In this module, students assess the relative amount of expression of a gene of interest throughout different stages in the Tetrahymena life cycle. The life cycle is complex and involves a number of physiological changes and DNA processing events (see Tetrahymena Facts). Gene expression is evaluated through assessing the relative production of gene transcripts at different time points in the life cycle by reverse transcriptase PCR, yielding an "expression profile". (Estimated time: 5 x 4-hour laboratory periods.)