Lecture 6 - Lecture 6 Gene interaction Variations on...

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Lecture 6 Gene interaction Variations on dominance
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Complete dominance Dominant negative Incomplete dominance Codominance Multiple alleles Recessive lethal alleles Gene interaction in pathways Complementation testing Double mutants of random mutations (variations on dihybrid ratio) Penetrance and Expressivity
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Mutations of haplosufficient genes are recessive
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Mutations of haplosufficient genes are recessive
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Mutations of haplosufficient genes are recessive
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Two models for dominance of a mutation Figure 6-3 One wild type (+) copy is not enough to confer full function in heterozygote. homodimer
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Incomplete dominance intermediate phenotypes Red X White c+/c+ X c/c P F1 Pink All c+/c F2 ¼ red c+/c+ ½ pink c+/c ¼ white c/c
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codominance ABO blood groups arise from interaction of 3 potential alleles of one gene (6 potential genotypes; 4 potential phenotypes) Both alleles are expressed in the heterozygote • Both I A and I B are full dominant over i (null allele) • But are codominant with respect to each other, that is both alleles are expressed and rbc has both forms of the molecule
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ABO blood types There may be multiple alleles within the population,  but individuals have only two of those alleles.  Why? Because in sexual reproduction, individuals have only two biological parents. We inherit half of our genes (alleles) maternally & the other half paternally, so we end up with two alleles for every trait in our phenotype.
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Jill is blood Type O. She has two older brothers with blood types A & B. What are the genotypes of her parents with respect to this trait? With some careful thinking we don't even need to do the Punnett  square thing:  Jill is Type O, meaning her genotype is "ii".  This means that her  parents each have at least one "i" in their genotype (since she  inherited one from each parent). Since one brother is Type B, one of the parents must have the I B   allele, making that parent I B i.   Since the other brother is Type A, the other parent must have the I A   allele & have a genotype of I A i.  Jill's parents are one I A i & one  I B i Example: inferring genotype of parent from offspring blood types (phenotype)
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The type of dominance inferred depends  on the phenotypic level at which the  evaluation is made.  
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