Beacon Lesson Plan Library

Marshmallow Babies

Suzan Smith
Marion County Schools


In this third lesson of the unit, Where We Come From, students pair up “chromosomes” and interpret the genotypes and phenotypes. Then, they use those genetic traits to create their own "Marshmallow Babies!" This is a modified version of an activity published by Patti Sorderberg in [The Science Teacher], November 1992, pp 28-31.


The student knows that the variation in each species is due to the exchange and interaction of genetic information as it is passed from parent to offspring.

The student knows how dominant and recessive traits are inherited.


-One envelope per group containing the “chromosomes” (instructions for making envelope, associated file)
-2 Packages multi-colored mini-marshmallows (green, orange, yellow and pink)
-2 Packages of large white marshmallows
-Extra marshmallows for eating (amount depends on class size)
-One box toothpicks
-Red and blue push pins
-One pipe cleaner per group, mixed colors, cut in half
-One string per group, about 5-6 inch in length; colored yarn or ribbon is best
-Package of nails
-Box of silver thumb tacks
-Paper towel or hand wipes; marshmallows are sticky
-Student copies of the Group Data Table (associated file).
-Overhead of the Group Data Table
-Student copies of the Individual Questions (DELETE THE ANSWER KEY BEFORE DUPLICATION)
-Student copies of the Rubric
-One copy of the Rubric for Marshmallow Babies per group
-Dixie cups
-Optional** Polariod camera and film


1. Make copies of the "chromosomes" to assemble one envelope of chromosomes per group (see associated file). This takes a while, so be prepared!!!
2. Purchase tangible items listed in Materials section (tacks, marshmallows, etc).
3. Cut pipe cleaners and string.
4. Make student copies of the Group Data Table, Decoder Key and Rubric. (see associated file)
5. Make an overhead of the Group Data Gable.
6. The morning of the activity, before the students enter, arrange the "building materials" on a counter or table that is easily accessible to all students. I usually place supplies such as the tacks, nails, pre-cut string, pre-cut pipe cleaners, red and blue push pins, and marshmallows on separate paper/plastic plates. Sort the yellow and pink marshmallows togethher on one plate, and place the green and orange mashmallows together on a separate plate since they represent different characteristics. The larger white marshmallows get their own plate or bowl.


Day one of this lesson:

1. Review the Individual Questions worksheet that students completed in the previous day's lesson plan, How Unique Are You? Since you already formatively assessed these answers, allow students to correct their copies to study for the summative at the end of the unit.

2. Tell students that they are going to become "parents" today and will actually get to design their own babies, that is, marshmallow babies! Place students in groups of 2 or 3. At this time, review the needed vocabulary from the vocab sheets that will be needed for this lesson plan. These words/definitions can be placed on the word wall or students may keep their vocab sheets handy.

3. Give each group a Group Data Table and provide each group with a copy of the rubric. (associated files). Review the rubric with students.

4. Tell the students that they will be assembling marshmallow babies by interpreting the traits provided to them in envelopes that
contain "chromosomes." Make sure students can describe or define chromosome.

5. Distribute the "chromosome" envelopes; 1 envelope per group. Ask the students to take out the chromosomes and instructions from the envelopes.

6. Point out to them that the small pieces of paper are the chromosomes. Some of them are pink and some are blue. Ask the students the reason for the color and what they represent. (mother and father; we each recieve half of our traits from each parent)

7. Some of the letters are lower case, and some of the letters are capital. Ask the students what that symbolizes/represents (capital = dominant traits, lower case = recessive traits).

8. Ask the students to look at the Group Data Table sheets. They must list the genotypes and phenotypes for their group's baby. Ask what these words mean (students can refer to the Genetics Vocab Sheet. (See extensions)

9. Point out to the students that they will have a genotype such as Aa for antennae. They write Aa in the genotype column. Have the students look at their Decoder Key from their envelopes. Ask what the phenotype would be for Aa. In such a combination (heterozygous) the dominant trait covers up the recessive. The phenotype would be 2 antennae in this case. You will need to model this. Ask about AA (both dominant) and aa (both recessive.) Model recording on the Group Data Table transparency and creating this trait on a marshmallow baby.

8. Instruct the students to match up the pink and blue chromosomes by letter. They will end up with 7 matching pairs and either an XX or a XY pair. Review that XX means a girl and XY means a boy.

9. Explain that the materials they will need for this activity are provided on the counter/table. They must use the decoder key to decide how to use the materials to construct their babies. They should record their information onto their Group Data Table FIRST and then raise their hands so you can quickly check to see if they've recorded it correctly. Provide feedback generously and if a group seems to understand how to record well, allow them to quickly help a group that is having great difficulty.

10. Once the students transfer the information to their Group Data Tables, they should get the necessary materials and assemble their marshmallow babies.

11. When students have assembled their babies, they should begin the bottom portion, naming the baby and creating hobbies/interests for him/her.

12. The marshmallow babies attract ants sometimes. You can choose to "impound" the babies overnight in the "nursery" in a sealed container. I also found that taking Polariod pictures of the babies works well, too. Later you can post the pictures on a bulletin board. Ziplock bags work well and student names can be written on them.

Day two of this lesson:

1. Provide students with a little more time to complete their Group Data Tables or babies if neccessary. Students need time to prepare for their presentations to the class as well. Review the appropriate vocabulary terms that students should use during their presentations. Limit the time that students have to get ready--10 minutes is sufficient.

2. Distribute the impounded babies or Polariod pictures to the groups.

3. Remind the students that they need to be looking for possible twins during the class presentations. During the presentation the students will list the genotypes and phenotypes of their babies, and provide the class with their baby's name and hobbies

4. Distribute Dixie cups with some fresh marshmallows for the students to eat. They tend to be more attentive for their classmates’ presentations while eating!

5. Groups present their babies to the class. As groups present their babies, be sure to orally ask and answer the questions that appear on the Individual Questions worksheet that students will do after the presentations. Use the vocabulary and encourage students to use it also.

6. Discuss what a twin is and how there might or might not be twin marshmallow babies (not only matching phenotypes, but also matching genotypes.)

7. Collect all materials concerning babies. Distribute the Indvidual Questions worksheet for students to complete.


Groups are formatively assessed based on completion of their marshmallow babies, and completion of the Group Data Table. See the provided Rubric in the associated file.

Cooperative Worker skills are also formatively assessed using the Rubric.

Individual formative assessment occurs through looking at the answers to the questions in the Individual Questions sheet. See the provided answer key in the associated file.


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).

Web Links

This site summarizes the concept of the Reebop babies that was originally published by Patti Sorderberg. Pictures of adult “Reebops” are included on this site.
“Marshmallow Meiosis”

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