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Identical Twins, Identical Fates?

An Introduction to Epigenetics


Sarah A. Wojiski
Genomic Education
The Jackson Laboratory


This case tells the story of Elise, a college freshman whose identical twin sister has recently been diagnosed with schizophrenia. Elise is concerned about her own risk for developing this disease. Through her research and interactions with a physician, students are introduced to the topic of epigenetics and learn about the data supporting an epigenetic contribution to this psychiatric disorder. This case was designed for a sophomore-level molecular biology course for majors and could easily be adapted for an undergraduate genetics course. The case may also be applicable in a course that covers biological psychology. Students should have a basic knowledge of Mendelian inheritance patterns and a good understanding of the structure of DNA and its packaging within the cell (particularly the role of histone proteins and chromatin). The case also provides an opportunity for students to examine figures and graphs from the primary literature.


  • Compare and contrast genetic and epigenetic modes of inheritance.
  • Describe how epigenetic modifications lead to changes in gene expression.
  • Describe the various epigenetic modifications that can occur to both DNA and chromatin, and predict the most likely effect of those modifications on gene expression.
  • List possible genetic and non-genetic causes of schizophrenia.
  • Explain how epigenetic factors could lead to different gene expression patterns in identical twins.
  • Describe how aberrant DNA methylation might play a role in the development of schizophrenia.
  • Describe how drugs that influence epigenetic modifications, such as DNA methylation, could potentially be used in the treatment of schizophrenia.


Epigenetics; DNA; schizophrenia; mental health; twins; twin studies; histones; DNA methylation; chromatin; reelin; graphs; data analysis

Topical Areas

Scientific method

Educational Level

High school, Undergraduate lower division, Undergraduate upper division



Type / Methods

Analysis (Issues), Discussion, Interrupted



Subject Headings

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

Date Posted


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Brenda From
Manhattan HS for Girls
New York, NY 10021
Is there any way I can access the referenced articles without having to pay for them?

Editor, National Center for Case Study Teaching in Science

Editor's Reply

Most often articles cited in the references to our cases are under copyright to the publishers of the journals they appear in. They own the rights to them, we do not. We do not have the right to reproduce them or to supply them. When we do reproduce a chart or table from a published article that is not from an open access source we enter into strict arrangements with the copyright holder (the publisher) to use that material as they have directed.

This is true for this case's cited references except for the Proceedings of the National Academy of Sciences, which is an open access journal. You can go to its website to retrieve the article cited in that journal at: Or connect directly to the article via:

Similarly, the Schizophrenia Bulletin is also available as an open access journal, for a certain span of years (from 2006 to 1 year ago) in PubMed Central; go to: Or connect directly to the article via:

You can try checking with your school or public library to see if they have the other journals. If they do not (and we realize that many will not have very specialized, scholarly, scientific journals), then you should ask your library if it offers an inter-library loan service through which you can request copies of articles from journals they don't own. Libraries are often part of larger consortia, which operate at a local, regional, and even national level, that allow libraries to lend to and to borrow from each other.

Nicole Benenati
Ithaca High School
Ithaca, NY
I appreciate the inclusion of actual research data for students to analyze.

Ryan Boylan
Pennsbury High School
Fairless Hills
This is excellent. My AP Biology students will really enjoy diving into this case study. Thank you very much!