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State Standard: (651) Cellular and Molecular concepts, (652) Interdependence of Organisms and Biological Change.

POPULATION GENETICS

Time: One or two 50-minute class periods
Grade Level: 9-12

Objectives: To understand the basics of evolution by natural selection. To calculate allele frequencies as they relate to inheritance. To understand the Hardy-Weinberg Law and how evolution takes place when this law is not in place.

Idaho Achievement Standards:

·648.01,648.02,648.03 Understand systems, order, organization, models and explanation.

·648.04 Understand that the theory of evolution is a process of gradual change.

·649.01 Understand scientific inquiry and critical thinking.

·651.02 Understand form and function of DNA.

·651.02 Understand theory of biological evolution.

·658.01,658.02 Understand personal relationships and technical communication

Materials:

·Data Collection Sheets
·Two colors of marbles in cups(2 x number of students for each color)
·Overhead Transparency and Pens

Background:
Students will review some basic genetic principles of inheritance and will review genetic terms such as allele, homozygous, heterozygous, dominant, recessive, gene pool.

Procedures:
Warm-up. Students will test their ability to taste PTC molecule by using a test strip with the molecule on it. If students taste the strip especially strongly, this indicates they carry two copies of the dominant gene, if only slightly then one copy, and if not at all, then no copy. Have students calculate genotype and allele frequencies of the class "gene pool."

Activity:
Students will do three simulations that will demonstrate the principles of inheritance. The first simulation will demonstrate genetic equilibrium (the Hardy Weinberg Law), the second will demonstrate genetic drift, and the third will demonstrate a lethal recessive. All three simulations will be recorded on data sheets and the results will be plotted on a graph to show the results visually.

Population simulation:
Each student starts the game as a heterozygote, with a marble of each color in their cup. To simulate meiosis, students remove (without looking) one marble from the cup. The color of the marble represents the allele type. To mate and form an offspring, two students undergo meiosis, then combine alleles to form an offspring. In each simulation they must mate twice in order to form two offspring (this keeps the population size constant). At the end of a generation, both parents die. Students assume the genotypes of one of their offspring (assigned randomly from the two produced).

*Teacher note: The easiest way to keep track of genotypes is to have students stand to mate, then sit down when they have produced two offspring. When all are seated, count off each of the genotypes by a show of hands. Have students calculate allele frequencies each generation. Do not allow inbreeding (must mate with a different student each time) or mate choice (based on genotype). Do not allow students to move on the next generation before counting and calculating allele frequencies.

Wrap-up:
Have students graph the allele frequency (y-axis) vs. generation (x-axis) for each simulation for their group. Have one group describe the results on an overhead. Have them expand on the concepts of processes that lead to change in the gene pools of populations.

Assessment:

Students should explain:

1. Which of the simulations would most likely lead to adaptation? Why?
2. What would happen if a mutation occurred in the population? Why?
3. Design a fourth and fifth simulation that would model the effects of migration and mate choice on allele frequencies.

* Extension: Have students design and carry out a simulation that would demonstrate how migration can counter the effects of genetic drift in small populations.

POPULATION GENETICS DATA COLLECTION SHEET

Frequency of "A" = 2 x #AA students + #Aa students
                                      2 x total # students
SIMULATION #1.
All students (large population, no mutation, no selection, no mate choice, no migration).

SIMULATION #2
Homozygous recessive genotype (aa) is lethal, parents reproduce until have 2 living offspring), otherwise same conditions as Simulation #1.

SIMULATION #3
Students in groups of 4 (otherwise same as Simulation #1). Avoid inbreeding!

Final allele frequency (A) of other student groups:
Group 1 _____  Group 2 _____  Group 3 _____  Group 4 _____