Cell division

1. G1 - biosynthesis - proteins made, organelles replicate
2. S - synthesis of new DNA - replication of chromosomes
3. G2 - growth - enlargement of developing cell
4. M - nuclear division - mitosis and cytokinesis - cleavage of cytoplasm
Mitosis
1. Need for mitosis
  1. Asexual reproduction
  2. Growth
  3. Repair
    1. identical - same function
  4. Replacement
    1. e.g. RBCs and skin cells
2. Prophase
  1. chromosomes supercoil (shorten and thicken)
    1. consist of pair of sister chromatids
  2. nuclear envelope breaks down and disappears
  3. centriole divides into 2
  4. each daughter centriole moves to poles to form the spindle
3. Metaphase
  1. chromosomes move to the equator
  2. each chromosome attaches to a spindle thread by its centromere
4. Anaphase
  1. centrome splits
    1. sister chromatids separate from each other
      1. each becomes an individual chromosome
  2. spindle fibres shorten
    1. chromatids pulled to opposite poles
      1. V shaped appearance as centromere leads
5. Telophase
  1. chromosomes reach poles
    1. New nuclear envelope forms around each set
  2. spindle breaks down and disappears
  3. chromosomes uncoil
6. Cytokinesis
  1. cells splits into 2 identical daughter cells
7. Budding in yeast
  1. asexual reproduction
  2. bud forms at surface
    1. cell undergoes interphase and mitosis
      1. budding cell contains a nucleus that has an identical copy of parent cell's DNA
        bud separates off
Meiosis
1. produces gametes in gonads (sex organs)
2. homologous chromosomes have same genes but different alleles
3. one chromosome from each pair goes to daughter cell
4. daughter cells are haploid (23 chromosomes in humans)
5. daughter cells are not genetically identical to parent cells or from each other

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