Mutations

1. Mutations

2. What Are Mutations? • Changes in the nucleotide sequence of DNA (big or small) • 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 • Six types exist: • Deletion • Inversion • Translocation • Insertion • Duplication • Aneuploidy by nondisjunction

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

9. Disorders due to chromosome deletions: • Cri du Chat – deletion of short arm of 5 • 1p36 Deletion Syndrome-deletion of short arm of 1 • Angleman Syndrome- deletion of short arm of maternal 15 • Prader-Willi syndrome- deletion of short arm of paternal 15

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

11. Disorders caused by inversions: • If they are “balanced” they cause no phenotype • If they are “unbalanced” they usually are associated with a deletion and several effects

12. Duplication • Occurs when a gene sequence is repeated

13. Translocation • Involves two chromosomes that aren’t homologous • Part of one chromosome is transferred to another chromosome and swapped with a region of that chromosome

14. Translocation

15. Disorders caused by translocations • “Robertsonian” usually show no phenotypes but often problems during meiosis leading to miscarriages in developing fetus. • Common to have Robertsonian traslocation of 13 and 14. • If translocation of long arm of 21 and long arm of 14-Down’s • Some cancer cells have translocations (leukemia, sarcoma)

16. Insertion • A piece of one • Chromosome gets • Inserted into • Another • Chromosome • Effect depends • on what was • Inserted and wheree

17. 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

19. Some Aneuploid Chromosomal Disorders • Patau Syndrome • Edward Syndrome • Klinfelter’s Syndrome • Turner Syndrome • Super Male Syndrome • Super Female Syndrome • Down’s Syndrome

20. Normal Male 2n = 46

21. Normal Female 2n = 46

22. 47, XY, +13 • serious eye, brain, circulatory defects as well as cleft palate. 1:5000 live births. Children rarely live more than a few months. • Patau Syndrome

23. Cleft Palate

26. Edward Syndrome • almost every organ system affected 1:10,000 live births. Children with full Trisomy 18 generally do not live more than a few months.

28. Male, Trisomy 21 (Down’s) 2n = 47

29. Female Down’s Syndrome 2n = 47

30. Down’s Syndrome

31. Down’s Syndrome Characteristics • One in 733 births • Slow cognitive ability and growth • Small chin • Round face • Almond shaped, often upslanting eyes • Heart defects • Gastric reflux disease • Thyroid problems

32. Klinefelter’s Syndrome 2n = 47

33. Kleinfelter’s Syndrome

34. Turner’s Syndrome 2n = 45

35. Turner’s syndrome

36. Chromosome Mutation Animation