Download Bio290-03-Mapping Chromosomes

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
• 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!