Gametogenesis (from Greek ldquo;gameterdquo; and ldquo;genesisrdquo; - ldquo;originrdquo;, ldquo;developmentrdquo;) - is the process o

Gametogenesis in animals [Gametophyte, Spermatogenesis oogenesis, Formation]

Gametogenesis (from Greek “gamete” and “genesis” — “origin”, “development”) — is the process of gametes maturation. This step is required for all multicellular organisms and some protozoa. The development of female germ cells is different from the development of male germ cells and in multicellular organisms takes place in the respective sex organs. Since the maturation of oocytes and sperm has its own features, these processes are different ones. The development of female gametes is called oogenesis or ovogenesis (from Greek “oon”- “egg” and “genesis”), and male — spermatogenesis (from Greek “spermatos” and “genesis”).

The haploid stage of development of animal is a period of gametes’ life. Gamete formation in higher animals, especially in human, has been studied in detail. This process fundamentally differs from the flowering plant gametogenesis, because the animal gametes that form as a result of meiosis but not as a result of mitotic divisions that follow the meiosis.

Gametogenesis occurs in the sex organs and has both common and distinctive traits in plants and animals. The main difference lies in the fact that animals’ gametes form as a result of meiotic divisions and in plants, this role is assigned to mitotic division that follow after meiosis.

Spermatogenesis in animals

Spermatogenesis in male occurs in testes and is a series of transformations of some cells into others (diagram 12). The stages of spermatogenesis are clearly tied to the areas of the seminiferous tubules.

At the beginning of the tubules are placed very small primary germ cells of round shape — spermatogonia (from Greek “spermatos” and “gonos” — birth). In the period of development of the body, they constantly divide via mitosis, increasing their amount in millions of times. This part of the testes is called a reproduction area. In adult organisms part of the cells increases in size. This process occurs in the growth area. Next, the germ cells transform into primary spermatocytes (from Greek “spermatos” and “cytos” — “receptacle”). They pass the stage of the first meiotic division, transform into secondary spermatocytes and, in turn, pass the stage of the second meiotic division. Meiosis occurs in maturation area.

As a result, four cells are formed — spermatids, which transform into sperm. The process of sperm maturation is accompanied by a sharp decrease in the nucleus and cytoplasm volume sizes, as well as the formation of a tail, due to which the sperm actively moves. Taken from http://worldofschool.org

Diagram 12. Spermatogenesis in animals: 1 — spermatogonia; 2 — spermatocyte of the I order (primary); 3 — spermatocyte of the II order (secondary); 4 — spermatids; 5 — spermatozoids. Black bodies inside the cell — are the mother’s chromosomes, blank — are father’s chromosomes. On the left the recombination of chromosomes took place, on the right — the recombination did not occur
Diagram 13. Oogenesis in animals: 1 — oogonia; 2 — oocyte of the I order (primary); 3 — first polar body; 4 — oocyte of the II order (secondary); 5 — second polar body; 6 — ootid; 7 — mature egg

Oogenesis in animals

Oogenesis in higher animals and human also consists of four stages and occurs in ovaries (diagram 13). First, in the period of embryonic development via mitosis multiply germ cells — oogonia (from Greek “oon” and “gonos”), from which develop primary oocytes (from Greek “oon” and “cytos”). In a period of growth that may last for years, the cell size increases in a thousand times. After the first meiotic division form secondary oocytes and the first polar body. In the future, there is a second division of meiosis, which yields a haploid egg — ootid and second polar body. Both polar bodies disintegrate in time. Thus, as a result of meiotic divisions in the process of oogenesis one oogonia produces only one egg, which absorbs all yolk accumulated during the development period. Development of female germ cells occurs sequentially in areas of ovarian similar to the areas of maturation of sperm in the testes.

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Questions:
  • What are oogenesis and spermatogenesis?

  • How do polar bodies appear?