Bio 10 - Genetics Mutations


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Key vocabulary:
Chromosome mutations
Sickle Cell Anemia
Cystic Fibrosis

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Bio 10 - Genetics Mutations

  1. 2. Chromosomes <ul><li>are 50% DNA and 50% protein </li></ul><ul><li>Have a characteristic shape, with a central centromere and ‘arms’ called chromatids. </li></ul><ul><li>The number of chromosomes in any species is fixed. E.g., humans = 46 </li></ul><ul><li>Chromosomes occur in pairs called homologous pairs in all cells except sex cells </li></ul><ul><li>Sex cells are haploid =23 chromosomes </li></ul><ul><li>Body cells are diploid = 2 pairs of 23 homologous chromosomes </li></ul>
  2. 4. Human female karyotype showing 23 homologous pairs of replicated chromosomes frozen at metaphase
  3. 5. Karyotypes <ul><li>Show all the chromosomes of an organisms body cells arranged into homologous pairs. </li></ul><ul><li>Use picto-micrographs taken during metaphase </li></ul><ul><li>Show condensed, replicated chromosomes with sister chromatids. </li></ul><ul><li>Used for screening fetuses for genetic disorders such as Down’s Syndrome (3 copies of chromosome #21 </li></ul>
  4. 6. Down’s Syndrome Karyotype
  6. 9. GENES <ul><li>Specific region of chromosome made into protein </li></ul><ul><li>Specific region of chromosome capable of determining a characteristic (‘trait’) </li></ul><ul><li>Unit of inheritance </li></ul><ul><li>Always occurs on the same chromosome, at the same position (‘locus’). </li></ul><ul><li>Have two or alternate forms (‘alleles’). </li></ul>
  7. 11. (Also called “substitution mutation”).
  9. 13. Sickle Cell Anemia <ul><li>Caused by a base substitution in the gene for ß-haemoglobin </li></ul>
  10. 14. Haemoglobin consists of 2 ß and 2 ά protein subunits, each with iron and haem.
  11. 15. Haemoglobin <ul><li>Haemoglobin is the oxygen transporting molecule in red blood cells. </li></ul><ul><li>It consists of 2 ß-globin and 2 ά -globin protein subunits, each bonded with iron and haem. </li></ul><ul><li>ß-globin is on chromosome 11. </li></ul><ul><li>A base substitution mutation in ß-globin gene changes Adenine to Thymine, resulting in amino acid Valine replacing Glutamic acid. </li></ul><ul><li>Mutant “haemoglobin S” (Hb s ), causes haemoglobin to clump together into long fibres and distort the red blood cell’s shape </li></ul>
  12. 16. Sickle cells carry less O 2 and can block capillaries, causing severe anemia and serious secondary complications. E.g., heart and kidney failure.
  13. 17. Symptoms of Sickle Cell Anemia
  14. 18. Inheritance of the Sickle Cell Allele <ul><li>The sickle cell allele (Hb s ) is recessive </li></ul><ul><li>Heterozygotes have ‘sickle cell trait’, are mildly anaemic and are resistant to malaria </li></ul><ul><li>Homozygote recessives have sickle cell anaemia </li></ul>
  15. 19. Malaria <ul><li>400,000,000 people have malaria </li></ul><ul><li>1,500,000 die each year </li></ul><ul><li>80% in Africa </li></ul><ul><li>Malaria is caused by a protist, (Plasmodium falciparum) which is transmitted in blood carried by female mosquitoes. </li></ul><ul><li>The protist completes part of it’s life cycle in red blood cells, but can’t do so in sickle cells. </li></ul>
  16. 20. Life cycle of Malaria parasite
  17. 21. Occurrence of Sickle Cell anemia
  18. 22. Cystic Fibrosis. Deletion Gene Mutation
  19. 24. What causes mutation? <ul><li>Mutation can occur naturally. DNA repair mechanisms exit in cells to repair damaged DNA. Obviously, repairs don’t always work (same with mechanics!). </li></ul><ul><li>These ‘mutagens’ increase DNA damage and mutation and increase the chances of permanent, unrepaired mutations: </li></ul><ul><li>X-ray radiation </li></ul><ul><li>Ultra-violet radiation </li></ul><ul><li>Smoking </li></ul><ul><li>Thalidomide </li></ul>
  20. 25. Somatic Mutation
  21. 26. Body Cell Mutation – “Somatic” <ul><li>Mutation in a body cell of an adult is almost always harmless. The cell dies, or is killed by immune system cells, and is replaced by mitosis from healthy cells. This happens all the time. </li></ul><ul><li>If a gene controlling cell division is mutated, the cell might start growing and dividing uncontrollably. </li></ul><ul><li>This is a tumour and leads to cancer. </li></ul>
  22. 27. Cancer and cell cycle
  23. 28. Sex Cell Mutation – “Gametes” <ul><li>Mutations in gametes are serious. If a zygote is formed at fertilisation with a mutant gamete, every cell of the new organism will carry the mutation. </li></ul><ul><li>When a person inherits the Hb s allele, every cell in their body has the mutant allele. </li></ul><ul><li>When a person has Down’s syndrome, every cell in their body has 47 chromosomes. </li></ul>