SCCS AP BiologyName:

Evolving Populations

In this lab, we will model how different scenarios affect evolution. According to the Hardy-Weinberg theory, there are five factors that can cause evolution:

1)Natural selection.

2)Non-random mating.

3)Mutation.

4)Small population size.

5)Migrations.

In this lab, we will look at three of these factors: natural selection, small population size, and migrations. The model we will use in class is a simplified version of real and complex situations. In building our model population, the following assumptions will be made:

1)All members of the population mate randomly.

2)All matings will produce the same number of offspring (2).

Hypothesis: If the frequency of alleles in a population does not vary from one generation to another, we say the population is in GENETIC EQUILIBRIUM (i.e., no evolution is occurring). If there is a change in the frequency of alleles, then the population is said to be evolving!

PART I: GENETIC EQUILIBRIUM

Once upon a time, there were happy little Skittles creatures in the world. They were happy because they lived on an island with no predators. There were three variations of Skittles creatures: red, yellow, and green. No color of Skittles creature had any advantages over the other. They were all equal.

  1. On the table, you will find containers with three types of Skittles. The color of the creature represents the genotype of the individual:

Red = RR

Yellow = Rr

Green = rr

In each container there should be 10 Red, 20 Yellow, and 10 GreenSkittles creatures. Thus, we are starting with 25% RR, 50% Rr, and 25% rr. Determine and record the initial p and q values (p = frequency of R alleles and q = frequency of r alleles).

  1. Before you begin this experiment, review the expected results of the following crosses.Using 6 half sheets of paper, draw the Punnettsquare for each of the possible matings – one Punnett square on each half sheet. Record the number of expected offspring (out of 4) in the EXPECTED RESULTS chart on your data sheet.
  2. Randomly draw out two Skittles creatures. We will assume that the two creatures mate and produce 2 offspring. To select which of the possible offspring they have, one partner spins the Punnett square on the half sheet of paper around and the other partner points to the paper while closing their eyes. The offspring in the Punnett square closest to where you point is the offspring you have. Repeat to determine the genotype of the second offspring. Use tally marks in Table 1 to indicate the type of offspring they will have.
  3. Continue to draw out all of the Skittles creatures two at a time and indicate the type of offspring in your chart with tally marks.
  4. Total your tally marks in each column, calculate and record the final frequency of R alleles (p) and the final frequency of r alleles (q).
  5. Return all 40 Skittles creatures to the container.

PART II: NATURAL SELECTION

One day, a population of Hot Tamales Creatures moved to the island. The Hot Tamales creatures were friendly enough, but they brought with them a terrible disease. Fortunately, most of the Skittles creatures were immune to the disease. However, the greenSkittles creatures were not. They all died.

  1. Remove all of the green (rr) creatures from your population to simulate their deaths (don’t eat them – we will need them again later). This represents NATURAL SELECTION.
  2. Again, randomly draw out each of the Skittles creatures by pairs and mate them as you did in part one to determine genotypes of offspring. If you create a green offspring, that offspring dies. If that happens, mate again until you have 2 viable offspring. Record the genotypes of the viable offspring in Table 2: Natural Selection.
  3. Total your tally marks in each column, calculate and record the final p and q for part 2.
  4. Return all 40 Skittles creatures to the container.

PART III: GENETIC DRIFT

There was a major catastrophe on Skittles island! An earthquake caused a small piece of land from the island to break off and drift out to sea. Those who were standing on that piece of land at the time became isolated from the rest of the group.

  1. To simulate this isolation, randomly remove 30 Skittles creatures from the container. DO THIS WITHOUT LOOKING TO MAKE SURE IT IS RANDOM! The remaining 10 represent those stuck on the drifting piece of land.
  2. Again, randomly draw out each of the 10 remaining Skittles creatures by pairs. Record the genotypes of their offspring in Table 3: Genetic Drift. Random fluctuations in the percentage of genotypes in a small population is referred to as GENETIC DRIFT.
  3. Total your tally marks in each column, calculate and record the final p and q for part 3.
  4. Return all 40 Skittles creatures to the container.

Part IV: MIGRATION

Skittles creatures located on the mainland learned how to build a boat. A group of 10 redSkittles creatures migrate over to the island.

  1. To simulate the migration, add an additional 10 red Skittles creatures to your container.
  2. Again, randomly draw out each of the Skittles creatures by pairs. Record the genotypes of their offspring in Table 4: Migration.
  3. Total your tally marks in each column, calculate and record the final p and q values for part 4.

A pblueator moves to the island! This pblueator is VERY smart—it understands evolution and the concept of genetic equilibrium. S/he is so cunning that he eats ALL of the Skittlescreatures on the island and the Skittlescreatures go extinct!

To simulate this portion of the model, eat all the Skittles creatures.

SCCS AP BiologyName ______

Period______Date______

DATA SHEET – EVOLVING POPULATIONS

EXPECTED RESULTS

Parents / Offspring
Genotype / Phenotypes / RR / Rr / rr
RR x RR / Red x Red
RR x Rr / Red x Yellow
RR x rr / Red x Green
Rr x Rr / Yellow xYellow
Rr x rr / Yellow xGreen
rr x rr / GreenxGreen

Initial p_____Initial q_____

Table 1:Genetic Equilibrium

Offspring
RR / Rr / rr
TOTAL

Final p_____Final q_____

Table 2: Natural Selection

Offspring
RR / Rr / rr
TOTAL

Table 3: Genetic Drift

Offspring
RR / Rr / rr
TOTAL

Final p_____Final q_____

Table 4: Migration

Offspring
RR / Rr / rr
TOTAL

Final p_____Final q_____

Final p_____Final q_____

Analysis:

1. Evolution occurs whenever allelic frequencies change from one generation to the next. Discuss each part of this activity, explaining whether or not evolution occurred and why (which H-W conditions were/were not met?)

2. Compare your results to other groups – were your results always the same? Why?

3. Explain an example where either non-random mating or mutation could lead to evolution.

SCCS AP Biology

Lab Report: Hardy-Weinberg Population

Your lab report must be typed, font size 12 in an easily readable font.

It is to be written with the following 6 components, in the following order:

1. Title: Should be relevant to the experiment

2. Introduction: This may include some background information and context. It includes the hypothesis that is tested by the lab.

3. Methods: This is a step-by-step procedure of the experiment IN YOUR OWN WORDS. Do not merely copy what is written in your lab procedure.

4. Results: The data from your experiment is presented. It can be in table form, but also include graphs to show the changes that take place in the population during the lab. It must be labeled clearly, using accurate units.

5. Analysis: This is explanation of your thought process as you reasoned why the initial hypothesis was correct or why it was incorrect. Use the following questions:

1. Why did we choose different colors of m&m’s?

2. How does this relate to sexual selection?

3. How does it show survival of the fittest?

4. What happened when the same colors were chosen repeatedly?

5. What biases would enter into later choices?

6. What happened when the green ones became diseased?

7. How does this activity show the concepts of Hardy-Weinberg principle?

6. Conclusion: This summarizes your data and states the conclusion (do you think the hypothesis was incorrect or correct? How would you change the hypothesis, if at all?)

Write about how this experiment is applicable to daily life.