lecture - cha 6-student

lecture - cha 6-student - CHAPTER 6 Gene Interaction...

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CHAPTER 6 Gene Interaction Copyright 2008 © W H Freeman and Company
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1. How do the alleles of a single gene interact? 2. What are multigene pathways? 3. How do separate genes interact in these pathways? 4. What is the genetic test for gene interaction? Inferred from the double mutant phenotype (if mutants interact can infer that wild types interact as well) Key Questions
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6.1 Interactions Between the Alleles of a Single Gene: Variations on Dominance Complete dominance and recessiveness. Haplosufficient: Mutations of PAH (phenylalanine hydroxylase) genes are recessive. P/P (two doses) and P/p (one dose) have enough PAH activity to result in the normal cellular chemistry. P: (wild type allele) dominant; p: (mutant allele) recessive Null mutation: a mutated allele produces a nonfunctional protein.
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6.1 Interactions Between the Alleles of a Single Gene: Variations on Dominance Complete dominance and recessiveness. Haploinsufficient: Mutations of Tbx1 (encoding a transcription factor) genes are dominant. Tb/tb (one dose of functional protein) does not produce enough transcription factors, which lead to normal cellular chemistry. Tb: (wild type allele) recessive tb: (mutant allele) dominant
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6.1 Interactions Between the Alleles of a Single Gene: Variations on Dominance Complete dominance and recessiveness. Dominant negative: displays the same consequence as haploinsufficiency. But, the mechanism is different. One copy of the mutant allele produces a “spoiler” protein product. In the heterozygote (+/M), the “spoiler” protein product binds to the wild-type protein (polypeptides) and distorts it or interferes with its function, which leads to a negative result, producing nonfunctional proteins. The mutated allele “spoiler allele” also acts as a dominant allele!
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Variations on Dominance Incomplete dominance. Each wild-type allele generally
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lecture - cha 6-student - CHAPTER 6 Gene Interaction...

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