PierceGenetics6e_ch05_Blackboard.ppt

PierceGenetics6e_ch05_Blackboard.ppt - Benjamin A Pierce...

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GENETICS A Conceptual Approach SIXTH EDITION GENETICS A Conceptual Approach SIXTH EDITION Benjamin A. Pierce CHAPTER 5 Extensions and Modifications of Basic Principles © 2017 W. H. Freeman and Company
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5.1 Additional Factors at a Single Locus Can Affect the Results of Genetic Crosses Genes at the same locus—two versions of the same gene; each version of the same gene is defined as allele Types of dominance Complete dominance Incomplete dominance Codominance
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TABLE 5.1 Differences between complete dominance, incomplete dominance, and codominance Type of Dominance Definition Complete dominance Phenotype of the heterozygote is the same as the phenotype of one of the homozygotes. Incomplete dominance Phenotype of the heterozygote is intermediate (falls within the range) between the phenotypes of the two homozygotes. Codominance Phenotype of the heterozygote includes the phenotypes of both homozygotes.
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Level of phenotype may affect dominance. Example: CFTR – Channel in the membrane that regulates chloride levels – Mutated in cystic fibrosis – In CF, mutated channel stays closed, so chloride ions build up in cell – In heterozygotes, enough functional CFTR is made to prevent cystic fibrosis 5.1 Additional Factors at a Single Locus Can Affect the Results of Genetic Crosses
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Penetrance: the percentage of individuals having a particular genotype that express the expected phenotype Expressivity: the degree to which a trait is expressed 5.1 Additional Factors at a Single Locus Can Affect the Results of Genetic Crosses
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Concept Check 1 Assume that long fingers are inherited as a recessive trait with 80% penetrance. Two people heterozygous for long fingers mate. What is the probability that their first child will have long fingers?
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A lethal allele causes death at an early
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