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I Scream for Ice Cream

Lactase Persistence in Humans


Nadia Sellami
Undergraduate Research Center - Sciences
University of California Los Angeles
Julie A. Morris
Department of Biological Sciences
University of Denver
Sheela Vemu
Department of Mathematics and Sciences
Waubonsee Community College


Lactose intolerance, caused by a lack of persistent lactase enzyme expression, is a trait commonly observed in adult humans, with varying geographic prevalence depending on dietary habits in different cultures. This case study follows a diverse group of undergraduate students on their quest to understand why some humans are able to digest lactose and others cannot. Students are asked to use quantitative reasoning to explore the geographic distribution of the trait of lactose intolerance as well as the enzymatic activity of the lactase enzyme. Students then explore eukaryotic gene regulation and how single nucleotide polymorphisms (SNPs) can affect the expression of the lactase gene. Students are asked to correlate genotypic data with phenotypic observations. Finally, students explore the effect of environmental factors on the evolution and geographic distribution of the lactase persistence trait by generating concept maps. The case was developed for introductory biology courses up to introductory molecular biology courses at the college level and emphasizes quantitative reasoning as well as integrating different concepts using the topic of lactose intolerance.


  • Describe and analyze enzymatic reactions using key terms and quantitative data.
  • Differentiate between monosaccharides, disaccharides, proteins and enzymes.
  • Describe the chemical reaction catalyzed by the lactase enzyme.
  • Predict the effect of the enzymatic activity of an enzyme such as lactase on a measurable product concentration such as blood glucose levels using quantitative data and graphs.
  • Describe the effect of small genetic differences in individuals such as SNPs on eukaryotic gene regulation.
  • Describe the eukaryotic transcription initiation and regulation machinery.
  • Explain how a SNP or other DNA mutation can alter protein binding and affect gene expression.
  • Evaluate the effect of DNA sequence alterations on the transcriptional efficiency of a eukaryotic gene.
  • Explain the importance of mutations and the effects of environmental factors on natural selection and evolution.


lactose, lactose intolerance, lactase, evolution, enzymes, regulation of gene expression, DNA sequence analysis, enhancer, SNP, transcription

Topical Areas


Educational Level

Undergraduate lower division, Undergraduate upper division



Type / Methods

Directed, Interrupted



Subject Headings

Biochemistry  |   Biology (General)  |   Cell Biology  |   Evolutionary Biology  |   Genetics / Heredity  |   Molecular Biology  |  

Date Posted


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Matt Simon
Northeast Iowa Community College
Calmar, Iowa
My students seemed to engage well with this case study. As I teach an intro biology course and haven't covered the gene expression portion of the case I dropped Part III, but they still worked on this case for about 1.5 hrs. Thanks!