cellular division

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  • Created by: wilby99
  • Created on: 28-01-16 18:01
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  • cellular divisions
    • Mitosis
      • cell cycle
        • INTERPHASE: the section of the cell cycle where the cell prepares for mitosis
        • GAP PHASE ONE: the cell grows and new organelles and proteins are made
          • G TWO CHECKPOINT: cell checks whether all the DNA has been replicated without any faults if it has the cell can enter Mitosis
        • SYNTHESIS:  cell replicates its DNA ready to divide
        • GAP PHASE TWO: cell keeps growing and the proteins needed for division are made
          • G ONE CHECKPOINT: cell checks that all the chemicals needed for replication are present and also checks for any damage to the DNA  before entering s-phase
      • The process
        • PROPHASE: chromosomes condense /centrioles move to the opposite poles of the cell forming the spindle/ nuclear envelope breaks down
        • METAPHASE: Chromatids line up along the equator/ spindle attaches to their centromere
        • ANAPHASE: centromeres divide/ the spindles contract pulling the chromatids to opposite ends of the cell
        • TELOPHASE: Chromatids reach the opposite ends of the cell and are called chromosomes again/ there are now two nuclei
    • Meiosis
      • Meiosis 1
        • PROPHASE ONE: same as in mitosis except homologous chromosomes paired up  and chiasmata are formed in recombination
        • ANAPHASE ONE: same as mitosis except the spindle pulls a full chromosome to each pole
        • METAPHASE ONES: homologous pairs line up along the equator
        • TELOPHASE ONE: a nuclear envelope forms around each homologous pair and cytokinesis occurs forming two new haploid cells.
      • Meiosis 2
        • The cell undergoes meiosis 1 again except with half the number of chromosomes
        • In ANAPHASE TWO the sister chromatids are separated and each daughter cell inherits a chromatid from each chromosome making four haploid daughter cells
      • Genetic variation
        • crossing over of chromatids
          • In prophase one the chromatids get tangled up a bit and some of the chromosomes swap parts.
          • They have the same genes but a different combination of alleles
        • Independant assortment of chromosomes
          • Each homologous pair contains a maternal and paternal chromosome
            • when they line up and are separated, it's completely random which chromosomes from each pair end up in which daughter cell
          • This is called independent assortment and leads to genetic variation in any potential offspring.
    • Cytokinesis
      • This is the splitting of the cytplasm
      • The way this happens is by a thin ring of actin filaments that form the contractile ring contract causing the two new ces to 'pinch off'


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