Cell division and stem cells

• A gene is a short piece of DNA which controls a characteristic e.g eye colour
• There are different versions of genes called alleles which control a version of the characteristic e.g blue eye colour
• • The nucleus of the cell contains chromosomes
  • A chromosome is a long strand of DNA divided into genes
  • A gene is a section of a chromosome, which code for making proteins
• Cell division

  Throughout an organisms life they need to make new cells for:

  • growth, repair, replace old cells, to make gametes
• Two types of cell division

  • mitosis
  • meiosis
• Mitosis

  • occurs in growth, repair, asexual reproduction and tumours
  • one cell division occurs, two daughter cells are produced
  • daughter cells are genetically identical
  • daughter cells contain the same amount of DNA as the parents
• Meiosis

  • occurs in the production of gametes for sexual production
  • two cell divisions occur, four daughter cells are produced
  • daughter cells are genetically different
  • daughter cells contain half the amount of DNA as the parents
• Mitosis and cancer

  Sometimes cells divide by mitosis in an uncontrolled way. This results in the development of a growth or tumour also known as cancer. This uncontrolled division can be caused by chemicals or radiation damaging the DNA.
• Stem cells

  • in mature tissues, cell have generally lost the ability to differentiate into different types of cells
  • Definition - stem cells are cells which have the ability to differentiate into some different types of cells in the body
  • Source - three sources in humans : adult tissue, umbilical cord, embryonic cells
  • Use - can be used to replace damaged tissue in the treatment of conditions
  • Ethical issues - expense of research, umbilical cords can mean having a baby for the wrong reasons