What methods of sexual reproduction are found in animals. animal breeding
Answers to school textbooks
Reproduction is the process of reproducing similar organisms. This process ensures the continuity and continuity of life.
2. Than sexual reproduction different from asexual?
A comparison of asexual and sexual reproduction is presented in the following table.
| asexual reproduction | sexual reproduction |
|
One parent |
Usually two parents |
|
Gametes are not formed |
Gametes are formed (with half a set of chromosomes) |
|
Meiosis is absent in the life cycle |
At some stage of the life cycle, meiosis occurs, which prevents the doubling of chromosomes in each generation. |
|
The offspring are identical to the parents |
The offspring are not identical to the parents. There is a variety of characters even in the offspring of the same parent pair |
|
It is typical for plants, some animals (lower) and microorganisms. Not found in higher animals |
Common to most plants and animals |
|
Leads to a rapid increase in the number of descendants (while maintaining existing forms) |
Leads to an increase in diversity (with a less rapid increase in abundance) |
3. Why is sexual reproduction the most common way for living organisms to reproduce?
Sexual reproduction provides enormous benefits to organisms. Individuals formed as a result of sexual reproduction carry hereditary traits from both parents, and therefore they better adapt to changing environmental conditions, and therefore become more resilient.
4. What are the sex cells called?
5. How are eggs different from sperm and why?
The specialized sex cells involved in the sexual process are called gametes. In most animals, they are of two types - male and female, respectively, sperm and eggs. Usually, spermatozoa are small mobile cells, and eggs, on the contrary, are most often motionless, large, with a large supply of nutrients, since they provide nutrients to the embryo. Each sex cell carries only half the set of chromosomes. When they merge in the zygote, a double set of chromosomes is restored, which is characteristic of all individuals of the species.
6. Where are germ cells formed?
Sex cells in most multicellular animals, starting with worms, are formed in special genital organs. In vertebrates, special devices also appear that facilitate the process of fusion of germ cells and ensure the development of the embryo.
7. What animals are called dioecious?
Dioecious animals are those animals that differ in individuals that can form only spermatozoa (males) or only eggs (females).
8. Who are hermaphrodites?
Hermaphrodites are called bisexual animals (from the names of the Greek gods Hermes and Aphrodite; hermaphrodite is a mythical bisexual creature). Such organisms are capable of simultaneously producing two types of germ cells - both male and female. These are, first of all, many coelenterates, all flatworms, some annelids, as well as some molluscs and even fish and lizards.
9. What is the essence of parthenogenesis?
Parthenogenesis (from the Greek "parthenos" - virgin, "genesis" - development) is the only form of sexual reproduction when the embryo develops from one germ cell - the egg - without fertilization.
10. What animals are capable of parthenogenesis?
Parthenogenesis occurs in both plants and animals. Among animals, this type of reproduction is common primarily for insects, some worms and crustaceans. So, in bees, the uterus - the female - can lay both fertilized eggs, from which worker bees and queens develop, and unfertilized ones - males develop from them. In aphids, several parthenogenetic generations are replaced by a generation resulting from normal sexual reproduction. Parthenogenesis also occurs in vertebrates (reptiles, birds). Thus, parthenogenesis is known in several species of lizards living in the Caucasus. It is also noted that up to 15% of eggs in turkeys develop without fertilization.
Parthenogenesis can be induced artificially in animals that do not naturally have it. To do this, it is enough to stimulate the egg to divide by mechanical or chemical influences.
11. What is fertilization?
Fertilization is the process of fusion of germ cells. As a result of fertilization, a double set of chromosomes is restored in the zygote - the resulting organism carries the chromosomes of both parents.
12. What animals are characterized by external fertilization?
External fertilization is characteristic of aquatic animals. In this case, the egg and sperm are released from the body directly into the water. Under such conditions, the meeting and combination of gametes becomes a matter of chance. Many germ cells die. Therefore, in order to increase the likelihood of fertilization, fish, for example, are forced to spawn a huge amount of eggs. So, perch females throw 200-300 thousand eggs, and cod females - up to 10 million.
Asexual reproduction.
In the animal kingdom, there are a number of methods of reproduction, for example, direct division or budding, characteristic of lower invertebrates, as well as parthenogenesis, observed even in higher vertebrates. It is quite obvious that it is asexual reproduction that is the simplest and least energy-intensive way to increase the number of individuals. However, for some reason, in the process of evolution, a complex process of sexual reproduction arose, associated with many problems and conventions.
Sexual reproduction.
1. Conjugation. Sexual reproduction appears in animals already at the lowest rungs of the evolutionary ladder. So, already in the simplest unicellular microorganisms - ciliates that reproduce by direct division, the so-called conjugation is observed, which is a kind of analogue of the sexual process. In the process of conjugation, two ciliates, as it were, grow together, for a time during which they exchange hereditary information. Then the ciliates separate, and then each continues to divide on its own.
2. Parthenogenesis. In a number of invertebrates, as well as many vertebrates, there is such a phenomenon as parthenogenesis, in which females lay eggs or give birth to live young without the participation of males. Only females hatch from these eggs or are born in this way, and it is interesting that in nature there are entire local populations of such species. A similar population of rock lizards has been found in Armenia. In other places of its habitat, this very common species reproduces in the usual way.
Parthenogenesis under experimental conditions is possible even in mammals. To do this, it is necessary in some way to stimulate the unfertilized egg to divide, which can be done in different ways, for example, simply by applying a microneedle injection.
3. Hermaphroditism. In a number of invertebrates, hermaphroditism occurs, in which each individual has both male and female gonads. Among the best-known animals, hermaphrodites are, for example, earthworms, leeches and many types of snails. However, despite the fact that in such animals each individual produces both eggs and spermatozoa, they mate with each other, producing a mutual exchange of germ cells. In large shellless Aplysia mollusks or sea hares living in the coastal zone of the sea, up to 10-12 individuals can simultaneously take part in the process of fertilization, playing both the roles of males and the roles of females at once.
However, despite the presence of both types of germ cells in hermaphrodite animals, they extremely rarely resort to self-fertilization, and, on the contrary, usually tend to mate with other, preferably unrelated individuals.
4. Sex change. Some animals, including a number of fish species, change sex with age. So, in swordfish well-known to aquarists, the transformation of middle-aged females into males is quite common. At the same time, they grow a xiphoid process on the tail, which is available only in males, and they begin to exhibit typical sexual behavior, successfully fertilizing females. A similar phenomenon is also observed in small marine junker fish living in the coastal zone of the Black Sea. In some fish species, the reverse process was also noted: the transformation of males into females.
5. Alternation of sexual and asexual types of reproduction. In such invertebrates as coelenterates, worms of various types, echinoderms, both sexual and asexual reproduction exist in parallel. Many invertebrates have alternating sexual and asexual generations. So, for example, coral polyps, which grow very actively due to vegetative reproduction, periodically produce a huge amount of mobile male and female germ cells. Fertilization takes place in the water column. From the zygotes formed in this case, mobile larvae develop, which settle on a suitable substrate and give rise to new coral colonies. All attached forms reproduce in a similar way: sponges, bryozoans, hydroid polyps, etc.
In some species, alternation of parthenogenesis with normal sexual reproduction is observed. So, for example, aphids reproduce throughout the summer by live birth, in which unfertilized females give birth to only females. Young female aphids begin to give birth to the next females already at the age of several hours.
Thus, during the summer there is a huge succession of asexual generations. Zoologists have calculated that if all the offspring of one aphid survived, then in one summer it could cover the entire globe with a continuous veil. Fortunately, since many other animals feed on aphids, this does not happen. It would seem that this method of reproduction of aphids is very successful and does not require anything better to be desired. However, in autumn, many aphids lay eggs, males hatch from them, which fertilize relatively a small amount of females.
While most aphids die in autumn, having completed their life cycle, fertilized females successfully survive the winter and lay eggs in the spring. Winged aphids hatch from eggs, they scatter in different directions, and, having settled on suitable fodder plants, they lose their wings and begin to reproduce by parthenogenesis. Obviously, in order to successfully survive in a continental climate, aphids need to expand the spectrum of variability in the genome, which is provided by sexual reproduction.
Thus, the main significance of sexual reproduction is not just to increase the number of individuals, but to expand the gene pool, further contributing to natural selection.
Features of the process of animal reproduction
The role of sexual reproduction in evolution
Types of marital relations in animals
Communication in sexual behavior, ritualization
Animal mating ceremonies
Methods of birth in animals
Caring for offspring in animals, invertebrates, reptiles
Features of reproduction of birds, mammals
Juvenile, early postnatal period
Features of ontogenesis of different taxonomic groups, its periodization
Education of animals in the process of ontogenesis
Leontief-Fabry concept
Elementary sensory psyche, evolution
Reproduction is the property of living organisms to reproduce their own similar individuals.
Animals reproduce asexually and sexually. asexual reproduction predominantly in lower animals. During asexual reproduction, a part of her body is separated from the mother or the whole individual is divided into two or more parts, each of which develops into an independent animal.
There are several ways of asexual reproduction of animals: division, budding, schizogony (Fig. 23).
23. Asexual reproduction of protozoa:
/- division of the amoeba;
2 -
budding of ciliates (suvoyki); 3
schizogony of malarial plasmodium
24. Sperm Shapes:
/ - ram; 2 - cancer; 3 - roundworm; 4
The division consists in the constriction of the mother individual into two more or less equal parts, each of which becomes a new organism.
Budding is such asexual reproduction when an outgrowth (bud) is formed on the body of the mother individual, gradually acquiring the shape and structure of an adult animal.
After separation (budding) from the mother's body, a new individual begins to lead an independent life.
sexual reproduction common to all types of animals.
During sexual reproduction, a new organism develops from a zygote, which is formed as a result of the fertilization of an egg by a spermatozoon.
The female reproductive cell - egg (ovum) usually has a round or oval shape and consists of cytoplasm and nucleus. The cytoplasm contains a certain amount of nutrients. The egg, as a rule, is covered with shells of various structures.
Male sex cells - spermatozoa have varied form(rice.
24), but usually consist of a head, a connecting part and a tail, which serves to move in a liquid medium.
reproduction
Most of the head is occupied by the nucleus.
In some multicellular animals (usually living in water), external fertilization is observed: both eggs and spermatozoa are released into the water, where they merge. Other animals tend to be internally fertilized and e: sperm is introduced into the genital tract of the female, and there the act of fertilizing the egg with a spermatozoon takes place. Sometimes an animal develops from an unfertilized egg; such reproduction is called virgin - parte-iogenetic.
Reproduction of multicellular animals
Animals, like plants, reproduce asexually and sexually. Features of reproduction of multicellular animals are largely determined by the conditions of their habitat.
asexual reproduction
Asexual reproduction is characteristic of the most simply arranged animals, for example, hydra.
Reproduction methods
In summer, under favorable conditions, it reproduces by budding. A protrusion of the body wall is formed on the body of the hydra - a night, which grows, forming a mouth and rudiments of tentacles at the top. The kidney at the base unfastens, falls to the bottom and passes to an independent life. Sometimes budding goes so vigorously that even before the first bud is torn off, 2-3 others have time to form on the hydra.
sexual reproduction
Many animals, including the hydra, reproduce sexually before the onset of cold weather.
This process begins with the formation of germ cells - gametes. Male sex cells of animals - spermatozoa. They are small and mobile, unlike sperm.
Spermatozoa are formed in males to the male gonads - the testes. The female sex cells of the egg are immobile and have a large supply of nutrients. They are formed in females in the female sex glands - the ovaries. During sexual reproduction, the fusion of two germ cells - the egg and the sperm. This process is called fertilization. From the formed cell - the zygote, a new organism is formed, combining the characteristics of both parents.
The advantage of sexual reproduction over asexual reproduction is that the offspring are similar to their parents and at the same time slightly different from them and from each other.
This allows organisms of the same species to better adapt to changing habitat conditions.
In most fish and amphibians (frogs, toads, newts), eggs are fertilized by spermatozoa in the surrounding aquatic environment.
Such fertilization is called external. If fertilization of the cell occurs inside the body of the female, it is called internal. Internal fertilization is characteristic of insects, reptiles, birds, and mammals.
Development of a new organism
The development of a new organism can occur in the external environment or inside the mother's body.
Many animals lay their eggs in places where there are conditions for their development. Insects - where there is food for the larva emerging from the egg (on leaves, in flower buds, next to fruit that has set).
Reptiles usually place their eggs in sand, soil, or rotting leaves. Under the influence of ambient temperature or as a result of the release of heat by rotting plant debris, embryos develop in the eggs.
Lizards, turtles, crocodiles, birds lay fertilized eggs with a large supply of nutrients.
The eggs of lizards and pits are covered with a leathery shell on the outside, and the eggs of crocodiles, turtles and birds have a calcareous shell.
All these animals are called oviparous. In mammals, the embryo from the zygote develops in a special organ of the female - the uterus. This development is called intrauterine. The embryo is well protected from the adverse effects of the environment. This provides a high survival rate for the offspring of mammals. Well-formed cubs are born.
Such animals are called viviparous.
Of course, in this case it is the main form of self-reproduction. Indirect evidence of this is the fact that modern prokaryotic organisms (bacteria) reproduce exclusively asexually - by dividing the mother cell-organism in two.
This method is also characteristic of many unicellular eukaryotic organisms - algae, fungi, protozoa. Moreover, for some of them (for example, in amoebas) it is the only one. The division of the body of the mother cell is preceded by mitotic division of the nucleus - two daughter nuclei are formed, identical both to each other and to the mother. This is followed by the division of the cytoplasm and the formation of two daughter cells.
Some unicellular organisms (for example, flagellates) reproduce by budding.
In this case, in parallel with the mitotic division of the nucleus in the mother cell, a small protrusion of the cytoplasm is formed, where one of the daughter nuclei moves. Then this fragment buds and a small daughter individual is formed. For some time, it grows and develops, then reaching the size of the mother's body.
A special form of asexual reproduction of unicellular organisms is schizogony - multiple division (for example, in fungi, protozoa): in the cell of the mother organism, the volume of the cytoplasm increases, and the nucleus repeatedly mitotically divides.
At a certain moment, the mother cell divides, simultaneously giving rise to many daughter individuals, the number of which corresponds to the number of nuclei formed.
At the stage of their appearance, a unicellular organism is inactive - it does not feed, does not move, etc. When a spore enters favorable conditions, its shell is destroyed and the released organism begins to behave actively.
The formation of spores is often combined with asexual reproduction of a unicellular organism, either by multiple fission or in two.
Asexual reproduction in multicellular organisms.
Many multicellular organisms are characterized by such forms of asexual reproduction as vegetative reproduction and sporulation.
In vegetative reproduction, the daughter organism is formed from a body part, vegetative organ, or group of somatic cells of the mother organism. Such reproduction is especially widespread in plants and fungi, as well as in various groups of invertebrates. At higher plants vegetative propagation is carried out with the help of various vegetative organs: rhizomes (lily of the valley, wheatgrass, iris), creeping shoots (strawberries, cranberries), tubers (potatoes), bulbs (onions, garlic, tulips), root suckers (raspberry, sow thistle, willow-herb ), leaves (begonia, bryophyllum) (Fig.
one). In lower plants, fungi and invertebrates, vegetative reproduction occurs by division or fragmentation of the body of the mother organism (thallus in multicellular algae, the body of sponges, coelenterates, worms, echinoderms).
Rice. one. Vegetative reproduction: 1 - brood buds (on the thallus of marchantia moss); 2 - adnexal buds (brionia leaf); 3 - adnexal buds (on the root system of thistle field); 4 - creeping stems (strawberries)
A special form of vegetative reproduction is budding, which occurs in some invertebrates.
The formed daughter individual separates from the parent and passes to an independent existence (for example, in the hydra; Fig. 2). If the individuals formed by budding do not separate from the mother, maintaining a close connection throughout life, a colony of organisms is formed (as, for example, in sponges, corals, ascidians).
Rice. 2.
10 examples of breeding without males from wildlife
Hydra: 1 - budding; 2 - with eggs
In addition to vegetative propagation, many species of fungi and plants are characterized by sporulation. It assumes that in special organs of a multicellular organism (sporangia) unicellular spores are formed, with the germination of one of which a whole organism develops (for example, the daughter mycelium in fungi).
The spores of many fungi and plants are covered with a dense shell, resistant to external influences, immobile and disperse passively. The zoospores of algae, equipped with flagella, actively swim in the aquatic environment.
A peculiar form of asexual reproduction is polyembryony (development from a zygote of several embryos), which is in direct connection with sexual reproduction. Several embryos develop during zygote cleavage due to the division of the embryonic cellular material (mass of blastomeres) into several parts.
As a result of the development of these embryos, identical twins with the same genotypes are born in animals. In many plants (for example, water lilies, tulips) and animals (for example, riders, armadillos), the phenomenon of polyembryony is natural.
However, it can also occur in those species that, in principle, are not characteristic, for example, in humans (twins are born once in a thousand singleton births).
The biological role of asexual reproduction
Maintaining the greatest fitness in little-changing environmental conditions. It reinforces the importance of stabilizing natural selection; provides fast reproduction rates; used in practical selection. Asexual reproduction occurs in both unicellular and multicellular organisms.
In unicellular eukaryotes, asexual reproduction is mitotic division, in prokaryotes, nucleoid division, and in multicellular forms, vegetative reproduction.
Krasnodembsky E. G. "General Biology: A Handbook for High School Students and Applicants to Universities"
N. S. Kurbatova, E. A. Kozlova "Summary of lectures on general biology"
Reproduction is the purpose of the power of living organisms to create similar ones, which is based on the transfer of decay information from fathers to offspring. There are two ways to create new organisms: Bezstateve and state of reproduction.
Article reproduction tse - the type of reproduction, for which specialization of the article of clitiny (gameti) is approved and the article of the process is approved.
Statement of reproduction of power to representatives of these types of creatures and roslins. On the view of somatic cells of the body, state cells (gametes), may be happoid (single) set of chromosomes. In case of splitting of two state cells, a diploid (subvarious) set of chromosomes is established.
In the new one, two organisms mainly take their fate, which spawn the appearance of new personalities, which grow up like the Batkivs. Forms of state reproduction: - copulation - conjugation - parthenogenesis - state reproduction from plodding
Porіvnyalny characteristic of forms of article reproduction
| FORMI | CHARACTERISTIC | APPLY | |
| One-celled organisms | Conjugation (lat. conjugatio - z'ednannya) |
Temporary angry clitin (cytoplasmic mist is established), under the hour of such a stench, parts of the nuclear apparatus and cytoplasm are exchanged | In the simplest (infusoria) |
| One-celled organisms | Copulation | Two individuals gain the power of stately clitins and get angry, satisfying the zygote | In the simplest (polystomeli, polytomy) |
| Bagatoclitin organisms | Parthenogenesis (gr. parthenos - unoccupied + genesis - exodus) |
The development of the body from the unoccupied egg. Distinguish between obligate (early eggs until hatching without hatching) and facultative parthenogenesis (harvest eggs develop along the path of parthenogenesis and as a result of hatching) | In roslins, spineless creatures (bjoli, daphnia, twigs, popelits), Caucasian skelny lizard |
| Bagatoclitin organisms | Articles of reproduction from fillings | Molding of two types of specialized clitins - gametes (human and female), which lead to the establishment of a zygote, for which an organism develops | At roslyn, creatures and mushrooms |
Type of state reproduction - Isogamy.
Human and female gametes are built to ruin and may have the same shape and size. - Anisogamy. Cholovіchі y zhіnоchі gameti zdatnі to ruin, stench mаyut similar form, аlе rіzny rіznіr (zhіnоchі bіlshі fіlshі rоzіrіm).
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- Oogamy. Human and female gametes create different shapes and roses-peace. To ruin the building is less than human gametes. With state reproduction, the formation occurs (crim to parthenogenesis). Zaplіdnennya is the process of merging the female state cell (ovum cell) with the human cell cell (sperm or sperm).
When zaplіdnennі vіdnovlyuєє diploidy set of chromosomes, with this vinicaє kіtin - Zygote, zakoї zakoї zakoї a new organism develops.
Biological significance of article reproduction
The backbone of the Statch pinkishness of the Poleg, in the same, in the POSCHADKIV, it is hard to have a lot of dwells, they have a great one to fit the frenzy of the livestock, and the vicilli is not in the same way.
The state of reproduction is to rob organisms of stable to the least and unacceptable minds of the superfluous middle ground, promoting their vitality.
To this is the diversity of the offspring that is born as a result of the union of the decline of the two organisms.
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All animals reproduce differently. Only a very few species (about 3%) give birth to live young. As a rule, these are animals that live on land. Whales and some fish also give birth to live babies.
Most animals lay eggs, from which, after a certain period, offspring appear.
The main part of animals reproduces sexually, that is, by combining male and female germ cells, as a result of which a new individual is born that contains the signs of both parents. But there are animals, such as sea sponges, that can also reproduce asexually (vegetatively), in which case the offspring is born from only one parent.
Mass fertilization
Coral reefs are clusters of millions of tiny animals called polyps.
To continue the genus, polyps secrete germ cells - sperm and eggs, which float up and connect with each other. The fertilized eggs develop into larvae that swim in the sea until they find a place where they attach and turn into polyps.
Many species of coral polyps can also reproduce asexually.
Nest in earthen burrow
Grape snails dig holes in the soft damp earth and lay their eggs there.
reproduction
They fill the hole with earth so that predators do not get to the eggs until the cubs hatch. After a few weeks, small, but completely formed snails crawl out of the ground.
live birth
The Arabian oryx lives in the Arabian deserts. Like almost all mammals, these antelopes give birth to live young. Usually only one calf is born. Within a few minutes after birth, the baby stands on its feet, and after a few hours it runs along with the rest of the herd.
asexual reproduction
Until the 19th century, sea sponges were thought to be plants.
Currently, biologists classify them as animals. Many species of sponges reproduce sexually, others asexually, called budding. At the same time, some part of it is separated from the adult individual, giving rise to a new sponge.
Last molt
Nymphs (larvae) of cicadas live underground for several years, molt five times before adult insects are born.
Development outside the mother's body
The female cat shark anchors the egg with the embryo it contains to an underwater plant, where it remains for six to eight months.
1) Division of unicellular(amoeba). At schizogony(malarial plasmodium) it turns out not two, but many cells.
2) Sporulation
- Spores of fungi and plants serve for reproduction.
- Spores of bacteria do not serve for reproduction, because. One spore is produced from one bacterium. They serve to experience adverse conditions and resettlement (by wind).
3) Budding: daughter individuals are formed from outgrowths of the body of the mother organism (kidneys) - in intestinal (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 forms both female and male gametes (most higher plants, coelenterates, flat and some annelids, mollusks).
2) Conjugation at green algae spirogyra: two threads of spirogyra approach each other, copulatory bridges are formed, the contents of one thread flows into another, one thread is obtained from zygotes, the second - from empty shells.
3) Conjugation in ciliates: two ciliates approach, exchange sex nuclei, then diverge. The number of ciliates remains the same, but recombination occurs.
4) Parthenogenesis: the child develops from an unfertilized egg (in aphids, daphnia, bee drones).
1. Establish a correspondence between the feature of sexual and vegetative reproduction and the method of reproduction: 1) asexual, 2) sexual. Write the numbers 1 and 2 in the correct order.
A) forms new combinations of genes
B) forms combinative variability
B) produces offspring that are identical to the parent
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 down the numbers 1 and 2 in the order corresponding to the letters.
A) Haploid nuclei fuse.
B) A zygote is formed.
C) Occurs with the help of spores or zoospores.
D) Combinative variability is manifested.
E) Offspring are formed that are identical to the original individual.
E) Genotype parent persisted over generations.
Answer
3. Establish a correspondence between the stages of the life cycle of plants and methods of reproduction: 1) asexual, 2) sexual. Write down the numbers 1 and 2 in the order corresponding to the letters.
A) controversy
B) accompanied by the fusion of gametes
B) sporophytes reproduce
D) the gametophyte reproduces
D) a zygote is formed
E) meiosis occurs
Answer
4. Establish a correspondence between the characteristics and the method of reproduction: 1) asexual, 2) sexual. Write down the numbers 1 and 2 in the order corresponding to the letters.
A) Gametes are not formed.
B) Only one organism is involved.
C) Fusion of haploid nuclei occurs.
D) Offspring are formed that are identical to the original individual.
E) The offspring show combinative variability.
E) Gametes are formed.
Answer
Choose three correct answers from six and write down the numbers under which they are indicated. Bacterial spores, unlike fungal spores,
1) serve as an adaptation to the transfer of adverse conditions
2) perform the function of nutrition and respiration
3) DO NOT serve for reproduction
4) provide distribution (settlement)
5) are formed by meiosis
6) are formed from the mother cell by the loss of water
Answer
Choose three options. Asexual reproduction is characterized by
1) offspring have only the genes of the mother organism
2) the offspring is genetically different from the mother's body
3) one individual participates in the formation of offspring
4) in the offspring there is a splitting of signs
5) offspring develop from an unfertilized egg
6) a new individual develops from somatic cells
Answer
Establish a correspondence between the characteristic and the method of reproduction of the plant: 1) vegetative, 2) sexual
A) carried out by modified shoots
B) is carried out with the participation of gametes
C) daughter plants remain very similar to the parent
D) is used by humans to preserve valuable traits of mother plants in offspring
D) a new organism develops from a zygote
E) the offspring combines the characteristics of the maternal and paternal organisms
Answer
Establish a correspondence between the feature of reproduction and its type: 1) vegetative, 2) sexual. Write the numbers 1 and 2 in the correct order.
A) due to the combination of gametes
B) individuals are formed by budding
B) provides genetic similarity of individuals
D) occurs without meiosis and crossing over
D) due to mitosis
Answer
1. Establish a correspondence between an example of reproduction and its method: 1) sexual, 2) asexual. Write the numbers 1 and 2 in the correct order.
A) sporulation in sphagnum
B) spruce seed propagation
B) parthenogenesis in bees
D) propagation by bulbs in tulips
D) birds lay eggs
E) spawning in fish
Answer
2. Establish a correspondence between a specific example and the method of reproduction: 1) asexual, 2) sexual. Write the numbers 1 and 2 in the correct sequence.
A) fern sporulation
B) the formation of chlamydomonas gametes
B) the 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 the numbers 1 and 2 in the correct order.
A) hydra budding
B) bacterial cell division into two
B) the formation of spores in fungi
D) parthenogenesis of bees
D) the formation of strawberry whiskers
Answer
4. Establish a correspondence between examples and methods of reproduction: 1) asexual, 2) sexual. Write the numbers 1 and 2 in the correct order.
A) live birth in a shark
B) dividing infusoria-shoes in two
B) parthenogenesis of bees
D) propagation of violet leaves
D) spawning by fish
E) hydra budding
Answer
5. Establish a correspondence between the processes and methods of reproduction of organisms: 1) sexual, 2) asexual. Write down the numbers 1 and 2 in the order corresponding to the letters.
A) lizards lay eggs
B) sporulation penicillium
C) propagation of wheatgrass by rhizomes
D) Daphnia parthenogenesis
D) division of euglena
E) propagation of cherries by seeds
Answer
6. Establish a correspondence between examples and methods of reproduction: 1) asexual, 2) sexual. Write the numbers 1 and 2 in the correct order.
A) raspberry cuttings
B) the formation of spores in horsetail
C) sporulation in cuckoo flax
D) lichen fragmentation
D) parthenogenesis of aphids
E) budding in a coral polyp
Answer
7 Sat. Establish a correspondence between examples and methods of reproduction: 1) asexual, 2) sexual. Write the numbers 1 and 2 in the correct order.
A) the formation of gametes in chlamydomonas
B) sturgeon spawning
B) sporulation in mosses
D) division of the common amoeba
E) fragmentation of mycelium in fungi
E) raspberry root suckers
Answer
8. Establish a correspondence between examples and methods of reproduction: 1) asexual, 2) sexual. Write the 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
Choose one, the most correct option. Reproduction, in which the daughter organism appears without fertilization from the cells of the body of the mother organism, is called
1) parthenogenesis
2) sexual
3) asexual
4) seed
Answer
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
Write down the numbers under which it is indicated what happens during the sexual reproduction of animals.
1) usually two individuals participate
2) germ cells are formed by mitosis
3) somatic cells are initial
4) gametes have a haploid set of chromosomes
5) the genotype of the offspring is a copy of the genotype of one of the parents
6) the genotype of the offspring combines the genetic information of both parents
Answer
Choose three traits that are 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) In 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 signs appear in the offspring
6) The vegetative parts of the plant are involved in reproduction
Answer
Choose two differences between sexual and asexual reproduction.
1) sexual reproduction is energetically more profitable than asexual
2) two organisms are involved in sexual reproduction, one asexual
3) during sexual reproduction, the offspring are exact copies of the parents
4) somatic cells are involved in asexual reproduction
5) sexual reproduction is possible only in water
Answer
1. All but two of the following terms 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 of the following terms, except for two, are used to describe the asexual reproduction of 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
All of the above characteristics, except for 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) In the reproduction of chordates, as a rule, individuals of different sexes participate.
3) The starting material for the formation of gametes are spores.
4) In the offspring, the characteristics of both parents are combined.
5) The chromosome set of the gamete is formed as a result of division by mitosis.
Answer
Establish a correspondence between the characteristics and the method of reproduction of plants: 1) sexual, 2) vegetative. Write down the numbers 1 and 2 in the order corresponding to the letters.
A) is carried out with the participation of gametes
B) a new organism develops from a zygote
C) carried out by modified shoots
D) offspring have signs of paternal and maternal organisms
D) offspring have characteristics of the mother's organism
E) is used by humans to preserve the valuable traits of the mother plant in the offspring
Answer
All but two of the examples below refer to the 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 spores of ferns
2) reproduction of earthworms by fragmentation
3) ciliate-shoe conjugation
4) budding of freshwater hydra
5) parthenogenesis of bees
Answer
1. All the methods of crop production below, except for two, are classified as vegetative propagation. Identify two tricks that “fall out” of the general list, and write down the numbers under which they are indicated.
1) division of tubers
2) propagation by rhizome
3) obtaining seedlings from seeds
4) artificial insemination
5) layering formation
Answer
2. All the examples below, except for two, characterize vegetative reproduction. Identify two examples that "fall out" from the general list, and write down the numbers under which they are indicated.
1) getting heterotic hybrids
2) propagation by dividing the bush
3) use of root offspring
4) propagation by seeds
5) rooting layering
Answer
All but two of the following organisms reproduce by spores. Identify two organisms that "fall out" from the general list. Write down the numbers under which they are indicated.
1) mukor mushroom
2) cholera vibrio
3) tuberculosis bacillus
4) fern shield
5) cuckoo flax
Answer
© D.V. Pozdnyakov, 2009-2019
Sexual reproduction is carried out with the participation of two parent individuals (male and female), in which specialized cells are formed in special organs - gametes. The process of formation of gametes is called gametogenesis, the main stage of gametogenesis is meiosis. The daughter generation develops from zygotes- a cell formed as a result of the fusion of male and female gametes. The process of fusion of male and female gametes is called fertilization. An obligatory consequence of sexual reproduction is the recombination of genetic material in the daughter generation.
Depending on the structural features of gametes, the following can be distinguished forms of sexual reproduction: isogamy, heterogamy and ovogamy.
isogamy(1) - a form of sexual reproduction in which gametes (conditionally female and conditionally male) are mobile and have the same morphology and size.
Heterogamy(2) - a form of sexual reproduction in which female and male gametes are mobile, but female gametes are larger than male and less mobile.
Ovogamia(3) - a form of sexual reproduction in which the female gametes are immobile and larger than the male gametes. In this case, the female gametes are called eggs, male gametes, if they have flagella, - spermatozoa if they don't have - sperm.
Ovogamy is characteristic of most animal and plant species. Isogamy and heterogamy are found in some primitive organisms (algae). In addition to the above, some algae and fungi have forms of reproduction in which germ cells are not formed: chologamy and conjugation. At chologamy unicellular haploid organisms merge with each other, which in this case act as gametes. The resulting diploid zygote then divides by meiosis to form four haploid organisms. At conjugations(4) the contents of individual haploid cells of the filamentous thalli are fused. Through specially formed channels, the contents of one cell flows into another, a diploid zygote is formed, which usually also divides by meiosis after a dormant period.
In eukaryotes, the sexual process is associated with the formation of germ cells - GAMET. Male gametes are sperm, female gametes are eggs. A new organism arises as a result of fertilization, MERGING THE NUCLEI OF THE EGG And SPERMATOZOID. Formed ZYGOTE.
Obviously, gametes must have half as many chromosomes as somatic cells, since otherwise the number of chromosomes in each subsequent generation would have to double. This does not happen due to a special type of cell division MEIOSIS.
Sexual reproduction creates a higher genetic variability in a population. As a result of a number of processes, the genes originally carried by the parents end up in a new combination in the offspring. It is due to recombination within the litter that numerous genetic differences are found, which increases the adaptive potential of the population and the species as a whole.
23 .Gametogenesis (spermatogenesis and ovogenesis).
1.1. Gametogenesis or pre-embryonic development is the process of maturation of germ cells, or gametes. Since during gametogenesis the specialization of eggs and sperm occurs in different directions, oogenesis and spermatogenesis are usually distinguished, respectively. Gametogenesis is naturally present in the life cycle of a number of protozoa, algae, fungi, spore and gymnosperms, as well as multicellular animals. In some groups, gametes are secondarily reduced (marsupials and basidiomycetes, flowering plants). The processes of gametogenesis have been studied in most detail in multicellular animals.
reproduction - the adaptation of organisms to the continuation of life. Reproduction is associated at the molecular level with DNA replication. There are sexual and asexual reproduction. In asexual reproduction, a new organism arises from somatic cells. With sexual - from special germ cells. Asexual - vegetative is more common in low-organized organisms. New individuals exactly repeat the parent individual (genetic copying of the parent individual). Genetically identical individuals in animals and humans is a rather rare phenomenon. Sexual reproduction is based on a mechanism aimed at preventing the copying of genetic information. More evolutionarily young organisms reproduce sexually.
Benefits of sexual reproduction
The ability of a population to change more rapidly.
Facilitate visualization.
Great genetic diversity in the offspring facilitates adaptation to unpredictable environmental conditions.
Mature germ cells contain a haploid set of chromosomes. Ripening - diploid. They have a nucleus, cytoplasm, cell organelles. Despite this, the structure of male and female germ cells is not the same. This is due to various functions. Functions sperm - fertilization (stimulation of the further development of the egg), providing genetic information to the male body. All spermatozoa have flagella, are motile, small in size (50-90 microns in humans). They consist of a head, neck, middle part and tail. The head is 5 microns, the neck is 5. The head of the spermatozoon is almost completely occupied by the nucleus, there is little cytoplasm, it is in a liquid-crystalline state (protection from harmful phenomena - ionizing radiation). It is located on the periphery of the nucleus. At the end of the head is an acrosome with a modified Golgi complex. Enzymes: hyaluronidase, mucinase. In the plasma membrane there is proacrosin, which turns into acrosin, passing through the female genital tract (the inhibitor is cleaved off). The function of acrosin is the cleavage of follicular cells, the cleavage of the zona pellucida.
The cervix contains a pair of centrioles. The microtubules of one of them elongate, the main thread of the tail is formed. The neck contains many mitochondria arranged in a spiral.
Organelles of movement - flagella, are capable of beating only when mixed with a secret. Prostate during ejaculation. In case of violation of the functions of the prostate gland - male sterility.
Egg.
Functions: transfers half of its future chromosome set to the embryo; during fertilization, the egg brings much more cytoplasm; the ovum supplies the embryo with food reserves before its own nutrition begins.
The size of the eggs is much larger than the size of spermatozoa (130-150 microns in humans). In a mature egg, all the materials that provide the initial stages of embryo development are stored. If the sperm, while maturing, tries to get rid of the cytoplasm, the egg, on the contrary, seeks to increase its amount. There are ribosomes, r-RNA, t-RNA, morphogenetic factors. Many proteins are synthesized in the liver, the fat body, and then transported to the egg. The ovum has a plasma membrane. During fertilization, the plasma membrane controls the supply of many ions (eg, sodium). Adjacent to it is the yolk membrane (glycoproteins - a specific attachment of a sperm of its own species to the corresponding egg), often transparent, the egg is surrounded by a layer of cells of the radiant egg - follicular feeding cells. For fertilization, the sperm must pass through all the membranes.
The hereditary material brought by the egg and sperm is the same in size.
The process of formation of eggs in the ovaries oogenesis, oogenesis. Spermatozoa are formed in the testes, the process is called spermatogenesis. Those and other cells are formed in different ways, but there are some common features.
spermatogenesis. Morphologically, the testis consists of many seminiferous tubules. Domed structure. Between the seminiferous tubules - Leiding cells (begin to work at 12-14 years old) synthesize testosterone - the development of secondary sexual characteristics. The testicle very early becomes an endocrine organ, under the influence of androgens, the formation of male genital organs occurs. The seminiferous tubule has zones:
breeding,
maturation and formation.
There are growth periods of the same name. The breeding zone in the outer part of the testis. The cells are rounded, there are many cytoplasms, the nucleus is large - spermatogonia. They reproduce by mitosis, and the testes increase in size until puberty, after which only stem cells divide. The supply of cells does not decrease and the testis does not decrease either. In the breeding zone 2n2c. the next phase is growth. The size of the nucleus and cytoplasm increases, DNA replication occurs (interphase 1), cells are spermatocytes of the first order 2n4c. These cells enter the zone of formation and maturation at the seminiferous tubules. Meiosis consists of 2 mitotic divisions, after the first division n2c, after the second - nc.
Ovogenesis (ovaries). Sex glands are laid on the 2nd month embryonic development. In humans, the yolk sac is laid very early (the function of the formation of primary germ cells, the provision of nutrients). Sex cells (primary) migrate to the developing sex gland, and the yolk sac degenerates. In embryogenesis, the ovaries are not active. The formation of female germ cells is passive. Primary sex cells are ovogonia, they divide. Oocytes of the first order are formed. The division period ends by the 7th month of embryogenesis - 7,000,000 primary cells. 400-500 mature during a lifetime, the rest are unclaimed. The development of eggs in humans is blocked in the prophase of the first meiotic division (at the diplotene stage). With the onset of puberty, the oocyte increases in size, and the size of the yolk also grows. Pigments accumulate, biochemical and morphological changes occur. Each oocyte is surrounded by small follicular cells that mature in the follicle. The ovum, maturing, approaches the periphery. Follicular fluid surrounds it at all stages. The follicle ruptures. The egg enters the abdominal cavity. Then into the funnel of the oviduct. Continuation of meiosis in 2/3 of the oviduct as a result of contact of the egg with the sperm.
During meiosis, chromosomes are distributed. The result is 4 cores. Chromosome conjugation occurs (due to highly repetitive DNA sequences in 1 gene). Each of the 4 nuclei during gametogenesis receives only 1 chromatid from a pair. As a result of meiosis during spermatogenesis, 4 chromatids are obtained from each first-order spermatocyte and 4 spermatozoa are formed. From one oocyte of the first order, 2 nuclei with a haploid set of chromosomes are formed. One of them, with a large amount of cytoplasm (because during cytokinesis, the division is uneven) and the other is a reduction (guide) body. With subsequent division, an egg and a guide body are formed. During oogenesis, each oocyte produces 1 egg and 3 guide bodies, which degenerate and disappear. The egg contains all the necessary reserves of nutrients.
Meiosis- a way of distribution of chromosomes, genes, providing their independent and random recombination. During oogenesis, it serves to redistribute the cytoplasm between cells. Crossing over is a method that brings together and redistributes the genes of individual homologous chromosomes.
Phases of meiosis
Meiosis consists of 2 consecutive divisions with a short interphase between them.
Prophase I- the prophase of the first division is very complex and consists of 5 stages:
Leptotena or leptonema- packing of chromosomes, condensation of DNA with the formation of chromosomes in the form of thin threads (chromosomes shorten).
Zygoten or zygonema- conjugation occurs - the connection of homologous chromosomes with the formation of structures consisting of two connected chromosomes, called tetrads or bivalents and their further compaction.
Pachytene or pachinema- (the longest stage) - in some places, homologous chromosomes are tightly connected, forming chiasmata. Crossing over occurs in them - the exchange of sites between homologous chromosomes.
Diploten or diplonema- partial decondensation of chromosomes occurs, while part of the genome can work, processes of transcription (RNA formation), translation (protein synthesis) occur; homologous chromosomes remain connected to each other. In some animals, chromosomes in oocytes at this stage of prophase of meiosis acquire the characteristic shape of lampbrush chromosomes.
diakinesis- DNA again condenses as much as possible, synthetic processes stop, the nuclear envelope dissolves; centrioles diverge towards the poles; homologous chromosomes remain connected to each other.
By the end of Prophase I, centrioles migrate to the poles of the cell, spindle fibers are formed, the nuclear membrane and nucleoli are destroyed.
Metaphase I- bivalent chromosomes line up along the equator of the cell.
Anaphase I- microtubules contract, bivalents divide, and chromosomes diverge towards the poles. It is important to note that, due to the conjugation of chromosomes in the zygotene, whole chromosomes consisting of two chromatids each diverge towards the poles, and not individual chromatids, as in mitosis.
Telophase I
The second division of meiosis follows immediately after the first, without a pronounced interphase: there is no S-period, since no DNA replication occurs before the second division.
Prophase II- condensation of chromosomes occurs, the cell center divides and the products of its division diverge to the poles of the nucleus, the nuclear envelope is destroyed, a division spindle is formed, perpendicular to the first spindle.
Metaphase II- univalent chromosomes (consisting of two chromatids each) are located on the "equator" (at an equal distance from the "poles" of the nucleus) in the same plane, forming the so-called metaphase plate.
Anaphase II- univalents divide and chromatids diverge towards the poles.
Telophase II Chromosomes despiralize and the nuclear membrane appears.
As a result, four haploid cells are formed from one diploid cell. In those cases where meiosis is associated with gametogenesis (for example, in multicellular animals), the first and second divisions of meiosis are sharply uneven during the development of eggs. As a result, one haploid egg and three so-called reduction bodies (abortive derivatives of the first and second divisions) are formed.
Every living organism has the ability to reproduce itself, to continue its species. There are two types of reproduction in animals: asexual and sexual.
In asexual reproduction, only one parent individual participates, which divides or buds, as a result of which two or more new individuals are formed, similar in their hereditary characteristics to the parent. This is how unicellular animals, such as amoeba, reproduce mainly. Hydras reproduce by budding, in which only a small part of the body separates from the parent organism and develops into an independent individual.
In some species, the entire body of the parent may break into pieces, each of which develops into a new animal. This method of reproduction is typical for starfish: a new star can grow from one beam. In the old days, oyster fishermen, finding starfish in places of accumulation of edible mollusks, tried to destroy them: they cut them in two and threw them into the water. As a result, the number of sea stars doubled.
Some species reproduce using spores, which are special cells. Spores reproduce, for example, the causative agent of malaria, Plasmodium, which, when bitten by a malarial mosquito-carrier of Plasmodium, enters the human blood. In red blood cells - erythrocytes - plasmodium is divided into 12-14 spores, the erythrocyte bursts, the spores enter the blood plasma and penetrate into new erythrocytes, causing malaria in humans. If such a patient is bitten by an uninfected mosquito, having sucked in a certain amount of blood with spores, then they multiply in the stomach of the mosquito and penetrate into the salivary glands. If such a mosquito bites a person, he will be infected with malaria.
The most perfect form is sexual reproduction. The simplest animals, such as paramecium, first conjugate - keep in pairs, and then the cells diverge and each divide into two new cells. In other animals, both female and male reproductive products are formed in one individual, which, merging, give rise to a new organism.
Some animals can also develop from an unfertilized egg. For example, in honeybees, the queen and workers develop from a fertilized egg, while the male drone develops from an unfertilized one.
In many vertebrates, reproduction occurs after the fertilization of an egg by a sperm (male sex cell) in the body of a female. After fertilization, a zygote is formed, which divides many times, turns into an embryo, and subsequently into an adult organism.
Each species of organisms is characterized by a certain intensity of reproduction. It depends on the habitat, temperature, nutrient medium or food, the size of the animal and the presence of natural enemies. For example, an elephant gives birth to one cub in 4-5 years. In order for him to survive and become an adult, the elephant feeds him, constantly takes care and protects him from enemies. And the cod does not care about the offspring. Therefore, for one spawning, she throws out up to 10 million eggs, the moon-fish even more - up to 300 million. In mammals, the development of the embryo occurs inside the mother's body, where the conditions are most favorable for it. Therefore, in mammals, the number of offspring is much lower than in animals whose development occurs in the external environment. The more endangered the offspring of any animal species, the more descendants appear so that the species can survive.