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(biology) The fusion of two nuclei within a cell, especially as the second stage of syngamy.

Karyogamy in the context of cell fusion. 1-haploid cells, 2-cell fusion, 3-single cell with two pronuclei, 4-fusing pronuclei (karyogamy), 5-diploid cell

(biology) The fusion of two nuclei within a cell, especially as the second stage of syngamy.

Step labeled number 4 indicates karyogamy's place in the context of the life cycle of the fungus Taphrina.

(biology) The fusion of two nuclei within a cell, especially as the second stage of syngamy.

(a) In fission yeast, the mating process is triggered by nitrogen starvation when compatible partners are present. (b) Budding yeast cells of opposite mating type can instead mate spontaneously on rich medium to form stable diploids that undergo sporulation upon starvation. In both organisms after pheromone exchange, cells grow in a polarized manner in the direction of their partner and undergo fusion, karyogamy and sporulation.