Fertilization - is the main form of sexual process at which occurs the fusion of male and female gametes to form a zygote - first cell of a ne

Fertilization [Conception, Fecundation, Syngamy, Impregnation]

Fertilization — is the main form of sexual process at which occurs the fusion of male and female gametes to form a zygote — first cell of a new organism. There forms diploid nucleus of zygote from two haploid gamete nuclei, and its cytoplasm almost entirely forms from the cytoplasm of the egg. Fertilization is common to all multicellular organisms that reproduce sexually, as well as some single-celled, in which sexual reproduction occurs in the form of copulation.

In colloquial speech fertilization and sexual reproduction are often equated, but it is not the same thing. In a number of organisms for which fertilization is mandatory, reproduction occurs only asexually. Example for this can be lots of single-celled organisms. The point of fertilization of ciliates and bacteria that is called a conjugation (from Latin “conjugation” — “connection”) is to transfer genetic material from one individual to another. Thus no increase in the number of individuals happens. Such results are given only by cell division that follows the fertilization. Also, no increase in the number of individuals happens during copulation (from Latin “copulation” — “connection”) — merger of the two single-celled organisms into one. This type of fertilization is observed in Plasmodium falciparum and in unicellular fungi — yeast (diagram 6). These single-celled organisms also reproduce only asexually — by multiple division of the zygote that was formed as a result of merger.

Diagram 6. Copulation and the formation of the zygote in the unicellular alga Chlamydomonas: 1 — the formation of gametes; 2 — release of gametes; 3-4 — copulation (merger) of gametes; 5 — a zygote; 6 — cleavage of the zygote into four individuals; 7 — adult individual

Copulation is also called the sexual intercourse of multicellular animals, associated with internal fertilization, which is carried out by special copulatory organs by introducing male gametes into the female body. Taken from http://worldofschool.org

Reproduction of multicellular organisms, which body is built up of millions and billions of cells, is very productive via the merger of the individual germ cells, as always lead to the initial increase in the number of individuals in each successive generation, and therefore reasonably called a reproduction.

Thus, fertilization — is a type of sexual process, inherent in all organisms that reproduce sexually, or unicellular organisms, which have copulation. Two haploid gametes, mostly men and women, merge and give rise to a zygote. Fertilization of representatives of the three kingdoms of eukaryotes — plants, animals and fungi has its own characteristics. In particular, in flowering plants it occurs in the form of double fertilization.

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Questions:
  • What is the mechanism of fertilization?

  • It is right to consider fertilization synonymous with sexual reproduction?

  • Is the sexual process always associated with sexual reproduction?