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The Complexity of a Human Genetic Disease


William Morgan
Department of Biology
The College of Wooster
Dean Fraga
Department of Biology
The College of Wooster


This case study follows a young couple that is consulting with a genetic counselor about their plans to have a child. Because of their family history with cystic fibrosis, they are concerned about their chances of having a child with this genetic disease. The case study reviews the basics of Mendelian and molecular genetics in humans, briefly examines the possibilities and limitations of genetic testing, and introduces students to online databases, including OMIM, a catalog of human genetic traits. The case also requires students to practice the scientific method, including hypothesis development, experimental design, and the analysis of primary research articles. Although developed for use as an introductory unit to an upper-level genetics course, the case could be adapted for an introductory biology course, perhaps as a closing exercise to a unit on molecular genetics.


  • Construct and analyze a human pedigree and a Punnett square.
  • Predict the effect of a mutation on the expression of a gene, specifically whether the mutation will alter the amount of the gene's mRNA, the structure of the gene's mRNA, the amount of the encoded protein, or the structure of the encoded protein.
  • Explain why a gene can have many alleles within a population.
  • Sketch the typical structure of a eukaryotic gene.
  • Explain the trade-offs in developing a genetic test for a complex genetic disease and the consequent limitations of testing for a subset of alleles.
  • Explain how a mutation outside of the coding region of a gene can cause a genetic disease.
  • Access OMIM, a commonly used online database of human genetic diseases and other traits.
  • Based on their knowledge of genetics, propose a possible explanation (hypothesis generation) and formulate a simple test (experimental design).
  • Read a scientific paper to access information relevant to a specific question.


Genetics; cystic fibrosis; CF; genetic disease; genetic testing; pedigree analysis; Punnett square; mutation; gene structure; gene regulation; human inheritance; experimental design

Topical Areas

Scientific method

Educational Level

Undergraduate lower division, Undergraduate upper division



Type / Methods

Interrupted, Journal Article



Subject Headings

Genetics / Heredity  |   Molecular Biology  |   Biology (General)  |   Medicine (General)  |  

Date Posted


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