Forms of reproduction of organisms. Breeding species table

The ability of living things to reproduce their own kind is called reproduction. In this case, the genetic material is transmitted to the offspring, and parental traits will, to one degree or another, be inherent in the emerging daughter organisms.

Types of reproduction of offspring

Scientists distinguish two main forms of reproduction of organisms. It can be sexual or asexual. In the first case, 2 individuals are needed to reproduce offspring, and in the second, only one is enough.

With asexual reproduction, a new organism emerges from somatic cells. In nature, there are several ways to reproduce offspring without the participation of the genitals. These include vegetative propagation, budding, fragmentation, sporulation, division, cloning.

During sexual reproduction, new organisms appear as a result of the fusion of specialized germ cells called gametes and the subsequent formation of a zygote. This method is more advanced than asexual.

Benefit Comparison

It is worth noting that both methods of reproducing offspring have their advantages. For example, biologists identify the following benefits of asexual reproduction:

• the ability to play a significant number of individuals;
• the offspring is similar to the parent organism in all respects.

This method of reproducing new individuals makes it possible to quickly obtain numerous offspring. This is beneficial for species that live in constant conditions. It is the fast, numerous and accurate reproduction of copies of the mother's body that is the meaning of asexual reproduction. This method of producing offspring is used by both plants and simple organisms.

But sexual reproduction is characteristic of the vast majority of living things. It is able to guarantee the genetic diversity of the resulting daughter individuals. This is what allows them to quickly adapt to changing living conditions. Indeed, during the formation of a new organism, a combination of parental genes occurs.

Types of asexual reproduction of offspring

There are several ways to obtain daughter organisms without the participation of germ cells. Biology studies them all. Reproduction, the species of subsidiary organisms in which there is no change, can be carried out on the basis of the division of one or more cells.

In the first case, the following forms are distinguished:

• single or multiple (schizogony) cell division;
• spore formation;
• budding unicellular.

When dividing a group of cells, the classification is carried out as follows:

• fragmentation;
• budding of multicellular organisms (e.g. hydra).

Each of these types of asexual reproduction has its own characteristics.

Breeding forms

The simplest option is regular division. It is characteristic of many of the simplest. Examples of asexual reproduction by binary division: amoeba, ciliates, slipper, green euglena.

Sporulation is considered widespread. It is characteristic of almost all plants, fungi, and some simple and prokaryotic organisms (for example, bacteria or blue-green algae).

In a number of unicellular and multicellular organisms , a form of reproduction such as budding occurs. This happens as follows: a tubercle appears on the mother's body, which increases in size. The rudiments of all organs then appear there. When the process ends, budding occurs. This method of reproduction is used by gastrointestinal (hydra), unicellular (yeast, some types of ciliates).

But there are other examples of asexual reproduction of organisms. So, do not forget about fragmentation. In this process, the mother is divided into several parts. Each of them forms a new organism. For example, the filamentous algae of spirogyra can be torn anywhere. Of the two parts, two new organisms will be created in the future.

Vegetative propagation is characteristic of plants. According to the principle of the course of processes, it does not differ from budding or fragmentation. The plant can form special structures necessary for reproduction. Also, the appearance of a daughter organism is possible from part of the mother's body.

Sexual reproduction

Most living things reproduce similar organisms by mixing the genetic material of two individuals. For this, two gametes merge, and as a result, a diploid zygote is formed. In the process of development, a complete new organism is obtained from it. Sexual forms of reproduction of organisms are characteristic of some flowering plants, most animals and, of course, humans.

Gametes are of two types - male and female. If the species is dioecious, then each of the cell types is produced respectively by male and female individuals. Some organisms are capable of producing both types of gametes on their own. In this case, they are called hermaphrodites.

It is also possible sexual reproduction, in which gametes are not involved. These are species such as conjugation, gametangiogamy, apogamy, gologamia.

Breeding process

All organisms are made up of cells. Their growth, development is possible due to the fact that they are constantly reproduced. In the process of life, part of the cells age and die. They are being replaced by others. The only way to obtain new cells is to divide their precursors. This is a vital process for every living creature. For example, in the human body, several millions of these structural units are divided every second.

Biologists have described three methods of cell reproduction. Direct division is called amitosis, indirect division is called mitosis, and reduction is called meiosis. Regardless of the form of propagation of organisms, these processes occur in each of them.

Amitosis and mitosis

The least common and poorly studied method of cell division is amitosis. In this process, the core is separated by a constriction. At the same time, it is impossible to ensure uniform distribution of genetic material. A cell that has split by amitosis in most cases cannot continue to enter the normal cycle of mitosis. Therefore, it is considered doomed to death.

A universal way to multiply eukaryotic cells is mitosis. In animal cells, it passes, usually within an hour. The biological significance of reproduction cannot be underestimated, because it is thanks to it that the development and growth of all organisms is ensured.

Stages of mitosis

The sequence of all processes that occur during the formation of new cells is called the cell cycle. It consists of three stages: interphase, mitosis, cytokinesis. The duration of the cycle depends both on the types of cells and on external factors. Affects temperature, availability of nutrients, oxygen. For example, in the intestinal epithelium, such formation of new cells occurs every 8-10 minutes, in bacteria - every 20 minutes.

The process begins with interphase. At this time, there are processes of intensive growth. Substances that contribute to the growth of the cell and the fulfillment of all its assigned functions are produced. During interphase, DNA replication occurs.

Directly during the mitosis phase , nuclear fission occurs. Chromatids during this process are separated from each other and redistributed between the formed daughter cells in the form of chromosomes.

The process during which it is divided between new formations of the cytoplasm is called cytokinesis.

During mitosis, cells are formed in which the hereditary information is completely identical to the mother's body. During this process, the number of chromosomes doubles.

Meiosis

With this method of cell division, the number of chromosomes is halved. This ensures sexual reproduction of animals and sporogenesis in plants. During meiosis, two consecutive divisions are observed, and one-time DNA reduction is preceded by them .

All the necessary substances for the implementation of these processes are stored during the preliminary stage - interphase. Each stage of the division consists of four periods: prophase, metaphase, anaphase and telophase. The same phases also occur during mitosis, but each of the processes has its own characteristics.

The first meiosis is cell division, in which the number of chromosomes decreases by 2 times. From one diploid formation, two haploid ones appear. At this time, DNA helical processes occur, a spindle of division is formed. In addition, in prophase, conjugation of homologous chromosomes is carried out . The resulting pairs form a bivalent. In some places, chromatids cross over. This process is called crossover.

The final stage is the so-called second meiosis. This is a division in which cells with a haploid set of chromosomes consisting of one chromatid are formed. As a result of the described processes, 4 cells emerge from one diploid formation (oogony or spermatogonia).

The biological value of meiosis is the formation of cells that provide sexual reproduction of animals or spore formation in higher animals. It is this reproduction method that guarantees the maintenance of the genetic constancy of the species.

Features of sexual and asexual reproduction of organisms

Depending on how cells divide to produce offspring, different types of this process are distinguished. Separately, it should be noted that the survival of many organisms in changing conditions is due precisely to the fact that they can combine different methods of reproduction.

Of course, sexual and asexual reproduction of similar organisms is significantly different. The table of breeding species will help to understand what the fundamental difference is.

It is clear that the sexual forms of reproduction of organisms are more perfect. But the asexual method guarantees the rapid reproduction of a large number of descendants. During sexual reproduction, the number of daughter organisms does not grow so intensely.