Genetic Code & Cell Function

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  • Genetic Code & Cell Function - Meiosis 1
    • Prophase 1
      • Chromosomes shorten and thicken (condense) to form visible chromatids
      • Centrioles move to the opposite poles and form microtubules
        • Spindle fibres begin to form
      • Homologous chromosomes pair up and form homologous bivalents
        • Each bivalent has 4 strands made up of two chromosomes each
      • Chromatids 'cross over' at certain points, where the chromatids break and exchange DNA
        • Chiasmata / Crossing over
        • Creates genetic variation
      • Nucleolus disappears and nuclear envelope breaks down
    • Metaphase 1
      • Homologous bivalents align themselves along the equator of the spindle
      • Maternal and paternal chromosomes are arranged randomly
        • Random Assortment
      • This leads to further genetic variation
    • Anaphase 1
      • Homologous bivalents separate
      • One of each pair is pulled to the opposite poles
        • Each pole receives only one of each homologous bivalent
        • As the spindle fibres contract
      • There is a mixture of maternal and paternal chromosomes
    • Telophase 1
      • Chromosomes remain in their condensed form
      • Cytokinesis
        • Cytoplasm splits and forms 2 haploid cells
      • Nuclear envelope reforms around the haploid chromosomes
        • Spindle disappears


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