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Meiosis

09 May

Meiosis is the type of cell division by which germ cells (eggs and sperm) are produced. Meiosis involves a reduction in the amount of genetic material.

Meiosis comprises two successive nuclear divisions with only one round of DNA replication.
Four stages can be described for each nuclear division.

  • Interphase: Before meiosis begins, genetic material is duplicated.
  • First division of meiosis
    • Prophase 1: Duplicated chromatin condenses. Each chromosome consists of two, closely associated sister chromatids. Crossing-over can occur during the latter part of this stage.
    • Metaphase 1: Homologous chromosomes align at the equatorial plate.
    • Anaphase 1: Homologous pairs separate with sister chromatids remaining together.
    • Telophase 1: Two daughter cells are formed with each daughter containing only one chromosome of the homologous pair.
  • Second division of meiosis: Gamete formation
    • Prophase 2: DNA does not replicate.
    • Metaphase 2: Chromosomes align at the equatorial plate.
    • Anaphase 2: Centromeres divide and sister chromatids migrate separately to each pole.
    • Telophase 2: Cell division is complete. Four haploid daughter cells are obtained.

One parent cell produces four daughter cells. Daughter cells have half the number of chromosomes found in the original parent cell and with crossing over, are genetically different.

Meiosis differs from mitosis primarily because there are two cell divisions in meiosis, resulting in cells with a haploid number of chromosomes.

 

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