Lesson "formation of germ cells". Meiosis is the main stage in the formation of germ cells. Development of germ cells presentation

“Sexual disease” - Immunity is not developed after syphilis. There are male, female and childhood gonorrhea. The disease is curable. Signs of the disease appear 3-4 weeks after contact. Syphilis. To detect hepatitis, you need to take a blood test. The disease is characterized by blistering rashes on the face, genitals and buttocks.

“Sexually transmitted diseases” - The book is intended for dermatovenerologists, gynecologists, urologists, family doctors and other specialists. The causative agents of STIs are pathogenic (disease-causing) microorganisms - bacteria, viruses, protozoa. The materials are intended for dermatovenerologists, clinical microbiologists, urologists, obstetricians and gynecologists.

“Early sexual intercourse” - Not everyone can cope with jealousy. The role of adolescent relationships in the formation of reproductive function. Try to explain the expression “...to love and be loved.” Includes 5 diseases: the most famous of which are: syphilis, gonorrhea. The attitude towards jealousy is no less contradictory than towards love.

“Sex education for adolescents” - Sex education is associated with complex medical, pedagogical and social problems. First option. And the relationship between parents is an example of gender relations. The problem of bad habits in children and adolescents. Third option. There are, for example, many bad habits that, without causing harm to the person himself, bother others.

“Sexual reproduction of animals” - Parthenogenesis - in bees. How many individuals participate in sexual reproduction? Males develop from unfertilized eggs. Hermaphrodites Annelids and flatworms, coelenterates, crustaceans, some fish, lizards. The advantage of parthenogenesis is an increase in the rate of reproduction. In bees, ants, aphids, wasps, daphnia.

“Formation of germ cells” - “Reproduction and individual development of organisms.” Phases of mitosis. The process of development of female reproductive cells. Types of reproduction. Reduction in the number of chromosomes by half. (Prophase I) 2. Spiralization of chromosomes. Cell structures containing genetic information -... 12. Determine whether the following judgments are correct.

What is the process in the pictures?

Gametes - sex cells

Egg

Sperm

SPERMATOGENESIS is the formation of spermatozoa (sperm cells)

OOGENESIS is the formation of an egg

Gametogenesis – formation of germ cells

Meiosis is a method of producing gametes

Independent work with the textbook Task 1. Consider divisions I and II of meiosis and its phases Task 2. Using the notes on

The meaning of gametogenesis:

Biological significance of meiosis

Let's do it again!

Select the features that characterize

Meiosis I Prophase I. The longest and most complex phase of meiosis. Consists of a number of successive stages. Homologous chromosomes begin to be attracted to each other by similar areas and conjugate. Conjugation is the process of close bringing together of homologous chromosomes. A pair of conjugating chromosomes is called a bivalent. The bivalents continue to shorten and thicken. Each bivalent is formed by four chromatids. That's why it's called a tetrad. The most important event is crossing over - the exchange of chromosome sections. Crossing over results in the first recombination of genes during meiosis. At the end of prophase I, the nuclear envelope and nucleolus disappear. The bivalents move to the equatorial plane. Centrioles, if present, move to the cell poles and a spindle is formed.

Meiosis I Metaphase I The formation of the spindle ends. Chromosome spiralization is maximum. The bivalents are located in the equatorial plane. Moreover, the centromeres of homologous chromosomes face different poles of the cell. The location of bivalents in the equatorial plane is equally probable and random, that is, each of the paternal and maternal chromosomes can be turned towards one or the other pole. This creates the preconditions for the second gene recombination during meiosis. Spindle strands are attached to the centromeres of chromosomes

Meiosis I Anaphase I. Whole chromosomes diverge to the poles, and not chromatids, as in mitosis. Each pole has half of the chromosome set. Moreover, pairs of chromosomes diverge as they were located in the equatorial plane during metaphase. As a result, a wide variety of combinations of paternal and maternal chromosomes arise, and a second recombination of genetic material occurs.

Meiosis I Telophase I In animals and some plants, chromatids despiral, and a nuclear envelope forms around them. Then the cytoplasm divides (in animals) or a dividing cell wall is formed (in plants). In many plants, the cell immediately goes from anaphase I to prophase II.

Formation of germ cells. Meiosis
Presentation by biology teacher, School No. 879, Moscow, Titova S.S.

Meiosis
This is a method of reduction division of primary germ cells, as a result of which germ cells are formed.
Conjugation is the process of fusion of homologous (paired) chromosomes along their entire length.
Crossing over is the mutual exchange of homologous regions of homologous chromosomes.

Phases of meiosis
Meiosis consists of 2 consecutive divisions with a short interphase between them.
Division I of meiosis
II division of meiosis
Prophase I
Prophase II
Metaphase I
Anaphase I
Telophase I
Metaphase II
Anaphase II
Telophase II

Phases of meiosis. Prophase I
Leptonema - packaging of chromosomes, condensation of DNA to form chromosomes in the form of thin threads (chromosomes are shortened).
Zygonema - conjugation occurs - the formation of structures consisting of two connected chromosomes, called tetrads or bivalents, and their further compaction.
Pachynema - in some places homologous chromosomes are tightly connected, forming chiasmata, crossing over occurs.
Diplonema - partial decondensation of chromosomes occurs.
Diakinesis - DNA condenses to the maximum again, synthetic processes stop, the nuclear membrane dissolves; Centrioles diverge towards the poles; homologous chromosomes remain connected to each other.

Phases of meiosis
Metaphase I
Homologous chromosomes line up in pairs (bivalents) above and below the equatorial plane.
Anaphase I
Homologous chromosomes, consisting of two sister chromatids, diverge to the poles of the cell. There is a reduction in the number of chromosomes.

Phases of meiosis
Telophase I
2 cells are formed with a haploid set of chromosomes, but each chromosome consists of 2 sister chromatids.
The cell begins division II.

Sexual reproduction

During sexual reproduction, individuals of each next generation arise as a result of the fusion of two specialized haploid cells - gametes.

Gametogenesis

- maturation of germ cells

spermatogenesis

ovogenesis

Maturation of the female reproductive cell - egg

Maturation of the male reproductive cell - sperm

Sperm maturation

Maturation of the egg

occurs in the testes

occurs in the ovaries

Gametogenesis

spermatogenesis

ovogenesis

Zone

reproduction

Zone

growth

Zone

maturation

Zone

maturation

Breeding area

Zone

growth

Sperm

Acrosome

head

Mitochondria

Core

Cytoplasm

Tail

Egg

Core

Shiny shell

radiant crown

Plasma membrane

At the moment of division, germ cells are especially sensitive to the action of harmful factors: radiation, chemicals, etc.

Adverse effects on eggs are especially dangerous. After all, these cells are formed in the embryo, and their supply is not replenished throughout life.

Thanks to meiosis during gametogenesis

A certain and constant number of chromosomes is maintained in all generations of each species of plants, animals and fungi;

• extreme diversity in the genetic composition of gametes is ensured as a result of both crossing over and different combinations of paternal and maternal chromosomes when they diverge in anaphase I.

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