The mutation lab utilizes Tetrahymena strains carrying temperature sensitive mutations in genes involved in cell division. At permissive temperatures, the cells are normal, but when shifted to the restrictive temperature, they exhibit easily observed and characterized changes in morphology. This is a clear and simple demonstration of mutations, how temperature sensitive mutations work, and the effects of permissive and restrictive temperatures in a safe, simple system. The module can be expanded to look at the long and short term effects of exposure to restrictive temperatures and recovery parameters, and can be combined with other modules, to stimulate student development of independent inquiry projects. For more advanced classes, these mutants can also be used as a basis for genetic investigation of dominance and recessiveness, and gene complementation.


“Fat” mutant

This cell line carries a temperature sensitive mutation that causes cells grown at a high temperature (restrictive or nonpermissive temperature) (> 37°C ) to become very round and fat, with abnormal swimming patterns, while cells grown at lower temperatures (permissive temperature) (< 32°C) show normal morphology and swimming patterns. Compare the shape and swimming motion of these mutants with the “balloon animal” mutants and the normal cells. “Fat” cells grown at the restrictive temperature can only survive for a few days. A nice discussion of different types of mutations can be found at

“Balloon animal” mutant

This cell line carries a temperature sensitive mutation that causes cells grown at a high temperature (restrictive or nonpermissive temperature) (>37°C) to become very misshapen, often forming long protrusions that stick out from the cell. When the cells are grown at lower temperatures (permissive temperature) (<32°C), morphology and swimming patterns are normal. Compare the shape and swimming motion of these mutants with “fat” cells and the normal cells. “Balloon animal” cells grown at the restrictive temperature can only survive for a few days. See the discussion of different types of mutations at

Normal Cells

Module Protocol

High School

Relevant Concepts

Mutation; Gene regulation; Science as a Process

Next Generation Science Standards Relationships

High School

HS-LS1-1 Construct an explanation based on evidence for how the structure of DNA determines the structure of proteins which carry out the essential functions of life through systems of specialized cells.

HS-LS2-6 Evaluate the claims, evidence, and reasoning that the complex interactions in ecosystems maintain relatively consistent numbers and types of organisms in stable conditions, but changing conditions may result in a new ecosystem.

HS-LS3-2 Make and defend a claim based on evidence that inheritable genetic variations may result from: (1) new genetic combinations through meiosis, (2) viable errors occurring during replication, and/or (3) mutations caused by environmental factors.

HS-LS4-3 Apply concepts of statistics and probability to support explanations that organisms with an advantageous heritable trait tend to increase in proportion to organisms lacking this trait.

HS-LS4-4 Construct an explanation based on evidence for how natural selection leads to adaptation of populations.

HS-LS4-5 Evaluate the evidence supporting claims that changes in environmental conditions may result in: (1) increases in the number of individuals of some species, (2) the emergence of new species over time, and (3) the extinction of other species.


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See our glossary for the terms used in the modules.