Transcript Mendel in and out of the Garden

Mendel in and out of the
Garden
Mendel’s Laws and some of their consequences
Mendel’s Peas and qs:
Carla Cáceres, Renée Dawson, Tracey
Hickox, Jonathan Marcot, Dick Mueller, Jon
Seger, Thayne Sweeten
Facilitators: Robin Wright, Lisa Lenertz
Set up
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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
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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
Outcomes
students 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
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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
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1. Different types of formative assessment
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2. We did not use a real disease
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Discussion (class and group)
What do you need to know
Predict risk of affected
Clicker questions
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 disease 1 in 25,000
Phenylketonuria
1 in 12,000
Hemophilia
1 in 10,000
Cystic fibrosis
1 in 2,000
How many of YOU are carriers for these
disorders? What is your risk?
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.
1. What are the chances YOUR
offspring will be a carrier or affected?
2. For the entire class population, how
many offspring in the next generation
will be 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%
IMPORTANT Mating Instructions
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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?
b
q = 0.2q = 0.5
B
p = 0.8
p = 0.5
B
b
p = 0.8
p = 0.5
q = 0.2
q = 0.5
BB
(25%)
Bb
(25%)
BB
(64%)
Bb
(25%)
Bb
(16%)
Bb
(16%)
bb
(25%)
bb
(4%)
p = 0.5
q = 0.5
Bb
(25%)
bb
(25%)
B
p = 0.5
b
BB
(25%)
b
q = 0.5
B
Bb
(25%)
b
p = 0.8
b
p = 0.8
q = 0.2
BB
(64%)
Bb
(16%)
Bb
(16%)
bb
(4%)
q = 0.2
B
B
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
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 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 inheritance
Can use to explore effects of recombination on
inheritance