Chromosomes and Mutations D r. Nichols Coronado HS

1. Chromosomes and MutationsDr. NicholsCoronado HS

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 in many organisms 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 • Five types exist: • Deletion • Inversion • Translocation • Nondisjunction • Duplication

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

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

9. Duplication • Occurs when a gene sequence is repeated

10. Translocation • Involves two chromosomes that aren’t homologous (the same) • Part of one chromosome is transferred to another chromosomes

11. Translocation

12. 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

14. Starting point

15. Real Life Deletions A portion of the chromosome is missing or deleted. Known disorders in humans include Wolf-Hirschhorn syndrome, which is caused by partial deletion of the short arm of chromosome 4; and Jacobsen syndrome, also called the terminal 11q deletion disorder.

16. Real Life Duplications A portion of the chromosome is duplicated, resulting in extra genetic material. Known human disorders include Charcot-Marie-Tooth disease type 1A.

17. Types of Translocations • Reciprocal translocation: Segments from two different chromosomes have been exchanged. • Robertsonian translocation: An entire chromosome has attached to another at the centromere - in humans these only occur with chromosomes 13, 14, 15, 21 and 22

18. Diseases of Translocation Recurring miscarriages, Leukaemia, Infertility, Breast Cancer, Schizophrenia, Muscular Dystrophy.

19. Real Life Inversions • Edwards syndrome: Ninety percent die in infancy; however, those that live past their first birthday usually are quite healthy thereafter. They have a characteristic clenched hands and overlapping fingers. • Patau Syndrome, also called D-Syndrome or trisomy-13. Symptoms are somewhat similar to those of trisomy-18, but they do not have the characteristic hand shape.

21. Normal Male 2n = 46

22. Normal Female 2n = 46

23. Male, Trisomy 21 (Down’s) 2n = 47

24. Female Down’s Syndrome 2n = 47

25. Klinefelter’s Syndrome 2n = 47

26. Turner’s Syndrome 2n = 45

27. Introducing the chromosome!

29. Human chromosomes Image believed to be in the Public Domain

30. The chromosomes of a human female