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Mutations

Mutations. What Are Mutations?. Changes in the nucleotide sequence of DNA May occur in somatic cells (aren’t passed to offspring, only to descendant cells) May occur in germ-line cells (eggs & sperm) and be passed to offspring. Are Mutations Helpful or Harmful?.

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Mutations

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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, only to descendant cells) • May occur in germ-line cells (eggs & sperm) and be passed to offspring

  3. Are Mutations Helpful or Harmful? • Mutations happen regularly • Almost all mutations are neutral • Chemicals & UV radiation cause mutations • Many mutations are repaired by enzymes

  4. Types of Mutations

  5. Point Mutations • Change in the nucleotide sequence of a one or a few base pairs • May be due to copying errors, chemicals, viruses, etc.

  6. Types of Point Mutations • Include: • Substitutions • Frame-shift Mutations (Insertion, Deletion)

  7. Substitution • One or more nucleotides are changed to a different base. • AAC GCC AGC • AAG GCC AGC • Can cause an amino acid to be changed…or not!

  8. Frame-shift Mutation • Inserting or deleting one or more nucleotides • Changes the “reading frame” like changing a sentence • Proteins built incorrectly

  9. Frameshift Mutation • Original: • The fat cat ate the wee rat. • Frame Shift (“a” added): • The fat caa tet hew eer at.

  10. Amino Acid Sequence Changed

  11. Gene Mutation Animation

  12. How Would the Phenotype Change?

  13. Missense Substitution • Sickle Cell disease is the result of one nucleotide substitution • Occurs in the hemoglobin gene

  14. Nonsense Substitution • Thallasemia is the result of a stop codon substitution that shortens the gene • Occurs in the hemoglobin gene

  15. Silent Mutation • The Genetic Code is repetitive – there are 64 codons that code for 20 amino acids. • A silent mutation makes no change in amino acid sequence:

  16. Deletion Cystic fibrosis (mucus in the lungs)is the result of one nucleotide deletion Causes a frame-shift!

  17. Insertion Huntington’s Disease (nerve cell deterioration)is the result of many nucleotide insertions (CAG repeats)

  18. Chromosome Mutations • May Involve: • Changing the structure of a chromosome • The loss or gain of part of a chromosome

  19. Chromosome Mutations • Five types exist: • Deletion/Insertion • Duplication • Inversion • Translocation • Nondisjunction

  20. Insertion Deletion An additional piece of chromosome is added • Due to breakage • A piece of a chromosome is lost

  21. Deletion Cri-du-Chat is caused by a deletion in one of the chromosomes. Causes an abnormal larynx

  22. Duplication • Occurs when a gene sequence is repeated

  23. Inversion • Chromosome segment breaks off • Segment flips around backwards • Segment reattaches

  24. Translocation • Involves two chromosomes that aren’t homologous • Part of one chromosome is transferred to another chromosomes

  25. Translocation

  26. Nondisjunction • Failure of chromosomes to separate during meiosis • Causes gamete to have too many or too few chromosomes • Disorders: • DownSyndrome – three 21st chromosomes • Turner Syndrome – single X chromosome • Klinefelter’s Syndrome – XXY chromosomes

  27. Chromosome Mutation Animation

  28. Normal Male

  29. Normal Female

  30. Male, Trisomy 21 (Down’s) 2n = 47

  31. Female Down’s Syndrome 2n = 47

  32. Turner’s Syndrome 2n = 45

  33. Turner’s Syndrome 35

  34. Klinefelter’s Syndrome

  35. Klinefelter’s Syndrome 37

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