Target Grade Level / Age Range:

8 th Grade


One 45-minute class period

Virtual Learning:

Use this document to convert the lesson into a virtual learning module for your students. Use the steps outlined to create the different elements of a Google Classroom or other online learning platform. You can also send the steps directly to students in a PDF, present them in a virtual meeting, or plug them into any other virtual learning module system. 


Students will learn about probability by learning about Gregor Mendel’s work with peas and then testing probability through a lab using Skittles.


  • 2 bags of Skittles (One bag of skittles for each group)
  • Brown paper lunch bags
  • Gregor Mendel: The Friar Who Grew Peas by Cheryl Bardoe

Suggested Companion Resources


  • Probability: the likelihood that a specific event will occur.
  • Probability: Number of times an event is expected to happen/Total number of possible outcomes
  • Ratio: a relationship between two numbers indicating how many times the first number contains the second number.
    • Example: 4 children: 3 girls and 1 boy. The RATIO is 3 girls to 1 boy a relationship between two numbers indicating how many times the first number contains the second number.
  • Punnett Square: a diagram that is used to predict an outcome of a particular cross or breeding experiment; it is used by biologists to determine the probability of an offspring having a particular genotype.
  • Genotype: the genetic constitution of an organism. Example: if a pea plant has red flowers, its genotype might either be RR or Rr, notating the alleles present at a specific locus.
  • Phenotype: the set of observable characteristics of an individual resulting from the interaction of its genotype and the environment.
  • Allele: one of two or more alternative forms of a gene that are found at the same place (or locus) on a chromosome.
  • Locus: a particular position, point, or place on a chromosome. 

Background – Agricultural Connections

Probability is used every day in the agriculture industry from selecting genetics of animals to predicting the outcome of the next generation of corn plants. Probability may be expressed as a decimal, a percentage, or a fraction. (decimal .25, percentage 25%, a fraction ¼). Ratio is written as 1:3 (1 boy: 3 girls) and read as 1 to 3 (1 boy to 3 girls). In selective breeding of any organism (as long as the trait is found only on 1 pair of chromosomes and it is complete dominant) a predetermined ratio can be expected. Example: If a red flower is cross-pollinated with a white flower the F generation will be 4:0 or 100% red (or the dominate color).   If the F 1 generation is cross pollinated the F 2 generation will be 3:1 red to white or 75% red to 25% white. In genetics, it’s important to note that the traits we notice physically (phenotypes) are results of the genes we carry (our genotypes). The genes we receive are given to us from our parents and are a random selection of the genes they have themselves. We know that we have two copies of each chromosome (one from each parent), so we have two copies of each gene. This is more or less the same for every living organism unless they have more than two copies of each gene (called polyploidy). These can vary, for instance, the gene for blue eyes is different from the gene for brown eyes. These different versions of the same trait are called alleles. When Gregor Mendel began studying genetics, he worked with traits that are simple dominant and recessive. This means that one trait is simply more dominant than the other. When he studied peas, red flowers were dominant over white flowers, smooth peas were dominant over wrinkled peas, and so on. Today, we know that not all genetic traits are that simple, but simple dominant and recessive genetics is a good place to start.

A good way to visualize probability in genetics is through a Punnett Square. Punnett Squares are a tool used to compare possible genotypic outcomes based on the genotypes of the parent organisms. To do this, the trait being measured will be given a letter to symbolize it. The dominant allele will be given the capital version, and the recessive allele will be given the lowercase version. To make a Punnett Square, draw a square with four quadrants of equal size. On the left side of the square, write the maternal genotype with one allele per row. Above the square, write the paternal genotype with one allele per column. Then in the square, match maternal and paternal alleles in each quadrant. Example:


In agriculture, probability in genetics is important for plant breeders, seed scientists, and animal scientists. People in these careers need to know about probability in genetics to help breed crops and livestock generations that are healthier, hardier, and more efficient than before!

Interest Approach or Motivator

  1. Read the book Gregor Mendel: The Friar Who Grew Peas. This book is for upper elementary but there is a lot of takeaway upper middle school students could take away from the book and gain a little bit of history on how Gregor Mendel came to discover heredity.


  1. Start class by recapping some facts about Gregor Mendel and what he studied.
    1. Talk about simple genetics, the traits he studied in peas, and the impact he had on genetics as a field of study.
  2. Remind students that depending on parent genotypes, the probability that the offspring have certain traits can be different.
    1. Take this time to talk about what probability is and how to calculate this. Also, explain what use this has in agriculture, and other real-world applications.
  3. Next, divide students into groups of 2 and pre-make bags of skittles for each group.
    • Place 12 yellow, 6 red and 2 green skittle candies in a brown paper bag.
  4. Make sure to tell the students to NOT EAT the candies or LOOK INSIDE the bag until AFTER the experiment.
  5. Tell the students there are 20 Skittles in each bag and that they are three different colors. Their task is to determine how many of each color are in the bag by calculating probability.
  6. Pull one skittle out of the bag and record the color on the Skittle Probability WS.doc.
  7. Return the skittle to the bag (without looking in the bag) and shake the bag to mix the candies.
  8. Repeat step 6 until they have examined and recorded 20 candies.
  9. S tudents will then determine the probability of drawing a skittle of a specific color with a single draw.  Do this for each color.
  10. Have students calculate the probability of each Skittle draw.
  11. F inally, tell students to write the ratio of yellow: red: green skittles on each line based on what each Skittle draw was.
  12. Have the groups compare their results with the rest of the class using the After Activity Analysis on the reverse side of the worksheet.

Essential Files

Did You Know?

  • The ratios and probabilities that Gregor Mendel determined with his pea plants are still relevant today.
  • I ncorporate another probability activity where students use Punnett Squares to find probabilities for different genotypes and phenotypes.

Extension Activities

  • Students can use this information to determine the best practices to increase biodiversity in an ecosystem.
  • Have students try explore and experiment with the Coat Color Calculator tool.



  • Hannah Pagel
  • Tim Anderlik

Organization Affiliation

Iowa Agriculture Literacy Foundation
Southeast Valley Middle School           

National Agriculture Literacy Outcomes 

  • T4.6-8.f: Explain the harmful and beneficial impacts of various organisms related to agricultural production and processing and the technology developed to influence these organisms.

Iowa Core Standards

  • MS-LS4-6: Use mathematical representations to support explanations of how natural selection may lead to increases and decreases of specific traits in populations over time.
  • MS-ESS3-3: Apply scientific principles to design a method for monitoring and minimizing a human impact on the environment.


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