Case Studies & Examples

• Chemical Mutagen - Smoking (Pt.1)

  • Chemicals are said to be mutagenic or carcinogenic if there is a clear correlation between exposure and signs of cancer/mutation
  • Tobacco contains mutagenic compounds, some of which are carcinogenic
  • Prior to widespread smoking of tobacco, lung cancer was an uncommon form of cancer (as smoking rates increased, so did the rate of lung cancer)
• Chemical Mutagen - Smoking (Pt.2)

  • Benzopyrene (BP) is a specific carcinogen found in cigarette smoke
  • BP binds to a Guanine (G) which forms bonds with an Adenine (A) on the complementary strand
  • Thymine (T) forms bonds with Adenine in the next round of DNA replication (all future cells will have this point mutation)
• Chemical Mutagen - Asbestos

  • Asbestos is the only known cause of pleural mesothelioma
  • Can also cause other diseases such as lung cancer and asbestosis
• Mesothelioma

  A rare but highly aggressive cancer that occurs in the lining of internal organs known as the mesothelium (comes into direct contact with asbestos fibres)
• Asbestosis

  A non-cancerous scarring of the tissue of the lungs due to asbestos exposure. People diagnosed with asbestosis have a higher chance of developing asbestos-related cancers (eg. lung cancer, mesothelioma)
• Proto-oncogenes

  • Genes that code for proteins that stimulate the cell cycle and promote cell growth and proliferation
  • If mutation occurs, it forms an oncogene that can cause cancer
• Tumor-suppressor genes

  • Genes that are able to slow down cell division, repair DNA mistakes, or tell cells when to die (apoptosis or programmed cell death)
  • If mutation occurs, cells can grow out of control which can lead to cancer
• Somatic Mutations (Examples)

  • Point Mutation: Carcinogenesis-melanoma, Struge-Weber syndrome
  • Chromosomal Mutation: Mosaic Down syndrome
• Germ-line Mutations (Examples)

  • Point Mutation: Haemophilia, cystic fibrosis, sickle cell anaemia
  • Chromosomal Mutation: Down syndrome, Klinefelter syndrome
• Mosaic Down Syndrome (Pt.1)

  • Exists when there are a mixture of two types of cells, some containing the usual 46 chromosomes and some containing 47
  • Those cells with 47 chromosomes contain an extra chromosome 21
  • This occurs during early embryonic development and results in all proceeding cells on the same lineage possessing 47 chromosomes
• Mosaic Down Syndrome (Pt.2)

  • Accounts for only about 1% of all cases of Down syndrome
  • Individuals with mosaic Down syndrome may have fewer characteristics of Down syndrome than those with other types of Down syndrome (however, broad generalizations are not possible)
• Cystic Fibrosis (Pt.1)

  • Most common genetic disorder in the Caucasian population
  • Main cause is a single point mutation in the cystic fibrosis membrane conductance regulator (CFTR) protein
  • Most common mutation is a deletion of three nucleotides that results in a loss of the amino acid phenylalanine at the 508th position on the protein
• Cystic Fibrosis (Pt.2)

  Symptoms include:

  • Persistent coughing, at times with phlegm
  • Frequent lung infections including pneumonia or bronchitis
  • Wheezing or shortness of breath
  • Frequent greasy, bulky stools or difficulty with bowel movements
• Down Syndrome (Pt.1)

  • Caused by a nondisjunction mutation of chromosome 21 during meiosis
  • Results in an embryo with three copies of chromosome 21 instead of two
  • Prior to or at conception, a pair of 21st chromosomes in either the sperm or the egg fails to separate, which leads to 47 chromosomes
• Down Syndrome (Pt.2)

  Symptoms include:

  • Decreased or poor muscle tone
  • Short neck, with excess skin at the back of the neck
  • Flattened facial profile and nose
  • Small head, ears, and mouth
  • Upward slanting eyes