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Why Did the Snake Cross the Road?

A Population Genetics and Habitat Conservation Case Study


Milton T. Drott
School of Integrative Plant Science, Plant Pathology and Plant-Microbe Biology Section
Cornell University
Mark A. Sarvary
Investigative Biology Teaching Laboratories
Cornell University


Although Hardy-Weinberg equilibrium is a fundamental part of introductory biology classes, students often have difficulty understanding its implications. This interrupted case study places students in the role of small teams who are conducting preliminary research into the impact of roads on the population structure of timber rattlesnakes in order to apply for a grant for further research. Research groups consisting of 3-4 students work through a series of questions allowing them to use HWE principles to discover for themselves how deviations from HWE can have implications for conservation biology. Periodic interruptions with help sheets (see Supplemental Materials) allow teachers to maintain an active role in the students' progress, while also demonstrating the collaborative nature of scientific research. Ultimately students formulate formal emails summarizing and interpreting their findings in order to "apply" for the grant. The case is designed for undergraduate students in introductory biology or in lower-level population genetics/conservation courses where connecting basic genetic principles to ecology and sustainability is key.


  • Address realistic scientific questions and practice  critical thinking.
  • Gain a better appreciation for the benefits and challenges of collaborative work.
  • Apply HWE equations to real-life data analysis.
  • Apply ecological genetic tools to interpret population subdivision.
  • Demonstrate how to compose formal emails communicating scientific results.


Hardy-Weinberg equilibrium; HWE; ecological genetics; population genetics; conservation; sustainability; timber rattlesnakes; landscape fragmentation; population structure; field science

Topical Areas

Policy issues

Educational Level

Undergraduate lower division, Undergraduate upper division



Type / Methods

Analysis (Issues), Interrupted, Role-Play



Subject Headings

Ecology  |   Evolutionary Biology  |   Genetics / Heredity  |   Wildlife Management  |   Science Education  |  

Date Posted


Teaching Notes

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Teaching notes are intended to help teachers select and adopt a case. They typically include a summary of the case, teaching objectives, information about the intended audience, details about how the case may be taught, and a list of references and resources.

Supplemental Materials

The following file contains two help sheets for instructors to distribute when running the case.

  Help Sheets

Answer Key

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