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More Than Meets the Eye

The Genetics of Eye Color


Annie Prud’homme-Genereux
Continuing Studies and Executive Education
Capilano University


The classic example of a human trait that behaves in a clear Mendelian fashion is human eye color. The gene that controls it exists in two forms: a dominant brown allele and a recessive blue allele. But the genetics of eye color is more complex than typically assumed.  How are green or hazel eyes formed, for example?  And how do blue-eyed couples give rise to brown-eyed offspring, as has been reported?  This case explores the molecular basis of eye color using the story of a blue-eyed couple with a brown-eyed child to explore the possible scenarios that could result in this outcome, emphasizing the link between Mendelian genetics and the underlying molecular basis of the phenotype. The case was designed for second- or third-year biology majors with a background in molecular biology and genetics. In particular, students should have some background in Mendelian genetics and a good understanding of the regulation of gene expression in eukaryotes.

  • Link Mendelian genetics and phenotype with the underlying molecular biology.
  • Explain the molecular basis of different eye colors.
  • Create and interpret Punnett squares for a single gene trait.
  • Create and interpret Punnett squares for two unlinked genes.
  • Explain the appearance of novel phenotypes in offspring that are not present in the parents.
  • Describe how biochemical pathways and genetic complementation can explain the appearance in offspring of novel phenotypes not present in the parents.
  • Describe ways in which epigenetics can create phenotypes in children not present in the parents.
  • Evaluate the likelihood of hypotheses based on evidence and real-world information.
Keywords: Eye color; allele; dominant; recessive; phenotype; genotype; point mutation; Mendelian genetics; gene regulation; genetic complementation; biochemical pathway; epigenetics; eye pigmentation; melanin; Punnett square
Topical Area: N/A
Educational Level: Undergraduate upper division
Formats: PDF
Type/Method: Discussion, Interrupted
Language: English
Subject Headings: Genetics / Heredity   Molecular Biology   Biology (General)  
Date Posted: 01/13/11
Date Modified: N/A
Copyright: Copyright held by the National Center for Case Study Teaching in Science, University at Buffalo, State University of New York. Please see our usage guidelines, which outline our policy concerning permissible reproduction of this work.

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