Materials Included In Kit

Additional Materials Required

Prelab Preparation

Prepare the fertilizer water.

1. The fertilizer water can be made in advance, but it will grow algae if exposed to light.
2. Add 2 mL fertilizer concentrate to 2 L of aged tap water or bottled water in a labeled container.
3. Store in a cool, dark place, in a sealed bottle.

1. Use scissors to cut wicking cord into 5-inch lengths.

1. Empty one bag of planting mix into a large bucket or container. Reserve the other bag for a second round of planting. Note: 10 quarts of soil will fill 32 pots to a depth of 2.5 inches. Each pot will hold just over 1 cup of soil and ¼ cup of vermiculite.
2. Add water and mix with the trowel until all the soil is moist.
3. Divide the soil into smaller containers for easier student access.
4. Put approximately 1 cup of vermiculite into each of eight smaller containers for easier student access.

1. Arrange the nine polypropylene cups upside down on the table into three rows (see Figure 2). Note: The cups are used to suspend the pots above the water reservoir.
   {11133_Preparation_Figure_2}
2. Place the 32 pots upside down on a table interspersed between the cups.
3. Place the greenhouse cover over the pots, and use a dissection needle to create holes through the greenhouse cover at the center of each pot for a total of 32 holes (see Figure 3).
   {11133_Preparation_Figure_3}
4. Move the nine polypropylene cups into the planting tray (see Figure 2). Place the greenhouse cover upside down over the cups to make a tray.
5. Place the greenhouse cover with cups under the grow lights.
6. Fill the planting tray halfway with the diluted fertilizer water.
7. After the students place the pots on the lid, add dilute fertilizer solution until the wicks in the pots are in the solution. Do not overfill or the pots will float.
8. Adjust the height of the grow lights so they are 2 inches from the tops of the pots. Turn on the lights.
9. See Figure 4 for a suggested timeline for planning purposes. Regularly check the water level. Adjust the height of the lightbulbs to keep them 2–3 inches from the tops of the plants throughout the experiment.
   {11133_Preparation_Figure_4_Suggested Timeline for Growing Wisconsin Fast Plants}

   *Pollinate on two different days at a minimum, starting 2–3 days after the first flowers appear. Usually, this will occur during the third week.

1. Prepare a 10% bleach solution no more than one week in advance. Bleach solutions have a poor shelf life—discard after one week.
2. Add 80 mL bleach to 720 mL of water in an Erlenmeyer flask or a bottle with a cap.

Safety Precautions

Bleach solution is a toxic and corrosive liquid, which may discolor clothing and cause skin burns. Avoid contact with acids, which can release toxic chlorine gas. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Remind students to wash their hands thoroughly with soap and water before leaving the laboratory. Please review current Safety Data Sheets for additional safety, handling and disposal information.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. All plant material and planting mix may be disposed of according to Flinn Biological Waste Disposal Type VI, common garbage waste. All excess solutions may be disposed of down the drain with plenty of excess water according to Flinn Suggested Disposal Method #26b.

Lab Hints

• The minimum number of plants for Parts A and B is 150 germinating plants per class.
• The calendar in Figure 4 is a rough outline based on trials conducted at Flinn Scientific and by other teachers. The actual time it takes for plants to flower and put on seed pods will vary depending on light, water, fertilizer and temperature.
• Enough materials are provided in this kit to plant 32 pots of Fast Plants^® in each of two generations. Fast Plants must be purchased separately.
• Wisconsin Fast Plants will not self-pollinate; therefore, the pollen flower must come from a different plant than the flower receiving the pollen.
• Bee sticks or cotton swabs may be used to pollinate without removing the flower.
• Separate the control and treatment plants by putting a barrier between them. This will help eliminate any accidental crosspollination.
• Adequate 24-hour light is necessary to achieve results in the amount of time prescribed. The lights must be adjusted regularly so the bulbs are 2" to 3" above the tops of the plants at all times.
• During the second week, add bamboo skewers to the pots, and train the plants to grow up the skewers.
• Trichome (hair) density is a good choice for measuring a polygenic trait. Hand lenses are necessary to count this trait. Students count the trichromes on the edge of the first true leaf only.
• While stem color is a Mendelian trait, it is not suitable for this experiment because all wild-type seeds are homozygous dominant, so no variation will be seen.
• Number of flowers or timing of first flower onset are strait forward, variable traits that take little time to document and may be more susceptible to environmental conditions.
• Reduce the number of plants in both the treatment group and the control group by 90% of the original number of treatment plants that germinate. For example, if the class planted six seeds per pot and 16 pots for the treatment group and had a germination rate of 90%, then 96 plants germinated. Ten percent of 96 is 9.6, which rounds to 10. Ten treatment plants and ten control plants would be pollinated. If less than 60 treatment plants germinate, keep 15% of the germinated plants.

Teacher Tips

• This lab is a long-term project that can fit in with a unit on plant physiology and evolution.
• Ensure that students can identify the parts of the plant before pollination.

Further Extensions

Alignment with the Concepts and Curriculum Framework for AP^® Biology 

Big Idea 1: The process of evolution explains the diversity and unity of life.

Enduring Understandings
1A1: Natural selection is a major mechanism of evolution.
1A2: Natural selection acts on phenotypic variations in populations.
1A3: Evolutionary change is also driven by random processes.

Big Idea 2: Biological systems utilize free energy and molecular building blocks to grow, to reproduce and to maintain dynamic homeostasis.

Enduring Understandings
2D1: All biological systems from cells and organisms to populations, communities and ecosystems are affected by complex biotic and abiotic interactions involving exchange of matter and free energy.

Learning Objectives

• The student is able to convert a data set from a table of numbers that reflect a change in the genetic makeup of a population over time and to apply mathematical methods and conceptual understandings to investigate the causes and effects of this change (1A1, SP 1.5, and SP 2.2).
• The student is able to evaluate evidence provided by data to qualitatively and quantitatively investigate the role of natural selection in evolution (1A1, SP 2.2, and SP 5.3).
• The student is able to apply mathematical methods to data from a real or simulated population to predict what will happen to the population in the future (1A1 and SP 2.2).
• The student is able to evaluate data-based evidence that describes evolutionary changes in the genetic makeup of a population over time (1A2 and AP 5.3).
• The student is able to connect evolutionary changes in a population over time to a change in the environment (1A1 and SP 7.1).
• The student is able to make prediction about the effects of genetic drift, migration and artificial selection on the genetic makeup of a population. (1A3 and SP 6.4)
• The student is able to analyze data to identify possible patterns and relationships between a biotic or abiotic factor and a biological system (cells, organisms, populations, communities or ecosystem). (2D1 and SP5.1)

Science Practices
1.5: The student can re-express key elements of natural phenomena across multiple representations in the domain.
2.2: The student can apply mathematical routines to quantities that describe natural phenomena.
5.3: The student can evaluate the evidence provided by data sets in relation to a particular scientific question.
6.4: The student can make claims and predictions about natural phenomena based on scientific theories and models.
7.1: The student can connect phenomena and models across spatial and temporal scales.

Answers to Prelab Questions

1. Wisconsin Fast Plants^® are derived from Brassica, which is an annual dicot. Review and describe the life cycle of an annual dicot.

   Answers will vary. Annual dicots go from seeds to flowering to producing seeds in one growing season. They die after producing seeds. Dicots have two cotyledons, also called seed leaves. The cotelydons are present inside the seed.

Sample Data

References

AP Biology Investigative Labs: An Inquiry-Based Approach. College Entrance Examination Board: New York, 2012.

Biology: Lab Manual. College Entrance Examination Board: New York, 2001.

Farming Ants Update Their Crops. http://www.sciencemag.org/news/2010/04/farming-ants-update-their-crops (accessed November 2017).

Lauffer D; Williams, P. (2007). Wisconsin Fast Plants^®. www.fastplants.org (accessed November 2017).

Introduction

How does natural selection drive evolution? Can we make changes on purpose to cause an organism to evolve? In this investigation, the techniques of artificial selection will be explored as one method to study the process of evolution.

Concepts

• Artificial selection
• Natural selection
• Plant life cycle
• Evolution
• Plant growth
• Pollination
• Germination

Background

The inherited change of characteristics within a population over successive generations is evolution. The changes within a population may or may not be visible to the naked eye because they originate from changes in the genetic code. In nature, these changes occur when one specimen produces more live offspring; more of its genes survive in the next generation. Over time, this leads to one variation of the gene becoming more prevalent in the overall population. Recall that it is variation within DNA that gives rise to a range of characteristics within a population, the species and eventually the entire ecosystem within which it lives. An increase or decrease in the frequency of one genotype based on the ability of the organism to reproduce and pass that gene to the next generation and the ability of the offspring to survive to reproduce are fundamental driving forces for the process of natural selection. Over time as an area’s local ecosystem changes (e.g., becoming more marsh-like), the population of plants that survive to reproduce will, on average, tolerate wet roots better than those that thrived when the soil was drier. A gradual shift in the genotype toward an average of wet-tolerant plants occurs. This gradual change due to natural selection is an important factor in evolution.

Artificial selection happens when humans or other animals control the process of evolution by allowing only select individuals to reproduce. Crops and livestock are all examples of artificially selected organisms, as are domesticated pets like dogs and cats. Artificial selection is not new. What is new is our awareness that other species, such as some farming ants, also have the ability to artificially select their crops. In part, Charles Darwin (1809–1882) relied upon his observations and knowledge of artificial selection to identify natural selection as a major mechanism that drives evolution.

Researchers have artificially selected certain traits in numerous species of bacteria, fungi, plants and animals so these organisms can be used in the lab as model organisms in scientific experiments. One such model organism, Fast Plants^®, was developed at the University of Wisconsin–Madison by Dr. Paul H. Williams. Over the course of 30 years Dr. Williams successfully bred a type of wild turnip to be conducive to experimentation. For example, the pollen does not cross-pollinate or self-pollinate. This allows the researcher to control fertilization. Dr. Williams’s research team bred flowers with heavy, sticky pollen so now the plant is totally reliant on a researcher. Another great research aspect of these plants is their short life cycle (about 50 days from seed to seed). Through selection, the ideal growing conditions for all of the wild type Fast Plants seeds are the same, which maximizes the controlled environment. The temperature must be kept between 60 and 80 °F; above 80 °F the plant will have sterile flowers. Fast Plants require constant light from grow lights, positioned close to the tops of the plants. Despite these conditional requirements, there are still many easily studied phenotype changes that make this plant ideal for use in studying artificial selection.

Experiment Overview

In the Baseline Activity, the natural variation of traits in a population of Fast Plants^® will be observed, measured and characterized, and the characteristics for artificial selection in a second generation will be identified. The results of this activity will be analyzed for statistical significance and provide a procedure and model for open inquiry and student-designed experiments in the Opportunities for Inquiry section. Explore whether specific traits may help a plant grow and survive, and investigate environmental conditions that may affect the survival of plants with different characteristics.

Materials

Prelab Questions

1. Wisconsin Fast Plants^® are derived from Brassica, which is an annual dicot. Review and describe the life cycle of an annual dicot.

Safety Precautions

Bleach solution is a toxic and corrosive liquid, which may discolor clothing and cause skin burns. Avoid contact with acids, which can release toxic chlorine gas. Wear chemical splash goggles, chemical-resistant gloves and a chemical-resistant apron. Wash hands thoroughly with soap and water before leaving the laboratory. Please follow all laboratory safety guidelines.

Procedure

Part A. First-Generation Plants

1. Thread a wicking cord through a hole in the bottom of each pot.
2. Fill each pot with light planting mix, and pack it gently but firmly into the pot until it is 2½" to 3" deep. Ensure that the wicking cord sticks up through the top of the planting mix.
3. Spread six seeds evenly on top of the planting mix in an appropriately labeled pot. Designate a clearly labeled control group and a treatment group.
4. Cover the seeds with a light layer of vermiculite.
5. Repeat steps 3 and 4 until all pots are planted.
6. Place the pots in the grow area. Thread the wicks through the holes in the tray so the wicks extend down into the dilute fertilizer reservoir.
7. Record all the conditions that are kept constant by the planned setup of the experiment.
8. Monitor the growth of the plants as instructed. The schedule that follows is a guideline that may change depending on the growth rate of the plants.
9. Days 2 and 3: Monitor seed germination and record the number and percentage of seeds that germinate.
10. Day 9 or 10: Thin the plants by removing all but the healthiest three plants in each pot. Use scissors to cut off the stem near the base. Placed a bamboo skewer into the soil near the base of each remaining plant, and train the plant stem to grow up the skewer. If Days 9 and 10 are not available, perform the thinning earlier.
11. Day 11: Take measurements. Height, stem width, stem color, number of buds and trichome density are some of the variables from which to choose. Calculate mean, median, range and standard deviation on the raw data. Plot a histogram of the frequency data, distinguishing between the control group and the treatment group plants. Note: The treatment has not yet been applied, but these baseline data will help determine how the treatment influences the results.
12. Day 11: Flowering may start around this day. It is a good idea to keep track of the number of flowers on each plant each day because the plants used for pollen should be 2–3 days old.
13. Day 12 (before pollinating): Thin the plants of the treatment group for the selected trait, deciding as a group the criteria and number of plants to keep. Thin the control group by randomly selecting the same number of plants as the treatment group.
14. Day 17: Take the same measurements that were taken on Day 11. Calculate mean, median, range and standard deviation of the raw data, and construct a histogram of the frequency data. Note: Flowering may begin sooner. Take these measurements before pollinating.
15. Pollinate 2 or 3 days after the first flowers emerge and again 5 days after the first flowers emerge. To pollinate:
    1. Harvest pollen flowers that are 2–3 days old. The anthers should have visible pollen on them. Squeeze gently near where the flower joins the stem, and pull to remove the flower. Record the plant number.
    2. The removed flower will splay outward from the pistil, and the anthers will be more accessible.
    3. To pollinate, touch the anthers of the removed flower to the stigma of flowers that have been open for 1 to 2 days and have little pollen on their anthers. Pollinate 3–4 flowers on a different plant. Record the plant number. Check the flowers with a magnifying glass to confirm that there is pollen on the stigma.
    4. Choose another pollen flower and repeat. Pollinate up to six flowers on each plant, keeping track of the pollinating flower plant and the pollinated plant. Wisconsin Fast Plants^® do not self-cross; therefore, the pollinating flower must come from a different plant than the pollinated plant.
16. About 1 or 2 days after the second pollination: Remove all flowers that were not pollinated using sharp dissection scissors. Note: Pollinated flowers will have elongated pistils as shown in Figure 1.
    {11133_Procedure_Figure_1}
17. Check pod development and continue to water the plants frequently. About 2 to 3 weeks later, the seeds will become visible through the pods. Remove the water reservoir and hand-water when the soil is dry.
18. 1 to 2 weeks later, the plants will begin to turn brown. When half the plant is brown, stop watering.
19. Seven days later, harvest the seeds from the pods and keep the seeds from each parent plant separate. Record the number of seeds harvested from each plant.

1. Use a new wicking cord and planting mix in each of 16 clean pots. Plant six of the harvested seeds from the treatment group in each pot. Prepare the same number of pots containing control seeds. All other conditions should remain consistent between the first-generation and second-generation plants.
2. Once the second-generation plants have reached the same life stage as the first-generation plants were when the trait was quantified, determine a mean, median, range, standard deviation, etc. This will occur on or about Day 12. Plot a histogram of the frequency distribution for the trait, distinguishing between the treatment group and the control group.
3. Compare the three sets of data collected in the two trials, and describe the mode of inheritance for the trait. Use appropriate statistical analysis to defend a hypothesis concerning the effect of artificial selection on the population.

1. Consider the following questions while reflecting on your knowledge about artificial selection in Brassica. a. Would altering the environmental conditions affect the rate of survival for plants with a certain characteristic? b. Could another characteristic be manipulated? c. Could another plant be manipulated through artificial selection to enhance or eliminate a specific trait?
2. Plan, discuss, execute, evaluate and justify an experiment to test a question regarding inherited traits and artificial selection.
   1. Decide on one question your group would like to explore.
   2. Develop a testable hypothesis.
   3. Discuss and design a controlled procedure to test the hypothesis.
   4. List any safety concerns and the precautions that will be implemented to keep yourself, your classmates and your instructor safe during the experimental phase of this laboratory.
   5. Determine what and how you will collect and record the raw data.
   6. How will you analyze the raw data to test your hypothesis?
   7. Share your hypothesis, safety precautions, procedure, data tables and proposed analysis with your instructor prior to beginning the experiment.
   8. Once the experiment and analysis are complete, evaluate your hypothesis and justify why or why not the hypothesis was supported by your data.
   9. Present and defend your findings to the class.
   10. Make suggestions for a new or revised experiment to modify or retest your hypothesis.