BIOLecture3 - Outline for today's lecture (Ch. 14, Part I)...

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Outline for today’s lecture (Ch. 14, Part I) Ploidy vs. DNA content The basis of heredity ca. 1850s Mendel’s Experiments and Theory Law of Segregation Law of Independent Assortment Introduction to Probability
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Reminder: Homologous chromosomes - Pair at meiosis (all pairs) - Same sequence (except sex chromosomes)
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Ploidy vs. DNA content in Meiosis 4 2 1 “C” (DNA per chromosome) G1 S G2 Meiosis I Meiosis II Diploid Haploid Diploid: Contains two chromosomes from a homologous pair one from each parent Haploid: Contains only one chromosome from a homologous pair
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The Nature of Heredity, ca. 1859 Observation: Offspring generally intermediate in phenotype (“trait value”) between those of parents Obvious example: Human children with one African and one Nothern European parent Proposed explanation: “ Blending Inheritance Genetic material miscible, like paint: Black + White = Gray Tall + Short = Medium Etc.
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Blending Inheritance: A logical difficulty Variation reduced every generation Ultimate consequence is a homogeneous population At odds with reality How to explain variation? “Sports” (Mutation in modern parlance)
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Gregor Mendel: The Origin of Genetics Austrian farm boy, entered Augustinian monastary in 1843 Attended University of Vienna in early 1850s Learned two things about science Do experiments Analyze your data (i.e., mathematically) ~1857, began an experimental program to investigate the basis of inheritance (i.e., heredity) with peas
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Mendel’s Experiments Peas were a fortuitous study organism for several reasons: Many variable characters (e.g., flower color, seed shape, seed color, etc.) Many varieties that bred “true” for particular traits (e.g., purple flowers, round seeds, etc.) Easy to do controlled crosses, both “ self ” and outcross
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Mendel’s Experiments – Choice of characters Used only discrete characters, i.e., “either-or”, not continuous frequency 0.5 1.0 0.0 Color B l a c k W h i te Height 0.5 1.0 0.0 2.0 3.0 4.0
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Mendel’s Experiments – Breeding design 1. Start with lines that breed true for different traits, e.g., purple and white flowers 2. First generation of a cross is called P (“parental”) 3. Offspring are F1 (“filial”) 4. Grand-offspring are F2 Self Self Self Self P F1 F2
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Mendel’s Experiments – Breeding design X P F1 F2 1. Cross two true-breeding lines (purple, white) 2. Self F1s 3. Observe phenotypes of MANY F2 offspring and COUNT THEM Self
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This note was uploaded on 07/03/2008 for the course BSC 2010 taught by Professor Bowes during the Spring '08 term at University of Florida.

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BIOLecture3 - Outline for today's lecture (Ch. 14, Part I)...

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