the fusion of two or more cells to become a single cell, Formation of a single hybrid cell resulting from: (1) fusion of two complete cells to form a hybrid "sum" of the parentals (heterokaryon); (2) formation of a viable cell with cytoplasm (cytoplast) from one parent and nucleus (minicell) from another; (3) fusion of an enucleated cell with a complete cell of a different type (cybrids); and (4) the addition of a few chromosomes from one cell to another by fusion of a microcell with a normal cell.