lec 18 - Lecture 18: Chromosomes Layers of chromatin...

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Lecture 18: Chromosomes
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Layers of chromatin packing in chromosomes
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Metaphase chromosomes Kodjabachian, Delaage, Maurel, Miassod, Jacq and Rosset The EMBO Journal (1998) 17, 1063 1075
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Model for chromatin folding in a metaphase chromosome
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Chromosomes maintain some degree of organization in the interphase nucleus: Identification of discrete domains FISH (fluorescence in situ hybridization) using probes spanning the whole chromosome 7 (green) and chromosome 8 (red) Blue = generic DNA staining
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Sister chromatids
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Chromosome identification G bands: mild heat/proteolysis -> Giemsa reagent (DNA dye) scanning electron microscope light microscope G bands = ~ very low G+C light microscope Number, sizes, shapes = Specific for each species = KARYOTYPE
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Chromosome identification reproducible band pattern
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Detection of chromosome breaks/translocations Ex: chronic myelogenous leukemia
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Detection of chromosome breaks/translocations: Chromosome “painting” same translocation detected by multicolor fluorescence in situ hybridization (FISH)
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Evolution of chromosomes Fusion: Primate 9 + 11 -> Human 1 Breakage: Primate 5 -> human 14 + 15 Reciprocal translocation: Primate 14 + 21 -> human 12 + 22 = Large scale changes in chromosome organization -> no inbreeding -> new species
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Polytene chromosome Ex: 4 th chromosome of Drosophila melanogaster Repeated replication without separation (10 cycles -> 1024 copies)
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Polytene chromosome
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Polytene chromosome ~ 5000 bands and 5000 interbands in the complete set of Drosophila chromosomes Numbered -> chromosome map Bands = relatively short sequences. 50-100,000 bases
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Localization of specific gene by in situ hybridization Polytene chromosome
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puff decondensation, gene expression Polytene chromosome
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Cover photograph (Copyright © 2003, American Society for Microbiology. All Rights Reserved.): Distribution of the
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This note was uploaded on 12/07/2010 for the course BIO BIOL 200 taught by Professor Frogatto during the Fall '10 term at McGill.