obsolete karyogamy involved in conjugation with mutual genetic exchange https://github.com/geneontology/go-ontology/issues/16248 https://github.com/geneontology/go-ontology/issues/31306 true OBSOLETE. During sexual reproduction, the creation of a single nucleus from two nuclei as a result of fusing the nuclear envelopes that surround each nuclei. This takes place following the mutual exchange of one of the two nuclei produced by the mitosis that follows the second meiotic nuclear division. This occurs in ciliated protozoans such as Tetrahymena. karyogamy involved in conjugation without cellular fusion biological_process GO:0000744 This term was obsoleted because it is a pre-composed term that should be captured as a GO-CAM model.