The mating lab addresses issues associated with sex and reproduction from an evolutionary perspective, using Tetrahymena as a model system for examining sexual and asexual reproduction. The lab takes advantage of the fact that, under appropriate conditions, Tetrahymena can propagate either vegetatively and sexually, addressing the relative impact of genetics, growth rate, and population size on reproductive advantage. Students design an experiment to identify the mating type of unknown clones of Tetrahymena by testing with clones of known mating type, based on the lack of self-mating within clones of the same mating type. The effects of various environments conditions on mating behavior can also be examined, and the module can be expanded to include a discussion of chemotaxis and the role of surface proteins in cell-to-cell communication.

Mating pair

Mating pair


In order to conjugate, Tetrahymena cells must be starved of at least one necessary nutrient, and they must be of different mating types. There are seven mating types (I-VII) in Tetrahymena thermophila, the species shown here. Following mating, progeny cells normally are unable to mate again until they have undergone about 50 to 80 cell divisions.

Early pairs

(licensed under Creative Commons by-nc-nd 4.0)

This clip shows pairs of Tetrahymena during the early stages of mating (called conjugation in Tetrahymena). Early in the mating process weakly bonded pairs are formed. These pairs can be disrupted by shaking or by adding food without damaging the cells. The reverse orientation and twisting motion is typical of cells during early mating. Since mating is not completely synchronous in any given culture of Tetrahymena cells, some boomerang-shaped pairs typical of a slightly later stage of mating are also visible. Compare the types of mating pairs in this clip to those found later in the mating process (see below).

Mating pairs

(licensed under Creative Commons by-nc-nd 4.0)

This clip shows the boomerang shape typical of mating pairs several hours after mixing. At this point the cells are joined at the anterior end by an actual membrane fusion event at the conjugation junction between the cells. Once membrane fusion has occurred, disruption of the pairs before mating is complete will result in the death of the cells. Compare to early stage mating cells shown above.

Module Protocols

High School

Glossary of Terms

Relevant Concepts

Population dynamics; Gene regulation; Science as a Process; Reproduction and Heredity

Next Generation Science Standards Relationships

High School:  |

Middle School: | | |

NYS Science Curriculum Guideline Relationships

Key Ideas | | | | | | |


Evaluate the evidence for the role of group behavior on individual and species’ chances to survive and reproduce.
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.
Conduct an investigation to provide evidence that living things are made of cells, either one cell or many different numbers and types of cells.
Develop and use a model to describe the function of a cell as a whole and ways parts of cells contribute to the function.
Use argument based on empirical evidence and scientific reasoning to support an explanation for how characteristic animal behaviors and specialized plant structures affect the probability of successful reproduction of animals and plants respectively.
Construct an argument supported by empirical evidence that changes to physical or biological components of an ecosystem affect populations.
Develop and use a model to describe why asexual reproduction results in offspring with identical genetic information and sexual reproduction results in offspring with genetic variation.
The central purpose of scientific inquiry is to develop explanations of natural phenomena in a continuing and creative process.
Beyond the use of reasoning and consensus, scientific inquiry involves the testing of proposed explanations.
The observations made while testing proposed explanations, when analyzed using conventional and invented methods, provide new insights into natural phenomena.
Organisms inherit genetic information in a variety of ways that result in continuity of structure and function between parents and offspring.
Individual organisms and species change over time.
The continuity of life is sustained through reproduction and development.
Organisms maintain a dynamic equilibrium that sustains life.
Plants and animals depend on each other and their physical environment.