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Mutations

Learn about mutations, changes in the DNA sequence that can occur in somatic or germ-line cells. Discover different types of mutations, such as point mutations and chromosome mutations, and understand how they can be helpful or harmful. Explore examples of mutations and their impacts on phenotypes.

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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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