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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 34. 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
• χ2 = 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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