Meiosis I

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  • Meiosis
    • Meiosis II
      • Anaphase II
        • Centromeres divide chromatids pulled to opposite poles by spindle fibres
        • Chromatids randomly segregate.
      • Metaphase II
        • Chromosomes arrange selves in on equator at spindle at centromeres.
        • Chromatids of each chromosome are randomly assorted.
      • Telophase II
        • Nuclear envelopes reform around haploid daughter nuclei.
        • In animals: two cells divide to form haploid cells.
        • In plants: tetrad of four haploid cells form.
        • Cells divide by cytokinesis
      • Prophase II
        • Nuclear envelope formed, breaks down again.
        • Nucleolus disappears, chromosomes condense, spindles form
    • Meiosis I
      • Metaphase I
        • Bivalents line up along equator of spindle attached at centromeres. Chiasmata still present.
        • Bivalents arranged randomly with each member of homologous pair facing opposite poles.
        • Allows chromosomes to segregate independently in next stage.
      • Telophase I
        • Cell divides by cytokinesis brief interphase, chromosomes uncoil.
        • Two new nuclear envelopes form around each set of chromosomes at each pole.
      • Prophase I
        • Chromatin condenses, supercoils. Chromosomes shorten and thicken.
        • Chromosomes come together in homologous pairs- form bivalents.
        • Non-sister chromatids wrap around each other and attach at chiasmata.
        • They may swap chromatid sections in crossing over.
        • Nucleolus disappears nuclear envelope disintegrates,spindle forms.
      • Anaphase I
        • Homologous chromosomes in each bivalent pulled to opposite poles by spindle microtubules.
        • Centromeres don't divide.
        • Chiasmata separate and lengths of chromatid crossed over remain with new chromatid.


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