Changes in Chromosome Structure

1. Changes in Chromosome Structure

2. Chromosome Structure Mutations

3. Breakage and Rejoining Unequal crossing-over Mechanisms of Chromosome Mutation

4. Duplications

5. Meiotic Structures

6. Consequences of Duplications • Altered phenotypes as a result of imbalances in amounts of gene products

7. Consequences of Duplications • Duplication can lead to other genetic changes • Alleles with new functions

8. Consequences of Duplications • Duplication can lead to other genetic changes • Higher degrees of duplication

9. Deletions

10. Meiotic Structures

11. Consequences of Deletions • Chromosome is lost if centromere is deleted. • Chromosomes with deletions do not revert to the wild type state. • Recombination frequencies between genes flanking the deletion are reduced. • Deletions are lethal in the homozygous state.

12. Solid tumors can accumulate deletions Cri du chat syndrome results from a deletion in chromosome 5 Consequences of Deletions 5. Multiple defects occur in heterozygotes due to • imbalances in the amounts of gene products

13. Wild Type Wing Notch Wing Consequences of Deletions 5. Multiple defects occur in heterozygotes due to • pseudodominance = recessive alleles on the non-deleted homolog are expressed • haploinsufficiency = certain genes must be present in two copies for normal function

14. Inversions

15. Meiotic Structures

16. Consequences of Inversions • Generally viable since amount of genetic material is unchanged. • Leads to lethal mutation if breakpoint is within an essential gene.

17. Consequences of Inversions • Position Effect = Gene regulation can be altered by a difference in chromosome location • Recombination frequency is reduced due to inhibition of pairing and since crossover in heterozygotes yields additional structural mutations.

18. Crossing Over in a Paracentric Inversion Heterozygote

19. Anaphase II Crossing Over in a Pericentric Inversion Heterozygote

20. Crossing Over in Inversion Heterozygotes

21. Inversions in Evolutionary History

22. Translocations

23. Robertsonian Translocation • Long arms of two acrocentric chromosomes are joined to the same centromere • Results in one large chromosome and one small chromosome • Smaller chromosome may be lost

24. Inheritance of Down Syndrome from the carrier of a Robertsonian translocation, joining the long arms of chromosomes 14 and 21.

25. Burkitt’s lymphoma is caused by a position effect. Consequences of Translocations • Behave as point mutationsif the breakpoint disrupts an essential gene. • Show new linkage arrangements. • Position Effect = Gene expression is altered as a result of the new environment for translocated material.

26. Consequences of Translocations Position-effect variegation of eye color in fruit flies due to translocation of w+ next to heterochromatin

27. Translocations found in cells of solid tumors

28. Consequences of Translocations Meiotic Structures • Leads to semisterility, where approximately half of the gametes carry structural mutations.

29. Meiotic Segregation in Translocation Heterozygotes

30. Meiotic Segregation in Translocation Heterozygotes