meiosis

(noun)

cell division of a diploid cell into four haploid cells, which develop to produce gametes

Related Terms

  • oocyte
  • polar body
  • spermatocyte
  • mitosis

Examples of meiosis in the following topics:

  • Comparing Meiosis and Mitosis

    • Mitosis and meiosis share some similarities, but also some differences, most of which are observed during meiosis I.
    • The main differences between mitosis and meiosis occur in meiosis I.
    • All of these events occur only in meiosis I.
    • Meiosis II is much more similar to a mitotic division.
    • Meiosis and mitosis are both preceded by one round of DNA replication; however, meiosis includes two nuclear divisions.
  • Meiosis II

    • Meiosis II initiates immediately after cytokinesis, usually before the chromosomes have fully decondensed.
    • In contrast to meiosis I, meiosis II resembles a normal mitosis.
    • In some species, cells enter a brief interphase, or interkinesis, before entering meiosis II.
    • The two cells produced in meiosis I go through the events of meiosis II together.
    • The process of chromosome alignment differs between meiosis I and meiosis II.
  • Introduction to Meiosis

    • Meiosis is the nuclear division of diploid cells into haploid cells, which is a necessary step in sexual reproduction.
    • Haploid cells that are part of the sexual reproductive cycle are produced by a type of cell division called meiosis.
    • Meiosis employs many of the same mechanisms as mitosis.
    • Thus, meiosis I is the first round of meiotic division and consists of prophase I, prometaphase I, and so on.
    • Meiosis II, the second round of meiotic division, includes prophase II, prometaphase II, and so on.
  • Disorders in Chromosome Number

    • Aneuploidy, an abnormal number of chromosomes in a cell, is caused by nondisjunction, or the failure of chromosomes to separate at meiosis.
    • Nondisjunction can occur during either meiosis I or II, with differing results.
    • If homologous chromosomes fail to separate during meiosis I, the result is two gametes that lack that particular chromosome and two gametes with two copies of the chromosome.
    • Nondisjunction occurs when homologous chromosomes or sister chromatids fail to separate during meiosis, resulting in an abnormal chromosome number.
    • Nondisjunction may occur during meiosis I or meiosis II.
  • Meiosis I

    • In meiosis I, the first round of meiosis, homologous chromosomes exchange DNA and the diploid cell is divided into two haploid cells.
    • Meiosis is preceded by an interphase consisting of three stages.
    • Finally, during the G2 phase (also called the second gap phase), the cell undergoes the final preparations for meiosis.
    • The crossover events are the first source of genetic variation produced by meiosis.
    • In each cell that undergoes meiosis, the arrangement of the tetrads is different.
  • Oogenesis

    • Immediately after meiosis I, the haploid secondary oocyte initiates meiosis II.
    • When meiosis II has completed, an ootid and another polar body would have been created.
    • Both polar bodies disintegrate at the end of meiosis II, leaving only the ootid, which then eventually undergoes maturation into a mature ovum.
    • The function of forming polar bodies is to discard the extra haploid sets of chromosomes that have resulted as a consequence of meiosis.
    • Oogenesis is the process of meiosis specific to the production of oocytes, particularly the uneven distribution of cellular components, including organelles and matrix, during divisions.
  • Gene rearrangement within genomes

    • During meiosis in eukaryotes, genetic recombination involves the pairing of homologous chromosomes.
    • During meiosis, as chromosomes condense and pair with their homologs (prophase I), they interact at distinct points.
    • In meiosis and mitosis, recombination occurs between similar molecules (homologs) of DNA.
    • Gene conversion occurs at high frequency at the actual site of the recombination event during meiosis.
    • Crossing over is essential for the normal segregation of chromosomes during meiosis.
  • Gametogenesis (Spermatogenesis and Oogenesis)

    • Gametogenesis, the production of sperm and eggs, takes place through the process of meiosis.
    • The cell starting meiosis is called a primary oocyte.
    • Meiosis begins with a cell called a primary spermatocyte.
    • The cell produced at the end of meiosis is called a spermatid.
    • Four sperm result from each primary spermatocyte that goes through meiosis.
  • Life Cycles of Sexually Reproducing Organisms

    • Fertilization and meiosis alternate in sexual life cycles.
    • The zygote immediately undergoes meiosis to form four haploid cells called spores.
    • Specialized cells of the sporophyte will undergo meiosis and produce haploid spores.
    • The zygote undergoes meiosis to produce haploid spores.
    • The diploid plant is called a sporophyte because it produces haploid spores by meiosis.
  • Life Cycle of a Conifer

    • In the male cones (staminate cones), the microsporocytes give rise to pollen grains by meiosis.
    • One megaspore mother cell (megasporocyte) undergoes meiosis in each ovule.
    • This phase may take more than one year between pollination and fertilization while the pollen tube grows towards the megasporocyte (2n), which undergoes meiosis into megaspores.
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