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Structural Abnormalities

Structural Abnormalities. Deletions. Translocations. Inversions. Duplications. Deletions. Small or large. Mutation in one or many genes. Homozygosity or heterozygosity for each. Consequences for gene function. Deletions. Loss of chromosomal material Large-scale deletions are lethal

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Structural Abnormalities

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  1. Structural Abnormalities Deletions Translocations Inversions Duplications Chapter 6 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning

  2. Chapter 6 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning

  3. Deletions Small or large Mutation in one or many genes Homozygosity or heterozygosity for each Consequences for gene function Chapter 6 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning

  4. Deletions • Loss of chromosomal material • Large-scale deletions are lethal • Example: Cri du chat • Deletion of short arm of chromosome 5 • Affects motor and mental function • Infant cry resembles a meowing cat • Specific chromosomal break points are associated with specific phenotypic changes Chapter 6 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning

  5. Cri du chat Syndrome Variation in phenotype associated with region deleted has been observed Researchers have identified regions with genes involved in larynx and nervous system development Fig. 6.26 Chapter 6 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning

  6. Cri-du chat syndrome Deletion in Chrom. 5 Prader-Willi Syndrome Angelman Syndrome Deletions in Chromosome 15 Chapter 6 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning

  7. Structural Abnormalities Deletions Translocations Inversions Duplications Chapter 6 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning

  8. Translocations • Exchange of chromosomal segments between nonhomologous chromosomes • Two major types • Reciprocal translocation • Non-reciprocal translocation Chapter 6 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning

  9. Types of Translocations Chapter 6 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning

  10. Burkitt’s lymphoma Ig- myc Chapter 6 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning

  11. Deletion and Duplication gametes Normal gametes • ABMN • KLMN • ABMN • KLCDE • ABCDE • ABMN • ABCDE • KLMN Reciprocal Translocation: yields normal and defective gamets • ABCDE • KLMN • ABMN • KLCDE Parent Has complete information Chapter 6 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning

  12. Types of Translocations • Robertsonian Translocation • Centromeres from two nonhomologous chromosomes fuse and chromosomal material from the short arms is lost • 5% of Down syndrome cases involve a Robertsonian translocation between chromosomes 21 and 14 Chapter 6 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning

  13. Robertsonian Translocation • A translocation between chromosome 14 and 21 may produce • Translocation carrier • Normal phenotype • Translocation Down syndrome • Lethal monosomy 21 • Lethal trisomy 14 • Lethal monosomy 14 Fig. 6.27 Chapter 6 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning

  14. Structural Abnormalities Deletions Translocations Inversions Duplications Chapter 6 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning

  15. Chapter 6 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning

  16. New context • Inversions reorganize DNA sequences Antennapedia • Antp protein is made in antennal primordial • cells, where the WT Antp does not express • Legs grow out in Antp mutant in place of • antenna Chapter 6 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning

  17. Antp expressed in head Expression of Antp in head results in legs forming in place of antennae Wild-type head Antp required for identity of T2 (Wings and legs) Chapter 6 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning

  18. Structural Abnormalities Deletions Translocations Inversions Duplications Chapter 6 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning

  19. Chapter 6 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning

  20. Chapter 6 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning

  21. ß family a family gene duplication divergence (~ 450 million years ago) myoglobin gene duplication divergence (~ 700 million years ago) Primordial gene Encodes O2 carrier protein Evolution of genes/gene families Hemoglobin family Chapter 6 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning

  22. Other Chromosomal Abnormalities • Uniparental disomy • Both copies of a chromosome are inherited from a single parent • Due to error in cell division • Examples • Females affected with rare X-linked disorders • Prader-Willi and Angelman syndromes • Fragile sites • Over 100 have been identified Chapter 6 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning

  23. Fig. 6.29 Uniparental Disomy Chapter 6 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning

  24. Fragile Sites on the Human X Chromosome Fig. 6.30 Chapter 6 Human Heredity by Michael Cummings ©2006 Brooks/Cole-Thomson Learning

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