cell division and stem cells

• Chromosome


  Linear DNA molecule tightly coiled around proteins that carries genetic information in the form of genes
• Chromosomes are found in pairs (one from each parent) in all body cells. Human body cells contain 23 pairs of chromosomes (46 chromosomes in total)
• Chromosome pairs are not identical as they may contain different alleles (versions of a gene)
• Sex chromosomes


  A pair of chromosomes that determine sex. Males have an X and a Y chromosome, females have two X chromosomes.
• Mitosis


  Division of a cell to produce two genetically identical daughter cells with a full set of chromosomes (46 chromosomes)
• Mitosis


  • Important for growth, replacement of old cells, and repair of damaged tissues
• Meiosis


  A type of cell division that creates four genetically different daughter cells known as gametes. Involves two divisions and produces cells with half the number of chromosomes (23 chromosomes)
• Meiosis


  • Important for creating genetic variation and ensuring the resultant zygote has a full set of chromosomes
• Cancer


  A non-communicable disease in which uncontrolled mitosis (due to damaged DNA) leads to the formation of a primary tumour. Tumour cells break off and spread to other tissues forming secondary tumours.
• Cell differentiation


  Produces specialised cells with specific functions. Some genes are switched on or off, determining cell type. Once a cell differentiates, it cannot divide to make an unspecialised cell, nor a cell which has a different specialised function.
• Stem cells


  Unspecialised cells capable of differentiating into a range of different cell types
• Types of stem cells

  • Embryonic stem cells - unspecialised and capable of differentiating into any cell type, enable the growth and development of tissues in embryos
  • Adult stem cells - can differentiate into a limited range of cell types, enable the replacement of dead or damaged cells
• In plants, stem cells are found in meristematic tissue in the root and shoot tips. They are capable of differentiating into any cell type throughout the life of a plant.
• Advantages of stem cell technology

  • Used to treat damage or disease e.g. type 1 diabetes, heart disease
  • Used to treat diseases that would otherwise be untreatable
  • Not rejected by the body
  • Do not have to be matched to the patient's tissue type
  • Can be used to grow organs for transplants
• Disadvantages of stem cell technology

  • May become contaminated during preparation and when transplanted transmit infections to the patient
  • Difficult to find suitable stem cell donors
  • No guarantee that treatment will work
  • Transplanted stem cells could cause tumours
  • Long term risks are unknown
  • Potential side effects
• There are also ethical issues surrounding the use of stem cells, in particular embryonic stem cells. Embryos used to provide these stem cells are usually destroyed which is controversial on ethical grounds.