Rad51 and Dmc1 promote the homologous and strand exchange steps of homologous recombination. The amino acid composition of both proteins is similar to that of RecA, containing a region of consensus sequence for nucleotide binding ss-and ds-DNA binding, and strand exchange. Dmc1 is a Recombinase involved in meiosis-specific repair of double strand breaks (DSBs) via homologous recombination, whereas Rad51 has been found to be involved in meiotic and non-meiotic DSBs repair. Microarray and RT-PCR data from previous studies in Tetrahymena have demonstrated that expression of DMC1 increases during meiosis and that the protein localizes to the micronucleus. Some studies in budding yeast show that when RAD51 is overexpressed, interhomolog recombination still occurs even when DMC1 is knocked out. . It is not known whether Dmc1 and Rad51 interact directly, but evidence suggests that they somehow work together. Rad51 and Dmc1 have not been fully characterized in the ciliate Tetrahymena thermophila. Previous studies demonstrated that without Rad51, DSBs were not repaired, but meiotic DSB repair is dramatically reduced in the absence of Dmc1 and the function of Dmc1 can be compensated by replacing with Rad51 promotor. The aim of this study is to further define the role of Rad51 verses Dmc1 in Tetrahymena and to determine if they interact with each other in a complex during the cell cycle and DNA repair. Overexpression of the RAD51 causes macronuclear division and chromosome copy number defects. Bioinformatics was used to compare Dmc1 and Rad51 homologues from various species. RT-PCR studies showed an increase in DMC1 mRNA expression after treatment with MMS, UV, and H2O2, suggesting a possible role for Dmc1in DNA repair outside of meiosis. Survivability studies show that knocking out DMC1 makes Tetrahymena more sensitive to MMS treatment, but not to UV or H2O2. Data suggests they may play both similar and distinct roles in meiotic recombination. The role of Tetrahymena Dmc1 in DNA repair will be further elucidated through immunoprecipitation, fluorescence microscopy, and overexpression studies.