Beacon Lesson Plan Library

Pair 'Em Up!

Suzan Smith
Marion County Schools


In the fourth lesson plan of the unit, Where We Come From, students learn how to use and verify the validity of Punnett squares by using a Weblink for instruction. They will also simulate a real-world situation by drawing “chromosomes” from a paper bag. Data will be tracked, students will calculate percentages, and cross check their predictions and results by using a Punnett square.


The student compares experimental results with mathematical expectations of probabilities.

The student determines odds for and odds against a given situation.

The student uses a Punnett square to predict the results of crosses between pure and hybrid organisms.


-Paper bags per group (lunch sack size)
-Construction paper per group (blue and yellow)
-Scissors for each student
-Student copies of the worksheet “Pair ‘Em Up!” (associated file)
-Student copies of Using Punnett Squares (associated file)
-Internet connected computer with presentation system
-Website bookmarked for easy access


1. Purchase lunch bags and construction paper.
2. Make student copies of the worksheet, Pair ‘Em Up!
3. Duplicate the Using Punnett Squares worksheet. You may wish to make 1 copy for the overhead, as well as enough copies for each student.
4. To minimize the time consumed in the class, the teacher may wish to prepare the “chromosomes” ahead of time.
5. If the students are going to make their own "chromosomes," then you will also need to provide scissors.


NOTE: Students should understand basic mathematical probability before beginning this lesson.

Day one of this lesson plan:
1. Review the Individual Questions from the previous lesson in this unit. Since you will have formatively assessed them, allow students to correct their copies to use as a review for the summative at the end of this unit. Also review the vocabulary that will be needed for today's lesson, by using the Genetics Vocabulary Sheet. (see extensions) Review making the marshmallow babies and what students have learned so far about genetics.

2. Display your overhead copy of the Using Punnett Squares worksheet, and pass student copies out. Tell the students that they will learn how to use a Punnett Square in class today. Display the Internet Weblink "Baby Steps Through Punnett Squares." (See Weblinks) Read and follow through the instruction provided on the Weblink. Stop for further explanation or class discussion as necessary.

3. When you get to the place on the Weblink where it walks through the example that corresponds to the Guided Practice section on the students' Using Punnett Squares worksheet, have the students work through it with you.

4. Complete discussion and viewing of the Weblink.

5. Model the first "independent practice" Punnett Square for students. Have the students independently work through the other Punnett Squares on the worksheet, either on their own paper, or on their copies. Circulate and give feedback and guidance.

6. When everyone is finished, share answers and allow for questions and corrections.

7. If the students are going to be cutting out their own chromosomes, you may have time to do that at the end of this lesson, without beginning the actual activity for day two. (See the instructions on Pair 'Em Up! in the associated file.)

Day two of this lesson plan:
1. Hand out the student copies of the worksheet Pair ‘Em Up!

2. Students answer Question 1 and Question 2 on the worksheet, then discuss the answers as a whole class. Tell the students that probability is the chance that an event or outcome will happen. Point out that when using a Punnett Square in genetics, they are already predicting probability. Make sure students understand that probability is just that--it doesn't guarantee. Use the analogy of a family having two children. Probability says that one will be a boy and one will be a girl, however, many families just have two boys or two girls.

3. Pair the students up into groups of 2 and distribute the supplies. review the directions on the sheet Pair 'Em Up! with students.

4. Students complete the activity as listed on the worksheet, Pair ‘Em Up!

5. Discuss the activity as a whole class by going over the students’ collected data . By analyzing the data from the groups in the class, they will find a majority of the data was very close, or even exactly the same as the percentages predicted by using the Punnett Square.

6. Ask the students why all of the groups’ results may not have reflected the percentages provided by using the Punnett Square.

7. Relate the answer to this question to flipping a coin. We know that the chances of getting Heads or Tails is 50%, but if each student flipped a coin 10 times, not all students will get 50:50. Some students would not be close to 50:50. ** Refer back to the lesson plan, How Unique Are You? (Day 2, Procedure #1) by pointing out that some of the dominant traits may not have been in the majority in your classroom, but if enough people were surveyed the results may be more accurate.

8. Ask how many of your students’ families have an even number of children. Are the boys and girls evenly distributed 50:50? This would be a good time to show a Punnett Square to predict gender.
9. Ask students what is the probability that a baby will be a boy? girl? Ask the students how many of the groups from the lesson plan, Marshmallow Babies, had a male vs female. Was it close to 50:50? Why or why not?

10. Ask students what the importance is of being able to predict the possible outcomes of offspring. Discuss a couple that wants to have children, but they are aware of a genetic disorder, like sickle-cell anemia, that runs in their family. They would want to know the chances of passing that disorder on to their children. If the probability is high, they may want to consider other options.

11. Students now complete the Conclusion Questions individually.


The students will be formatively assessed on the completion of the Using Punnett Squares worksheet and correctly answering the Conclusion Questions. Answer keys are provided. (see associated file)

Groups are formatively assessed as they work through the activity and complete the Pair 'Em Up! worksheet.


The Beacon Unit Plan associated with this lesson can be viewed by clicking on the link located at the top of this page or by using the following URL: Once you select the unit’s link, scroll to the bottom of the unit plan page to find the section, Associated Files. This section contains links to the Unit Plan Overview, Diagnostic and Summative Assessments, and other associated files (if any).

Use the Weblink "Genetics Practice Problems" to expose the students to sex-linked traits, dihybrid crosses, etc.

Web Links

This weblink provides basic review and instruction on using Punnett squares. Also included are examples that could be used with the students in class.
“Baby Steps Through Punnett Squares”

This weblink provides additional practice problems regarding the cross between two organisms, including the dihybrid cross, trihybrid cross, and sex-linked traits.
“Genetics Practice Problems

Return to the Beacon Lesson Plan Library.