Lisa Viktorin

Merit Winner: TMA Excellence in Science Teaching Awards

Lisa Viktorin
Johnston Middle School
Houston, TX

Brays Bayou Spiderwort Genetic Study
Sample Lesson Plan

Lesson Overview

The Brays Bayou Spiderwort Genetic Study was designed for eighth grade science students at Johnston Middle School. This genetic study was a subsection of a larger, six-week ecosystem study of a one-mile section of Houston's Brays Bayou, which is less than a mile from the school.  The genetic study lesson requires two 90-minute classes and an additional 45 minutes for presentations and discussion.

The study provided a hands-on approach to genetics.  Following a review of basic genetic concepts in the classroom, teams of students conducted individual field studies of six different-colored spiderwort plants. The individual team results were compiled with the results of 18 other science classes, and from the collective results, students were challenged to explain the genetic makeup of the six species, the dominant and recessive traits, genotypes, phenotypes, and possible genetic combinations.  Individual teams presented their findings, and a class discussion followed.  The discussion included possible reasons for the occurrence of certain species of the plant, the relationship between a spiderwort's flower color and its location, and the role of insects in pollination.

The lesson provided students with a relevant application of the study of genetics and a connection to an ecosystem near their school.  The lesson connected genetics to plant physiology.

Learning Objectives

• Conduct a random sampling of the spiderwort populations at Brays Bayou.
• Distinguish between inherited traits and traits that result from interactions with the environment.
• Identify and describe the dominant and recessive traits and genotypes and phenotypes of the six species of spiderworts found at Brays Bayou. 
• Formulate hypothesis based upon data gathered by examining possible crosses of spiderworts using Punnett squares.
• Present explanations for the physiological adaptations of the spiderworts that resulted from interactions within the environment.

Materials Used

Method of Implementation

The field study portion of the lesson takes 90 minutes including travel time to Brays Bayou.  Compiling data and group predictions can be completed in a second 90-minute class. The group presentation and class discussion can be completed in 45 minutes of the third class.

Prior to the field study, students reviewed various genetic concepts. Using worksheet activities, students identified genotypes and phenotypes in humans, animals, and plants. The Punnett square was reviewed and a series of inherited trait crosses were predicted. Students learned how to use the quadrants in a prelab plant survey of the bayou.

Identification information for the six species of spiderworts was distributed and students were divided into groups. On the first day, students randomly sampled their area with the quadrants and recorded their findings on a data table in their lab notebook. Students recorded the location of study, weather conditions, and time of day. On the second day, the data was compiled from all groups. Students then worked with their individual teams to determine possible genetic patterns among the different species of spiderworts. Using guiding questions, students created a presentation of their findings. The presentation included a data table of the total population of spiderworts studied and two Punnett square crosses.

Guided questions included:

• What are phenotypes and possible genotypes of the spiderwort population of Brays Bayou?
• Which traits are dominant? Which traits are recessive?
• Predict two Punnett square crosses of the six spiderwort species studied.
• Do you think the spiderwort flower color is an inherited trait or a trait that resulted from interactions with the environment? Explain your answer.
• What is the possible relationship between spiderwort flower color and location along Brays Bayou?

On the final day of the lesson, groups presented their findings using poster boards. A class discussion followed and students suggested that the dominant traits of spiderworts are blue and purple. The recessive traits are a result of insect pollination.

Evaluation Tools

Using the following rubric, students were graded using a combination of scores of their lab notebook (60 percent) and class presentation (40 percent):

The students also were given a post test at the end of the larger ecosystem project.  The test consisted of a series of short-answer questions about the different field study techniques and findings from each study.

Effectiveness of Lesson

Traditionally genetics is taught at the middle school level with cute activities involving probability and many worksheets. Students' understanding rarely extends past a simple Punnett square cross.

Through this genetic study, students can successfully describe phenotypes and predict genotypes of different species of spiderworts.  They also can distinguish between inherited traits and adaptations that result from interactions with the environment.    

The cumulative data provides a broader understanding of the study, and patterns are conclusive. The classroom discussion is lively, and students enjoy the presentations.

The lesson takes our students out of the traditional classroom and into the outdoors.  They are able to visit an ecosystem that they pass daily en route to school, creating a relevant application to their genetics study. 

This lesson was initially created by a team of three Johnston Middle School science teachers:  Allison Benjamin, Bruce Hartman, and Lisa Viktorin, following the team's award of a Chase Active Learning Grant in 2002. Lisa Viktorin enhanced the lesson plan in three ways: the addition of the guided questions, the addition of the rubric, and the requirement that the student teams present their findings to their class. 

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