Download Evolution of a Bead Population

Primary Type: Lesson Plan
Status: Published
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Resource ID#: 76050
Evolution of a Bead Population
Students practice modeling the processes of genetic drift, gene flow, the founder effect and natural selection using a population of colored pony
beads.
Subject(s): Science
Grade Level(s): 9
Intended Audience: Educators
Instructional Time: 55 Minute(s)
Resource supports reading in content area: Yes
Freely Available: Yes
Keywords: genetic drift, speciation, natural selection, founder effect, gene flow, evolution
Resource Collection: FCR-STEMLearn Diversity and Ecology
LESSON CONTENT
Lesson Plan Template: General Lesson Plan
Learning Objectives: What should students know and be able to do as a result of this lesson?
1. Students will be able to identify which mechanisms of evolutionary change are at work in a population where resources are limited, natural disaster has occurred or
a small section of the population breaks off to start a new population.
2. Students will be able to predict how genetic drift, gene flow and natural selection could affect a hypothetical population.
Prior Knowledge: What prior knowledge should students have for this lesson?
1. Students should have a basic understanding of natural selection as a driver of evolution.
2. Students should have been introduced to the concept that sexual reproduction increases diversity.
3. Students should know what alleles are and that a genotype determines a phenotype.
Guiding Questions: What are the guiding questions for this lesson?
1. What does it mean for a population to become genetically isolated? (not interbreeding with others outside their group)
2. How can new alleles be introduced into a population? (territories overlap, immigration, mutations)
3. How might certain alleles disappear from a population? (illness, war, climate change, emigration)
4. If the genetic makeup of a population changes dramatically after it is separated from a parent population, what can happen? (speciation)
Teaching Phase: How will the teacher present the concept or skill to students?
For a quick review of natural selection:
https://www.youtube.com/watch?v=aTftyFboC_M
(10 minutes) Bell Ringer: Use the guiding questions. Give students five minutes to reflect and write responses individually. Teachers should then discuss responses
with class briefly before beginning lesson. End by saying something like, "Different types of events can be responsible for changing the frequency of certain alleles
within a population. Today, we'll look at four different mechanisms, or drivers, of evolutionary change -- Natural Selection, Genetic Drift, Gene Flow and the Founder
page 1 of 3 Effect."
Guided Practice: What activities or exercises will the students complete with teacher guidance?
(25 minutes) Evolution of a Bead Population
Teacher demonstrates each concept, student teams recreate the demonstration at their tables
- Teams have the following items available at their table: a beaker full of pony beads in at least 10 different colors, worksheets for each student titled "Mechanisms of
Change," and two bowls. The worksheet is divided into a graphic organizer of these four basic drivers of evolutionary change. Students will recreate each
demonstration after the teacher demonstrates each concept and take notes on their worksheets. Mechanisms of Evolutionary Change Table.docx
Teacher uses a large glass beaker full of different colors of pony beads (at least 10 colors) as the starting population in each demonstration.
1) gene flow: pour about half of the beads into another glass beaker. Then pour beads back and forth between the two containers noting that the available alleles
are approximately the same in each population.
2) founder effect: Take four or five beads at random from the big container and place them in the other beaker. Explain that these are the genes carried by a few
individuals moving away from the main population to start their own colony. Now pull out beads that are the same color as the new population and put them in the
new colony. Explain that as the small population reproduces, their gene pool is essentially limited to what they started with. What are some potential problems with
this? (immunity to disease may be an issue)
3) genetic drift: remove 3/4 of the starting bead population at random. Explain that they died in a wildfire that swept across the island where they live. Now "build"
the new population using more beads of the same color randomly selected. Discuss how this is very similar to the founder effect, but that it is caused by a single,
disastrous event.
4) natural selection: Explain that the red, yellow and orange beads are typically slower runners and are regularly taken by predators. This pressure tends to remove
these individuals from the breeding population before they get to pass on their genes. Pour some beads into the other beaker but remove most of the red, yellow and
orange ones.
**Be sure to give students time to try modeling each concept with their own beads and make notes on their worksheets**
Independent Practice: What activities or exercises will students complete to reinforce the concepts and skills developed in the
lesson?
Following the guided practice, give students the individual reading assignment here.
Individual Reading Comprehension - Amish.docx
The summative assessment questions are attached to the document and relate the individual reading to the guided practice and the original learning objectives.
Closure: How will the teacher assist students in organizing the knowledge gained in the lesson?
Once the students have completed the individual reading assignment, discuss the summative assessment attached to the reading. Ask individual students to share their
answers with the class and help them develop their responses so that each student has a clear understanding of the four mechanisms of evolutionary change
discussed.
Summative Assessment
The summative assessment should be attached to the individual reading assignment regarding the Amish and the founders effect.
Answer key:
1) Ellis-van Creveld syndrome is more prevalent among the Amish than in the rest of the world because of which mechanism of evolutionary change? (founders
effect)
2) The essay says that the founder effect is an extreme example of genetic drift. Use your imagination and think of a scenario that would also be genetic drift, but NOT
the founder effect. (Answers vary but responses should suggest a single disastrous even like a flood or a bomb that wipes out the majority of the population)
3) What would happen to the genetic makeup of the Amish community if they began to marry outside of their group? Which mechanism of evolutionary change would
increase? (They would increase gene flow and genes for dwarfism and polydactyly would show up less frequently because they would represent a lower percentage
of possible alleles.)
4) We don't usually talk about natural selection as a mechanism for evolutionary change in modern Homo sapiens. Why not? (Because humans alter their environment
with heating, a/c, grocery stores, engineered housing, medicine and we share resources world-wide. We are less subject to direct pressure from nature than other
animals)
Formative Assessment
Ask the following questions as the students model each mechanism with their own beads:
Gene Flow: Imagine a two frog populations along the same river bank. What sorts of things might restrict gene flow? (physical barriers like a waterfall or different
"songs" from the males)
Founder Effect: How could the Founder Effect help explain why species on islands are often very different from related species on the mainland? (individuals that
started the population carried only certain genes to the island and the population evolves from that)
Genetic drift: What kinds of chance events can you imagine that would wipe out most members of a population? (Floods, fire, tsunami)
Natural selection: What kinds of pressure do we classify as natural selection? (competition for food, predators -- things in the environment) How does that differ
from pressures that cause genetic drift? (genetic drift is caused by one-time disasters whereas natural selection is more of a slow grind, persistent pressure over
time)
Feedback to Students
Students will be given feedback during the bead activity to ensure that they properly model and understand the four mechanisms of evolution discussed. Review
questions at the end of the lesson following the individual reading assignment regarding the Amish should be discussed aloud.
page 2 of 3 ACCOMMODATIONS & RECOMMENDATIONS
Accommodations:
The individual reading assignment could alternatively be presented as a mini-lesson. The teacher could share the material in a short lecture accompanied by photos on
the overhead. The summative questions could also be covered verbally with individuals or teams answering together.
If students do not have the motor skills to work with glassware safely, use clear plastic bottles instead of beakers.
Extensions:
This video from Bozeman science goes more in depth regarding genetic drift and brings in the Hardy-Weinberg equation:
https://www.youtube.com/watch?v=mjQ_yN5znyk
Special Materials Needed:
Colored beads -- pony beads work best. 6 bags of 1000 count with assorted colors
Glass beaker or container -- one for teacher and one for each group of four
Plastic or paper bowls -- two for teacher and two for each group of four
Further Recommendations:
Have students work in groups to create posters that illustrate each of the mechanisms of evolutionary change reviewed in this lesson: natural selection, gene flow,
genetic drift and founder effect.
Additional Information/Instructions
By Author/Submitter
Although sexual selection is another very important mechanism of evolutionary change, it is not addressed in this lesson because it was not included in the standard. The
lesson could easily be adjusted to include it if desired.
SOURCE AND ACCESS INFORMATION
Contributed by: Donna Hesterman
Name of Author/Source: Donna Hesterman
District/Organization of Contributor(s): Clay
Is this Resource freely Available? Yes
Access Privileges: Public
License: CPALMS License - no distribution - non commercial
Related Standards
Name
SC.912.L.15.14:
Description
Discuss mechanisms of evolutionary change other than natural selection such as genetic drift and gene flow.
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