Mitosis and the Cell Cycle

• What is the cell cycle?

  The process by which cells grow and divide
• What are the main stages of the cell cycle?

  1. Interphase

  • Cell grows, DNA is replicated, organelles made

  1. Mitosis

  • The nucleus divides

  1. Cytokinesis

  • The cytoplasm divides, forming two new cells
• Why is the cell cycle important?

  It enables growth, repair, and asexual reproduction
• What does mitosis produce?

  Two identical daughter cells
• What are the key facts about mitosis?

  • Produces genetically identical cells
  • Used for growth, repair, and asexual reproduction
  • Produces two diploid cells (46 chromosomes in humans)
  • Happens in somatic (body) cells
• What are the stages of mitosis?

  1. Prophase

  • Chromosomes condense, nucleus breaks down, spindle fibers form

  1. Metaphase

  • Chromosomes line up in the middle of the cell

  1. Anaphase

  • Chromosomes are pulled apart to opposite sides

  1. Telophase

  • Two new nuclei form, spindle fibers disappear

  1. Cytokinesis

  • The cytoplasm divides, forming two identical diploid cells
• What is the importance of mitosis?

  Ensures genetic consistency in new cells
• What does meiosis produce?

  Four genetically different gametes
• What are the key facts about meiosis?

  • Produces genetically different cells
  • Creates gametes (sperm and egg cells in animals, pollen and ovules in plants)
  • Produces four haploid cells (23 chromosomes in humans)
  • Increases genetic variation
• What are the stages of meiosis?

  1. Meiosis I

  • Prophase I: Chromosomes condense, nucleus breaks down, spindle fibers form
  • Metaphase I: Chromosomes pair up and line up in the middle
  • Anaphase I: Chromosome pairs are separated to opposite sides
  • Telophase I & Cytokinesis: Two new haploid cells formed (chromosomes still doubled)

  1. Meiosis II

  • Prophase II: Spindle fibers form again
  • Metaphase II: Chromosomes line up in the middle of each new cell
  • Anaphase II: Chromosomes are pulled apart to opposite sides
  • Telophase II & Cytokinesis: Cytoplasm divides, forming four haploid gametes
• How do mitosis and meiosis compare?

  • Mitosis: Produces 2 identical cells, diploid (46 chromosomes), for growth and repair
  • Meiosis: Produces 4 genetically different cells, haploid (23 chromosomes), for sexual reproduction
• What is the importance of meiosis in genetic variation?

  It increases genetic diversity in offspring
• What mechanisms contribute to genetic variation during meiosis?

  • Crossing over (Prophase I): Chromosomes swap DNA
  • Independent assortment (Metaphase I): Chromosomes line up randomly
  • Fertilisation: Each sperm and egg cell is unique
• Why is genetic variation important for species?

  It helps species adapt to changing environments
• What is the chromosome number in diploid cells?

  46 chromosomes in humans
• What is the chromosome number in haploid cells?

  23 chromosomes in humans
• What type of cells does meiosis produce?

  Gametes (sperm and egg)
• What type of cells does mitosis produce?

  Body (somatic) cells
• Cell division by mitosis in multicellular organisms is important in their growth and development when replacing damaged cells. Mitosis is also a vital part of asexual reproduction as this type of reproduction only involves one organism so to produce offspring it simply replicate its own cells.
• Embryonic stem cells

  • Form when an egg and sperm to form a zygote.
  • They can differentiate into any type of cell in the body.
  • Scientists can clone these cells and direct them to differentiate into almost any cell in the body.
  • These could potentially be used to replace insulin producing cells in those suffering from diabetes and neural cells for diseases such as Alzheimer’s or nerve cells for those paralysed with spinal cord injuries.
• Adult stem cells

  • If found in bone marrow they can form many type types of cells including blood cells.
• Meristems in plants

  • Found in root and shoot tips
  • They can differentiate into any type of plant and have this ability throughout the life of a plant.
  • They can be used to make clones of the plant this may be necessary if the parent plant has certain desirable features for research or to save a rare plant from extinction
• The benefits include being used to replace damaged or diseased body parts, unwanted embryos from fertility clinics can be used instead of being discarded, for the research into the processes of differentiation
• The problems include not being able to understand the process of differentiation, so it is hard to control stem cells to form the cell, removal of stem cells results in destruction of the embryo, people may have religious or ethical objections as it is seen as interference with the natural process of reproduction, if the growing stem cells are contaminated with a virus and infection can be transferred to the individual, money and time could be spent into the other areas of medicine
• Therapeutic cloning involves an embryo being produced with the same gene as the patient. The embryo produced could then be harvested to obtain the embryonic stem cells. These could be grown into any cells the patient needed such as new tissues or organs. The that they would not be rejected as they would have the exact same genetic make up as the individual.