Karyogamy is the last phase in the process of fusing two haploid eukaryotic cells together, and it refers to the fusion of the two nuclei in particular.
Each haploid cell possesses one complete copy of the organism's DNA before karyogamy.
For karyogamy to occur, each cell's membrane and cytoplasm must fuse together in a process known as plasmogamy.
The nuclei are referred to as pronuclei once they are inside the connected cell membrane.
Karyogamy is the merging of two nuclei during sexual reproduction.