Germline

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In humans and in most animals, the germline is the sequence of cells that, starting with the fertilized egg cell ( zygote ), in the course of the individual development of the living being, finally to the formation of its gonads and the germ cells formed in them (egg cells and sperm ) leads.

The concept of the germline was developed by August Weismann in the 1880s ( germplasm theory ). Weismann opposed the prevailing view at the time that the entire parental organism influences the characteristics of the offspring and that characteristics that the parents acquired during their life can also be transferred to the offspring ( Lamarckism ). Weismann now distinguished between the germ line and the soma as the totality of all other cells from which no germ cells can emerge and from which no effects on the germ line proceed. (In terms common today: only mutations in the germ line, not those in somatic tissues, are passed on to the offspring .) This theory was initially very controversial and did not gain acceptance until the early 20th century.

In most animals, the germline is secreted at a very early embryonic stage , before the somatic cells begin to differentiate in different directions . In many invertebrates , this even begins in the egg cell before fertilization, in that a certain area of ​​the cytoplasm is reserved for future germline cells. A well-studied example is the fruit fly Drosophila melanogaster : its zygote initially develops as a polynuclear syncytium , i.e. This means that nuclear divisions ( mitoses ) take place without cell divisions . After the 8th or 9th nucleus division, some cell nuclei migrate to one end of the elongated syncytium, where the pole plasma, which is specialized for the germ line, is located. The syncytium is then subdivided into many mononuclear cells, of which only the pole cells form the origin of the germ line ( primordial germ cells ).

In mammals , the primordial germ cells arise in the epiblast during early embryonic development . At a later stage they migrate to the genital ridges , from which the gonads finally emerge.

Plants, mushrooms and various groups of "lower" animals do not have a separate germ line.

See also

Individual evidence

  1. ^ François Jacob : The logic of the living - From spontaneous generation to the genetic code . Frankfurt am Main 1972, pp. 232-235.
  2. ↑ Ilse Jahn , Rolf Löther, Konrad Senglaub (eds.): History of Biology. Theories, methods, institutions, short biographies . 2nd, revised edition. VEB Fischer, Jena 1985, p. 554 f.
  3. ↑ Ilse Jahn, Rolf Löther, Konrad Senglaub (eds.): History of Biology. Theories, methods, institutions, short biographies . 2nd, revised edition. VEB Fischer, Jena 1985, pp. 410-412.
  4. ↑ Bernard John: Meiosis . Cambridge University Press, 1990. p. 104.
  5. ↑ Bernard John: Meiosis . Cambridge University Press, 1990. pp. 104f.
  6. ↑ Bernard John: Meiosis . Cambridge University Press, 1990. p. 105.