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Thomas and Sally

The Interplay of Scientific and Historical Evidence

By Eric Ribbens, Andrew C. Lydeard

Thomas and Sally



Did Thomas Jefferson, third president of the United States, have children with his slave Sally Hemings? This PowerPoint clicker case explores this controversial question as students consider the evidence for Jefferson as the father of Eston Hemings, as well as the limitations of that evidence. In the process, students learn about Y-chromosomal and mitochondrial DNA and how they are passed down through generations. They also learn about the role of genetic tests in examining family lineages. In addition, the case serves to illustrate how science cannot always provide a direct and definitive answer and how conclusions often must be based on a mixture of scientific and historical (or other) evidence. The case was designed for an introductory biology course for non-majors but could easily be adapted for a majors' course or for the introductory portion of a genetics course. Students should have some prior knowledge of chromosomes and hereditability.


Date Posted




  • Understand the concept that Y chromosomal DNA can only be passed between male lineages.
  • Explain that mitochondrial DNA is passed solely from mother to offspring.
  • Explain the role of genetic tests when examining family lineages.
  • Analyze and interpret family pedigrees.
  • Explore the concept of scientific evidence within a larger social context that includes attitudes and other forms of evidence.


Chromosomal genetics; inheritance; mitochondrial DNA; Y chromosome; short tandem repeats; STRs; family pedigree; forensics; Thomas Jefferson; Sally Hemings


Subject Headings

Biology (General)
Forensic Science
Genetics / Heredity


High school, Undergraduate lower division



PDF, PowerPoint



Ethics, History of science, Scientific method, Scientific argumentation, Social issues






Clicker, Dilemma/Decision, Interrupted



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