1. Chromosomes and Mutations Dr. Nichols Coronado 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:
Down Syndrome – 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

25. Klinefelter’s Syndrome

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