cell division

• how many stages is the interphase section split into

  • 3 - G1, S,G2
• what are the cell cycle stages

  • interphase
  • mitosis
  • cytokinesis
• what is the G1 phase

  • biosynthesis (making new organelles), organelles replicate growth of cell
  • checks for any damages to the DNA before entering the S phase
• s phase

  • synthesis of new DNA (chromosomes replicated/duplicated)
• G2 phase

  • second growth phase
• G2/M phase

  • where replicated DNA is checked for errors /mutations
• G0 not apart of the cell cycle

  • when the cell leaves the cell cycle due to differentiation , due to DNA or apoptosis (programmed cell death)
• 1. prophase

  • chromosomes coil, condense and become visible
  • centrioles move to opposite poles
  • nuclear membrane breaks down
  • spindle fibres form
• 2. metaphase

  • chromatids line up along the equator
  • they attach by their centromeres to the spindle fibres
• 3. anaphase

  • sister chromatids are pulled apart by the contraction of the spindle fibres
• 4. telophase

  • chromosomes pulled to the poles
  • nuclear membrane reforms
  • chromosomes start to uncoil
• cytokinesis

  • cytoplasm divides
• stages of meiosis 1

  • prophase 1 : chromatin condenses and each chromosome supercoils, nuclear envelope breaks down, spindle threads of tubulin proteins form from the centriole in animal cells, come together in homologous pair - each pair consists of 2 chromatids, crossing over occurs where non-sister chromatids wrap around each other= chiasmata
• stages of meiosis 1


  metaphase 1 :

  • the pairs of homologous chromosomes, still in crossed over state , attach along the equator of the spindle attached by its centromere
  • homologous pair arranged randomly, with members of each pair facing opposite poles of the cell = independent assortment
• stages of meiosis 1


  anaphase 1:

  • each pair is pulled apart by motor proteins that drag them along the tubulin threads of the spindle
  • centromeres do not divide, each chromosome consists of 2 chromatids
  • exchange between non-sister chromatids
• stages of meiosis 1

  telophase 1:

  • 2 nuclear envelopes from around each set and cell divides into 2 by cytokinesis
  • 2 haploid cells
• stages of meiosis 2 - same as mitosis

  • straight from telophase 1 to prophase 2
  • nuclear envelope disappears again, DNA coils and condenses more
  • already have a crossed over bit in the chromatids
• stages of meiosis 2 


  metaphase 2:

  • chromatids line up along the equator - independent assortment (sister chromatids)
• stages of meiosis 2 


  anaphase 2 :

  • separation of sister chromatids
  • centromeres split
• stages of meiosis 2 


  telophase 2:

  • 4 haploid cells , nuclear envelope reforms and DNA is visible
• mitosis

  • produces identical cells
  • growth and repair
  • asexual reproduction
• meiosis

  • produces non-identical cells
  • gametes for sexual reproduction- these gametes are haploids (1 copy- 23)
• bivalents


  pair of homologous chromosomes