Metagenesis: Definition, Process, Examples and Explanations

Metagenesis: Definition, Process, Examples and Explanations – What is meant by metagenesis? On this occasion About the knowledge.co.id will discuss it and of course about other things that also cover it. Let's look at the discussion together in the article below to better understand it.

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Metagenesis: Definition, Process, Examples and Explanations

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Alternation of descent or metagenesis is the life cycle experienced by organisms where each phase or the stages involve individuals with different genetic content, usually the haploid (n) stage and the diploid stage (2n).

Another definition of metagenesis, namely, metagenesis is the alternation of offspring from the asexual phase to the sexual phase and vice versa. In metagenesis, there is a life cycle in which organisms will periodically carry out sexual and asexual phases. Not all organisms experience metagenesis, examples of metagenesis are metagenesis in mosses, metagenesis in ferns, and metagenesis in seed plants.

In plant metagenesis, there is an alternation of generations between gametophyte and sporophyte generations. The gametophyte generation is the generation that produces gametes or sex cells (haploid generation), while the sporophyte generation is the generation that produces spores (diploid generation).

The term from the word metagenesis is used to be able or able to explain the echoes of changes that occur occurs in living things in the essence of life, which occurs in two ways of reproduction in the cycle his life. The two ways of reproduction are by means of marriage (sexually) and also asexually (not married) as well as forming spores.

The term metagenesis in a complex sense is a shift from a multicellular diploid form as well haploid within an organism's life cycle, regardless of whether the organism is freely living or not colonize.

With the understanding of metagenesis above, there is a lot of debate going on among researchers about metagenesis occurring in multicellular animals. One example of Cnidarian, Cnidarian in several junior and senior high school books, it is explained that as an example of metagenesis in animals, however, if you use the definition of metagenesis described above, it turns out that the two sexual and asexual phases of Cnidarian are diploid. Then it is not referred to as metagenesis but referred to as heterogamy.

But if you are asked about or about a process of metagenesis in animals, you can or can provide an example of metagenesis from jellyfish (Obelia), because for some researchers they still think metagenesis occurs in jellyfish animal. Even if according to Barnes (2001) and Scott (1996) metagenesis does not occur in multicellular animals.

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Process of Metagenesis

This process of metagenesis occurs in plants. This process of metagenesis is the basis of metagenesis (there are many variations in the future and it also depends on the organism, such as mosses and ferns).

Two single haploid gamete cells, each of which contains n chromosomes (haploid), which after merging become one diploid single-cell zygote (fuse to form a single-celled diploid zygote), which contains n pairs of chromosomes (2n / diploid).

The diploid zygote then undergoes germination or division by mitosis, so that the chromosomes in the cell remain 2n (diploid). The result is a multicellular diploid organism called a sporophyte. It is called a sporophyte because when it matures it produces sporophytes).

When the sporophyte matures, the sporophyte then produces one or more sporangia (singularly called a sporangium). This sporangium is a diploid organ that produces sporocytes (diploid single cells). The process of producing a sporocyte is carried out by means of meiotic division after which the spore cells that produce only half of the chromosomes will be reduced to n (haploid).

After these single spore cells (which are haploid / n) it germinates by mitosis so it will multicellular organisms are formed which are called gametophytes (ie gamete producers when mature). Because the method used is mitosis, the chromosomes in the gametophyte must remain haploid or also n chromosomes.

When the gametophyte matures, it produces one or more gametangia (when singular it is called the gametangium). This gametangium is the organ that produces haploid gametes in plants. Each of these gametangia has a mechanism so that the resulting gametes can or can reach a different type of gamete to be able to fuse into a zygote (and return to the first step of metagenesis).

It needs to be remembered that this is not a re-life cycle that keeps repeating itself, so don't assume that this is something the method of being able to re-make plants young, this is purely as two changes from the method of reproduction for survival kind.

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Example of Metagenesis

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  Moss Plant Metagenesis

In mosses, such as mosses, the spores grow into protonema. Protonema grows into a moss plant. Moss plants will produce anteridium or male breeding tools and archegonium or female breeding tools. This organ can be in one plant (one house) or it can be in different plants (two houses). The anteridium will produce sperm, and the archegonium will produce ova (egg cells). That is why, moss plants are called gametophytes or gamete-producing plants. Moss plants are haploid (n).

The meeting of sperm and ovum will produce a zygote which eventually develops into a sporophyte or spore-producing plant. The sporophyte is diploid (2n). In mosses, the sporophyte remains attached to the end of the plant (gametophyte). Spore formation in the sporophyte occurs through division of the spore mother cell within the spongarium.

• Fern Metagenesis

Fern spores will grow into prothallium. The prothallium grows to produce male (anteridium) and female (archegonium) reproductive organs. Therefore, the prothallium is referred to as the gametophyte. If the antheridium and archegonium are produced in one prothallium they are called monoecious and if the antheridium and archegonium are produced in different prothallium they are called two-homed.

Sperm and ovum produced from the reproductive organs will experience fertilization to become a zygote. The zygote develops into a fern. Mature ferns will have leaves that produce spores called sporophylls. Therefore, ferns are called sporophytes.

• Metagenesis of Seed Plants

Seed plants are the sporophyte generation. The female gametophyte generation develops within the ovule and attaches to the parent plant. The development of the male gametophyte begins with the formation of microspores and continues after pollination. The difference between seed plants and ferns is that the gametophyte generation of seed plants is smaller. development is more protected, and life dependence on the mother plant is more tall.

Microspores develop into pollen grains after leaving the spore box. During pollination, pollen that falls on the stigma will develop to form pollen reeds. In the pollen reeds will form sperm cells. In angiosperms, the so-called microgametophyte generation is the pollen tube. Meanwhile, the megagametophyte generation (macrogametophyte) is an institutional bag (embryonic bag).

After fertilization of the ovum by the sperm cell, a zygote is formed which then develops into an embryo in the seed. When the seeds germinate, the embryo will develop into sprouts, then into young plants and mature plants. Mature plants produce flowers, and so their life cycle begins again.

• Metagenesis in Jellyfish

Several types of invertebrate animals experience alternation of generations, for example jellyfish. In its life cycle, jellyfish undergo alternation of generations, namely the polyp phase which settles on the bottom of the water and the medusa phase which can swim freely.

Stages of jellyfish metagenesis are as follows.

• • Spermatozoids emerge from the mouth of the male medusa and enter the intestines of the female medusa to fertilize the eggs.
  • The result of fertilization is a zygote which will develop into a blastula followed by a ciliated larva called a planula.
  • The larval planula is formed by external fertilization and will settle on the substrate in a polypoid form known as a scyphistoma.
  • The planula grows into a polyp, then the polyp reproduces asexually by forming a medusa and so on.

Jellyfish polyp is a vegetative generation that reproduces asexually by forming buds. Medusa is a generative generation that reproduces sexually by fusion of male and female sex cells.

The difference between metagenesis and metamorphosis

Metagenesis and metamorphosis are two terms related to the growth and life cycle of organisms. Metagenesis is defined as the alternation of sexual and asexual generations of an organism in the life cycle. Metamorphosis is defined as the process in which an organism exhibits a different structural form or different structural stages from the adult organism during normal development.

This is the main difference between metagenesis and metamorphosis. There are two alternative sexual and asexual generations in the life cycle of organisms which show metagenesis whereas there are four different structural forms in the life cycle of organisms that show metamorphosis

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