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Biology lecture 6
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  • 1. Mutations
  • 2. What Are Mutations?
    • Changes in the nucleotide sequence of DNA
    • May occur in somatic cells (aren’t passed to offspring)
    • May occur in gametes (eggs & sperm) and be passed to offspring
  • 3. Are Mutations Helpful or Harmful?
    • Some type of skin cancers and leukemia result from somatic mutations
    • Some mutations may improve an organism’s survival (beneficial)
  • 4. Types of mutations
        • Spontaneous
        • Induced
  • 5.
    • Spontaneous mutations
        • Occurs every 10 6 to 10 10 replications
        • 1 mutation in every billion bacteria
        • Example: Neisseria gonorrhoeae penicillin resistance original mutation was spontaneous strains antibiotic resistance
  • 6.
    • Induced mutations
        • Chemical or Physical agents enhance mutation rate
        • Mutagens
          • Ultraviolet light—mechanism of action
          • Chemicals
          • Chromosomal changes
  • 7.  
  • 8.  
  • 9. Types of Mutations
  • 10. Change in genotype
    • Chromosomal Mutations
    • Gene Mutations
    • Genom Mutations
  • 11. Chromosome Mutations
  • 12. Chromosome Mutations
    • May Involve:
      • Changing the structure of a chromosome
      • The loss or gain of part of a chromosome
  • 13. Chromosome Mutations
    • Four types exist:
      • Deletion
      • Inversion
      • Duplication
      • Translocation
  • 14. Deletion
    • Due to breakage
    • A piece of a chromosome is lost
  • 15. Inversion
    • Chromosome segment breaks off
    • Segment flips around backwards
    • Segment reattaches
  • 16. Duplication
    • Occurs when a gene sequence is repeated
  • 17. Translocation
    • Involves two chromosomes that aren’t homologous
    • Part of one chromosome is transferred to another chromosomes
  • 18. Translocation
  • 19. Chromosome Mutation Animation
  • 20.  
  • 21. Gene Mutations
  • 22. Gene Mutations
    • Change in the nucleotide sequence of a gene
    • May only involve a single nucleotide
    • May be due to copying errors , chemicals , viruses , etc.
  • 23. Types of Gene Mutations
    • Include:
      • Point Mutations(Substitutions)
      • Frameshift
      • Insertions
      • Deletions
  • 24. Point Mutation
    • Change of a single nucleotide in a gene
    • Point (substitution)
    • (leu) (ser) (arg)
    • Normal AAT AGT GCC
    • (leu) (cyst) (arg)
    • Mutant AAT T GT GCC
  • 25. Point Mutation
    • Sickle Cell disease is
    • the result of one nucleotide substitution
    • Occurs in the hemoglobin gene
    • Hb A val his lei try pro glu gly lys
    • Hb S val his lei try pro val gly lys
  • 26.  
  • 27.  
  • 28. Frameshift Mutation
    • Inserting or deleting one or more nucleotides
    • Changes the “ reading frame ” like changing a sentence
    • Proteins built incorrectly
  • 29. Frameshift Mutation
    • Original:
      • The fat cat ate the wee rat .
    • Frame Shift (“a” added):
      • The fat c a a tet hew eer at.
  • 30.
    • Mutation Type
    • Frameshift (deletion)
    • (leu) (ser) (arg)
    • Normal AAT AGT GCC
    • (leu) (val) (pro)
    • Mutant AAT A GT G CC A
  • 31.
    • Mutation Type
    • Frameshift (insertion)
    • (leu) (ser) (arg)
    • Normal AAT AGT GCC
    • (leu) (glut) (cyst)
    • Mutant AAT CAG T GC C
  • 32. Amino Acid Sequence Changed
  • 33. Gene Mutation Animation
  • 34. Nonsense Mutation
  • 35.
    • Genom Mutations
  • 36. Nondisjunction
    • Failure of chromosomes to separate during meiosis
    • Causes gamete to have too many or too few chromosomes
  • 37.  
  • 38. Non-disjunction during meiosis
    • Spindle fibre fails during meiosis
    • Members of one pair of homologous chromosomes fail to become separated
    • 2 gametes receive extra copy of affected chromosome
    • 2 gametes lack that chromosome
  • 39.  
  • 40. Down’s Syndrome
    • Non-disjunction in chromosome 21
    • Occurs in human egg mother cell
    • One or more abnormal eggs formed (n = 24)
    • Fertilised by normal sperm (n = 23)
    • Formation of abnormal zygote (2n = 47)
  • 41.  
  • 42.  
  • 43.  
  • 44. Non dis-junction of sex chromosomes
  • 45. Turner’s syndrome
    • Gamete with no sex chromosomes fuses with normal X gamete
    • Zygote has chromosome complement 2n = 45
    • Individuals are female and short in stature
    • Infertile because ovaries haven’t developed normally
  • 46.  
  • 47. Klinefelter’s syndrome
    • XX egg fertilised by normal Y sperm
    • or
    • Normal X egg is fertilised by an XY sperm
    • Zygote has chromosome complement 2n = 47 (44 + XXY)
    • Always male
    • Normally infertile
    • Cannot produce sperm
  • 48.  
  • 49. Complete non-disjunction and polyploidy
    • All the spindle fibres in a gamete mother cell fail
    • All homologous pairs fail to become separated
    • Production of abnormal diploid gametes
    • Each contains 2 complete sets of chromosomes instead of one
  • 50. Polyploidy
    • Fertilisation of abnormal gametes
    • Formation of mutant plants which possess complete extra sets of chromosomes
    • This type of chromosome mutation is called polyploidy
  • 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)
  • 52. Economic significance
    • Polyploid plants are larger than diploid relatives
    • Increased seed and fruit size
    • Many commercially developed crop plants are polyploid
    • -apples -strawberries
    • -tomatoes -wheat
    • Give greater yields
  • 53. Effects of polyploidy
    • Uneven sets of chromosome
    • -polyploidy plants are sterile
    • Produce seedless fruit
    • Increase in vigour
    • Resistance to disease
  • 54.
    • Repair Mechanisms
        • DNA repair enzymes
          • Many enzymes
          • Constantly checking for errors
        • Repair mechanisms
          • Damage repair
            • Excision repair
            • Dimer repair (UV light)
  • 55. Mismatch Repair
  • 56. Excision Repair