Cell Division and Stem Cells

• Chromosomes


  Found in the nucleus of every cell, but are only visible when a cell is about to divide. Made of the chemical deoxyribonucleic acid (DNA).
• Genes


  Sections of DNA that control features of the organism
• A chromosome contains many genes
• Human body cells


  Have 46 chromosomes, 23 from each parent
• Chromosome pairs


  • Not identical, although they look the same and have the same genes. The form of the gene (allele) can vary.
• The full set of human 23 pairs of chromosomes, arranged in their pairs, is shown in the diagram
• The two pairs at the bottom are the gender chromosomes. Each person gets a different pair depending on whether they are male or female.
• Cell division


  1. Growth

  2. Repair

  3. Replacement of old or damaged cells and tissues
• Mitosis


  The type of cell division that occurs in these processes, where one cell (the 'mother' cell) divides to form two new (daughter) cells. The daughter cells are genetically identical to the mother cell.
• Meiosis


  Another type of cell division that only occurs when sex cells (gametes) are formed. Four new cells are formed instead of two, and each cell receives a half set of chromosomes.
• In humans, the sperm and egg cells each have 23 chromosomes, so that a new zygote will have 46 chromosomes as it should.
• The chromosomes in meiosis, unlike mitosis, are not genetically identical.
• Mitosis


  • Carefully regulated to allow cells time to grow and become specialised
  • Sometimes control fails, mitosis gets out of control and the cells produce cancerous tumours
• Stem cells


  Undifferentiated cells in the embryo that can become any cell type
• Advantages of using embryonic stem cells


  • Could be used to treat diseases such as cancer and type 1 diabetes
  • Could be used to repair damaged tissue, such as in brain damage or spinal cord injuries
• Objections to using embryonic stem cells

  • The embryo which provides them is destroyed in the process
  • Some are worried embryos might be created specifically to produce stem cells
• Adult stem cells


  Stem cells found in mature tissues that have not lost the ability to differentiate into different cells, but cannot develop into as many different types as embryonic stem cells
• Umbilical cord blood stem cells


  Stem cells collected from the blood from the umbilical cord at birth, which would be genetically identical to the baby and not attacked by the immune system
• Plant stem cells


  Found in the growing areas (called meristems) in roots and shoots, can be used to cultivate new plants but have no medical uses