# Welcome to Week 3!. Today’s Agenda: 1. Follow-up from last week: “Big Ideas” from Pedigrees and Probabilities 2. Group Discussion: Genetics and Agriculture.

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Welcome to Week 3!

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)

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

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

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

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

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?

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

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?

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?

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

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….

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.

Reference Chi squared chart

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

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?

Independent assortment of chromosomes

Independent Assortment in diploid organisms

Stages of Neurospora cross

Meiosis in Neurospora Meiosis followed by mitosis results in 8 ascospores

Meiotic Recombinants? Why is this important?

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

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

Organelle Genes

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

What is cytoplasmic segregation?

Pedigree of mtDNA disease

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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