PhET Activity for MS-LS2-4: Natural Selection

DIRECTIONS:
1. Click on the 'Intro' image on the bottom left side of the screen to begin.
2. Once the simulation loads, click the 'Add a Mate' button in the center of the simulation area to introduce a second rabbit.
3. Press the Play button (▶) or the Fast Forward button (▶▶) at the bottom of the screen to start the passage of generations.
4. Observe the rabbits hopping around and reproducing.
5. Look at the graph at the bottom of the screen, which shows the total population over time.
Spend 2-3 minutes exploring the simulation in its default state. Watch the population grow and familiarize yourself with the Play/Pause controls and the population graph. Do not add any mutations or environmental factors yet.

QUESTION: Are you acquainted with the tools in this simulation?

DIRECTIONS:
1. Reset the simulation by clicking the orange circular arrow button in the bottom right corner.
2. Click the 'Add a Mate' button.
3. Press the Fast Forward button and let the simulation run for about 3-4 generations.
4. In the 'Add Mutation' panel on the right, click the 'Fur' button. A message 'Mutation Coming...' will appear.
5. Continue to let the simulation run and observe what happens when the new brown-furred rabbit appears.

QUESTION: In an environment with no predators, the brown fur mutation is neither an advantage nor a disadvantage. Over time, the population of brown rabbits will likely ___ while the population of white rabbits will also continue to ___.

(a)  

DIRECTIONS:
1. Continue the simulation from the previous slide, with both white and brown rabbits present.
2. In the panel on the bottom right of the screen, select the 'Proportions' radio button.
3. Observe the bar chart that appears. This shows the percentage of the total population that has each trait.

QUESTION: What key information does the 'Proportions' graph provide that the 'Population' graph does not?

DIRECTIONS:
1. Reset the simulation by clicking the orange button.
2. Click 'Add a Mate'.
3. In the 'Add Mutation' panel, click the 'Fur' button to add the dominant brown fur mutation.
4. Let the simulation run until you have a population of at least 50 rabbits, with both white and brown present.
5. In the 'Environmental Factors' panel on the right, check the 'Wolves' box to introduce predators while it is running.

QUESTION: In this environment, adding wolves introduces a selection pressure. This pressure causes the proportion of brown rabbits to (a)   .

DIRECTIONS:
1. Continue running the simulation from the previous slide with wolves present in the 'Equator' environment.
2. Ensure the graph is set to the 'Population' view.
3. Let the simulation run for at least 15-20 generations.
4. Observe the trend lines for the 'White Fur' and 'Brown Fur' populations.

QUESTION: After many generations with wolves in the 'Equator' environment, what is the most likely outcome shown by the simulation?

DIRECTIONS:
1. Let the simulation run from the previous slide until the brown rabbit population is clearly dominant (over 90% in the 'Proportions' view).
2. Pause the simulation.
3. At the top of the simulation area, click the snowflake icon to switch the environment to 'Arctic'.
4. Press Play and observe what happens.

QUESTION: After switching the environment to 'Arctic' with wolves still present, describe the effect on the populations of brown and white rabbits. Why does this shift occur?

DIRECTIONS:
1. Continue running the simulation in the 'Arctic' environment with wolves.
2. Watch the 'Proportions' graph as the population shifts from being majority brown to majority white.
3. Notice that even when the brown rabbit population was dominant, a few white rabbits were still being born.

QUESTION: The allele for white fur is recessive. In the 'Equator' environment with wolves, the allele was able to persist in the population because it was carried by ___ individuals who themselves had brown fur. When the environment changed to 'Arctic', this hidden ___ allowed the advantageous white fur trait to re-emerge.

(a)  

DIRECTIONS:
1. Pause the simulation while you have a mix of brown and white rabbits in the population.
2. In the bottom right panel, select the 'Pedigree' radio button.
3. The prompt 'Select a Bunny' will appear over the graph.
4. Click on a white rabbit in the simulation. Its family tree and genotype (ff) will appear.
5. Now, click on one of its parents to see their genotype.

QUESTION: If a rabbit has white fur, its genotype is 'ff'. This means it must inherit one 'f' allele from each parent. Which of the following parental genotype pairings could NOT produce a white-furred offspring?

DIRECTIONS:
1. At the bottom of the screen, click on the 'Lab' tab.
2. If needed, reset the simulation using the orange circular arrow button.
3. Examine the 'Add Mutation' and 'Environmental Factors' panels on the right. Note the new options for 'Ears', 'Teeth', and 'Tough Food'.

QUESTION: Match the environmental factor from the simulation to the trait it is designed to select for.

DIRECTIONS:
1. Ensure you are in the 'Lab' tab and have reset the simulation.
2. Click 'Add a Mate'.
3. In the 'Add Mutation' panel, click the 'Teeth' button to add the dominant long teeth mutation.
4. Let the population grow for 5-6 generations so you have a mix of long- and short-toothed rabbits.
5. In the 'Environmental Factors' panel, check the box for 'Tough Food'.

QUESTION: When 'Tough Food' is introduced, it becomes a limiting factor for rabbits that cannot eat it efficiently. This pressure favors rabbits with the (a)   trait.