Examples of methods of asexual reproduction. Forms of reproduction of organisms

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Reproduction is the ability of all organisms to reproduce their own kind, which ensures the continuity and acceptability of life. The main methods of reproduction are presented:

Asexual reproduction is based on cell division through mitosis, in which two equal daughter cells (two organisms) are created from each mother cell (organism). The biological role of asexual reproduction is the emergence of organisms identical to the parents in the content of hereditary material, as well as anatomical and physiological properties (biological copies).

The following are distinguished: methods of asexual reproduction: division, budding, fragmentation, polyembryony, sporulation, vegetative propagation.

Division- a method of asexual reproduction characteristic of unicellular organisms, in which the mother is divided into two or more daughter cells. We can distinguish: a) simple binary fission (prokaryotes), b) mitotic binary fission (protozoa, unicellular algae), c) multiple fission, or schizogony (malarial plasmodium, trypanosomes). During the division of the paramecium (1), the micronucleus is divided by mitosis, the macronucleus by amitosis. During schizogony (2), the nucleus is first divided repeatedly by mitosis, then each of the daughter nuclei is surrounded by cytoplasm, and several independent organisms are formed.

Budding- a method of asexual reproduction in which new individuals are formed in the form of outgrowths on the body of the parent individual (3). Daughter individuals can separate from the mother and move on to an independent lifestyle (hydra, yeast), or they can remain attached to it, in this case forming colonies (coral polyps).

Fragmentation(4) - a method of asexual reproduction, in which new individuals are formed from fragments (parts) into which the maternal individual breaks up ( annelids, starfish, spirogyra, elodea). Fragmentation is based on the ability of organisms to regenerate.

Polyembryony- a method of asexual reproduction in which new individuals are formed from fragments (parts) into which the embryo breaks up (monozygotic twins).

Vegetative propagation- a method of asexual reproduction, in which new individuals are formed either from parts of the vegetative body of the mother individual, or from special structures (rhizome, tuber, etc.) specifically designed for this form of reproduction. Vegetative propagation is typical for many groups of plants and is used in gardening, vegetable gardening, and plant breeding (artificial vegetative propagation).

Sporulation(6) - reproduction through spores. Controversy- specialized cells, in most species they are formed in special organs - sporangia. In higher plants, spore formation is preceded by meiosis.

Cloning- a set of methods used by humans to obtain genetically identical copies of cells or individuals. Clone- a collection of cells or individuals descended from a common ancestor through asexual reproduction. The basis for obtaining a clone is mitosis (in bacteria - simple division).

During sexual reproduction in prokaryotes, two cells exchange hereditary information as a result of the passage of a DNA molecule from one cell to another along a cytoplasmic bridge.

1) Division of single-celled organisms(amoeba). At schizogony(malarial plasmodium) it turns out not two, but many cells.

2) Sporulation

Spores of fungi and plants serve for reproduction.
Bacterial spores do not serve for reproduction, because One spore is formed from one bacterium. They serve to survive unfavorable conditions and dispersal (by wind).

3) Budding: daughter individuals are formed from outgrowths of the body of the mother organism (buds) - in coelenterates (hydra), yeast.

4) Fragmentation: The mother organism is divided into parts, each part turns into a daughter organism. (Spirogyra, coelenterates, starfish.)

5) Vegetative propagation of plants: reproduction using vegetative organs:

roots - raspberries
leaves - violet
specialized modified shoots:

bulbs (onions)
rhizome (wheatgrass)
tuber (potato)
mustache (strawberry)

Methods of sexual reproduction

1) With the help of gametes, sperm and eggs. Hermaphrodite- this is an organism that produces both female and male gametes (most higher plants, coelenterates, flat and some annelids, mollusks).

2) Conjugation green algae Spirogyra: two filaments of spirogyra come together, copulation bridges are formed, the contents of one filament flow into the other, one filament is formed from zygotes, the second from empty shells.

3) Conjugation in ciliates: two ciliates come closer, exchange sex nuclei, and then separate. The number of ciliates remains the same, but recombination occurs.

4) Parthenogenesis: a child develops from an unfertilized egg (in aphids, daphnia, bee drones).

Choose the one that suits you best correct option. Reproduction in which a daughter organism appears without fertilization from the body cells of the mother organism is called
1) parthenogenesis
2) sexual
3) asexual
4) seed

Answer

Asexual
Choose three options. Asexual reproduction is characterized by the fact that
1) the offspring has genes only from the mother’s body
2) the offspring is genetically different from the maternal organism
3) one individual participates in the formation of offspring
4) in the offspring there is a splitting of characters
5) offspring develop from an unfertilized egg
6) a new individual develops from somatic cells

Answer

Asexual EXCEPT
1. All but two of the terms listed below are used to describe asexual reproduction. Identify two terms that “fall out” from the general list and write down the numbers under which they are indicated.
1) schizogony
2) parthenogenesis
3) fragmentation
4) budding
5) copulation

Answer

2. All but two of the terms below are used to describe the asexual method of reproduction in living organisms. Identify two terms that “fall out” from the general list and write down the numbers under which they are indicated.
1) fragmentation
2) seed propagation
3) sporulation
4) parthenogenesis
5) budding

Answer

3. All but two of the examples below refer to asexual reproduction of organisms. Identify two examples that “fall out” from the general list and write down the numbers under which they are indicated.
1) reproduction by fern spores
2) reproduction of earthworms by fragmentation
3) ciliate-slipper conjugation
4) budding of freshwater hydra
5) parthenogenesis of bees

Answer

Asexual - SEXUAL CHARACTERISTICS
1. Establish a correspondence between the characteristics of the sexual and vegetative propagation and method of reproduction: 1) asexual, 2) sexual. Write numbers 1 and 2 in the correct order.
A) forms new combinations of genes
B) forms combinative variability
C) produces offspring identical to the mother’s
D) occurs without gametogenesis
D) due to mitosis

Answer

2. Establish a correspondence between the characteristics and methods of reproduction: 1) asexual, 2) sexual. Write numbers 1 and 2 in the order corresponding to the letters.
A) Haploid nuclei fuse.
B) A zygote is formed.
B) Occurs with the help of spores or zoospores.
D) Combinative variability appears.
D) Offspring are produced that are identical to the original individual.
E) The genotype of the parent individual is preserved over a number of generations.

Answer

3. Match the steps life cycle plants and methods of reproduction: 1) asexual, 2) sexual. Write numbers 1 and 2 in the order corresponding to the letters.
A) disputes are formed
B) accompanied by the fusion of gametes
B) sporophyte reproduces
D) the gametophyte reproduces
D) a zygote is formed
E) meiosis occurs

Answer

Asexual - SEXUAL EXAMPLES
1. Establish a correspondence between an example of reproduction and its method: 1) sexual, 2) asexual. Write numbers 1 and 2 in the correct order.
A) sporulation in sphagnum
B) seed propagation of spruce
B) parthenogenesis in bees
D) propagation by bulbs in tulips
D) laying eggs by birds
E) spawning of fish

Answer

2. Match concrete example and method of reproduction: 1) asexual, 2) sexual. Write numbers 1 and 2 in the correct order.
A) fern sporulation
B) formation of chlamydomonas gametes
B) formation of spores in sphagnum
D) yeast budding
D) fish spawning

Answer

3. Establish a correspondence between a specific example and the method of reproduction: 1) asexual, 2) sexual. Write numbers 1 and 2 in the correct order.
A) hydra budding
B) division of a bacterial cell into two
B) formation of spores in fungi
D) parthenogenesis of bees
D) formation of strawberry whiskers

Answer

4. Establish a correspondence between the examples and methods of reproduction: 1) asexual, 2) sexual. Write numbers 1 and 2 in the correct order.
A) live birth in a shark
B) division in two of the ciliate-slipper
B) parthenogenesis of bees
D) propagation of violets by leaves
D) fish spawning
E) hydra budding

Answer

5. Establish a correspondence between the processes and methods of reproduction of organisms: 1) sexual, 2) asexual. Write numbers 1 and 2 in the order corresponding to the letters.
A) laying eggs by lizards
B) penicillium sporulation
C) propagation of wheatgrass by rhizomes
D) parthenogenesis of daphnia
D) division of euglena
E) propagation of cherries by seeds

Answer

6. Establish a correspondence between the examples and methods of reproduction: 1) asexual, 2) sexual. Write numbers 1 and 2 in the correct order.
A) raspberry cuttings
B) formation of spores in horsetail
C) sporulation in cuckoo flax
D) fragmentation of lichen
D) parthenogenesis of aphids
E) budding in a coral polyp

Answer

7 Sat. Establish a correspondence between the examples and methods of reproduction: 1) asexual, 2) sexual. Write numbers 1 and 2 in the correct order.
A) formation of gametes in Chlamydomonas
B) sturgeon spawning
B) sporulation in mosses

D) division of amoeba vulgaris
D) fragmentation of mycelium in fungi
E) root suckers at the raspberry

Answer

8. Establish a correspondence between the examples and methods of reproduction: 1) asexual, 2) sexual. Write numbers 1 and 2 in the order corresponding to the letters

A) tissue culture
B) unfertilized eggs
B) tubers
D) eggs

D) somatic cells
E) parts of the rhizome

Answer

VEGETATIVE EXCEPT
1. All of the following plant growing techniques, except two, are classified as vegetative propagation. Identify two techniques that “fall out” from the general list, and write down the numbers under which they are indicated.
1) division of tubers
2) propagation by rhizome
3) obtaining sprouts from seeds
4) artificial insemination
5) formation of layering

Answer

2. All the examples below, except two, characterize vegetative propagation. Identify two examples that “fall out” from the general list and write down the numbers under which they are indicated.
1) obtaining heterotic hybrids
2) propagation by dividing the bush
3) use of root suckers
4) propagation by seeds
5) rooting of cuttings

Answer

VEGETATIVE - SEXUAL
1. Establish a correspondence between the peculiarity of reproduction and its type: 1) vegetative, 2) sexual. Write numbers 1 and 2 in the correct order.
A) due to the combination of gametes
B) individuals are formed by budding
C) ensures the genetic similarity of individuals
D) occurs without meiosis and crossing over
D) due to mitosis

Answer

SEXUAL
Select three characteristics characteristic of sexual reproduction of seed plants and write down the numbers under which they are indicated.
1) Sperm and eggs are involved in reproduction
2) As a result of fertilization, a zygote is formed
3) During the process of reproduction, the cell divides in half
4) The offspring retains all the hereditary characteristics of the parent
5) As a result of reproduction, new characteristics appear in the offspring
6) Vegetative parts of the plant participate in reproduction

Answer

All of the above characteristics, except two, are used to describe the sexual reproduction of animals. Find two characteristics that “fall out” from the general list and write down the numbers under which they are indicated.
1) Gametes are formed as a result of gametogenesis.
2) As a rule, the reproduction of chordates involves individuals of different sexes.
3) The starting material for the formation of gametes is spores.
4) The offspring combines the characteristics of both parents.
5) The chromosome set of the gamete is formed as a result of division by mitosis.

Answer

SEXUAL EXCEPT
All but two of the terms below are used to describe the sexual reproduction of organisms. Identify two terms that “fall out” from the general list and write down the numbers under which they are indicated.
1) gonad
2) dispute
3) fertilization
4) ovogenesis
5) budding

Answer

SEXUAL - Asexual DIFFERENCES
1. Select two differences between sexual and asexual reproduction.
1) sexual reproduction energetically more favorable than asexual
2) two organisms participate in sexual reproduction, and one organism in asexual reproduction
3) during sexual reproduction, offspring are exact copies of parents
4) somatic cells participate in asexual reproduction
5) sexual reproduction is possible only in water

Answer

2. Choose three correct answers out of six and write down the numbers under which they are indicated. What is the difference between sexual and asexual reproduction?
1) promotes the appearance of modifications
2) increases the number of offspring
3) enhances the genetic diversity of offspring
4) increases the fertility of individuals
5) forms new combinations of genes
6) leads to a variety of combinations of alleles in gametes

Answer

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Choose three correct answers out of six and write down the numbers under which they are indicated. Bacterial spores, unlike fungal spores,
1) serve as an adaptation to endure unfavorable conditions
2) perform the function of nutrition and breathing
3) NOT used for reproduction
4) ensure distribution (settlement)
5) are formed by meiosis
6) are formed from the mother cell by loss of water

Answer

All but two of the following organisms reproduce by spores. Identify two organisms that “drop out” from the general list. Write down the numbers under which they are indicated.
1) mushroom mukor
2) cholera vibrio
3) tuberculosis bacillus
4) shield fern
5) cuckoo flax

Answer

One of the main properties of an animal organism is the ability to reproduce, or self-reproduction.

In a multicellular animal organism, cells reproduce throughout life by nuclear division, or mitosis (karyokinesis). After mitosis, each daughter cell has the same number of chromosomes (diploid set of chromosomes) and the same type as in the mother cell.

In developing germ cells, after two successive divisions, during which the chromosomes are split longitudinally only once, the number of chromosomes decreases by half (the haploid set of chromosomes). This division is called meiosis. During reproduction as a result of the fusion of a sperm and an egg cell, which have a haploid set of chromosomes, the set of chromosomes in the fetal cells is restored to diploid.

After meiosis, all egg cells of women contain X chromosomes in the 23rd pair of chromosomes, and in men, one half of the sperm contains an X chromosome, and the other half contains a Y chromosome. If an egg cell is fertilized by a sperm with an X chromosome, then a girl develops from it, and a boy develops from an egg cell fertilized with a Y chromosome.

Reproduction function is adjustable nervous system and products of the endocrine glands - hormones.

As a result of reproduction, parents pass on to their offspring hereditary information that provides them with the ability to survive in a particular environment and also produce offspring. During reproduction, conditions are created for changes in the properties of organisms due to the exchange of hereditary factors characteristic of the parents. Reproduction ensures long-term existence various types, evolutionary processes and the “immortality” of life on Earth (from the moment of its origin).

On Earth, organisms have two fundamentally different forms of reproduction: asexual and sexual.

General characteristics of asexual reproduction

In the implementation of asexual reproduction, one individual of one or another species participates, while the formation of gametes does not occur; offspring identical in hereditary characteristics arise, if under the influence external conditions no mutations (changes in the structure of genes or chromosomes) occur.

The offspring resulting from asexual reproduction from an individual is called a clone. There are several types of asexual reproduction, which are discussed below.

Reproduction by division, in which the number of chromosomes or the amount of nuclear matter does not change compared to the parent individual

Many organisms reproduce by simple division, which can be amitotic (for example, rhizomes) or mitotic (unicellular algae, etc.). In most cases, division occurs and two daughter cells are formed.

In nature, there is also a principle of division in which a large number of daughter cells are formed from one parent cell. This division is called multiple. An example of organisms in which multiple divisions occur is Plasmodium falciparum (the causative agent of malaria). This division occurs at a certain stage of development (schizogony), during which the nucleus in the mother cell divides repeatedly, forming up to a thousand new nuclei. These nuclei subsequently develop into cells.

Budding

Reproduction by budding comes down to the fact that an outgrowth (“bud”) appears on the parent organism, which after some time is separated from of a given organism and from it a new organism develops, completely similar to the parent. This is how coelenterates, unicellular fungi (for example, yeast), etc. reproduce.

Fragmentation

Reproduction in which the original parent organism is divided into several parts (two, three, four, etc.) and each gives rise to a new organism is called fragmentation. This is how filamentous algae, such as spirogyra, reproduce. Fragmentation also occurs in animals, for example in primitive worms. Closely related to fragmentation is the phenomenon of regeneration, when individual parts of an organism (if its integrity is violated), new organisms arise. Regeneration as a method of reproduction is characteristic of organisms with low level organizations (coelenterates, some worms, etc.). In higher organisms, regeneration is also possible, but it does not lead to the emergence of new organisms (for example, restoration of the tail in lizards when it is lost).

Vegetative propagation

Reproduction of an organism using vegetative organs is called vegetative reproduction. This reproduction is characteristic of higher plants. Plants can reproduce using stems, leaves and special formations: rhizomes, bulbs, tubers, root crops, etc. The ability of plants to reproduce vegetatively is an important difference between them and animals.

Reproduction by spores or asexual reproduction

Many organisms reproduce by special cells - spores: bacteria, fungi, plants. For bacteria, the spore is a “means” for enduring unfavorable living conditions and a way of settling in the habitat.

For plants and fungi, spores are cells from which a special generation of organisms is formed - the gametophyte. For these organisms, spores are small haploid cells, covered with a dense membrane, resistant to external unfavorable environmental factors, giving rise to the sexual generation of these organisms. These spores serve for reproduction, to endure unfavorable living conditions (except for seed plants), and for the settlement of the organism in its habitat. Spores of higher plants and fungi are formed as a result of sporulation, which is accompanied by a reduction in the number of chromosomes, i.e. spores are formed as a result of meiotic division. Actually, asexual reproduction of plants and fungi, in which there is a strict alternation of asexual (sporophyte) and sexual (gametophyte) generations, is a specific feature of these kingdoms of organisms and distinguishes them from organisms of the animal kingdom.

Some algae produce special, motile spores (zoospores), which under certain conditions can perform the functions of gametes (for example, Chlamydomonas, a single-celled green algae).

General characteristics of sexual reproduction

Reproduction in which an organism arises with the participation of sex cells - gametes - is called sexual reproduction.

During sexual reproduction, fertilization occurs (except for parthenogenesis).

Fertilization is the process of fusion of a female reproductive cell (egg) with a male reproductive cell (sperm or sperm).

During fertilization, the diploid set of chromosomes is restored, and a cell appears - a zygote, from which a new organism subsequently develops.

There are external and internal fertilization. External fertilization is typical for organisms that reproduce in an aquatic environment (fish, amphibians, etc.). In terrestrial animals, fertilization occurs inside the mother's body (animals) or in the corresponding plant organ (flower in angiosperms, cones in gymnosperms). Internal fertilization allows organisms to spread more widely over the surface and occupy larger number ecological niches.

As a rule, two parent organisms participate in sexual reproduction - male and female. This occurs in dioecious organisms. Most animals are dioecious. However, among animals there are organisms that have both female and male genital organs. Such organisms are called hermaphrodites. Many coelenterates, worms, and some are hermaphrodites. However, even among hermaphrodites, different individuals participate in the sexual process, some of which play the role of the maternal organism, while others play the role of the paternal one, and only in rare cases is self-fertilization possible, because biologically it is less beneficial than cross-fertilization.

In plants, different gametes are formed in different organs (male - in antheridia, female - in archegonia), but these organs can be contained on different plants(male and female) - the plants are called dioecious. Many plants from the angiosperm division have flowers that are bisexual.

The biological significance of sexual reproduction is that the descendants' hereditary material is significantly renewed; they have a greater opportunity to adapt to their environment than organisms that arose through asexual reproduction, when the descendants are practically no different from their parents in their hereditary characteristics.

4. Forms of reproduction of organisms

The succession of generations of organisms in nature is carried out through reproduction. Reproduction- This is the ability of an organism to reproduce its own kind. In nature, there are two types of reproduction: asexual and sexual.

Types of asexual reproduction

Asexual reproduction- the formation of a new organism from one cell or group of cells of the original maternal organism. In this case, only one parent individual participates in reproduction, which passes on its hereditary information to its daughter individuals. Asexual reproduction produces identical offspring. The only source of variability is random hereditary changes that can arise during the process of individual development.

Asexual reproduction is based on mitosis. There are several types of asexual reproduction.

Asexual reproduction in bacteria is interesting (Fig. 7).

Rice. 7. Asexual reproduction of bacteria: A - general scheme reproduction; B - cell division diagram

A circular DNA molecule is attached to cell membrane and is replicated. A transverse partition begins to form in the cell on the side where DNA molecules attach. The transverse septum then bifurcates, moving the anchored DNA to different parts of the cell. Ribosomes are evenly distributed between the two daughter cells, and a constriction is formed that divides the cell into two daughter cells.

Budding - This is a form of asexual reproduction in which a small outgrowth (bud) is separated from the parent individual and a daughter organism is formed. A new organism develops from a group of cells of the original organism. This type of asexual reproduction is characteristic of coelenterates (hydra) and some other animals and plants. Single-celled fungi - yeasts - also reproduce by budding. In contrast to simple division, during budding the mother cell is divided into unequal parts, budding a constantly smaller daughter cell (Fig. 8, B).

Rice. 8. Types of asexual reproduction: A - simple division in two of green euglena (longitudinal); B - budding of yeast and hydra; B - sporulation of mosses; G - vegetative propagation by begonia leaves

Reproduction by spores (sporulation) is typical for spore-bearing plants (algae, mosses, ferns). Reproduction occurs with the help special cells- spores formed in the mother’s body (Fig. 8, B). A spore is a small cell consisting of a nucleus and a small amount of cytoplasm. They are formed in large quantities in the original maternal organism. Each spore, germinating, gives rise to a new organism. Since they are microscopically small, they are easily transported by wind, water or other organisms, which facilitates the spread of these plants. Fungi, such as penicillum and cap mushrooms, also reproduce by spores.

Vegetative propagation- reproduction by individual organs, parts of organs or the body. Vegetative propagation most often occurs in plants that can reproduce by roots, shoots and parts of shoots (stems, leaves), modified shoots. Methods of vegetative propagation of plants are very diverse. This is propagation by bulbs (tulip), underground stolons - tubers (potatoes), rhizomes (wheatgrass), root cones (dahlia), layering (currants), root suckers (raspberries), leaves (begonia, violet), aboveground stolons - tendrils (strawberries ) etc. (Fig. 8, D).

Fragmentation- this is the division of an individual into two or more parts, each of which can give rise to a new organism. This method is based on regeneration- the ability of organisms to restore missing parts of the body. It is characteristic of lower invertebrate animals (coelenterates, flatworms, starfish, etc.). The animal's body, divided into separate parts, completes the missing fragments. For example, when not favorable conditions The planarian flatworm breaks up into separate parts, each of which, when favorable conditions occur, can give rise to a new organism.

Fragmentation also occurs in plants, for example, multicellular algae can reproduce by parts of the thallus.

Cloning. An artificial reproduction method that appeared relatively recently, in the early 60s. XX century It is based on obtaining a new organism from one cell of the original one. Since the cell nucleus contains the entire set of chromosomes, and therefore genes, under certain conditions it can be forced to divide, which will lead to the formation of a new organism. The formation of a clone is based on mitosis. To clone plants, the cells of the educational tissue are separated and grown on special nutrient media. A plant cell, dividing successively, gives rise to a whole organism. This method is currently widely used to obtain valuable plant varieties.

There is experience in animal cloning. It was first put forward by the English biologist D. Gurdon and gave positive results in experiments with the South American toad. Tadpole intestinal cells were used as a nuclear donor. The nuclei of the recipient eggs were destroyed ultraviolet rays and transplanted intestinal epithelial nuclei into these cells. As a result of the experiment, it was possible to obtain several cloned toad individuals, completely identical to each other. In 1995, English scientists managed to obtain a clone of sheep that were similar to the original maternal individual. However, the lambs died in early age, before reaching nine months.

In 1997, Dolly the sheep was obtained by cloning. To do this, the nuclei of mammary gland cells from a sheep of one breed (nucleus donor) were taken and transplanted into eggs with previously destroyed nuclei from a sheep of another breed (recipient). The cloned sheep was no different from the nuclear donor, but very different from the recipient.

The use of the cloning method will make it possible not only to preserve economically valuable animals, but also to reproduce them without limit. Currently, work is underway on human cloning, which causes heated debate not only among scientists, but also among various groups of the population. However, using this method, it is intended to reproduce only individual organs and tissues for subsequent transplantation into the donor’s body, and not to create individual individuals. This method will solve the problem of incompatibility of tissues of different organisms.

Features of sexual reproduction

Sexual reproduction - This is the formation of a new organism with the participation of two parent individuals. The new organism carries hereditary information from two parents, and the resulting offspring differ genetically from each other and from their parents. This process is characteristic of all groups of organisms; in its simplest form, it occurs even in prokaryotes.

During sexual reproduction, special cells are formed in the body sex cells - gametes male and female types that are capable of merging. Male gametes - spermatozoa, or sperm(if they are motionless). Female gamete - egg. Gametes are different from all other cells in the body, which are called somatic(from lat. soma - body). They always have haploid set of chromosomes (n).

As a result of the fusion of two gametes, the diploid set of chromosomes is restored again. In this case, half of all chromosomes are paternal, and the other half are maternal. For example, a person has 46 chromosomes, of which 23 are received from the mother and 23 from the father.

Sexual reproduction has a number of advantages. As a result of this process, a change in hereditary information occurs, and new individuals combine the characteristics of two parents. This leads to the emergence of new combinations of traits and genes. Sexual reproduction makes the body more competitive and adapted to changing conditions environment, as it increases the chances of survival. In the process of evolution, sexual reproduction turned out to be more preferable and progressive.

Questions for self-control

1. What types of reproduction occur in organisms? How are they different from each other?

2. What type of cell division underlies asexual reproduction?

3. Compare reproduction by spores and vegetative reproduction in plants. What are their similarities and differences?

4. What advantage does spore reproduction provide to the body?

5. Describe the features of each type of asexual reproduction.

6. What are the features of sexual reproduction? What advantages does this type of reproduction provide?

7. What cells are called gametes? What makes them special?

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4.1. Types of reproduction In the process of the evolution of living organisms, there was also an evolution of methods of reproduction, the diversity of which is observed in living species. All reproduction options can be divided into two fundamentally different types - asexual and

Reproduction is the property of organisms to leave offspring.

Forms of asexual reproduction, definition, essence, biological significance.

Two forms of reproduction: sexual and asexual.

Sexual reproduction is a change of generations and the development of organisms based on the fusion of specialized germ cells and the formation of a zygote.

With asexual reproduction, a new individual appears from unspecialized cells: somatic, asexual; bodies.

Asexual reproduction, or agamogenesis, is a form of reproduction in which an organism reproduces itself independently, without any participation of another individual.

Reproduction by division

Division is primarily characteristic of unicellular organisms. As a rule, it is carried out by simply dividing the cell in two. In some protozoa, for example, foraminifera, division occurs into a larger number of cells. In all cases, the resulting cells are completely identical to the original one. The extreme simplicity of this method of reproduction, associated with the relative simplicity of the organization of single-celled organisms, allows reproduction very quickly. Thus, under favorable conditions, the number of bacteria can double every 30-60 minutes. An organism that reproduces asexually is capable of endlessly reproducing itself until a spontaneous change in the genetic material occurs - a mutation. If this mutation is favorable, it will be preserved in the offspring of the mutated cell, which will represent a new cell clone. Same-sex reproduction involves one parent organism, which is capable of forming many organisms identical to it.

Reproduction by spores

Asexual reproduction of bacteria is often preceded by the formation of spores. Bacterial spores are resting cells with reduced metabolism, surrounded by a multilayer membrane, resistant to desiccation and other unfavorable conditions that cause death ordinary cells. Sporulation serves both to survive such conditions and to spread bacteria: once in a suitable environment, the spore germinates, turning into a vegetative dividing cell.
Asexual reproduction with the help of unicellular spores is also characteristic of various fungi and algae. Spores in many cases are formed by mitosis of mitospores, and sometimes especially in fungi in huge quantities; upon germination, they reproduce the mother's organism. Some fungi, such as the harmful plant pest Phytophthora, form motile spores equipped with flagella, called zoospores or wanderers. After floating in droplets of moisture for some time, such a wanderer “calms down”, loses its flagella, becomes covered with a dense shell and then, under favorable conditions, germinates.

Vegetative propagation

Another option for asexual reproduction is carried out by separating from the body a part of it, consisting of a larger or smaller number of cells. From them the adult organism develops. An example is budding in sponges and coelenterates or propagation of plants by shoots, cuttings, bulbs or tubers. This form of asexual reproduction is usually called vegetative reproduction. At its core, it is similar to the regeneration process. Vegetative propagation plays an important role in plant growing practices. So, it may happen that a sown plant, for example an apple tree, has some successful combination of characteristics. The seeds of this plant have this good combination will almost certainly be disrupted, since seeds are formed as a result of sexual reproduction, and this is associated with gene recombination. Therefore, when growing apple trees, vegetative propagation is usually used - by layering, cuttings or grafting buds onto other trees.

Budding

Some species of unicellular organisms are characterized by a form of asexual reproduction called budding. In this case, mitotic division of the nucleus occurs. One of the resulting nuclei moves into the emerging local protrusion of the mother cell, and then this fragment buds off. The daughter cell is significantly smaller than the mother cell, and it takes some time for it to grow and complete the missing structures, after which it takes on the appearance characteristic of a mature organism. Budding is a type of vegetative propagation. Many lower fungi, such as yeast and even multicellular animals, such as freshwater hydra, reproduce by budding. When yeast budding, a thickening forms on the cell, which gradually turns into a full-fledged daughter yeast cell. On the hydra’s body, several cells begin to divide, and gradually a small hydra grows on the mother individual, which forms a mouth with tentacles and an intestinal cavity connected to the intestinal cavity of the “mother.”

Fragmentation body division

Some organisms can reproduce by dividing the body into several parts, and from each part a full-fledged organism grows, similar in all respects to the parent individual (flatworms, annelids, and echinoderms).

Sexual reproduction is a process in most eukaryotes associated with the development of new organisms from germ cells.

The formation of germ cells, as a rule, is associated with the passage of meiosis at some stage of the life cycle of the organism. In most cases, sexual reproduction is accompanied by the fusion of germ cells, or gametes, and a double set of chromosomes, relative to gametes, is restored. Depending on the systematic position of eukaryotic organisms, sexual reproduction has its own characteristics, but as a rule, it allows the genetic material from two parent organisms to be combined and produces offspring with a combination of properties not found in the parental forms.

The effectiveness of combining genetic material in descendants obtained as a result of sexual reproduction is facilitated by:
chance meeting of two gametes

random arrangement and divergence to division poles of homologous chromosomes during meiosis

crossing over between chromatids.

This form of sexual reproduction, known as parthenogenesis, does not involve the fusion of gametes. But since the organism develops from the germ cell of the oocyte, parthenogenesis is still considered sexual reproduction.
In many groups of eukaryotes, the secondary disappearance of sexual reproduction has occurred, or it occurs very rarely. In particular, the department of deuteromycetes includes a large group of phylogenetic ascomycetes and basidiomycetes that have lost the sexual process. Until 1888, it was assumed that among higher terrestrial plants, sexual reproduction had been completely lost in sugar cane. The loss of sexual reproduction has not been described in any group of metazoans. However, many species of lower crustaceans are known - daphnia, some types of worms, capable of reproducing parthenogenetically under favorable conditions for tens and hundreds of generations. For example, some species of rotifers reproduce only parthenogenetically for millions of years, even forming new species!
In a number of polypliodic organisms with an odd number of sets of chromosomes, sexual reproduction plays a role small role in maintaining genetic variability in a population due to the formation of unbalanced sets of chromosomes in gametes and descendants.
The ability to combine genetic material during sexual reproduction has great importance for the selection of model and economically important organisms.

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