Welcome to Bio 290,Introduction to Genetics!

Today’s Agenda:

1. In-Class Assignment 22. Group Discussion about Gene Therapy Paper3. Introduction to Independent Assortment of

Genes (Ch 3)4. Poster Project-Identify topic and decide if you

will work in groups

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!