Final answer:
Heterokaryons are the result of the fusion of nuclei from different cells, leading to cells with multiple nuclei that can form a hybrid with properties of both parent cells, crucial in vitro research, and an important concept for understanding the evolution of eukaryotic cells.
Step-by-step explanation:
The term heterokaryons refers to cells formed when nuclei from two different sources are fused, a process facilitated by agents like polyethylene glycol (PEG), sendai virus, or high voltage direct current pulses. In in vivo cultures, heterokaryons, which are cells with multiple nuclei from distinct cells, can combine to form hybrid cells. These hybrids benefit from the characteristics of both parent cells, such as immortality for continuous culture when one parent cell is inherently capable of indefinite growth.
Plas`mogamy is the step prior to karyogamy in the process of cellular fusion, where haploid cells merge without immediately combining their nuclei, resulting in a di`karyotic condition important in fungi life cycles.