What is a diploid

Under Diploidy (from Greek diploe = Duplicity) In genetics, the presence of two complete sets of chromosomes is understood as a so-called double set of chromosomes. Each chromosome is thus present in double number, whereby in the gonosomes of male individuals no distinction is made between the normally different X and Y chromosomes. Since this is the common condition in humans as well as in many animals and plants, it is also known as euploidy. But there are also exceptions, e.g. B. due to generation cycles or different genders.

Plants with a phase change

Most plants go through a generation change, nuclear phase change, in which a haploid (simple set of chromosomes) and a diploid phase alternate:

  • Seaweed
  • In mosses (Bryophytina), the haploid generation (gametophyte) is what you see as a green moss plant (leafed or as a thallus). Fertilization creates a smaller diploid sporophyte that grows out of the moss plant, forms a spore capsule in which meiosis takes place, so that haploid spores are formed. The spores are scattered in the wind or by rain, germinate and a new haploid gametophyte grows.
  • In ferns (Pteridophytina), horsetail (Equisetopsida, belongs to the Pteridophytina) and club moss plants (Lycopodiopsida, also belongs to the Pteridophytina), the large visible plant is the diploid sporophyte, which forms haploid spores after meiosis. A small gametophyte, the prothallium, arises from them. The sporophyte grows again from its fertilized egg cells. But there are also polyploid ferns (sporophytes).
  • In seed plants (Spermatophytina), the diploid sporophyte is what we see as trees, shrubs or herbaceous plants. The gametophytes are greatly reduced: the pollen grains (together with the egg cell) represent the haploid generation. In the naked samers (gymnosperms), the pollen reaches the ovule directly, which is not surrounded by an ovary, i.e. has no stigma or stylus. Fertilization then takes place in the ovule. In angiosperms (= Magnoliopsida), the pollen grows after pollination through the stylus to the egg cell, where fertilization takes place.

Animals

Some animals, for example insects (Insecta), are sexed by whether they are haploid or diploid (haplodiploidy). The female bees or ants are diploid (workers and queens), while the males (drones) are haploid.

Higher set of chromosomes

Polyploidy (three to eight chromosome sets) leads to e.g. B. in cereals to particularly high-yielding varieties, but in most organisms to malformations. Only a few organisms are polyploid, including animal life forms.

See also

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  • Seyffert, Genetics textbook, 2nd edition, Spektrum, Akad. Verl., Heidelberg 2003.