Biology lecture 6


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Biology lecture 6

  1. 1. Mutations
  2. 2. What Are Mutations? <ul><li>Changes in the nucleotide sequence of DNA </li></ul><ul><li>May occur in somatic cells (aren’t passed to offspring) </li></ul><ul><li>May occur in gametes (eggs & sperm) and be passed to offspring </li></ul>
  3. 3. Are Mutations Helpful or Harmful? <ul><li>Some type of skin cancers and leukemia result from somatic mutations </li></ul><ul><li>Some mutations may improve an organism’s survival (beneficial) </li></ul>
  4. 4. Types of mutations <ul><ul><ul><li>Spontaneous </li></ul></ul></ul><ul><ul><ul><li>Induced </li></ul></ul></ul>
  5. 5. <ul><li>Spontaneous mutations </li></ul><ul><ul><ul><li>Occurs every 10 6 to 10 10 replications </li></ul></ul></ul><ul><ul><ul><li>1 mutation in every billion bacteria </li></ul></ul></ul><ul><ul><ul><li>Example: Neisseria gonorrhoeae penicillin resistance original mutation was spontaneous strains antibiotic resistance </li></ul></ul></ul>
  6. 6. <ul><li>Induced mutations </li></ul><ul><ul><ul><li>Chemical or Physical agents enhance mutation rate </li></ul></ul></ul><ul><ul><ul><li>Mutagens </li></ul></ul></ul><ul><ul><ul><ul><li>Ultraviolet light—mechanism of action </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Chemicals </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Chromosomal changes </li></ul></ul></ul></ul>
  7. 9. Types of Mutations
  8. 10. Change in genotype <ul><li>Chromosomal Mutations </li></ul><ul><li>Gene Mutations </li></ul><ul><li>Genom Mutations </li></ul>
  9. 11. Chromosome Mutations
  10. 12. Chromosome Mutations <ul><li>May Involve: </li></ul><ul><ul><li>Changing the structure of a chromosome </li></ul></ul><ul><ul><li>The loss or gain of part of a chromosome </li></ul></ul>
  11. 13. Chromosome Mutations <ul><li>Four types exist: </li></ul><ul><ul><li>Deletion </li></ul></ul><ul><ul><li>Inversion </li></ul></ul><ul><ul><li>Duplication </li></ul></ul><ul><ul><li>Translocation </li></ul></ul>
  12. 14. Deletion <ul><li>Due to breakage </li></ul><ul><li>A piece of a chromosome is lost </li></ul>
  13. 15. Inversion <ul><li>Chromosome segment breaks off </li></ul><ul><li>Segment flips around backwards </li></ul><ul><li>Segment reattaches </li></ul>
  14. 16. Duplication <ul><li>Occurs when a gene sequence is repeated </li></ul>
  15. 17. Translocation <ul><li>Involves two chromosomes that aren’t homologous </li></ul><ul><li>Part of one chromosome is transferred to another chromosomes </li></ul>
  16. 18. Translocation
  17. 19. Chromosome Mutation Animation
  18. 21. Gene Mutations
  19. 22. Gene Mutations <ul><li>Change in the nucleotide sequence of a gene </li></ul><ul><li>May only involve a single nucleotide </li></ul><ul><li>May be due to copying errors , chemicals , viruses , etc. </li></ul>
  20. 23. Types of Gene Mutations <ul><li>Include: </li></ul><ul><ul><li>Point Mutations(Substitutions) </li></ul></ul><ul><ul><li>Frameshift </li></ul></ul><ul><ul><li>Insertions </li></ul></ul><ul><ul><li>Deletions </li></ul></ul>
  21. 24. Point Mutation <ul><li>Change of a single nucleotide in a gene </li></ul><ul><li>Point (substitution) </li></ul><ul><li> (leu) (ser) (arg) </li></ul><ul><li>Normal AAT AGT GCC </li></ul><ul><li> (leu) (cyst) (arg) </li></ul><ul><li>Mutant AAT T GT GCC </li></ul>
  22. 25. Point Mutation <ul><li>Sickle Cell disease is </li></ul><ul><li>the result of one nucleotide substitution </li></ul><ul><li>Occurs in the hemoglobin gene </li></ul><ul><li>Hb A val his lei try pro glu gly lys </li></ul><ul><li>Hb S val his lei try pro val gly lys </li></ul>
  23. 28. Frameshift Mutation <ul><li>Inserting or deleting one or more nucleotides </li></ul><ul><li>Changes the “ reading frame ” like changing a sentence </li></ul><ul><li>Proteins built incorrectly </li></ul>
  24. 29. Frameshift Mutation <ul><li>Original: </li></ul><ul><ul><li>The fat cat ate the wee rat . </li></ul></ul><ul><li>Frame Shift (“a” added): </li></ul><ul><ul><li>The fat c a a tet hew eer at. </li></ul></ul>
  25. 30. <ul><li>Mutation Type </li></ul><ul><li>Frameshift (deletion) </li></ul><ul><li> (leu) (ser) (arg) </li></ul><ul><li>Normal AAT AGT GCC </li></ul><ul><li> (leu) (val) (pro) </li></ul><ul><li>Mutant AAT A GT G CC A </li></ul>
  26. 31. <ul><li>Mutation Type </li></ul><ul><li>Frameshift (insertion) </li></ul><ul><li> (leu) (ser) (arg) </li></ul><ul><li>Normal AAT AGT GCC </li></ul><ul><li> (leu) (glut) (cyst) </li></ul><ul><li>Mutant AAT CAG T GC C </li></ul>
  27. 32. Amino Acid Sequence Changed
  28. 33. Gene Mutation Animation
  29. 34. Nonsense Mutation
  30. 35. <ul><li>Genom Mutations </li></ul>
  31. 36. Nondisjunction <ul><li>Failure of chromosomes to separate during meiosis </li></ul><ul><li>Causes gamete to have too many or too few chromosomes </li></ul>
  32. 38. Non-disjunction during meiosis <ul><li>Spindle fibre fails during meiosis </li></ul><ul><li>Members of one pair of homologous chromosomes fail to become separated </li></ul><ul><li>2 gametes receive extra copy of affected chromosome </li></ul><ul><li>2 gametes lack that chromosome </li></ul>
  33. 40. Down’s Syndrome <ul><li>Non-disjunction in chromosome 21 </li></ul><ul><li>Occurs in human egg mother cell </li></ul><ul><li>One or more abnormal eggs formed (n = 24) </li></ul><ul><li>Fertilised by normal sperm (n = 23) </li></ul><ul><li>Formation of abnormal zygote (2n = 47) </li></ul>
  34. 44. Non dis-junction of sex chromosomes
  35. 45. Turner’s syndrome <ul><li>Gamete with no sex chromosomes fuses with normal X gamete </li></ul><ul><li>Zygote has chromosome complement 2n = 45 </li></ul><ul><li>Individuals are female and short in stature </li></ul><ul><li>Infertile because ovaries haven’t developed normally </li></ul>
  36. 47. Klinefelter’s syndrome <ul><li>XX egg fertilised by normal Y sperm </li></ul><ul><li>or </li></ul><ul><li>Normal X egg is fertilised by an XY sperm </li></ul><ul><li>Zygote has chromosome complement 2n = 47 (44 + XXY) </li></ul><ul><li>Always male </li></ul><ul><li>Normally infertile </li></ul><ul><li>Cannot produce sperm </li></ul>
  37. 49. Complete non-disjunction and polyploidy <ul><li>All the spindle fibres in a gamete mother cell fail </li></ul><ul><li>All homologous pairs fail to become separated </li></ul><ul><li>Production of abnormal diploid gametes </li></ul><ul><li>Each contains 2 complete sets of chromosomes instead of one </li></ul>
  38. 50. Polyploidy <ul><li>Fertilisation of abnormal gametes </li></ul><ul><li>Formation of mutant plants which possess complete extra sets of chromosomes </li></ul><ul><li>This type of chromosome mutation is called polyploidy </li></ul>
  39. 51. A: the strawberry plant is exposed to a chemical B: due to the effect of chemical, total non-disjunction at meiosis produces diploid gametes(2n) C: two diploid gametes fuse at fertilisation D: a new plant develops which has four sets of chromosomes (4n)
  40. 52. Economic significance <ul><li>Polyploid plants are larger than diploid relatives </li></ul><ul><li>Increased seed and fruit size </li></ul><ul><li>Many commercially developed crop plants are polyploid </li></ul><ul><li>-apples -strawberries </li></ul><ul><li>-tomatoes -wheat </li></ul><ul><li>Give greater yields </li></ul>
  41. 53. Effects of polyploidy <ul><li>Uneven sets of chromosome </li></ul><ul><li>-polyploidy plants are sterile </li></ul><ul><li>Produce seedless fruit </li></ul><ul><li>Increase in vigour </li></ul><ul><li>Resistance to disease </li></ul>
  42. 54. <ul><li>Repair Mechanisms </li></ul><ul><ul><ul><li>DNA repair enzymes </li></ul></ul></ul><ul><ul><ul><ul><li>Many enzymes </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Constantly checking for errors </li></ul></ul></ul></ul><ul><ul><ul><li>Repair mechanisms </li></ul></ul></ul><ul><ul><ul><ul><li>Damage repair </li></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Excision repair </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Dimer repair (UV light) </li></ul></ul></ul></ul></ul>
  43. 55. Mismatch Repair
  44. 56. Excision Repair