Genetics Notes Exam 2 Chapter 22; 9-14

Genetics Notes Exam 2 Chapter 22; 9-14 - Chapter 22...

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Chapter 22 Notes—Quantitative Genetics & Transgressive Variation Quantitative Genetics 1. Study of Inheritance of Continuous Characteristics a. Crop Yield b. Some plant disease resistances c. Weight gain in animals d. Fat content of meat e. Milk production f. IQ g. Learning ability h. Blood pressure 2. Qualitative vs. Quantitative—Qualitative char. Exhibit a few, easily distinguished phenotypes, but quantitative char. Exhibit a continuous range of phenotypes. Discontinuous and continuous char. Differ in the number of phenotypes exhibited. a. Qualitative Quantitative Char. Of ‘kind’-------------------------------------------- Char. Of ‘degree’ Disc. Variation; discreet phen. Classes------------- Cont. variation; spectrum of phenotypes Single-gene effects-------------------------------------- Polygenic control; effects of single genes too slight to be detected Concerned w/ indiv. Matings & progeny----------Concerned w/ population matings Analyzed by counts & ratios-------------------------- Analysis [stat] give est. of pop. Parameters such as mean & stand. Deviation 3. Types of Quan. Characteristics a. Continuous—displays range of expression [weight, height…] rather than all-or-none appearance [white, red…] b. Meristic—quantitative traits that are represented by integers. c. Threshold
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i. Expressed when liability reaches certain level ii. Freq. under polygenic control, but may gall in to two classes—expressing or not. With special techniques, more may be revealed. iii. Pathologic syndromes can fall here; difficult to determine genetic control mechanisms. iv. G+E=P Two possible phenotypes, present or absent, quan. b/c susceptibility varies continuously. 4. Relation Between Geno. & Pheno. [Table 22.1] i. For a quantitative trait, each genotype may produce a range of possible phenotypes 5. Inheritance of Polygenic Characteristics a. Ex. Kernel color in wheat b. Assumption—encoded by genes c. See Sample problem in notes. Trangressive Variation 1. Progeny phenotypes outside range of parents. See example in notes 2. Concept to remember: the principles that determine the inheritance of quantitative traits are the same as principles that determine inheritance a. Polygenic traits inherited just like simple traits, just more loci involved
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