Lecture 17 Chapter 16_2 - Anthony Griffiths Susan Wessler...

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    Introduction to Genetic Analysis Eighth Edition Chapter 15: Large-Scale Chromosomal Changes Copyright  ©  2005 by W. H. Freeman & Company Anthony Griffiths • Susan Wessler • Richard Lewontin William Gelbart • David Suzuki • Jeffrey Miller
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    Chromosome Abnormalities
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    Large-Scale Chromosomal Changes
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    Large-Scale Chromosomal Changes Results from cell division errors. Cell cycle Error S-phase Replication small-scale mutations Prophase Chromosome pairing Duplication/deletion Recombination translocation/inversion Anaphase Segregation Aneuploidy Telophase /cytokinesis Cell division Euploidy/Polyploidy
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    Meiosis I Late Prophase I: Chromosome pairing & recombination -errors:structural changes
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    Chromosomal Rearrangements   Changes in  Chromosome Structure Chromosomal rearrangements are induced by 1. Chromosome Breakage 2. Illegitimate crossing-over between repetitive DNA  Two categories 1. Balanced rearrangements Change in gene order on chromosome but no change in gene  copy number. 1. Inversions 2. Some Translocations 2. Unbalanced rearrangements Changes in gene copy number 1. Polyploidy Aneuploidy 2. Deletions Duplication 3. Some translocations 
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    Chromosomal Rearrangements   1. Double Stranded Break Induced Chromosomes are intact double stranded DNA molecules. Occurrence of two or more double stranded breaks is the  initiating event in chromosome rearrangement. DS-breaks are lethal unless repaired. DS-break repair systems identify DS-breaks and immediately join two  DS-breaks together. If the two end of the same break are rejoined then the chromosome is  properly reconstituted. If different ends are joined or material is lost – a chromosome  rearrangement takes place.
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    Chromosomal Rearrangements   2. Repetitive DNA Induced Short DNA stretches are repeated all over our genome. When two homologous repeats  located in different regions  of the genome..  Undergo complementary base pairing and recombination  during meiosis or mitosis  Aberrant chromosomes are produced.
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    Chromosome Rearrangements 1. Deletions Loss of a chromosome segment. 1. Duplications Doubling of a chromosome segment. 1. Inversions Flipping of a chromosome segment in the reverse orientation. 1. Translocations Double stranded break in DNA which is left un repaired sometimes  join with a different chromosome.
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    Chromosome Rearrangements
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    Chromosome Rearrangements Result in genetic imbalance.
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