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Class 13 - Gene Interactions The next two questions will...

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Gene Interactions
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2 The next two questions will not affect your grade , we are interested in how much time you are studying for this course. You can also click in that you prefer not to answer
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3 How many hours did you spend studying for exam 1? A. less than 2 hours B. 3-4 hours C. 5-6 hours D. more than 6 hours E. I would prefer not to answer
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4 I felt that exam 1 was: A. easy B. medium C. difficult D. I would prefer not to say
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Moving Ahead... What we should now know about genes 1.Genes on different chromosomes assort independently 2.Linked genes assort by the rules or recombination 3.The output of gene expression (phenotype) follows rules of dominance, recessivity, co- dominance, incomplete dominance 5
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Genes interact ALL GENES INTERACT - NO EXCEPTIONS Types of interactions: Gene X Gene - one protein binds to or affects expression of another Gene X Environment - the phenotype is affected by extracellular events like temperature, solution, light, or behavior 6
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Next few classes We will explore how genetics reveals gene interactions Genetics combined with molecular biology and biochemistry allow the discovery of both gene interactions and the mechanisms of those interactions We will sample the most important types of interactions, but the same principles apply to all imaginable interactions! 7
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Epistasis (noun from greek ephistanai means stoppage) Gene X Gene interaction When one gene masks or modifies expression of another Generally negative interaction but not always Not allelic interaction like dominance 8
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How to identify epistasis Epistasis affects the outcome of dihybrid crosses Previously, with simple dominance rules in the absence of epistasis a dihybrid cross gave a 9:3:3:1 ratio of offspring phenotypes 9
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No epistasis Cross RrYy X RrYy Note the ratio: R_Y_ = 9 R_yy = 3 rrY_ = 3 rryy = 1 10
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Epistasis consider flower color: (C_ means CC, cC, & Cc) C_pp = white & ccP_ = white ccPP X CCpp = CcPp CcPp = Purple So F2 CcPp X Cc Pp => 11
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Epistasis consider flower color: (C_ means CC, cC, & Cc) C_pp = white & ccP_ = white ccPP X CCpp = CcPp CcPp = Purple So F2 CcPp X Cc Pp => 11 2 phenotypes 9:7 ratio
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Epistasis peas - no epistasis R_Y_ = 9 round yellow R_yy = 3 round green rrY_ = 3 wrinkled yello rryy = 1 wrinkled green flowers - epistasis C_P_ = 9 purple C_pp = 3 white ccP_ = 3 white ccpp = 1 white 3+3+1 = 7:9 phenotypic ratio!! 12 2 phenotypes 9:7 ratio cc is epistatic to P and pp is epistatic to C
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Dihybrid cross phenotypes under epistatic conditions Genotypes are still 9:3:3:1 Phenotypes however, will be masked depending on how the epistatic gene alters expression In “recessive” epistasis, like the flower, the ratio is 9:7 phentypically 13
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