Alternation of generations is ... Alternation of generations in plants

In the modern world it has become customary to call technical terms all that surrounds us. The mechanism of reproduction ... This is how the scientists "dubbed" the minds of the miracle of the birth of a new life.
A miracle in which any component is so harmonious, diverse and at the same time indispensable, which sometimes remains to be surprised. For many millennia, mankind has been racking its brains over the question of the primacy of eggs and chicken, and nature has long had an answer to all questions. Rationalism and the diversity of decisions in maintaining the stability of a particular species and at the same time acquiring a diversity of characters in animate nature are unparalleled.

Genetic basis of life

One such device is the alternation of generations. The diversity of animal and plant species is achieved through the creation of various combinations of gene material. Alternation of generations is a special form of species conservation in the changing conditions of the external environment, which is found mainly in many plants and inferior invertebrates. It is a change of sexual and asexual reproduction. What triggers the launch of one or another method of reproduction and what are the goals they pursue? In order to answer this question, it is necessary to understand more deeply what are sexual and asexual reproduction and what are the advantages for the biological species and the minuses they represent.

Sexual reproduction

The process of sexual reproduction involves the participation in the creation of a new life of two individuals, which, in and of themselves, are carriers of their individual set of chromosomes in a spiral double strand of DNA. This unique set of gene material is expressed in the presence of this individual, and only her, of certain characteristics, which she partially transfers to her offspring.

With the participation of two individuals in the process of sexual reproduction, each of which gives the potential continuer of the species its half-set of chromosomes, the next generation will have the characteristics of both parent organisms. That is why the alternation of generations is observed in both simple and complex forms of life, which produce reproduction through sexual reproduction.

What contribution does the sexual reproduction make to the gene pool of the species?

Even within a relatively small population, a set of combinations of gene material can be infinitely wide. This type of breeding pursues a policy of introducing diversity into the genetic background of the species population. Diversity can also be achieved through the use within the established population of new specimens of this species, which in various ways can penetrate from the outside. Or, as, for example, in plants or some coelenterates, due to sex cells "delivered to the house" with the help of wind, water or insects.

An important point in sexual reproduction is to indicate the possibility of participation in it of mostly healthy and strongest individuals. Thus, this type of reproduction makes it possible to realize natural selection, which contributes to the possibility of fixing the signs working for the benefit of this species.

Asexual reproduction as the formula of the multiplier of the number of individuals

Alternation of generations is a system used to increase and preserve a species in which asexual reproduction plays an important role. From its advantages, we can safely note the possibility of rapidly increasing the population size when favorable environmental conditions for a given species appear. Preservation and multiplication of the genetic fund of the population by means of multiple cloning of already existing gene combinations, which significantly increases the chance of participation of these combinations in future sexual reproduction.

Alternation of phenotypes in different kingdoms

The alternation of generations in algae depends on the temperature background, the chemical composition of the water (especially the salt concentration in it), the duration of the diurnal light period, the intensity of illumination, and the seasonal variation. All these factors regulate the production of certain reproductive cells. Some plants produce spores, the basis of asexual reproduction, and are called sporophytes. Plants that produce gametes for reproduction reproductive sex (a sex cell with a single set of chromosomes in the nucleus) are called gametophytes. There are algae that produce both types of gametes (gametes and spores), respectively, they were called gametosporophytes. Algae of all these types can differ from each other both morphologically and biologically. So the red seaweed of Porphyry Tener in the form of a sporophyte looks like threads branching in one row, penetrating into the substrate, which can serve as calcareous rocks or shells of mollusks. Sporophytes of this species live in great depth, prefer low illumination. Individuals involved in the production of cells for sexual reproduction (gametophytes) live in the form of plates in the tidal zone at a shallow depth in intense light. Red algae, being more highly organized, show diverse and more complex cycles of development, in which there is a change of different forms of existence of organisms of one species during the life cycle - heteromorphic development.

Who is characterized by reproduction by means of gametosporophytes

Gametosporophytes are typical for many species of green, brown and red algae. Alternation of generations is observed in them in the development of reproductive cells of both types: spores and gametes, occurring at different times and conditioned by changes in environmental conditions. The consistency between the manifestations of features in the phenotype and the corresponding changes in the environment is the main evolutionary factor that provides the driving form of selection.

Alternation of generations in plants and animals: what are the two different kingdoms like

Classification, dividing the living world into four kingdoms, greatly simplifies the perception of biological science in the early stages of its study. However, with a more in-depth course, it becomes clear that there are many intermediate cases in the existing classification. Thus, the alternation of generations in coelenterates has a particularly interesting character. In the life cycle of the generation of sexual and asexual reproduction have a different appearance, lead a radically different lifestyle, live in different places and eat differently. In metagenesis, there is an alternation of life forms: polyps and jellyfish. Attached to the substrate polyps lead a sedentary lifestyle. Polyps are characterized by asexual reproduction by budding from the mother's body of new, identical in genetic make-up, daughter individuals who spend their lives also in the form of polyps. The food is carried out by filtration of water masses, with the current of which microscopic particles of organic matter are fed, which serve as a food for the organism.

Polyps can organize huge communities. Similarly, the alternation of generations in coelenterates creates for a long time colonial forms of polyps in the form of coral reefs. When there are certain conditions that are individual for each species (changing the temperature regime, the season, changing the underwater currents, the moon phase, the time of migrations, etc.), polyps bud off small jellyfish. Jellyfish are mobile, easily move in the water column, in the form of food are predators. Growing up to the age of sexual readiness, jellyfish continue the cycle of development of the species through sexual reproduction. From the fertilized cells, mobile larvae develop which settle to the bottom, attach to the substrate, lose mobility and grow into a polyp. Alternation of generations is a life cycle undergoing a kind that invariably closes, returning to its original stage, but with a different set of chromosomes, and therefore with other characteristics.

Mosses also reproduce sexually

Alternation of generations is observed in higher plants, including mosses. A characteristic feature of the life cycle of this plant department is the fact that the dominant life form is the gametophyte in the form of a green perennial plant that has leaf-like outgrowths and rhizoids, which we observe. Alternation of generations in mosses provides a sporophyte, which is an asexual stage of the developmental cycle, represented by a small box on the pedicle with spores, associated with the gametophyte by feet, through which physiological supply of the spores takes place. The sporophyte has a short lifespan, can not take root independently. Drying after ripening and rash spores.

Why in biology 1 + 1 = 3

By stating the above, it can be concluded that both ways of reproduction have their evolutionary significance. Alternation of generations is a process that ensures the fixation of necessary characteristics and the rejection of unnecessary, manifested in the phenotype, through natural selection. Only in the case of asexual reproduction of natural selection, spontaneous mutations will be "exposed" to the trial, and in the case of sex, in addition to mutations, the signs of both parents will show up in the phenotype.

Why, in evolutionary biology, when they talk about sexual reproduction, the sum of two units is not equal to two (1 + 1 ≠ 2)? Because as a result of fertilization, the child is given a set of genes that is not identical with any parent. The individual will bear not the maternal and non-parental gene, but develop based on the information that came from the parents. It will bear the third, unique and unique genotype, so biologists solve the mathematical example a little differently. This is what provides alternation of generations in plants and mammals, where with every new degeneration of genetic material it becomes more and more complex, elegant and perfect!