2011 Lect 14 Gene linkage

2011 Lect 14 Gene linkage - Genetic Geneticlinkage 1 Mendel...

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enetic linkage Genetic linkage 1
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endel’s 2nd Law Mendel s 2nd Law Principle of independent assortment : The genetic units for different characters move into gametes independently This is for genes on non homologous chromosomes only What happens when genes are on the same chromosome? 2
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How do we know genes are on chromosomes? X linkage and the case of the white eyed fruitfly 3
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Fruitflies and genetics Thomas H. Morgan’s lab worked on fruitflies 4
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re genes on chromosomes? Are genes on chromosomes? One day Thomas Morgan found a male with a new utation: white eyes instead of red mutation: white eyes instead of red ypothesis: Hypothesis: The gene for this trait is located on the chromosome nd hite is cessive X chromosome And white is recessive 5
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ther possibilities: Other possibilities: 1. Gene is located on the Y chromosome : Y XY W . The trait is ppressed females 2. The trait is suppressed in females (eg hormone dependent) ht i l l l i l rr shows up phenotypically only in males 6
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Approach: ross 1: white ed male with red Cross 1: white eyed male with red eyed female Parentals : Females: X R X R males: X r Y Prediction? 7
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Approach: ross 1: white ed male with red Cross 1: white eyed male with red eyed female This phenotype would also fit a suppression hypothesis 8
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ross 2: F1 X F1 Cross 2: F1 X F1 Parentals : X R X r females X R Y males Prediction for F2: 9
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ross 2: F1 x F1 Cross 2: F1 x F1 R Y X X R X r 10
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ross 2: F1 x F1 Cross 2: F1 x F1 female and red eyed R Y ½ female and red eyed X ¼ male and red eyed X R X R X R X R Y male and X r X R X r X r Y ¼ male and white eyed 11
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onclusion? Conclusion? data fit the X kage ut to invalidate the F2 data fit the X linkage hypothesis well But to invalidate the suppression hypothesis Especially the phenotypic ratios: You need to see white eyed females: 3:1 red to white r r But linked to sex X X 12
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This note was uploaded on 04/18/2011 for the course BIO 182 taught by Professor Jacobson during the Fall '11 term at ASU.

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2011 Lect 14 Gene linkage - Genetic Geneticlinkage 1 Mendel...

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