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Mendel’s Peas and qs: Carla Cáceres, Renée Dawson, Tracey Hickox, Jonathan Marcot, Dick Mueller,...
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Transcript of Mendel’s Peas and qs: Carla Cáceres, Renée Dawson, Tracey Hickox, Jonathan Marcot, Dick Mueller,...
Mendel’s Peas and qs:Carla Cáceres, Renée Dawson, Tracey
Hickox, Jonathan Marcot, Dick Mueller, Jon Seger, Thayne Sweeten
Facilitators: Robin Wright, Lisa Lenertz
Mendel in and out of the Garden
Mendel in and out of the Garden
Mendel’s Laws and some of their consequencesMendel’s Laws and some of their consequences
Set up
Prepare one envelope for each student in class with 4 blue paper clips representing homozygous dominant 2 blue and 2 green paper clips representing
homozygous recessive About 60% of the envelopes should be homozygous
and 40% heterozygous to start with; in a 50 person class you’ll expect 1 or 2 (4%) of the offspring after the mating to be affected
Clickers will be useful for questions but not essential
Whiteboard or flip chart to record frequencies
Heredity Teachable Unit
The context A large introductory biology course (>150
students) Students are typically biology majors
Knowledge of students prior to this unit Basic probability Genes, alleles, chromosomes, chromatids,
homologs, dominant and recessive
Goals Outcomesstudents will be able to:
1. Understand and apply chromosome dynamics in meiosis to explain Mendel's law of segregation and independent assortment
A. Draw chromosomes in gametes produced by heterozygous and homozygous parents
B. Relate the products of meiosis to potential offspring of parents of known genotypes by using a Punnett square
C. Calculate the probabilities of the various genotypes and phenotypes from well-defined crosses.
2. Extend Mendel’s principles from a pair of individuals to an entire natural population.
A. Use a Punnett square to explain why the frequency of the recessive homozygote is q2 in a randomly mating population.
B. Generalize this principle to cases with multiple alleles (for example, the ABO blood-group locus).
C. Given a clinically motivated case study, calculate probabilities of potential offspring genotypes and phenotypes.
Assessment
Formative assessments are woven throughout the teaching tidbit think-pair-share exercises iClicker polling group discussion
Summative assessment Bloom’s lower and higher order questions
aimed at determining if the concepts can be transferred to other scenarios
Example: populations with different allele frequencies and applications to genetic counseling.
Assessment
Lower Order Blooms
• Question 1: In a population, where are the majority of recessive alleles for a lethal single-gene disorder found?• Homozygous recessive• Heterozygote• Individuals who died because of the recessive disease
• Question 2: In a large population, 49% of individuals are BB, 42% are Bb, and 9% are bb. What percentage of the gametes produced will contain the little “b” allele?
Higher Order Blooms
• Question 3: Explain why a deadly recessive disease persists in the population even though all people who are affected die before they reproduce.
Diversity
1. Different types of formative assessment Discussion (class and group) What do you need to know Predict risk of affected Clicker questions
2. We did not use a real disease Sensitivity to the risk among friends or
family Risks vary among populations
3. Unifying: we ALL carry potentially deadly mutations
The Teachable Tidbit Goal
Provide concrete experiences that students can use to extend Mendelian laws from individuals to populations
Give students a basis on which to build the subsequent graphs and simulations of population genetics
Huntington diseaseHuntington disease 1 in 25,000
Cystic fibrosisCystic fibrosis 1 in 2,000
HemophiliaHemophilia 1 in 10,000
How many of YOU are carriers for these disorders? What is your risk?
How many of YOU are carriers for these disorders? What is your risk?
PhenylketonuriaPhenylketonuria 1 in 12,000
Today we’ll examine the inheritance of a genetic disorder Green Paperclip Syndrome(GPS)
This disorder is determined by a single gene with two alleles:
Blue and Green
In your envelope, you’ll find four paperclips.
Think-Pair-Share:
Why did we give you four?What does each paperclip
represent?
Your GPS genotype
Some of you may lack any green alleles.
Some of you may be carriers.
Some of you may be affected.
Which allele is dominant?What terms do geneticists use for these
allele combinations?
In a few minutes, you will combine your gametes
(wink, wink)
link the ol’ paperclips...
to make offspring for the next generation.
2. For the entire class population, how many offspring in the next generation will be affected?
1. What are the chances YOUR offspring will be a carrier or affected?
Think-Pair-Share:
Do you need more information to answer these questions? If so,
what information?
Clicker: Indicate your genotype
A. Unaffected
B. Carrier
C. Affected
Prediction (via clicker)
After mating, what percentage of offspring from the entire class do you think will have Green Paperclip Syndrome?
A. Zero
B.1-5%
C.6-24%
D.25%
E.Greater than 25%
Write down your
prediction in a safe place.
You’ll need it later.
IMPORTANT Mating Instructions
Pair up with your neighbor. Hold your envelope above your head Without looking into your envelope, randomly
choose a gamete Link your two gametes together to represent
your offspring
Clicker: ONE person in each mating pair should indicate whether your offspring is:
A. Unaffected
B. Carrier
C. Affected
Earlier, we asked you to predict the percentage of
offspring in the class population with Green Paperclip Syndrome.
Does your prediction match the results?
Given that almost ½ of you had a recessive allele,
why is the number of affected offspring so
small?
Given that almost ½ of you had a recessive allele,
why is the number of affected offspring so
small?
B b
B
b
BB(25%)
Bb(25%)
bb(25%)
Bb(25%)
p =
0.5
q =
0.5
p = 0.5 q = 0.5
BB(64%)
Bb(16%)
bb(4%)
Bb(16%)
p = 0.8 q = 0.2
p =
0.8
q =
0.2
B b
p =
0.5
q =
0.5
p = 0.5 q = 0.5
B
b
BB(25%)
Bb(25%)
bb(25%)
Bb(25%)
B b
p =
0.8
q =
0.2
p = 0.8 q = 0.2
B
b
BB(64%)
Bb(16%)
bb(4%)
Bb(16%)
Things go crazy when Mendel
escapes from the garden...
Where to next?
Try with different allele frequencies. Try with mating limited to a table (island)
and then repeat allowing an isthmus to form between some tables. Initial populations should have different allele frequencies.
Gene pool Pool all of the paper clips into a single
collection. Each person randomly picks a clip and links
to the clip chosen by the following person. See if prediction still works.
Other possibilities
Link up paperclips into a chain, representing a chromosome. Use colored paperclips to represent genes/alleles. Can use to explore effects of linkage on
inheritanceCan use to explore effects of recombination
on inheritance