lecture - cha 3-student

lecture - cha 3-student - CHAPTER 3 Independent Assortment...

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CHAPTER 3 Independent Assortment of Genes Copyright 2008 © W H Freeman and Company
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1. What progeny ratios are produced by dihybrids, trihybrids, and so forth, if the genes are on different chromosome pairs? 2. How does chromosome behavior at meiosis explain these ratios? 3. Can Mendelian inheritance explain continuous variation? 4. What are the inheritance patterns of organelle genes? Key Questions
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The development of superior crop genotypes through cross breeding – The principle of independent assortment of genes at work. Combining desired (mutant) alleles (recessive or dominant) into one pure line requires intercrossing between mutant lines. Such practice depends on whether the genes are on the same or different chromosome, and the inheritance pattern --
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3.1 Mendel’s law of independent assortment General symbolism to represent genotypes that include two genes: If two genes are on different chromosomes we use semicolon to separate the gene pair : A/a ; B/b If two genes are on the same chromosome, there is no punctuation between two genes we use : AB/ab or Ab/aB If it is not known whether the genes are on the same chromosome or on different chromosomes, we use a dot to separate the genes: A/a . B/b. i.e. a dihybrid crosses (A/a . B/b x A/a . B/b)
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3.1 Mendel’s law of independent assortment Mendel’s Second Law: Gene pairs on different chromosome pairs assort independently at meiosis.
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3.1 Mendel’s law of independent assortment Mendel’s Second Law: Gene pairs on different chromosome pairs assort independently at meiosis. The predicted genotypic and phenotypic constitution of the F 2 generation from a dihybrid cross.
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3.2 Working with independent assortment Predicting progeny ratios: Product rule: the probability of independent events both occurring together is the product of their individual probabilities. Sum rule : the probability of either of two mutually exclusive events occurring is the sum of their individual probabilities.
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3.2 Working with independent assortment What is the probability of obtaining the a/a;b/b;c/c;d/d;e/e combination from a cross of A/a;b/b;C/c;D/d;E/e X A/a;B/b;C/c;d/d;E/e ? Take each gene pair individually and multiply the independent probabilities.
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This note was uploaded on 11/06/2011 for the course BIL 250 taught by Professor Wang during the Fall '08 term at University of Miami.

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lecture - cha 3-student - CHAPTER 3 Independent Assortment...

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