Case Study: Why Are There No Male Calico Cats?

This presentation case study asks two important questions regarding cat coloration:

  • Why are there no male calico cats?
  • Why is it that clones of calico cats do not look like the original?

The case is presented as a slide presentation where students consider evidence and data related to cat coloration and chromosomes.  Working in small groups, they discuss the case and eventually answer the two main questions. I usually collect their answers at the end of class to keep students on task.  This activity can be adjusted for any grade level, younger students might need more guidance with answering questions.

The activity explores concepts that might not be directly included in typical chapters on meiosis, such as Barr bodies and cloning, though I find students really enjoy talking about cats and looking at cat pictures.  (Who doesn’t!)

PDF printout of slides 


  • Understand how genes located on sex chromosomes are inherited
  • Make predictions about the genotypes of male and female calico cats
  • Examine a karyotype and identify abnormalities
  • Understand how errors in meiosis can produce these abnormalities
  • Discuss how the inactivation of X chromosomes can affect phenotype

Activity is probably best done after students have learned the basics of Mendelian genetics.

Grade Level: 9-12
Time Required:  50-60 minutes

HS-LS3-1 Ask questions to clarify relationships about the role of DNA and chromosomes in coding the instructions for characteristic traits passed from parents to offspring.

HS-LS3-2 Make and defend a claim based on evidence that inheritable genetic variations may result from: (1) new genetic combinations through meiosis, (2) viable errors occurring during replication, and/or (3) mutations caused by environmental factors.