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Mutations

Mutations are changes in the nucleotide sequence of DNA that can occur in somatic cells (not inherited) or gametes (inherited). Frequents and often neutral, mutations can be caused by environmental factors like UV radiation and chemicals, or may arise from copying errors. They fall into two categories: chromosome mutations (deletions, duplications, inversions, translocations, and nondisjunction) and gene mutations (point mutations, insertions, deletions, and frameshifts). While most mutations are harmless, some can lead to diseases or provide benefits for survival.

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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) • May occur in gametes (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. 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)

  5. Types of Mutations

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

  7. Chromosome Mutations • Five types exist: • Deletion • Inversion • Translocation • Nondisjunction • Duplication

  8. Deletion • Due to breakage • A piece of a chromosome is lost

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

  10. Duplication • Occurs when a gene sequence is repeated

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

  12. Translocation

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

  14. Chromosome Mutation Animation

  15. 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.

  16. Types of Gene Mutations • Include: • Point Mutations • Substitutions • Insertions • Deletions • Frameshift

  17. Point Mutation • Change of a single nucleotide • Includes the deletion, insertion, or substitution of ONE nucleotide in a gene

  18. Point Mutation • Sickle Cell disease is the result of one nucleotide substitution • Occurs in the hemoglobin gene

  19. Frameshift Mutation • Inserting or deleting one or more nucleotides • Changes the “reading frame” like changing a sentence • Proteins built incorrectly

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

  21. Amino Acid Sequence Changed

  22. Gene Mutation Animation

  23. FYI

  24. Normal Male 2n = 46

  25. Normal Female 2n = 46

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

  27. Female Down’s Syndrome 2n = 47

  28. Klinefelter’s Syndrome 2n = 47

  29. Turner’s Syndrome 2n = 45

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