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LECTURE 22 LARGE-SCALE CHROMOSOME CHANGES II

LECTURE 22 LARGE-SCALE CHROMOSOME CHANGES II. chapter 15 overview chromosome number chromosome structure problems. CHANGES IN CHROMOSOME NUMBER. what are the genotypic & phenotypic probabilities in the progeny of a P cross A/A/A/a  A/A/A/a ?

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LECTURE 22 LARGE-SCALE CHROMOSOME CHANGES II

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  1. LECTURE 22 LARGE-SCALE CHROMOSOME CHANGES II • chapter 15 • overview • chromosome number • chromosome structure • problems

  2. CHANGES IN CHROMOSOME NUMBER • what are the genotypic & phenotypic probabilities in the progeny of a P cross A/A/A/a A/A/A/a? • P gametes: P(A/A) = P(A/a) = ½, P(a/a) = 0 • F1 genotypes: P(A/A/A/A) = (½)2 = ¼ P(A/A/A/a) = 2(½)2 = ½ P(A/A/a/a) = (½)2 = ¼ • F1 phenotypes: all A • A/A/a/a? • A/a/a/a? • autopolyploids }work out these ones for next class

  3. OVERVIEW • 3 classes of chromosome change   

  4. OVERVIEW • 2 general questions to consider... • is the genome complete? • is the genome balanced?

  5. CHANGES IN CHROMOSOME STRUCTURE • implications • chromosome structure mutations phenotypes • abnormal gene # segmental aneuploids • abnormal gene environment position effect • break points disrupt gene function

  6. CHANGES IN CHROMOSOME STRUCTURE • things to keep in mind • each chromatid is has a single DNA molecule • need either... • 2+ double strand breaks • crossing over between repetative sequences • chromosome breakage ends highly reactive (normal telomeres not) • double strand breaks are lethal unless repaired • repaired by joining broken ends

  7. CHANGES IN CHROMOSOME STRUCTURE • more things to keep in mind • repair can restore original sequence or • generate rearrangement • acentric products are lost & inviable • dicentric products are broken & inviable • rearrangements can be • spontaneous • induced by radiation... X- or -rays • mainly studied in heterozygotes

  8. CHANGES IN CHROMOSOME STRUCTURE • 2 types of rearrangements • unbalanced change gene dosage • deletions • uncover deleterious alleles usually lethal • duplications • extra material evolutionary divergence

  9. CHANGES IN CHROMOSOME STRUCTURE • 2 types of rearrangements • balanced change gene dosage • inversions • reduced fertility • reduced recombination in inverted region • translocations • reorganizes linkage 50% sterility fertility • novel linkage of genes on translocated chromosomes

  10. CHANGES IN CHROMOSOME STRUCTURE • origins of rearrangements by 2 processes • break / rejoining • spontaneous • radiation

  11. CHANGES IN CHROMOSOME STRUCTURE • origins of rearrangements by 2 processes • break / rejoining • spontaneous • radiation • crossing over • illegitimate

  12. CHANGES IN CHROMOSOME STRUCTURE • visualization in heterozygotes • strong pairing affinity during meiotic prophase I • abnormal patterns seen in rearrangement heterozygotes (–/+)

  13. CHANGES IN CHROMOSOME STRUCTURE • biological importance • research tools • new combinations of genes • mapping • recombination suppression • mutant rescue • applied research medicine & agriculture • evolutionary significance genome reshuffling

  14. CHANGES IN CHROMOSOME STRUCTURE • deletions • 1 chromosome break terminal • 2 chromosome break interstitial

  15. CHANGES IN CHROMOSOME STRUCTURE • deletions • intragenic  within 1 gene • do not revert ( point mutations) • can be viable if gene not vital • multigenic > 1 gene • do not revert • usually homozygous lethal • sometimes heterozygous lethal

  16. CHANGES IN CHROMOSOME STRUCTURE • deletions • multigenic > 1 gene • uncovers recessive alleles on homologue • pseudodominance • deletion mapping

  17. CHANGES IN CHROMOSOME STRUCTURE • deletions • multigenic > 1 gene • uncovers recessive alleles on homologue • pseudodominance • deletion mapping

  18. CHANGES IN CHROMOSOME STRUCTURE • deletions • multigenic > 1 gene • deletion mapping ~ linkage maps

  19. CHANGES IN CHROMOSOME STRUCTURE • deletions • multigenic > 1 gene • deletion mapping ~ human disease, e.g.: cri du chat syndrome

  20. CHANGES IN CHROMOSOME STRUCTURE • duplications (2 chromosome breaks) • adjacent, same order tandem • adjacent, reverse order reverse

  21. CHANGES IN CHROMOSOME STRUCTURE • duplications • intragenic  within 1 gene • do not revert ( point mutations, see below) • can be viable if genetic balance not critical • multigenic > 1 gene • do not revert (see below) • homozygous lethal if genetic balance critical • can be heterozygous lethal if balance critical

  22. CHANGES IN CHROMOSOME STRUCTURE • duplications • illegitimate recombination possible, e.g.: Bar

  23. CHANGES IN CHROMOSOME STRUCTURE • duplications • important for gene evolution, e.g.: human hemoglobin genes

  24. CHANGES IN CHROMOSOME STRUCTURE • duplications • important for gene evolution, e.g.: human hemoglobin genes

  25. CHANGES IN CHROMOSOME STRUCTURE • inversions • does not include centromere  paracentric • does include centromere pericentric

  26.  CHANGES IN CHROMOSOME STRUCTURE • inversions • does not include centromere  paracentric A B C D E F G H

  27.  CHANGES IN CHROMOSOME STRUCTURE • inversions • does not include centromere  paracentric A B C D E F G H

  28. CHANGES IN CHROMOSOME STRUCTURE • inversions • does not include centromere  paracentric A C B D E F G H

  29.  CHANGES IN CHROMOSOME STRUCTURE • inversions • does include centromere  pericentric A B C D E F G H

  30.  CHANGES IN CHROMOSOME STRUCTURE • inversions • does include centromere  pericentric A B C D E F G H

  31. CHANGES IN CHROMOSOME STRUCTURE • inversions • does include centromere  pericentric A B F E D C G H

  32. CHANGES IN CHROMOSOME STRUCTURE • inversions • no change in total genetic material • breakpoints can (but not always) disrupt genes • no disruption  viable homozygotes • disruption  heterozygotes only (majority) • do not revert • recombination in inversion segm. aneuploidy • recombinant gametes lethal , fertility  • recombinationsuppression

  33. CHANGES IN CHROMOSOME STRUCTURE • inversions • breakpoints between genes

  34. CHANGES IN CHROMOSOME STRUCTURE • inversions • breakpoints between genes... disruption of 1 • breakpoints within genes... gene fusion

  35. CHANGES IN CHROMOSOME STRUCTURE • inversions • loops

  36. CHANGES IN CHROMOSOME STRUCTURE • inversions • loops

  37. CHANGES IN CHROMOSOME STRUCTURE • inversions • loops

  38. CHANGES IN CHROMOSOME STRUCTURE • inversions • crossing over in a paracentric inversion heterozygote

  39. CHANGES IN CHROMOSOME STRUCTURE • inversions • crossing over in a paracentric inversion heterozygote • 1 normal  viable • 1 inversion  viable • 1 acentric  lost • 1 dicentric  2 lethal deletion products

  40. CHANGES IN CHROMOSOME STRUCTURE • inversions • crossing over in a pericentric inversion heterozygote

  41. CHANGES IN CHROMOSOME STRUCTURE • inversions • crossing over in a pericentric inversion heterozygote • 1 normal  viable • 1 duplication  lethal • 1 deletion  lethal • 1 inversion  viable

  42. CHANGES IN CHROMOSOME STRUCTURE • translocations (reciprocal or Robertsonian) • no change in total genetic material • do not revert • meiosis segmental aneuploidy • lethality • semi-sterility • rearrangement of linkage groups • can restructure genomes

  43. CHANGES IN CHROMOSOME STRUCTURE • translocations • heterozygotes • adjacent-1 4 lethal • adjacent-2 rare, 4 lethal • alternate 2 normal + 2 carrier

  44. CHANGES IN CHROMOSOME STRUCTURE • translocations • pseudolinkage observed from test cross of translocation heterozygote: a/; a+b+/ba/a; b/b

  45. CHANGES IN CHROMOSOME STRUCTURE • translocations • position-effect variegation

  46. PROBLEMS • #1-55 on pp. 512-520 • consider (read & think about) all of the questions • at the very least you should do #s 22, 23, 26, 40, 49

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