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Snow White Apples?

RNAi and Genetically Modified Foods


Ann T.S. Taylor
Department of Chemistry
Wabash College


The protagonist of this two-day flipped case study, “Maria,” has two problems. She doesn’t like it when the apple slices in her lunch turn brown, and she needs to find a project for her biology class that includes molecular biology, preferably one that incorporates plants. Students are enlisted to help Maria understand Arctic Apples™, which don’t turn brown because they have been genetically modified to suppress the expression of polyphenol oxidase via RNAi. The case also explores the health, environmental, and safety aspects of growing and eating plants that have been genetically modified to use RNAi. The case applies the central dogma of biology to the creation of genetically modified foods and RNAi and includes a discussion of whether genetically modified foods should be labeled. Several videos are included with the case, including one created by the author specifically for the case. The case is appropriate for use in an introductory level biology or survey level biochemistry course.


  • Describe RNAi, including necessary components.
  • Interpret a plasmid map.
  • Describe how a transgenic plant is made, including the role of species specific promoters, virulence genes and antibiotic resistance selection markers.
  • Apply issues involved in the use of GM foods to a discussion of whether GM foods should be labeled. Such issues include the non-target effects for RNAi, the role of polyphenol oxidase in plant disease resistance, and how antibiotic resistance is transferred between species.


RNAi; transgenic plants; central dogma of biology; RNA; DNA; genetically modified organisms; gene silencing; antibiotic resistance; plant disease resistance; labelling; GMO

Topical Areas

Ethics, Policy issues, Regulatory issues

Educational Level

Undergraduate lower division, Undergraduate upper division



Type / Methods

N/A, Discussion, Flipped, Jig-Saw, Journal Article



Subject Headings

Biology (General)  |   Biochemistry  |   Biotechnology  |   Cell Biology  |   Environmental Science  |   Food Science / Technology  |   Genetics / Heredity  |   Molecular Biology  |  

Date Posted


Teaching Notes

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Answer Key

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The following video(s) are recommended for use in association with this case study.

  • Central Dogma of Biology
    This compilation of three HHMI Biointeractive videos provides an overview of the central dogma of biology and covers transcription, splicing and translation. Running time: 5:51 min. Produced by HHMI Biointeractive, 2003.
  • RNA interference (RNAi)
    This narrated animation gives an overview of RNAi. Running time: 5:06 min. Produced by Nature Video, 2011.
  • How to Make a Genetically Modified Plant
    This video provides an overview of how transgenic plants are made, including creation of the Ti plasmid and transfer into the plant cell. Running time: 10:26 min. Created by Ann T.S. Taylor for the National Center for Case Study Teaching in Science, 2017.