In today's world it has become customary to call technical terms all that surrounds us.The mechanism of reproduction ... That's right, "dubbed" scientific minds miracle of new life.
Miracle, in which each component is so harmonious, diverse and at the same time, indispensable that sometimes one can only wonder.Many thousands of years mankind has racked their brains over the question of the primacy of eggs and chicken, and from nature for a long time is the answer to all questions.Rationalism and a variety of solutions in preserving the stability of individual species and, at the same time, the acquisition of a variety of symptoms in wildlife are unmatched.
genetic basis of life
One of these devices is the alternation of generations.The diversity of flora and fauna is achieved by creating different combinations of genetic material.The alternation of generations - is a special form of species conservation in a changing external environment, mostly found in many plants and lower invertebrates.It is a change of sexual and asexual reproduction.What causes the launch of a particular mode of reproduction and what goals they pursue?To answer this question should more deeply understand what are and the differences between sexual and asexual reproduction, which benefits the species, and they are cons.
Sexual reproduction
process of sexual reproduction involves in the creation of a new life of two individuals who, each in itself, are the bearers of their own individual sets of chromosomes in a double helix strand of DNA.This unique set of genetic material is expressed in the presence at this individual, and only her, certain signs that it is partially transmits to its offspring.
With the participation in the process of sexual reproduction of two individuals, each of which gives a potential successor type your half set of chromosomes, the next generation will be inherent attributes of both parental organisms.That is why the alternation of generations is observed both in simple and in complex forms of life, carrying the reproduction by sexual reproduction.
What contribution to the gene pool of the species makes sexual reproduction
Even within a relatively small population of a set of combinations of genetic material can be infinitely wide.This type of breeding pursues policy to diversify the species in the genetic background of the population.Diversity can also be achieved by using established within the population of new instances of a given species, which in many ways can penetrate from the outside.Or, for example, in plants or certain coelenterates, through germ cells "home delivery" by wind, water and insects.
important moment in sexual reproduction is necessary to indicate the possibility of participation in the predominantly healthy and most powerful individuals.Thus, this type of implementation allows reproduction of natural selection, thereby fixing capability attributes working for the given species.
Asexual reproduction as a factor of the number of individuals formula
alternation of generations - a system that is used to increase and preservation of the species, which plays an important role asexual reproduction.Because of its advantages can safely mention the possibility of rapidly increase population size under favorable for this species environmental conditions.Preserve and increase the genetic pool of the population using the multiple cloning existing combinations of genes, which significantly increases the chance to attend these type of combinations in the future sexual reproduction.
Alternating phenotypes in different kingdoms
alternation of generations in algae background depends on the temperature, chemical composition of the water (especially salt concentration in it), the duration of daily photoperiod, light intensity, the change of seasons.All these factors regulate production of certain reproductive cells.Some plants produce spores, the basis of asexual reproduction, and called the sporophyte.Plants that produce gametes for reproduction to sexual reproduction (sexual cells with a single set of chromosomes in the nucleus), called the gametophyte.There algae producing both types of reproductive cells (gametes and spores), and their respectively named gametosporofitami.Algae of all these types can differ from each other both morphologically and biologically.So red alga Porphyry Tener in the form of sporophyte looks like a thread, branching in a row, to introduce into the substrate, which can serve as calcareous rocks or shells of mollusks.Sporophytes of this species live at great depths, prefer low light.Individuals involved in the production of cells for sexual reproduction (gametophytes), live in the form of plates in the zone of the tide at a shallow depth under intense lighting.Red algae, being more highly demonstrate the diverse and challenging development cycles in which there is a change of the different forms of existence of organisms of the same species during the life cycle - heteromorphic development.
For whom is characterized by the proliferation of gametosporofitov
Gametosporofity typical of many species of green, brown and red algae.The alternation of generations have seen in the development of the reproductive cells of both types of spores and gametes originating at different times due to changes in environmental conditions.Consistency between the manifestations of signs in the phenotype and the corresponding changes in the environment - the main evolutionary factor, which provides the driving form of selection.
alternation of generations of plants and animals: what look like two different kingdoms
classification that divides the living world to the realm of 4, simplifies the perception of biological science in the early stages of its study.However, a more advanced course it is clear that the existing classification there are many intermediate cases.Thus, the alternation of generations in coelenterates is particularly interesting character.The life cycle of generations of sexual and asexual reproduction have a different appearance, are radically different from each other lifestyle, live in different places and different feed.In metagenesis an alternation of life forms: polyp and jellyfish.Attached to the substrate polyps sedentary.For polyps reproduce asexually by budding from the parent body's new identical in genetic composition subsidiaries individuals who spend their lives in the form of polyps.Powered by filtering water masses, with a current that brings the microscopic particles of organic matter that serve food for the body.
Polyps can organize a huge community.Similarly, the alternation of generations from the cnidarian organisms creates a long-term colonial forms polyps in the form of coral reefs.When certain conditions occur that are unique for each species (change of temperature, time of year, changing undercurrents, the lunar phase, migration, etc.), small jellyfish polyps bud.Jellyfish are mobile and can be easily moved in the water, in the image of power are predators.Grow up to the age of sexual readiness, jellyfish continue the cycle of species by means of sexual reproduction.Cells develop from fertilized movable larvae, which settle on the bottom, attached to the substrate to lose motility and grow into a polyp.The alternation of generations - a life cycle to undergo air which always closes, returning to its initial step, but with a different set of chromosomes, and hence with other features.
Mosses also reproduce sexually way
alternation of generations occurs in higher plants, including mosses.A characteristic feature of the life cycle of the plant department is the fact that the dominant life form in the gametophyte is a green perennial having a leaf-growths and rhizoids, which we observe.The alternation of generations mosses provides a sporophyte, which is asexual stage of the development cycle, represented by a small box on the leg with disputes related to the gametophyte stops through which the physiological maintenance of the dispute.The sporophyte has a short shelf life, can not take root on their own.Dries after maturation and rashes dispute.
Why Biology 1 +1 = 3
Noting the above, it can be concluded that both methods have their breeding evolutionary significance.The alternation of generations - a process that secures the necessary signs and unnecessary rejection, manifested in the phenotype, due to natural selection.Only in the case of asexual reproduction, "a court" of natural selection would be "exposed" spontaneous mutations, as in the case of sex, in addition to mutations in the phenotype showed signs of both parental species.
Why in evolutionary biology, when they talk about sexual reproduction, the sum of the two units is not equal to two (1 + 1 ≠ 2)?Because as a result of fertilization individual gets a set of children's genes are not identical to any of the parent birds.An individual will not carry the maternal and paternal gene, but to develop on the basis of the information that was received from parents.It will be the third carrier, unique and unrepeatable genotype, so biologists solve math example is a bit different.That is what provides the alternation of generations in plants and mammals, where with each new rebirth of genetic material becomes more complex, elegant and perfect!
