1. Karyogamy is the fusion of pronuclei of two cells, as part of syngamy, fertilization, or true bacterial conjugation. It is one of the two major modes of reproduction in fungi. In fungi that lack sexual cycles, it is an important source of genetic variation through the formation of somatic diploids. (wikipedia.org)
2. The fusion of two nuclei within a cell, especially as the second stage of syngamy. (wiktionary.org)
3. The fusion of two nuclei. (biology-online.org)
4. Fusion of the nuclei of two cells, as occurs in fertilization or true conjugation. (medilexicon.com)
Word origin: From the Greek karuo- (from karuon) meaning nut and -gamos meaning marriage.It is mainly found in fungal phylum ascomycetes.