Meiosis

    Cards (17)

    • gamete - sex cells i.e. sperm & egg cells. Fuse to form zygote (fertilisation)
    • diploid - a cell with 2 copies of each chromosome
    • haploid - a cell with 1 copy of each chromosome
    • meiosis - a type of cell division which results in 4 non-identical cells being produced.
    • chromosome - in eukaryotes, is composed of DNA wrapped around histone proteins, contains the genes of the organism
    • chromatid - one half of a chromosome when it is a 'double structure'
    • homologous chromosomes - a pair of chromosomes containing the same gene but different alleles.
    • centromere - joins 2 chromatids together
    • centriole - attach to centromeres at the poles of each cell
    • spindle fibres - attach centrioles to centromeres and draw centromere/chromatids apart.
    • Meiosis
      • initially, DNA is replicated causing chromosomes to form as 'double structures' i.e., 2 sister chromatids joined together by a centromere.
      • the long, thin chromosomes condense and become visible, revealing these double structures.
    • Meiosis I Metaphase
      • the homologous chromosomes line up in pairs in double file at the equator. The order, within the pair is random - independent segregation. This is a source of variation.
      • During crossing over, the arms of adjacent homologous chromosomes wrap around each other, snap off and alleles are exchanged. This is a source of variation.
      • This gives new allelic combinations.
    • Meiosis I Anaphase
      • The spindle fibres contract and the homologous chromosomes are pulled to either pole
    • Meiosis I telophase and cytokinesis
      • the chromosomes have reached either pole and the cytoplasm divides. Meiosis I ends with 2 daughter cells - each containing half the number of chromosomes
    • Meiosis II Metaphase - chromosomes line up on the equator in single file
    • Meiosis II Anaphase - the centromeres are pulled apart as the spindle fibres contract and the sister chromatids are drawn to opposite poles.
    • Meiosis II telophase and cytokinesis - the chromatids reach the poles and the cytoplasm divides. These are now 4, non-identical daughter cells.
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