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  2. Biological life cycle - Wikipedia

    en.wikipedia.org/wiki/Biological_life_cycle

    Zygotic meiosis. A zygotic meiosis is a meiosis of a zygote immediately after karyogamy, which is the fusion of two cell nuclei. This way, the organism ends its diploid phase and produces several haploid cells. These cells divide mitotically to form either larger, multicellular individuals, or more haploid cells. Two opposite types of gametes ...

  3. Zygote - Wikipedia

    en.wikipedia.org/wiki/Zygote

    The other product of meiosis is the second polar body with only chromosomes but no ability to replicate or survive. In the fertilized daughter, DNA is then replicated in the two separate pronuclei derived from the sperm and ovum, making the zygote's chromosome number temporarily 4n diploid .

  4. Meiosis - Wikipedia

    en.wikipedia.org/wiki/Meiosis

    In the haplontic life cycle (with post-zygotic meiosis), the organism is haploid, by the proliferation and differentiation of a single haploid cell called the gamete. Two organisms of opposing sex contribute their haploid gametes to form a diploid zygote. The zygote undergoes meiosis immediately, creating four haploid cells.

  5. Nondisjunction - Wikipedia

    en.wikipedia.org/wiki/Nondisjunction

    In general, nondisjunction can occur in any form of cell division that involves ordered distribution of chromosomal material. Higher animals have three distinct forms of such cell divisions: Meiosis I and meiosis II are specialized forms of cell division occurring during generation of gametes (eggs and sperm) for sexual reproduction, mitosis is the form of cell division used by all other cells ...

  6. Sporogenesis - Wikipedia

    en.wikipedia.org/wiki/Sporogenesis

    They will undergo zygotic meiosis upon germinating. In oomycetes, the zygote forms through the fertilization of an egg cell with a sperm nucleus and enters a resting stage as a diploid, thick-walled oospore. The germinating oospore undergoes mitosis and gives rise to diploid hyphae which reproduce asexually via mitotic zoospores as long as ...

  7. Cleavage (embryo) - Wikipedia

    en.wikipedia.org/wiki/Cleavage_(embryo)

    Zygotic transcription starts at the two-, four-, or eight-cell stage depending on the species (for example, mouse zygotic transcription begins towards the end of the zygote stage and becomes significant at the two-cell stage, whereas human embryos begin zygotic transcription at the eight-cell stage). Cleavage is holoblastic and rotational.

  8. Reproductive isolation - Wikipedia

    en.wikipedia.org/wiki/Reproductive_isolation

    Pre-zygotic isolation mechanisms are the most economic in terms of the natural selection of a population, as resources are not wasted on the production of a descendant that is weak, non-viable or sterile. These mechanisms include physiological or systemic barriers to fertilization.

  9. Human embryonic development - Wikipedia

    en.wikipedia.org/wiki/Human_embryonic_development

    Human embryonic development or human embryogenesis is the development and formation of the human embryo.It is characterised by the processes of cell division and cellular differentiation of the embryo that occurs during the early stages of development.