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History of genetics
Learn introductory genetics with Braimy- B.Sc agriculture
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i) Production of male gamete:

  • Each anther has 4 pollen sacs, which contain numerous pollen mother cells (PMCs).
  • The PMC has 2n number of chromosomes which forms 4 haploid cells (microspores) containing n number of chromosomes.
  • Microspore nucleus divides mitotically to produce a generative and a vegetative nucleus. The generative nucleus undergoes mitotic cell division producing two male gametes.
  • Hence, at the end, one microsporocyte produces 4 microspore or 8 male gametes.

ii) Production of female gamete:

  • A single cell in each ovule differentiates in a megaspore mother cell (MMC) which has 2n number of chromosomes.
  • This MMC undergoes meiosis cell division to produce 4 haploid megaspores containing n number of chromosome.
  • Three megaspore degenerates leaving one functional megaspore per ovule.
  • The nucleus of functional megaspore divides mitotically to produce 8 nuclei.
  • Three of these nuclei move to one pole and produce a central “egg cell” and 2 synergids.
  • Another 3 nuclei migrate to the opposite pole to give rise to antipodal cells.
  • Two nuclei remaining in the center, the polar nuclei, fuse to form a secondary nucleus (diploid).

iii) Fertilization and double fertilization:

  • The fusion of the remaining male gamete with the secondary nucleus leading to the formation of triploid endosperm nucleus is known as triple fusion or double fertilization and has 3n number of chromosomes.
  • Hence, one of the two male gametes unites to the egg cell (female gamete) to form a zygote and it divides mitotically to produce diploid embryo.
  • During seed development, endosperm provides nutrition to the developing embryo.

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