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Welcome to Week 3!

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Today’s Agenda: 1. Follow-up from last week: “Big Ideas” from Pedigrees and Probabilities 2. Group Discussion: Genetics and Agriculture in the Developing World 3. In-Class Assignment 3 4. Introduction to Chromosome Mapping (Ch 4)

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Why is it important to understand independent assortment of genes? In agriculture? In animal breeding? In genetics research?

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What does independent assortment mean? Chromosome pairs act independently at meiosis Alleles of the heterozygous gene pairs show an “independent assortment”

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Mendel’s peas again… He performed a dihybrid cross Used the genes for seed shape and seed color

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Mendel crossed two homozygous dihybrids What is the expected genotypes of the F1? What is the expected phenotype if the F1 is selfed?

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Mendel’s 2nd Law (Principle of Independent Assortment) He concluded that different gene pairs assort independently in gamete formation What type of genes would not follow this law?

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Predicting ratios of progeny: Branch diagrams Perform a dihybrid cross of self A/a;B/b How many different genotypes? How many different phenotypes?

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Statistical approach to predicting progeny is easier Product rule: Probability of independent events both occurring together is the product of individual probabilities Ex: What is the probability that I can roll a “6” on two dice?

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Statistical approach to predicting progeny is easier Sum rule: Probability of either two mutually exclusive events occurring is the sum of their individual probabilities Ex: What is the probability of rolling two 5’s or two 6’s?

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What is the chi-squared test? Statistical analysis to compare predicted ratios to an actual observed ratio…to determine if a hypothesis is correct

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An example You have a jar with 200 marbles, 100 of them are red and 100 of them white. You remove 100 marbles – What ratio would expect of red:white? – How can you interpret that you actually have 60 red and 40 white….

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Use Chi-squared χ 2 = Σ (O − E) 2 /E – for all classes in which E is the expected number in a class, O is the observed number in a class, and Σ means sum of.

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Reference Chi squared chart

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Why are pure lines important? What types of alleles are expressed if a monohybrid (A/a) is selfed? What happens over more successive generations?

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What is meant by hybrid vigor? When two lines are united in an F1 hybrid, hybrid shows greater size and vigor First seen with corn….any other examples?

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Independent assortment of chromosomes

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Independent Assortment in diploid organisms

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Stages of Neurospora cross

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Meiosis in Neurospora Meiosis followed by mitosis results in 8 ascospores

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Meiotic Recombinants? Why is this important?

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Polygenic Inheritance Can you think of any examples of characteristics that exhibit a lot of variation?

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Polygenic Inheritance Progeny of dihybrid self can be expressed as additive allelic “doses”

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Organelle Genes

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How are organelles inherited? Remember the composition of the egg and sperm?

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What is cytoplasmic segregation?

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Pedigree of mtDNA disease

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Reminders for Next Week 1. Agriculture Paper - Start Reading! (Pre-class assignment on Review Paper due Thursday at 2) 2. Read Chapter 3: Focus on key points we’ve identified today to help you prepare for the Quiz 3. Quiz 3- Posted by Monday at noon, due by Wednesday at noon. 4. Don’t forget to use our fabulous Discussion Room!

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