Natural Selection

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Natural Selection and Heritability:
From Butterflies to humans
Created for SPICE by Amy Non and Carmella O’Steen
March 2007

Natural Selection Simulation
Lesson 2
(as modified from Robert Gendron’s “Simulating Natural Selection” for Introductory Biology Lab College Course, Indiana University of Pennsylvania)

Key Question(s): What is natural selection? How does natural selection change allele frequencies over time? Does natural selection work differently on large versus small populations? What is genetic drift?

Science Subject: Biology

Grade Level: 7th-8th grade

Science Concepts: Natural Selection, Evolution

Overall Time Estimate: 2 90 minute class periods

Learning Styles: Kinesthetic

Natural Selection: The process by which organisms with more favorable traits in a particular environment are more likely to survive and reproduce than those with unfavorable traits. Because these traits are heritable, favorable traits become more common in the population over time.

Genetic Variation: Variation amongst the genomes of individuals within a population or between populations. For example, although all humans are members of one species, no two individuals have the exact same genetic code. Variation usually comes from random genetic mutations or migrations of new individuals into a population.

Heritability: The proportion of variation in a population that is attributed to genetic variation, and is therefore passed on genetically from parent to offspring.

Allele: any one of a number of versions of a gene at a given locus (position) on a chromosome. For example, one allele of a gene that controls petal color of flowers may encode red flowers while a different allele of the gene may encode white flowers.

Genetic Drift: the tendency of any allele to vary randomly in frequency over time due to statistical variation alone. Genetic drift has more of an impact on allele frequencies in smaller populations than larger populations.

Different Reproductive Success: The differential ability among individuals of a population to survive long enough to successfully reproduce viable offspring.

Lesson summary: In this lesson, students are introduced to the ideas of natural selection via a hands-on inquiry simulation activity with game-boards, dice, and butterflies and bird game pieces to represent populations of butterflies and birds. In groups of four, students play multiple rounds of the simulation until time is up or one species goes extinct, all the while recording the data of the number of surviving pieces in each round, along with the camouflage and visual acuity scores of the surviving birds and butterflies. The simulation game is followed up with instructions on how to create graphs of the data and guided discussion on what they learned about natural selection through this activity.

Student Learning Objectives:
Student will be able to:
1. Define natural selection, alleles, genetic drift, heritability, etc. 2. Understand the three important components needed for natural selection to occur on any trait: variation, heritability, and differential reproductive success. 3. Understand the value of a simulation in biology.

4. Be able to take averages and graph results of each round of the simulation by hand. 5. Be able to answer questions about the graphs, e.g. did visual acuity change over time? Or did camouflage increase over time? 6. Understand what the range of a dataset is, and see how the range changes from initial and final frequency distributions. 7. Be able to explain how natural selection causes allele frequencies to change over time.

Materials: (all essential)
Per group of 3 to four students:
1 gameboard with 6x6 grid
1 set of butterflies and bird game pieces (~100 of each)
2 Sharpie non-permanent markers
Paper towels
Per Student:
Worksheet with...
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