Karyogamy is the fusion

Cell fusion

Cell fusion is an important cellular process that occurs during differentiation of muscle, bone and trophoblast cells, during embryogenesis, and during morphogenesis...

 of pronuclei of two cell

Cell (biology)

The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....

s, as part of syngamy, fertilization, or true bacterial conjugation

Bacterial conjugation

Bacterial conjugation is the transfer of genetic material between bacterial cells by direct cell-to-cell contact or by a bridge-like connection between two cells...

.

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

Genetic variation

Genetic variation, variation in alleles of genes, occurs both within and among populations. Genetic variation is important because it provides the “raw material” for natural selection. Genetic variation is brought about by mutation, a change in a chemical structure of a gene. Polyploidy is an...

 through the formation of somatic diploids.

The term comes for the Greek karuo- (from karuon) meaning nut and -gamos meaning marriage.