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Changes in Chromosome Structure

Changes in Chromosome Structure. Chromosome Structure Mutations. Breakage and Rejoining. Unequal crossing-over. Mechanisms of Chromosome Mutation. Duplications. Meiotic Structures. Consequences of Duplications. Altered phenotypes as a result of imbalances in amounts of gene products.

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Changes in Chromosome Structure

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  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

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