is very convenient for counting chromosomes and studying their morphology. "
Microtome preparations for chromosome counting are usually made from root cross sections so that the metaphase is visible from the pole. In this position, it is clearly seen that the chromosomes are located at some distance from each other. At this time, they can be sketched and counted.
Anaphase begins with the division of the centromere, and then the separation of the chromatids occurs. Sister chromatids of each chromosome diverge to different poles. This is how the exact distribution of the genetic material occurs, and at each pole there is the same number of chromosomes as the original cell had before they were duplicated. For example, rye has 14 chromosomes in its somatic cells. In metaphase, she
14 doubled (dichromatid) "chromosomes. In anaphase, after the sister chromatids diverge at the poles, there are again 14 chromosomes at the poles.
After separation of the centromere, each chromatid acquires the functions of an independent chromosome.
The movement of chromatids to the poles occurs due to the contraction of the pulling filaments and the elongation of the supporting filaments of the mitotic spindle. When watching a training film, it is clear that this process is very fast in comparison with other
different phases and is more difficult to catch. Therefore, anaphase is less common on preparations than prophase.
In telophase, the chromosomes at each pole undergo decondensation, i.e., a process opposite to what occurs in prophase. The contours of chromosomes lose their clarity, the mitotic spindle is destroyed, the nuclear envelope is restored and nucleoli appear. Thus, after various structural transformations, the slow-moving nucleus was divided into two daughter ones. During telophase, a cell wall is formed from the phragmoplast, which divides the entire contents of the cytoplasm into two equal parts - cytokinesis occurs. This is how mitosis ends.
The duration of individual phases of mitosis can be judged from in vivo observations. It has been established that in the pea endosperm, prophase lasts 40 minutes, metaphase - 20, anaphase - 12, telophase - 1.10 minutes, i.e. the first and last phases of mitosis are the longest. The entire mitosis lasts about 3 hours. The duration of the mitotic cycle is several times longer. So, in horse beans (Vicia fab a), the entire mitotic cycle lasts 30 hours, with mitosis being 4 hours, and interphase - 26 hours, of which the period G \ - 12 hours, S - 6 hours, C2 - 8 hours. In green, the shortest mitotic cycle in some cells lasts 8 hours, and most cells go through it in 10–12 hours. Of the three periods of interphase, the Gi period is the most variable in duration. The kinetics of mitosis depends on various internal and external factors, the level of iloidality, the pH of the environment, hormonal activity, temperature, lighting conditions, etc.