Blood Critters in GridWorld

Overview & Concepts

Students will use the GridWorld case study to create BloodCritters that extend the Critter class. These BloodCritters will have two alleles for their blood types and will be able to reproduce, randomly giving their children one allele each. These two alleles will determine the child's blood type. The color of each critter will be determined based on the blood type.

Grade Level: 

Concepts Covered: 

Genetics, blood types, alleles, inheritance, randomization, GridWorld

Prior Knowledge Required: 

Students must be familiar with the GridWorld case study and randomization. They must also know about blood types and how they are inherited from parents, which can be covered using some of the resources provided.

Activity Notes

Days to Teach: 

3 - 5 days


  • BloodCritter Project Description (Word document)
  • Blood Genotypes and Phenotypes (Word document)
  • GridWorld case study from Collegeboard (See Resource section)
  • Blood Type Worksheet (See Resource Section)
  • Video about how one inherits blood types from parents (See Resource section)

Teaching Tips / Activity Overview: 

  • The amount of time for this project must be adjusted based on length of class periods, how much students have been exposed to GridWorld and overall programming experience of students.

Day One

  1. Introduce the students to blood type inheritance with video from Materials section.  Go over some examples of punnet squares and have students work in pairs on the Blood Type Worksheet.
  2. Pass out BloodCritter Project document.

Day Two

  1. Review Critters from the GridWorld case study.  Have students work in pairs to discuss what additions/changes will need to be made to create the BloodCritter class.  Teacher should walk around to facilitate the discussion and guide students when necessary. 
  2. When pairs have an outline of what the new BloodCritter class should contain, they must have it approved by the teacher and then begin to program this class.

Days Three to Five

  1. Review the details of the project.  Go over any questions from the class. 
  2. Students will continue to program the BloodCritter class.
  3. Students will test their class in a BoundedGrid.  Note:  Depending on the teacher's expectations, a test driver may be provided for the students or they can create a test driver themselves.


On Day Two, the teacher should look at the BloodCritter outline from each pair and give suggestions and feedback. Each day, partners should review each other's work and give feedback. The teacher should circulate around the room and answer questions and give suggestions throughout the programming assignment.


  • Students could keep track of each child's blood type and calculate the percentages of each phenotype.
  • Students could keep track of each child's blood type and create a bar chart of the phenotypes.
  • The idea of inheritance of alleles can be expanded to look at various diseases.  Simulations for a population could be done to determine if or when the disease dies out, the number of carriers of the disease, etc.


These teacher notes and resources were produced by Sandy Czajka, Riverside Brookfield High School.

Academic Standards
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Type of Activity: 

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