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 or 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 environmental 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


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

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

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

Relevant Concepts

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

Next Generation Science Standards Relationships

High School: HS-LS2-8 | HS-LS3-2

Middle School: MS-LS1-1 | MS-LS1-2 | MS-LS1-4 | MS-LS2-4 | MS-LS3-2

NYS Science Curriculum Guideline Relationships

Key Ideas 1.1 | 1.2 | 1.3 | 4.2 | 4.3 | 4.4 | 4.5 | 4.6