Subject: Biology – Disturbing Hardy and Weinberg
Title: Hardy and Weinberg, inbred, hybrid or just disturbed.
Date: June 2 2005
Grade: 12 Biology
Age: 15-17
Standards Met:
- Define the concept of speciation and explain the mechanisms of speciation.
- Solve problems related to evolution using the Hardy-Weinberg equation.
- Analyze evolutionary mechanisms and their effects on biodiversity and
extinction.
- Identify Hardy-Weinberg equilibrium and its conditions.
Anticipatory Set:
Can a population evolve if it is in equilibrium? If you think so, how would it do
so? If you think not, why not? Is it even possible for a population to realistically be in
equilibrium today? Why is evolution so essential? Why would disequilibrium of HardyWeinberg be important also? When would Hardy-Weinberg equilibrium be good for a
population? (If trait is not deleterious but provides diversity)
Objective:
SWBAT orally identify 2/2 mechanisms by which Hardy-Weinberg equilibrium
is disrupted.
SWBAT solve in writing 5/6 punnett squares involving inbreeding and
hybridization.
Materials:
- Pens
- Inbreeding Handout
- An example relationship web
Procedure:
1) Housekeeping, attendance, welcome students, joke or thought for the day.
(2 Min)
2) Use the anticipatory set to introduce disruption of Hardy-Weinberg
equilibrium. Discuss why evolution is important and why disequilibrium of
Hardy-Weinberg could be helpful to this process. (7 Min)
3) Review the five rules of Hardy-Weinberg equilibrium with students. Have
students discuss possible ways/events/things that could disrupt this
equilibrium. Try to guide students to both natural disturbances and
disturbances imposed by humans. (8 Min)
4) Discuss ways that humans alter Hardy-Weinberg equilibrium in themselves
and in other species. Question students as to why people might do this and
possible effects it might have on species that are being affected. (8 Min)
5) Present the concepts of inbreeding, hybridization, hybrid vigor and inbreeding
depression (not what you feel when you find out you’re inbred). Use the
handout on inbreeding to have students figure out what would happen over
time in the case of inbreeding and in the case of hybridization. Put this
information on the board once it is solved. (Hybridization = more
heterozygous and inbreeding = more homozygous) (10 Min)
6) Discuss with students ways in which inbreeding or hybridization could and
does occur. Discuss why, in many cases humans are using these mechanism in
livestock species or pets. Ask students to speculate on why humans don’t do
this with more types or species of animals. It is because humans cannot
control them easily. (8 Min)
7) Present the equations that account for inbreeding or hybridization in
calculating population allele frequencies, relationships, genotype and
phenotype and for calculating inbreeding coefficients. (17 Min)
8) Show students how to create a relationship web by having them direct you in
drawing it on the board. Tell them how to get inbreeding and relation levels
from the web and what that means about genetics. (8 Min)
9) Wrap-up and use closure statements. For homework have students draw a
relationship web of their family going back for three generations. (2 Min)
Closure:
What is biodiversity? Is it a good thing or a bad thing? How are people altering
biodiversity? What impacts could this have on, the species, other species, humans, the
environment and the world?
Evaluation:
Formative: Discussing with the students will provide an assessment of how much
the students know and how much they have learned. Walking around and
monitoring student progress and accuracy while students fill out their
worksheet.
Summative: Students give answers during class and will be assessed.
Homework questions will be handed in to check for completeness
and understanding.
Reflective Statement:
Enrichment: Using books or computers, students will attempt to find four human
examples of inbreeding or hybridization scenarios that have occurred
either presently or in the past. Students will then answer the question, Why
do humans frown on inbreeding in humans, but not in animals?
Remediation: Using books or computers students must attempt to come up with
ten arguments for and against the use of inbreeding. Students will then
explain in writing if they are for or against the use of inbreeding and
justify their position.
Other: N/A
Example of a relationship web
X
Y
A
W
Z
B
M
G
F
R
I
Inbreeding
Let us track an inbred trait for a moment. We have an individual Jamie, with alleles BB.
To tack this alleles when you draw your punnet square make sure you mark only one of
Jamie’s alleles with a star or other mark so you know who it came from belong to.
Below is a sample pedigree. Jamie is “J”
J
B
M
C
D
E
A
F
We are interested in F. To find out how likely it is that F has the same allele from Jamie
we will do some punnet squares.
First Fill out a punnet square for the mating between Jamie and “M”. You don’t need to
know “M”s genotype for this. You just need to know were the alleles are going. Your
first square should look like this. The * represents the allele we are looking at and the -‘s
represent the
other persons alleles.
B
B-
B-
B*
B* -
B* -
You’ll notice that there is only a 0.5 of 50% chance of Jamie passing on that specific
allele to any child. Thus on the chart, for each arrow leading away from Jamie you can
put a 1/2. If we assume that each of Jamie’s children got this allele then the same punnett
square would exist for them as well……try it out below.
See. Now using punnett squares try and figure out what the chance is of individual “F”
getting two B* alleles is. Remember that two B* alleles means that it is actually just two
copies of that SAME single allele that Jamie had to start with.