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