Fancy Fish: Gene Frequency – Grade Ten
Ohio Standards
Connection:
Life Sciences
Benchmark H
Describe a foundation
of biological evolution
as the change in gene
frequency of a
population over time.
Explain the historical
and current scientific
developments,
mechanisms and
processes of biological
evolution.
Indicator 20
Recognize that a
change in gene
frequency (genetic
composition) in a
population over time
is the foundation of
biological evolution.
Lesson Summary:
The purpose of this lesson is to help students recognize that
a change in gene frequency (genetic composition) in a
population over time is biological evolution. Students will
participate in two activities that model evolutionary change
via the processes of gene flow and natural selection.
Students will work in pairs to report on the activity,
describing their data and explaining what they learned
about genetic change. Students will explain their results
referring to specific data and will turn in their data with
their reports.
Estimated Duration: Two hours and 15 minutes
Commentary:
This lesson helps students understand the effects of natural
selection and gene flow on the genetic diversity of diploid
populations. Students will model gene flow by holding
colored fish cards and migrating around the room, in and
around barriers to disperse. Students then model allele
frequency change via natural selection using colored
candies as alleles. As a reflection exercise, students then
consider how natural selection and gene flow together affect
the genetic diversity of populations. This last step provides
a window into the real complexity of naturally-occurring
populations and helps clarify how multiple processes affect
genetic diversity at the same time.
Pre-Assessment and Post-Assessment:
Have students respond to the following questions:
1. Define allele. Give an example of a gene with two alleles.
2. Describe dominant and recessive alleles.
3. Define gene flow. Give a specific example of gene flow
and describe how it causes changes in allele frequencies
over time.
4. List and briefly describe examples of two real barriers to
gene flow.
5. Describe how natural selection affects the allele
frequencies of a population.
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Fancy Fish: Gene Frequency – Grade Ten
6. Give an example of a population of organisms that is affected by natural selection. Your
example should include a description of the animal population, what trait is being
selected, what alleles control the expression of that trait, and how the allele frequencies
are affected by natural selection.
7. Imagine that individuals from another population migrate into the one that you described
in the previous question. How would this affect the allele frequencies of your population?
Scoring Guidelines:
See Attachment A, Pre-and Post-Assessment Answers, for a key to assessing student work.
Instructional Procedures:
Engagement
1. Construct a set of cards, each with a drawing of a colored fish on it.
2. Pass one card out to each student. Have the class pretend to be a population of brightly
colored fish.
Instructional Tip:
Initially, students near each other will have the same color card. Keep it simple, four colors is
enough.
3. Divide the class into four sections. Have students determine the dominant color of fish in
their section- just a quick count will do it!
4. Simulate gene flow by having students “swim” around the room for 10 seconds, repeat
step above in new section. Do this two to three times until they understand that their
mixing has homogenized the four populations.
5. Put up a pretend "dam" to separate off one section of the room; the other fish will
continue to mix for a few more rounds.
6. Discuss the effects the “swimming” or wandering had on the characteristics of the group,
and how the isolated group was affected. Help students see that the barrier prevented
gene flow, and that the color frequency of the isolated population did not change.
Exploration
7. Use licorice candies that are colored pink and white to simulate alleles for a gene in a fish
population. The white candies simulate the normal dominant allele (A) and the pink
candies represent a recessive allele (a) that is lethal.
Instructional Tip:
You can use a variety of objects for this exercise, game pieces, colored paper, or colored
candies. Have contrasting colors so that one color will represent the recessive allele (a) and
the other will represent the dominant allele (A).
8. Divide the class into two-person teams.
9. Distribute 80 white candies and 20 pink candies to each student team. Each team will
begin the exercise with the same population. The candies represent alleles, so that each
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Fancy Fish: Gene Frequency – Grade Ten
beginning population has a gene pool of 100 alleles, with 80% dominant (white) alleles
and 20% recessive (pink) alleles.
10. Tell students to mix the candies together well in a bowl and then spill the candies out on a
table. Explain the allele frequencies that are present in each population, and have students
record the number of each allele they have and the relative frequencies of each that are
present. In the beginning, the numbers of each allele will be 80 and 20, and the relative
frequencies will be 80% and 20%.
11. With their eyes closed, have each student choose two candies (two alleles) at random as
one would find in a diploid individual. Then have them look at their choice.
12. Explain that the recessive (a) allele is lethal, so that if they picked two pink candies (aa
genotype), then their individuals died. If they had a homozygous dominant (AA) or
heterozygous (Aa) genotype, their individuals lived.
13. Tell students with "dead" alleles to discard them in the "graveyard" (a separate bowl at
the front of the room, NOT returned to the gene pool bowl). Then have students figure
out the surviving number of dominant and recessive alleles in each group. Have them
record this number on their paper.
14. After this first round of selection, explain how to calculate the new relative frequencies of
alleles in the population. This can be done by dividing the total number of remaining
alleles (candies) into the number of each type of alleles (white, then pink candies). For
example, if each student had picked two pink candies, then four recessive alleles (pink
candies) would be removed in the first round, and the resulting gene pool would be 80
dominant (white candies) and 16 recessive (pink candies), for a total of 96 remaining
alleles (candies). The percent of dominant alleles is then 80/96 = 83%, and the recessive
alleles are 16/96 = 17%. Tell students to calculate the relative frequencies of alleles in the
population.
15. To begin the next generation, the survivors must reproduce. We will assume that the
reproductive capability of the candies keeps the population of alleles at 100 for each
generation, and that the pink and white candies reproduce equally well. Using the percent
values calculated, have students adjust the number of candies by adding white and pink
candies (from a supply in the front of the room) to bring the total candies to 100 in the
ratio calculated. In the example given, three white candies would be added to bring the
total white candy count to 83, and one pink would be added to bring that count to 17.
There are now 100 candies in the correct proportions to begin round two.
16. Have the students put the candies for the second generation in the bowl. Mix and spill
them onto the table again. This is the second generation. Have students choose their
diploid pairs, record allele numbers and relative frequencies.
17. Have students repeat the process until all pink candies are gone OR until they have
sampled 10 generations. While repeating rounds of selection, have students record their
results in a chart like the one in Attachment B, Data Sheet. Sample data are found in
Attachment C, Data Sheet Example.
Instructional Tip:
It is highly unlikely that the recessive allele will be purged from the population, even though
it is lethal. As long as the heterozygous carriers are not affected by the recessive allele, the
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Fancy Fish: Gene Frequency – Grade Ten
allele can "hide" in these individuals.
18. Circulate around the room while students complete the exercise. Students should see a
trend in an increase in number of white and a decrease in number of pink alleles over
time.
19. Have students write up the activity (students can work in pairs). Ask them “What did you
learn about the change in a population?” Have students explain their results referring to
specific data points. Have students turn in their data with their write-ups.
Explanation:
20. Lead a student discussion about the results of the exercise. Help students understand that
they modeled natural selection, with homozygous dominant and heterozygous individuals
"selected" to survive and reproduce, and homozygous recessive individuals selected to
die.
21. Challenge students to think about the effects of natural selection and gene flow occurring
in a population at the same time. Explain that these two processes normally affect
populations of organisms simultaneously. For example, if the population of (80 white to
20 pink) alleles experienced a constant emigration of individuals from a similar
population, the frequency of recessive alleles would have remained higher, despite the
die-off of homozygous recessive individuals.
Differentiated Instruction:
Instruction is differentiated according to learner needs, to help all learners either meet the
intent of the specified indicator(s) or, if the indicator is already met, to advance beyond the
specified indicator(s).
• Students are paired or grouped to complete the activities such as the gene frequency
activity.
• Students are provided with opportunities to use a variety of skills to reinforce concepts
such as organization, communication, observations, etc.
• Students are provided with access to a variety of resources both in and out of the
classroom.
• Instructional procedures are delivered through multi-sensory modes and a variety of
teaching styles.
Extensions:
• Carry out the allele selection activity with gene flow (exchange of colored candy alleles)
occurring among populations (two-student teams).
• Find news articles concerning man-made barriers to gene flow.
• Create visual representations of the data.
Materials/Resources:
The inclusion of a specific resource in any lesson formulated by the Ohio Department of
Education should not be interpreted as an endorsement of that particular resource, or any of
its contents, by the Ohio Department of Education. The Ohio Department of Education does
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Fancy Fish: Gene Frequency – Grade Ten
not endorse any particular resource. The Web addresses listed are for a given site’s main
page, therefore, it may be necessary to search within that site to find the specific information
required for a given lesson. Please note that information published on the Internet changes
over time, therefore the links provided may no longer contain the specific information related
to a given lesson. Teachers are advised to preview all sites before using them with students.
For the teacher:
Copies of gene frequency datasheet, vocabulary list colored candies,
colored cards, overhead to show sample data
For the students: Copy of gene frequency datasheet, vocabulary list, calculators
Key Vocabulary:
• allele
• barrier
• dominant
• emigration
• evolution
• gene flow
• gene frequency
• gene pool
• immigration
• population
• recessive
• species
Technology Connections:
• Students can use computers to work on reports and data collection sheets.
• Students can use calculators to figure percentages of gene frequencies.
Research Connections:
Marzano, R. et al. Classroom Instruction that Works: Research-Based Strategies for
Increasing Student Achievement. Alexandria: Association for Supervision and Curriculum
Development, 2001.
Cooperative learning grouping has a powerful effect on student learning. This type of
grouping includes the following elements:
• Positive interdependence;
• Face-to-face promotive interaction;
• Individual and group accountability;
• Interpersonal and small group skills;
• Group processing.
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Fancy Fish: Gene Frequency – Grade Ten
Nonlinguistic representations or imagery mode help students think about and recall
knowledge. This includes the following:
• Creating graphic representations (organizers);
• Making physical models;
• Generating mental pictures;
• Drawing pictures and pictographs;
• Engaging in kinesthetic activity.
Attachments:
Attachment A, Pre- and Post-assessment Answers
Attachment B, Data Sheet
Attachment C, Data Sheet Example
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Fancy Fish: Gene Frequency – Grade Ten
Attachment A
Pre- and Post-Assessment Answers
1.
Allele – an alternative form of a gene (e.g., for plant height, T for tall, t for short).
Each organism receives one from each parent.
2.
Dominant – the trait that is expressed when its allele is either homozygous
dominant (TT) or heterozygous (Tt). If either parent passes on this allele, the trait
will be expressed in the offspring.
Recessive –this allele must be received from BOTH parents in order to be
expressed in the offspring, homozygous recessive (tt).
3.
Gene flow – the movement of alleles into or out of a population due to migration of
individuals in and out of the population. If new individuals are introduced into a
population, new alleles would be added.
4.
The answer could include any of a wide variety of examples. As long as their
examples reduce or impede gene flow, then they are acceptable.
5.
Natural selection changes the frequency of alleles by allowing some organisms to
survive and reproduce, while disallowing others. As a result, the allele frequency of
a population may not remain the same.
6.
The student answers may be creative and unusual. It is important that the student
describes a population of organisms that has a trait controlled by at least two alleles,
and that the alleles confer differential survival and reproduction to the organisms
that possess them.
7.
Students should state that gene flow affects the rate at which allele frequencies
change in a population. Gene flow could slow down or speed up allele frequency
changes that would otherwise occur in the population.
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Fancy Fish: Gene Frequency – Grade Ten
Attachment B
Data Sheet
Dominant
Alleles
Generation Number
1. Beginning Numbers
(White
Candies)
Recessive
Alleles
(Pink
Candies)
80
20
Recessive
Alleles (Pink
Candies)
Removed
Total Alleles
Remaining
(100 - column 3)
Ending Percent
2. Beginning Numbersa
Ending Percent
3. Beginning Number.
Ending Percent
4. Beginning Numbers
Ending Percent
5. Beginning Numbers
Ending Percent
6. Beginning Numbers
Ending Percent
7. Beginning Numbers
Ending Percent
8. Beginning Numbers
Ending Percent
9. Beginning Numbers
Ending Percent
10. Beginning Numbers
Ending Percent
Beginning numbers for the next generation are calculated by dividing the remaining alleles
for each type (dominant/white, then recessive/pink) by the total remaining alleles.
a
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Fancy Fish: Gene Frequency – Grade Ten
Attachment C
Data Sheet Example
Generation No.
1. Beginning Numbers
Ending Percent
Dominant
Alleles
(White
Candies)
Recessive
Alleles
(Pink
Candies)
Recessive
Alleles (Pink
Candies)
Removed
Total Alleles
Remaining
(100 - column
3)
80
20
4
96
2
98
0
100
2
98
0
100
80/96 = 83% 16/96 = 17%
2. Beginning Numbersa
83
17
Ending Percent
83/98 = 85
15/98 = 15
3. Beginning Numbers
85
15
Ending Percent
85
15
4. Beginning Numbers
85
15
Ending Percent
85/98 = 87% 13/98 = 13%
5. Beginning Numbers
87
13
Ending Percent
87
13
6. Beginning Numbers
Ending Percent
7. Beginning Numbers
Ending Percent
8. Beginning Numbers
Ending Percent
9. Beginning Numbers
Ending Percent
10. Beginning Numbers
Ending Percent
a
Beginning numbers for the next generation are calculated by dividing the remaining alleles for each
type (dominant/white, then recessive/pink) by the total remaining alleles.
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