Gametogenesis of female germ cells presentation. Gametogenesis. Ovogenesis. stages of spermatogenesis. The structure of the egg and sperm. Meiosis is the basis of genetic combinative variability

Gametogenesis In the formation of gametes, three phases are distinguished: the reproduction phase, the growth phase, and the maturation phase. In spermatogenesis, there is another phase - the formation phase. Gametogenesis is the process of development of germ cells of gametes. Stages of gametogenesis The process of sperm formation is called spermatogenesis, and the formation of eggs is called oogenesis.

Multiplication phase: Diploid cells divide repeatedly by mitosis. They are called oogonia and spermatogonia. Set of chromosomes 2n. Growth phase: The essence of this phase is the growth of spermatogonia and ovogonia, in addition, DNA replication occurs in this phase, each chromosome becomes two-chromatid (2n 4c). The resulting cells are called oocytes of the 1st order and spermatocytes of the 1st order. Gametogenesis

Maturation phase: Essence of the meiosis phase. Gametocytes of the 1st order enter the first meiotic division. As a result of the first meiotic division, gametocytes of the 2nd order are formed (a set of chromosomes n2c), which enter the second meiotic division, and cells with a haploid set of chromosomes (nc) are formed. Ovogenesis at this stage practically ends, and spermatogenesis includes another phase, during which the spermatozoa acquire their specific structure. Gametogenesis

During puberty, the diploid cells in the seminiferous tubules of the testes divide mitotically, resulting in many smaller cells called spermatogonia. Sertoli cells provide mechanical protection, support and nutrition for developing gametes. Leydig cells produce male sex hormones. Spermatogonia enter the growth phase and increase in size. Spermatogonia that have grown in size are called first-order spermatocytes. spermatogenesis

The maturation period begins when the 1st order spermatocyte undergoes the first meiotic division, resulting in the formation of two 2nd order spermatocytes. Then these newly formed cells divide (the second meiotic division), and as a result, haploid spermatids are formed. Thus, four haploid spermatids arise from one spermatocyte of the 1st order. spermatogenesis

The Golgi apparatus moves to one of the poles of the nucleus and forms the acrosome. Centrioles occupy a place at the opposite pole of the nucleus. At the base of the flagellum, mitochondria are concentrated in the form of a spiral sheath. Almost all of the spermatid cytoplasm is rejected. spermatogenesis

What happens in the reproductive zone during spermatogenesis? Diploid cells divide repeatedly by mitosis. They are called spermatogonia. Set of chromosomes 2n. What happens in the zone of growth and maturation during spermatogenesis? In the growth zone - the accumulation of nutrients, the growth and replication of DNA, in the maturation zone - meiosis. What is the set of chromosomes and DNA after the first and second divisions of meiosis? After the first n2c, after the second nc. What is spermatogonia? Spermatocytes of the 1st and spermatocytes of the 2nd order? Spermatogonia are the precursors of gametes in the reproduction zone, spermatocytes of the 1st order are cells entering the first division of meiosis, spermatocytes of the 2nd order are cells entering the second division of meiosis. What are the functions of Sertoli cells? They provide mechanical protection, support and nutrition for developing gametes. What are the functions of Leydig cells? Produce male sex hormones. What is an acrosome? Modified Golgi complex in the head of the spermatozoon. Contains enzymes necessary to dissolve the membranes of the egg. Let's summarize:

All periods of egg development are carried out in animals in the ovaries. In contrast to the formation of spermatozoa, which occurs only after reaching puberty (in particular, in vertebrates), the process of formation of eggs begins even in the embryo. The reproduction period is fully carried out at the embryonic stage of development and ends by the time of birth (in mammals and humans). Ovogenesis

1. Breeding zone. The ovogonia undergo mitotic division. 2. Zone of growth. Daughter cells resulting from the division of ovogons after DNA replication are called oocytes of the 1st order (2n4c). Oocytes increase in size, accumulating nutrients. 3. Maturing zone. Oocytes of the 1st order enter prophase I, which stops at the diplotene stage. There is a looping of "housekeeping genes", the chromosomes look like "lamp brushes". Ovogenesis

In years, monthly one of the oocytes of the 1st order continues meiosis. The first meiotic division produces two daughter cells. One of them, relatively small, is called the first polar body, and the other, larger, is the 2nd order oocyte. Ovogenesis

The second division of meiosis is carried out up to the stage of metaphase II and will continue only after the 2nd order oocyte interacts with the spermatozoon and fertilization occurs. Thus, strictly speaking, not an egg cell comes out of the ovary, but an oocyte of the 2nd order. Only after fertilization does it divide, resulting in an egg (or egg) and a second polar body. However, traditionally, for convenience, an oocyte is called an oocyte of the 2nd order, ready to interact with a spermatozoon. Thus, as a result of oogenesis, one normal egg and three polar bodies are formed. Ovogenesis

The mammalian egg was discovered in 1821 by K. M. Baer. The final maturation of the egg occurs after fertilization, therefore, in fact, a mature egg does not exist. The size of the eggs varies widely from several tens of micrometers to several centimeters (a human egg is about 100 microns, an ostrich egg, which has a length with a shell of about 155 mm, is also an egg). In most animals, the eggs have additional membranes located on top of the cytoplasmic membrane. Depending on the origin, there are: Primary membranes resulting from the release by the oocyte and, possibly, follicular cells of substances that form a layer in contact with the outer cytoplasmic membrane of the egg. In mammals, this membrane is called the zona pellucida. Ovogenesis

Secondary membranes formed by secretions of ovarian follicular cells. Not all eggs have. The secondary membrane of the eggs of many insects, for example, contains a micropyle canal through which the sperm enters the egg. Tertiary membranes, formed due to the activity of special glands of the oviducts. For example, in birds, the formation of protein, under-shell parchment, shell and supra-shell membranes occurs. Secondary and tertiary membranes, as a rule, are formed in the eggs of animals, the embryos of which develop in the external environment. Their structure corresponds to environmental conditions. Ovogenesis

Since mammals have intrauterine development, their eggs have only a primary membrane, on top of which there is a radiant crown layer of follicular cells that deliver nutrients to the egg. Depending on the amount of yolk contained in the eggs, there are: alecithal eggs (mammals, flatworms); isolecithal eggs (lancelet, sea urchin); moderately telolecithal eggs (fish, amphibians); sharply telolecithal eggs (birds). Ovogenesis

There are two types of fertilization: external, in which the meeting of spermatozoa and eggs occurs in the external environment; internal, in which the meeting of sperm and eggs occurs in the genital tract of the female (reptiles, birds, mammals). Most often, the spermatozoon is completely drawn into the egg, sometimes the flagellum remains outside and is discarded. From the moment the sperm enters the egg, the gametes cease to exist, as they form a single cell - the zygote. The sperm nucleus swells, its chromatin loosens, the nuclear membrane dissolves, and it turns into a male pronucleus. Fertilization

Pronuclei move to the center of the egg, DNA replication occurs, and after their fusion, the set of chromosomes and zygote DNA becomes 2n4c. The union of pronuclei is actually fertilization. Thus, fertilization ends with the formation of a zygote with a diploid nucleus. Fertilization is an irreversible process, that is, once a fertilized egg cannot be fertilized again. This occurs simultaneously with the completion of the second division of meiosis of the egg nucleus, which was resumed due to fertilization. Gradually, the nucleus of the egg turns into a female pronucleus. Fertilization

When does division of oogonia occur in humans (in the breeding zone)? Even before birth, starting at the age of three months. At what stage does the first-order oocyte division stop? Oocytes of the 1st order enter prophase I, which stops at the diplotene stage. What is formed from the first order oocyte after the first division of maturation? Oocyte of the second order and the first polar body. At what stage does second-order oocyte ovulation occur? At the metaphase stage - 2. When does the second division of meiosis end? After penetration of the spermatozoon, the first polar body divides and the division of the second-order oocyte ends. What is formed as a result of two divisions of meiosis from an oocyte? Ovum and three polar bodies. What is the meaning of such uneven divisions? Preservation of nutrients in one cell - the egg. What membranes are distinguished in the egg? Brilliant and radiant. Let's summarize:

Which animals have alecithal eggs? In mammals. Which animals have isolecithal eggs? In the lancelet, sea urchin. Which animals have moderately telolecil ova? In fish and amphibians. Which animals have sharply telolecithal oocytes? In birds and reptiles. Which pole of the egg is called the animal pole? Vegetative? The pole at which the active cytoplasm with the nucleus is animal, opposite, with a large amount of yolk is vegetative. What fertilization is called external? Internal? If fertilization occurs in water - external, if in the genital tract of the female - internal. On what day of the monthly cycle does the egg ovulate? On the 14th day. How long after ovulation is the egg capable of fertilization? Up to 48 hours. Let's summarize:

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.

GAMETOGENESIS IN ANIMALS Spermatogenesis Ovogenesis (in the testes) (in the ovaries) Reproductive period (mitosis) In the reproductive period In the embryonic period Growth period (interphase) Insignificant Long period First and second meiotic irregular division meiotic division 4 spermatozoa 1 ovum

Types and structure of gametes 1 2 Fig.1. Spermatozoa: 1 – rabbit, 2 – rat, 3 – guinea pig, 4 – human, 5 – crayfish, 6 – spider, 7 – beetle, 8 – horsetail, 9 – moss, 1О – fern. Fig.2. Mammalian egg: 1 - shell, 2 - nucleus, 3 - cytoplasm, 4 - follicular cells. The terms spermatozoon and ovum were coined by Karl Baer in 1827.

Even if the offspring receive identical genes from both parents, the effect of these genes may be different, because. genes carry a parental "imprint", different in males and females, which affects the normal development of the organism, and also plays a role in the occurrence of diseases. The phenomenon when, during the formation of gametes in the offspring, the previous chromosomal "imprint" received from the parents is erased and its genes are marked in accordance with the sex of this individual, called genomic imprinting.

Development of gametes in flowering plants Development of pollen grains. Each pollen grain develops from a microspore mother cell, which undergoes meiosis to produce 4 pollen grains. The development of the germinal grain. The embryo sac develops from a haploid megaspore resulting from the meiotic division of the macrospore mother cell.

Gametogenesis and Meiosis Gametogenesis should not be confused with meiosis. The essence of these processes is completely different: the formation of specialized germ cells and a specific variant of cell division with a decrease in the number of chromosomes. In groups that are characterized by a life cycle with a zygotic (for example, fungi) or spore reduction (for example, vascular plants) of the number of chromosomes, meiosis precedes gametogenesis and, as a rule, is separated from it by a significant time interval, since the formation of gametes occurs on haploid organisms. In groups that are characterized by a life cycle with gametic reduction (for example, multicellular animals), meiosis is associated with gametogenesis, but even here one cannot speak of the complete identity of these processes. Thus, a mature spermatozoon, ready for fertilization, is formed only after the completion of meiosis, while the oocyte matures before its completion, moreover, the fusion of gametes occurs even before the completion of meiosis in the oocyte.

slide 1

Gametogenesis

slide 2

GAMETOGENESIS

or pre-embryonic development - 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.

slide 3

GAMETOGENESIS IN ANIMALS

Spermatogenesis ♂ Ovogenesis ♀ (in the testes) (in the ovaries) Reproductive period (mitosis) In the reproductive period In the embryonic period Growth period (interphase) Insignificant Long period and second meiotic uneven division meiotic division 4 spermatozoa 1 ovum

slide 4

Types and structure of gametes

Fig.1. Spermatozoa: 1 - rabbit, 2 - rat, 3 - guinea pig, 4 - human, 5 - crayfish, 6 - spider, 7 - beetle, 8 - horsetail, 9 - moss, 1O - fern. Fig.2. Mammalian egg: 1 - shell, 2 - nucleus, 3 - cytoplasm, 4 - follicular cells. The terms spermatozoon and ovum were coined by Karl Baer in 1827.

slide 5

Even if the offspring receive identical genes from both parents, the effect of these genes may be different, because. genes carry a parental "imprint", different in males and females, which affects the normal development of the organism, and also plays a role in the occurrence of diseases. The phenomenon when, during the formation of gametes in the offspring, the previous chromosomal "imprint" received from the parents is erased and its genes are marked in accordance with the sex of this individual, called genomic imprinting.

slide 6

Development of gametes in flowering plants

development of pollen grains. Each pollen grain develops from a microspore mother cell, which undergoes meiosis to produce 4 pollen grains. The development of the germinal grain. The embryo sac develops from a haploid megaspore resulting from the meiotic division of the macrospore mother cell.

Slide 7

Diverse life cycles (alternation of generations)

A - zygotic meiosis: green algae, fungi. B - gamete meiosis: vertebrates, mollusks, arthropods. B - spore meiosis: brown, red algae and all higher plants.

Slide 8

gametogenesis and meiosis

Gametogenesis should not be confused with meiosis. The essence of these processes is completely different: the formation of specialized germ cells and a specific variant of cell division with a decrease in the number of chromosomes. In groups that are characterized by a life cycle with a zygotic (for example, fungi) or spore reduction (for example, vascular plants) of the number of chromosomes, meiosis precedes gametogenesis and, as a rule, is separated from it by a significant time interval, since the formation of gametes occurs on haploid organisms. In groups that are characterized by a life cycle with gametic reduction (for example, multicellular animals), meiosis is associated with gametogenesis, but even here one cannot speak of the complete identity of these processes. Thus, a mature spermatozoon, ready for fertilization, is formed only after the completion of meiosis, while the oocyte matures before its completion, moreover, the fusion of gametes occurs even before the completion of meiosis in the oocyte.

Presentation topic: gametogenesis, fertilization Performed: Todorova E.M.

• This is the individual development of an individual, the totality of its interrelated transformations that naturally take place in the process of implementing the life cycle from the moment the zygote is formed to death.

spermatogenesis

Spermatogenesis takes place in the testicles and is divided into four phases:

• breeding,

3) ripening,

4) formations.

spermatogenesis

During the reproduction phase, diploid spermatogonia divide repeatedly by mitosis. Part of the formed spermatogonia may undergo repeated mitotic divisions, resulting in the formation of the same spermatogonia cells. The other part stops dividing and increases in size, entering the next phase of spermatogenesis - the growth phase.

spermatogenesis

The growth phase corresponds to interphase 1 of meiosis, i.e. during it, the cells prepare for meiosis. The main event of the growth phase is DNA replication. During the maturation phase, cells divide by meiosis; during the first division of meiosis, they are called spermatocytes of the 1st order, during the second - spermatocytes of the 2nd order. From one spermatocyte of the 1st order, four haploid spermatids arise. The formation phase is characterized by the fact that initially spherical spermatids undergo a series of complex transformations, as a result of which spermatozoa are formed. It involves all elements of the nucleus and cytoplasm.

spermatogenesis in humans

In humans, spermatogenesis begins at puberty; the period of sperm formation is three months, i.e. every three months, spermatozoa are renewed. Spermatogenesis occurs continuously and synchronously in millions of cells.

• Mammalian sperm is shaped like a long filament. The human sperm length is 50–60 µm. In the structure of the spermatozoon, one can distinguish the “head”, “neck”, intermediate section and tail. The head contains the nucleus and acrosome. The nucleus contains a haploid set of chromosomes. Acrosome is a membrane organoid containing enzymes used to dissolve the membranes of the egg. There are two centrioles in the neck, and mitochondria in the intermediate section. The tail is represented by one, in some species - two or more flagella. The flagellum is an organelle of movement and is similar in structure to the flagella and cilia of protozoa. For the movement of flagella, the energy of macroergic bonds of ATP is used, ATP synthesis occurs in mitochondria.
• The spermatozoon was discovered in 1677 by A. Leeuwenhoek.

Spermatozoa: 1 - rabbit; 2 - rats; 3 - guinea pigs: 4 - humans; 5 - decapod cancer; 6 - spider; 7 - beetle; 8 - horsetail; 9 - moss; 10 - fern.

It is carried out in the ovaries, is divided into three phases:

1) reproduction,

3) maturation.

• During the reproductive phase, diploid ovogonia divide repeatedly by mitosis. The growth phase corresponds to interphase 1 of meiosis, i.e. during it, the preparation of cells for meiosis occurs: the cells increase significantly in size due to the accumulation of nutrients. The main event of the growth phase is DNA replication. During the maturation phase, cells divide by meiosis. During the first division of meiosis, they are called oocytes of the 1st order. As a result of the first meiotic division, two daughter cells arise: a small one, called the first polar body, and a larger one, an oocyte of the 2nd order. During the second meiotic division, the 2nd order oocyte divides to form the egg and the second polar body, and the first polar body divides to form the third and fourth polar bodies. Thus, as a result of meiosis, one egg and three polar bodies are formed from one oocyte of the 1st order.

• Unlike the formation of spermatozoa, which occurs only after reaching puberty, the process of formation of eggs in humans begins even in the embryonic period and flows intermittently. In the embryo, the phases of reproduction and growth are fully realized, and the maturation phase begins. By the time the girl is born, her ovaries contain hundreds of thousands of oocytes of the 1st order, stopped, "frozen" at the diplotene stage of prophase 1 of meiosis - the first block of oogenesis.
• During puberty, meiosis will resume: approximately every month, under the influence of sex hormones, one of the oocytes (rarely two) will reach metaphase 2 of meiosis - the second block of oogenesis. Meiosis can go to the end only under the condition of fertilization; if fertilization does not occur, the 2nd order oocyte dies and is excreted from the body.

• The shape of the eggs is usually round. The size of the eggs varies widely - from a few tens of micrometers to several centimeters (a human egg is about 120 microns). The structural features of the egg cells include: the presence of membranes located on top of the plasma membrane and the presence in the cytoplasm of a more or less large amount of reserve nutrients.

• Due to the accumulation of nutrients, polarity appears in the eggs. Opposite poles are called vegetative and animal. Polarization is manifested in the fact that there is a change in the location of the nucleus in the cell (it shifts towards the animal pole), as well as in the distribution of cytoplasmic inclusions (in many eggs, the amount of yolk increases from the animal to the vegetative pole).
• The human egg was discovered in 1827 by K.M. Baer.

The structure of the egg in hydra (1), annelids from the genus Urechis (2), sea urchin (3), Drosophila (4, egg shortly after fertilization), perch (5), chicken (6), human (7)

Fertilization

• Fertilization is an irreversible process, that is, once a fertilized egg cannot be fertilized again.

Depending on the number of individuals participating in sexual reproduction, there are:

• cross fertilization - fertilization in which gametes formed by different organisms take part;
• self-fertilization - fertilization in which gametes formed by the same organism merge (tapeworms).

"Sexual reproduction of organisms" - After the formation of the blastula, the process of gastrulation begins. For example, in intestinal. As a result of a series of crushings, a blastula is formed. Indirect development occurs in the larval form, direct - in non-larval and intrauterine. Division. All vital functions of the embryo are carried out through the maternal organism.

"Forms of reproduction" - Spores of mosses and ferns are formed by mitosis. 2. Sporulation. Bacteria reproduce by mitotic divisions. 3. Budding. Sexual reproduction is characteristic of most living organisms (except for prokaryotes). 6. Polyembryony. Some bacteria, under favorable conditions, are able to divide every 20 minutes.

"Individual development of the organism" - Double fertilization. Press conference. Some of the students were given a task ahead of the curve. External fertilization. Zygote. What is the significance of the biogenetic law? A - embryonic B - postembryonic C - direct development D - indirect development. Parthenogenesis. Stages of embryonic development.

"Embryonic development of organisms" - Stages of embryogenesis. Grade 11. Generalization. The concept of embryogenesis. Deformities. The concept of ontogenesis. Bookmark organs. Neither preformism nor epigenesis provide a correct understanding of the processes of embryonic development. From what moment does the stage begin and end: crushing, gastrula? Why do scientists need to know the patterns of ontogeny?

"Biology Sexual reproduction" - Internal: testes; vas deferens; seminal vesicles; prostate. Chlamydomonas. Without the participation of germ cells. Menstrual cycle. With the participation of germ cells. Zygote 46 chromosomes. =. Yeast budding. The organism develops from a part of the mother. Fertilization and embryonic development.